Cambered blade in Veritas BUS

[Mike Holbrook]

I made a post a while back about hollow grinding larger cambers in my old A2 plane blades with my CBN wheel....

I have been doing glue ups for raised panel shutter doors. I sharpened up one of the A2 cambered blades and tried it in my BUS this morning. I was surprised that it worked as well as it did. I was expecting the LA, low angle, and wide blade to be hard to push. The camber reduces or eliminates the depth of cut at the edges, as we know. The extra blade width ends up providing more options for rough planing. The weight, low center of gravity, low grip all seem to help when working across boards taking larger shavings. The norse adjuster works quickly, on the fly, to increase or decrease depth of cut. This may be an odd choice for a scrub plane but it seems to be working.

338338

Maybe the camber works well in thick LA blades? I can see why there has not been much experimenting with this in the past as hollow grinding these blades via conventional means is quite a challenge.

[Patrick Chase]

I made a post a while back about hollow grinding larger cambers in my old A2 plane blades with my CBN wheel....

I have been doing glue ups for raised panel shutter doors. I sharpened up one of the A2 cambered blades and tried it in my BUS this morning. I was surprised that it worked as well as it did. I was expecting the LA, low angle, and wide blade to be hard to push. The camber reduces or eliminates the depth of cut at the edges, as we know. The extra blade width ends up providing more options for rough planing. The weight, low center of gravity, low grip all seem to help when working across boards taking larger shavings. The norse adjuster works quickly, on the fly, to increase or decrease depth of cut. This may be an odd choice for a scrub plane but it seems to be working.

338338

Maybe the camber works well in thick LA blades? I can see why there has not been much experimenting with this in the past as hollow grinding these blades via conventional means is quite a challenge.

Low bed angle actually *dilutes* camber. You have to put about 3.5X as much camber on a 12 deg BU blade to achieve the same center projection (amount the center of the blade extends into the wood when the corners are flush with the sole) as on a 45 deg BD blade.

I posted the math here: http://www.sawmillcreek.org/showthread.php?238371-WoodRiver-5-v3-Review&p=2501105#post2501105

It would appear that you've discovered that you like to rough with a minimally cambered blade :-). You could probably get the same results by re-cambering your BD plane blades to achieve similarly small extension.

[Reinis Kanders]

Those are pretty thin shavings for a scrub plane. Watch out for a tearout with BU plane. I like scrubbing with german style wood plane, they are light so one can really go at it.

[Jim Koepke]

It is also possible to add camber from the back side of the blade:

http://www.sawmillcreek.org/showthread.php?158373

There are many paths to the same result.

jtk

[Mike Holbrook]

Patrick, the problem I see with your math is it may not be relevant to my point. I do know how much "bite" the blade takes. Assuming your math is correct then maybe my heavily cambered blade becomes "less" cambered. Unless my math is wrong, a blade with a curved edge at an acute angle meets less resistance than a straight edge at a higher angle, which is my point. My suggestion is, if you have your doubts try it out before assuming ;-).

I figured someone would say the shavings are thin vs heavy. They do not look as thick in the picture as they do in person, maybe not the best picture/perspective... Certainly cross planing is not normally taking a full length shaving, especially early on. The shavings I get with this set up are also different than those I get with a narrower higher angled blade. Specifically, these shavings are more tapered on either side, actually leaving the edges thinner than the center section. I am able to work with a heavier camber. It is hard to sink a 8" camber full depth and then push the plane even with a narrow blade. The shavings from the BUS are wider than those I get with a #5 or #5 1/4 and in the center they are at least as deep, resulting in more not less wood being removed.

My other scrubs are a Stanley 5 & 5 1/4, with 2 & 1 3/4" blades. The Veritas scrub has a 1 1/2" blade. Less blade width makes a high angle and heavy camber manageable. My point is the BUS with the highly cambered blade seems to me to slide through the wood easier while still taking a sizable shaving. Certainly the reason for this would have something to do with the angle the blade meets the wood at and how the camber relates to that angle.

[Pat Barry]

The shavings I get with this set up are also different than those I get with a narrower higher angled blade. Specifically, these shavings are more tapered on either side, actually leaving the edges thinner than the center section.
This is what a camber blade should do



The shavings from the BUS are wider than those I get with a #5 or #5 1/4 and in the center they are at least as deep, resulting in more not less wood being removed.
This is to be expected also.


My point is the BUS with the highly cambered blade seems to me to slide through the wood easier while still taking a sizable shaving. Certainly the reason for this would have something to do with the angle the blade meets the wood at and how the camber relates to that angle.
As Patrick pointed out, the combination of camber and low angle of attack leads to this end directly.

I question why you want to use a smoother in this manner - a tad bit of camber does make sense though.

[Patrick Chase]

As Patrick pointed out, the combination of camber and low angle of attack leads to this end directly.

I question why you want to use a smoother in this manner - a tad bit of camber does make sense though.

Thanks for rewording my point in human-readable terms. What you say is basically the point I was trying to make.

I should have known better than to answer that question with a snippet of my Python code (I use it to automatically track of camber depths in my previously described spreadsheet 'o blades. Let the mocking resume!).

[Patrick Chase]

It is also possible to add camber from the back side of the blade:

http://www.sawmillcreek.org/showthread.php?158373

There are many paths to the same result.

jtk

Indeed, though that brings its own issues. For starters you have to be super careful about clearance, and it may also increase susceptibility to chatter etc because the bed will now only supports the center of the blade.

[Jim Koepke]

Indeed, though that brings its own issues. For starters you have to be super careful about clearance, and it may also increase susceptibility to chatter etc because the bed will now only supports the center of the blade.

When I have done this I do not carry the 'back bevel' that far back. It only takes a little bit of bevel.

jtk

[Patrick Chase]

When I have done this I do not carry the 'back bevel' that far back. It only takes a little bit of bevel.

jtk

Ah, but then you're reducing clearance to even less than the 12 deg nominal (and weren't you one of the folks arguing for higher clearance in that other thread?).

There's no free lunch here - if you camber the underside then you must either carry that camber a fair way back uch that constant thickness is maintained throughout the cutting portion of the blade, or you must accept reduced clearance. There are no other possibilities.

[Jim Koepke]

Ah, but then you're reducing clearance to even less than the 12 deg nominal (and weren't you one of the folks arguing for higher clearance in that other thread?).

You got me there... It must be a full half degree of lost clearance. How much of a clearance angle is needed when that portion of the blade isn't cutting, touching or entering the wood?

If you want a radius on your blade, then it should be done on the bevel side.

If you want to soften the edges to reduce tracks when smoothing then a few swipes with a stone on the back of the bevel will have a similar result to 'clipping' the corners.

jtk

[Patrick Chase]

You got me there... It must be a full half degree of lost clearance. How much of a clearance angle is needed when that portion of the blade isn't cutting, touching or entering the wood?

If you want a radius on your blade, then it should be done on the bevel side.

If you want to soften the edges to reduce tracks when smoothing then a few swipes with a stone on the back of the bevel will have a similar result to 'clipping' the corners.

jtk

If you'll look back to the OP, you'll see that he's talking about using a BUS with "larger cambers" as a *scrub*. This thread is about applying significant camber, not edge-clipping, and my reply reflected that.

[Mike Holbrook]

The reason I tried this type camber on a LA plane and made the post is, I have not been able to get a response from anyone who has actually tried it. I understand the reasons. The main reason in the past has been the lack of any way to do it quickly. Derek Cohen has a very good explanation in the sharpening area of his Blog. Now that Derek and others have CBN wheels this job can be done much more quickly. I decided to try a high camber on an old A2 blade that needed a whole new bevel anyway. Having a CBN wheel made the work relatively quick. Once I had the blade, why not try it in my various BU planes?

I understand Patricks theories about how the high camber will essentially be wasted but theories are just that. Mathematics and engineering are fine but useless if ALL the “right" formulas are not being applied. It is easy to blur rather than clarify with partial facts, and who is smart enough to be sure they have accounted for all the facts? I’m one of those people who thinks you don't know until you actually try it.

I'm not sure the argument about how much the blade protrudes is actually relevant in the way Patrick assumes it is. I am assuming that the major part or all of the camber is actually in the wood as if it isn't it isn’t being used. My question becomes how much of a heavy camber can I push through the wood's surface and actually plane with at a high angle? My theory is it should be easier to penetrate the woods surface deeper with a curved blade at a lesser angle. The curved edge at a low angle slices the wood while the straighter edge at a higher angle tends to work more like a scraper.

I find it very hard to get all of a large camber into the wood at a high angle, even with a narrow blade. A higher angle blade tends to chatter at that depth. Following Patricks logic I actually need a highly cambered blade in my smoother just to get any result out of the camber.

[Patrick Chase]

I understand Patricks theories about how the high camber will essentially be wasted but theories are just that. Mathematics and engineering are fine but useless if ALL the “right" formulas are not being applied. I’m one of those people who thinks you don't know until you actually try it.


In this case the formulae are extremely meaningful. Derek's post to which you refer says exactly the same thing without the math, as do bazillions of other writeups out there. I know of at least one "online camber calculator" that spits out exactly the same answers as the math I posted. Some may find the mathless versions more comforting, but that doesn't change reality.

Also, I've tried it with basically every radius from 3" to 24". So has Derek (probably much more than I), so have many others who are trying to tell you the same thing. This isn't a theoretical exercise as you assume.

If different projection from center to edge isn't the point of cambering, then what is? It's impossible for the edge to be "in the wood" and yet "not being used" as you posit.

I absolutely DID NOT say that you "need a highly cambered blade... just to get use out of the camber". Plenty of people do roughing with nearly-straight blades, so it's obviously possible to get "use" out of minimal camber.

What I said is that you've accidentally discovered that you're one of those people who prefers to work with a nearly-straight blade (i.e. you're more comfortable taking wide-but-shallow cuts instead of narrow-but-deep). There's nothing wrong that - as with many things in woodworking technique there's a lot of subjectivity here and no single right answer.

[Andrey Kharitonkin]

Did it occurred to anyone that high camber on BU plane has more cutting effect at the sides of the blade? I mean it would be kind of skewed blade if you look at the small portion of the blade at the sides where it meets the wood. Geometry is different when compared to BD plane. I have to try that with my spare A2 blade that I've got exactly for this.

[Pat Barry]

The reason I tried this type camber on a LA plane and made the post is, I have not been able to get a response from anyone who has actually tried it. I understand the reasons. The main reason in the past has been the lack of any way to do it quickly. Derek Cohen has a very good explanation in the sharpening area of his Blog. Now that Derek and others have CBN wheels this job can be done much more quickly. I decided to try a high camber on an old A2 blade that needed a whole new bevel anyway. Having a CBN wheel made the work relatively quick. Once I had the blade, why not try it in my various BU planes?

I understand Patricks theories about how the high camber will essentially be wasted but theories are just that. Mathematics and engineering are fine but useless if ALL the “right" formulas are not being applied. It is easy to blur rather than clarify with partial facts, and who is smart enough to be sure they have accounted for all the facts? I’m one of those people who thinks you don't know until you actually try it.

I'm not sure the argument about how much the blade protrudes is actually relevant in the way Patrick assumes it is. I am assuming that the major part or all of the camber is actually in the wood as if it isn't it isn’t being used. My question becomes how much of a heavy camber can I push through the wood's surface and actually plane with at a high angle? My theory is it should be easier to penetrate the woods surface deeper with a curved blade at a lesser angle. The curved edge at a low angle slices the wood while the straighter edge at a higher angle tends to work more like a scraper.

I find it very hard to get all of a large camber into the wood at a high angle, even with a narrow blade. A higher angle blade tends to chatter at that depth. Following Patricks logic I actually need a highly cambered blade in my smoother just to get any result out of the camber.


Mike, perhaps what is needed is to understand exactly how much camber you put into your BUS blade. Can you provide the measurements you used. Then it would simple to use the calculators to see what you ended up with for effective camber on a 2 1/4" plane blade at 12 degree bed angle with the bevel angle you chose to use.

[Mike Holbrook]

Patrick, actually I asked Derek if he had tried a large camber on a LA blade since he got his CBN wheel. He said he had not, which is one of the reasons I tried it. I believe Derek has been doing much more research with the new custom planes and chip breakers recently and less with BU planes. I believe that many people, myself included, point people to Derek's page regarding how to sharpen BU planes. I believe Derek responded in a fairly recent post that all of his research on BU planes is dated in some regards and he has not taken the time to revisit it as he has moved to other interests. I am not assuming I understand all of Derek's theories. I am assuming they change as he gets more information and does further testing as just about anyones do.

Patrick are you saying you have tested BU plane blades with every radius from 3" to 24"? If so I would be interested to hear about your results. I just do not think a mathematical formula or even some chart reflects the full range of functions that are occurring when we are planing. It seemed to me that you were implying that your information was some sort of definitive answer to whether or not a highly cambered plane blade might be useful on a BU plane blade. A 8" camber is an 8" camber regardless of whether it is on a BU or BD plane. Certainly that degree of camber works differently on a BU vs BD plane which is my point. Maybe you are making the same point?

All I am saying is "facts" are only valid if applied in context. There are often more facts than we can account for in our theories. Facts may not even turn out to be facts in the face of other facts.

The possible hole in my theory has to do with tear out. Working at a low angle can cause tear out, as the blade may lift instead of cut fibers. I am also interested in whether the cambered blade helps with tear out or makes it worse.

[Pat Barry]

The effective amount of camber on a BU plane at 12 degree bedding is only about 1/3 as compared to that same camber on a blade bedded at 45 deg.

[Mike Holbrook]

Pat, my guess is the blade I am using started at around an 8" camber but I am not sure and it has been honed several times since I ground it. Lately I do not mark a camber on my blades before I grind them. I also tend to round the corners more, leaving the center section with a lesser curve. I do not necessarily believe there is mathematical formula, equation, calculation that will provide a simple answer here. I am not arguing with the math. I am just not sure that such a calculation would contain all the variables at play. Neither am I convinced that any camber or angle we might plug into any formula would be accurate. I am grinding a hollow, there is no flat surface in at least two dimensions.

[Patrick Chase]

Did it occurred to anyone that high camber on BU plane has more cutting effect at the sides of the blade? I mean it would be kind of skewed blade if you look at the small portion of the blade at the sides where it meets the wood. Geometry is different when compared to BD plane. I have to try that with my spare A2 blade that I've got exactly for this.

Yes, that had occurred to me long ago, enough so that I calculated the maximum resulting skew. It's:

max_skew_angle = asin(blade_width/(2*camber_radius))

For an 8" radius on a 2.25" blade (Mike's numbers earlier in the thread) that works out to 8 degrees at the very corners. That will make a small difference in cutting action, though bear in mind that the average across the entire cutting edge is less than half that.

IMO that's "homeopathic skew" - Not enough to objectively achieve anything, but if you believe in it enough it might seem to work anyway.

[Mike Holbrook]

Pat, I hate to keep referring to Derek's posts on his Blog regarding sharpening, but they are one of the better sources of information in my experience. Derek's more recent work reveals that he had a custom frog made for one of his newer Veritas custom planes. The frog he requested was 42 degrees. Apparently another very experienced wood worker, Warren, liked that frog angle too. I ordered a Custom #4 with a 42 degree frog and find I like the results I am getting.

There is only 3 degrees difference between a 45 and 42 degree frog, which started me thinking that smaller differences might be more significant than I customarily have considered. How does one accurately calculate the actual angle of a hollow ground blade, especially at the exact level as the camber? Doesn't the angle of the blade change along multiple curved surfaces? I have a Batty devise that helps me determine that I am grinding an accurate bevel on my grinding wheel. If I had to guess I would guess it is measuring at the center of the bevel which would be the high point on the wheel. That point is way above the base of the plane where the blade meets wood.

As has been discussed in detail in more recent posts, the deflection angle of the chip/shaving coming off the plane blade is a significant factor in how the blade cuts. I believe this is at least part of the argument for a chip breaker. Certainly a cambered, hollow ground blade will make a different shaving and move it over the hollowed blade differently.

[Patrick Chase]

Pat, I hate to keep referring to Derek's posts on his Blog regarding sharpening, but they are one of the better sources of information in my experience. Derek's more recent work reveals that he had a custom frog made for one of his newer Veritas custom planes. The frog he requested was 42 degrees. Apparently another very experienced wood worker, Warren, liked that frog angle too. I ordered a Custom #4 with a 42 degree frog and find I like the results I am getting.

There is only 3 degrees difference between a 45 and 42 degree frog, which started me thinking that smaller differences might be more significant than I customarily have considered. How does one accurately calculate the actual angle of a hollow ground blade, especially at the exact level as the camber? Doesn't the angle of the blade change along multiple curved surfaces?

You can easily and accurately determine that angle in one of 3 ways:

1. If like Derek (http://www.inthewoodshop.com/WoodworkTechniques/BeyondSharpASharpeningStrategy.html) you hone by "balancing" the hollow-ground face on the cutting edge (face-to-back intersection) and top edge (face-to-top intersection) then resting a protractor across those edges and the back gives an extremely accurate measurement of the tip angle. That's the beauty of Derek's approach - the edges where the hollow-ground face meets the top and back constitute a built-in guide, and you can easily measure its angle. Precisely controlling the angle (via tool rest setup) is a bit harder in my experience, which is the only reason I don't use that approach.

2. If like Charlesworth you grind a secondary bevel on only the face-to-back edge with a jig, then you can easily determine the jig's angle in the usual way (by measuring extension from the guide).

3. If all else fails, it is possible to directly measure the angle of a secondary bevel with a good protractor, strong backlight, and lots of magnification. It's a pretty bone-simple exercise as metrology goes.



I have a Batty devise that helps me determine that I am grinding an accurate bevel on my grinding wheel. If I had to guess I would guess it is measuring at the center of the bevel which would be the high point on the wheel. That point is way above the base of the plane where the blade meets wood.

As has been discussed in detail in more recent posts, the deflection angle of the chip/shaving coming off the plane blade is a significant factor in how the blade cuts. I believe this is at least part of the argument for a chip breaker. Certainly a cambered, hollow ground blade will make a different shaving and move it over the hollowed blade differently.

It's different all right, but not in a good way. To avoid tearout you want a sudden *increase* in angle just behind the edge. A bevel-up blade with a hollow grind provides exactly the opposite (the angle decreases behind the micro-bevel, and doesn't significantly increase again until well back from the cutting edge).

[Mike Holbrook]

Patrick, as far as I am concerned you are making the same case I am. You name three ways to determine the angle. Two different ways for two well known woodworkers..Apparently there is no "standard", which is my point. In my experience more people do not measure any of those angles than measure them. Derek has mentioned in threads and his blog that one of the reasons he does not like to use his method for sharpening BU planes is he can't do it by hand. It requires a MkII and set up time to sharpen.

I'm not sure I just accept your evaluation of what makes a reliable chip breaker angle either. The information on that subject that I have read is not well defined or consistent enough to base much on as far as I know. I have not seen any testing that defines exactly where and at what angle an object needs to be to deflect a specific kind of wood chip. I believe the type of wood certainly affects the elasticity of that wood and how it will deflect. Sure it seems that setting a chip breaker close to the edge works better, and there are posts suggesting that rounding the deflecting surface may help but what "angle" is the curve at? Doesn't how "rapidly" a hollow ground blade curves up relate to how thick the blade is and at what angle the bevel is ground?

[Jim Koepke]

If you'll look back to the OP, you'll see that he's talking about using a BUS with "larger cambers" as a *scrub*. This thread is about applying significant camber, not edge-clipping, and my reply reflected that.

He also mentioned:


I can see why there has not been much experimenting with this in the past as hollow grinding these blades via conventional means is quite a challenge.

My post merely offered another option for experimenting. If the OP wants to try experimenting with a very slight round tapered bevel on the back of their bevel down plane, I would hope he will post the results.

jtk

[Mike Holbrook]

Jim thanks for the link and another idea worth experimenting with. I liked something you said in that thread which is also a goal of mine:

"The pursuit is finding a blade that holds an edge long enough so we can do enough work so that the sharpening seems like a quick break from the more difficult work at hand."

I do not mind taking a while when I first get a new blade to grind the kind of bevel I want, but when I am working I want to pop the blade out of the plane swipe it across a stone and maybe some buffing compound and get right back to work. I don't want to have to haul out jigs, rulers, protractors, squares...I don't like to interrupt the rhythm of the work. I think there are a good many people who feel the same way.

[Jim Koepke]

Jim thanks for the link and another idea worth experimenting with. I liked something you said in that thread which is also a goal of mine:

"The pursuit is finding a blade that holds an edge long enough so we can do enough work so that the sharpening seems like a quick break from the more difficult work at hand."

I do not mind taking a while when I first get a new blade to grind the kind of bevel I want, but when I am working I want to pop the blade out of the plane swipe it across a stone and maybe some buffing compound and get right back to work. I don't want to have to haul out jigs, rulers, protractors, squares...I don't like to interrupt the rhythm of the work. I think there are a good many people who feel the same way.



Thanks Mike, I think you have gotten the full meaning of my comment. Sharpening should be quick and simple, not a drawn out ritual.

jtk

[Mike Holbrook]

I hate to resort to my own math here as I don't believe we have accurate numbers to work with. However, the "pertinent angle" of my BUS is not the 12 degree bed angle.

The pertinent number is actually the bed angle, 12 degrees + the angle of the camber of my blade. I have two cambered A2 blades, one at 25 and one at 30. I am not exactly sure 25 and 30 are "correct" numbers either as they are cambered and I am not sure exactly where and how one measures a meaningful number on these blades. However, assuming my Batty devices is correct and I have 25 & 30 bevels. The actual pertinent number for comparison is 12+25=37 or 12+30=42. 37 is only 8 degrees from 45, 42 is only 3 degrees from 45. In a response to Andrey above Patrick states:



"For an 8" radius on a 2.25" blade (Mike's numbers earlier in the thread) that works out to 8 degrees at the very corners. That will make a small difference in cutting action, though bear in mind that the average across the entire cutting edge is less than half that.

IMO that's "homeopathic skew" - Not enough to objectively achieve anything, but if you believe in it enough it might seem to work anyway."



If 8 degrees of difference is "homeopathic","Not enough to objectively achieve anything, but if you believe it enough it might seem to work"... then I guess the entire difference between the BU planes combined bed angle and the bed angle of a BD plane, 3-8 degrees, is insignificant, following that logic.

I do not agree, I admit I have no idea how much angle may or may not be significant which is why I tried cambering old blades to see what it actually does. I think Andrey's comment has merit and I do not find 8 degrees to be insignificant. I have actually moved toward working the edges of my cambers more like Andrey and Jim suggest.

The other reason I made the test is a BD plane blade is dead flat where the shaving comes off the blade. Certainly one of the functions of a chip breaker is to move the shaving. My hollow ground BU blade, however, has a curve built into the bevel of the blade where the shaving comes out. Any BU blade presents a bevel at some angle to the exiting shaving. The shaving is "handled" at some distance behind where the shaving is made. A chip breaker needs to be very close to the leading edge of the blade to function. My question is whether or not we know where and at what angle the shaving is best dealt with? I'm not sure that a hollow ground blade might not deal with the shaving more efficiently than a chip breaker.

[Derek Cohen]

The other reason I made the test is a BD plane blade is dead flat where the shaving comes off the blade. Certainly one of the functions of a chip breaker is to move the shaving. My hollow ground BU blade, however, has a curve built into the bevel of the blade where the shaving comes out. Any BU blade presents a bevel at some angle to the exiting shaving. The shaving is "handled" at some distance behind where the shaving is made. A chip breaker needs to be very close to the leading edge of the blade to function. My question is whether or not we know where and at what angle the shaving is best dealt with? I'm not sure that a hollow ground blade might not deal with the shaving more efficiently than a chip breaker.

Mike, if you believe that the hollow bevel has a function to play on a BU plane, something akin to a chipbreaker, then you need to compare a BU plane with hollow grinds at different angles, and with another blade with the same bevel angle but on a secondary micro bevel on a flat primary bevel. This would help determine whether it is the hollow grind is making a contribution distinct from the cutting angle.

Regards from Perth

Derek

[Pat Barry]

One thing you can imagine that is happening, if you have a significant camber on your blade, is that the left and right edges of the blade will slice into the wood at a complex angle as compared to the center section of the blade which will be head on to the work. The result of this is further lessening of the apparent bevel angle (at the edges) - couple this with the fact that the edges of the blade are less engaged in the material due to the camber and you can see that this will make your work easier of course. No one will refute that. I'm in no position to say whether the hollow grind by itself creates some sort of chipbreaker substitute but I can say that the hollow grind lowers the effective angle of the bevel at the edge. The effect of this is dependent on the depth and breadth of your hollow grind. The angle right at the edge after grinding and before honing can approach tangency to the bedding angle. That's why its important to talk about bedding angle. A question that comes to mind is how can we quantify your hollow grind and how can we quantify the amount of honing you do? Would you say that the hollow grind is about 1/4" in breadth? What would you say is the width of the honed edge, 0.010"? Having a few dimensions will remove the ambiguity in the math.

I did find an interesting website on the topic of camber, calculations etc. Here is a link to it (http://www3.telus.net/BrentBeach/Sharpen/camber.html)

[Patrick Chase]

I hate to resort to my own math here as I don't believe we have accurate numbers to work with. However, the "pertinent angle" of my BUS is not the 12 degree bed angle.

The pertinent number is actually the bed angle, 12 degrees + the angle of the camber of my blade. I have two cambered A2 blades, one at 25 and one at 30. I am not exactly sure 25 and 30 are "correct" numbers either as they are cambered and I am not sure exactly where and how one measures a meaningful number on these blades. However, assuming my Batty devices is correct and I have 25 & 30 bevels. The actual pertinent number for comparison is 12+25=37 or 12+30=42. 37 is only 8 degrees from 45, 42 is only 3 degrees from 45. In a response to Andrey above Patrick states:


We're talking about different things. The "8 degrees" I cited is a skew angle, i.e. about the Z-axis (axis normal to the wood surface). The angles you cite above are bed/cutting angles, i.e. about the Y-axis (axis perpendicular to the plane's long axis and tangential to the wood surface).

Andrey (correctly) pointed out that grinding a camber into a BU blade causes the edges to make a slightly skewed cut. I replied with the math for that amount of skew.

Pat correctly points out that the skew at the edges does also reduce the cutting angle a teeny tiny bit (by <1 deg @ 8 deg skew)

[Jim Koepke]

I can usually hold my own at math. When it comes to working in the shop I do not want to break out the calculus when a blade is being honed.

The blade will either work or it won't. Some blade tricks make a plane easier to use for a particular type of work. Once a 'new' trick is picked up it can be 'developed' to work better until it stops working better.

This minutia of angles, axis, tangents, binomial coefficients and such doesn't get the work done.

One of the things I love about my old Stanley/Bailey planes is they work. I do not even know the precise angle of the bevels on my blades. I know some are around 25º and some are around 30º. If they need to be reground then the angle is checked and either ground the same or it is changed.

It is enjoyable to experiment with different methods at times. If time was taken to derive an exact scientific formula as to why it worked, nothing would ever get done in my shop.

Sorry for the rant, I haven't had my coffee yet.

jtk

[Patrick Chase]

I can usually hold my own at math. When it comes to working in the shop I do not want to break out the calculus when a blade is being honed.

The blade will either work or it won't. Some blade tricks make a plane easier to use for a particular type of work. Once a 'new' trick is picked up it can be 'developed' to work better until it stops working better.

This minutia of angles, axis, tangents, binomial coefficients and such doesn't get the work done.

One of the things I love about my old Stanley/Bailey planes is they work. I do not even know the precise angle of the bevels on my blades. I know some are around 25º and some are around 30º. If they need to be reground then the angle is checked and either ground the same or it is changed.

It is enjoyable to experiment with different methods at times. If time was taken to derive an exact scientific formula as to why it worked, nothing would ever get done in my shop.

Sorry for the rant, I haven't had my coffee yet.

jtk

Err, everything in this thread has been simple 9th-grade geometry, stuff that can be derived and done in seconds (once you memorize a couple handy tricks and approximations)

[Jim Koepke]

Err, everything in this thread has been simple 9th-grade geometry, stuff that can be done in your head in seconds (once you memorize a couple handy tricks and approximations)

And I am saying it is completely unneeded when freehand sharpening a blade. I would rather listen to some music and use some common sense when sharpening a blade.

jtk

[Patrick Chase]

And I am saying it is completely unneeded when freehand sharpening a blade. I would rather listen to some music and use some common sense when sharpening a blade.

jtk

OK, so don't. Nobody's saying you should or have to, and nobody's forcing you to engage in this discussion, so I'm frankly mystified that you'd take the time to rant if all you really want to do is work wood.

[Mike Holbrook]

.Derek thanks for posting. I experimented with hollow grinding using two old A2 BU blades. I ground one at 25 and one at 30 as practice and just to see what kind of results I got. I also hollow ground a few of my Stanley plane blades. Once I felt comfortable hollow grinding on my CBN wheel, I ground all the Stanley blades I use with hollows at 30 degrees, including three PM-V11 blades. I took a suggestion you made on another post regarding grinding BU blades at 25 and hollow ground both of my PM-V11 BU blades at 25. I also reground the blade for my new Veritas Custom #4, with a hollow at 30 degrees.

It might be fair to say I am a raving fan of hollow ground plane blades. I like the fact that I can hone the hollows freehand quickly without loosing track of the woodworking task at hand. I use to spend too much time sharpening at the expense of projects.

I decided to try my relatively heavily cambered A2 blade in my BUS the other night, as I was trying to work out some rough spots on glue ups that my longer planes were missing. I was surprised at how easily the blade worked in the wood. Thus this post...I think I will wait to experiment with how a hollow may or may not change how a shaving is ejected. Maybe I will pursue that topic in another post, this one seems to be plenty complicated enough ;-)

The Math
In my humble opinion, too much weight is often given to remarks containing math or geometry. Math is suppose to prove or disprove, but for math to do that it has to have accurate numbers used in all the correct variables. In my opinion, the numbers in this case are not constants for all the reasons I have explained above and all the others no one has thought of yet. Even if we could be entirely sure we had totally accurate numbers and our formula accounted for each and every variable, whatever number or numbers our formula came up with would still be susceptible to error introduced by inaccurate human interpretation of how and where to apply the "perfect" numbers. Even if we knew exactly where to apply our numbers, ultimately human coordination is required, which although it certainly is not perfect is all we have to work with, as Jim I believe astutely observes.

The interesting thing to me about sharpening any kind of blade is ultimately it ends up being a "hand" process. In it's basic form I find it to be the ultimate "hand tool" skill set. If that were not the case I think we would all just buy Rob Lee's machine that sharpened our blades for us and let it make all of our blades perfectly sharp. The sharpening devices Rob Lee sells all require some sort of interaction with human hands for a very specific reason. Only our hands can make all the minor adjustments to pressure & angles...while constantly monitoring heat on a continually changing basis. No jig or machine does the job on its own. Any jig which is ostensibly built to hold a blade at an exact angle requires a human hand to guide it at specific pressures against abrasives of different grits. The fact is our hands still constantly change the pressure in all sorts of directions in order to create the best edge.

If a jig holding a blade at some "perfect angle" solved all of our sharpening needs everyone would use them and there would be lots of testing posted indicating how well it worked. Such posts do not exist because human hand pressure is still required to make the jig work and that human hand pressure does cause the results to "skew".

Many people eventually find that sharpening by hand is faster and arguably a more accurate way to sharpen. The relative accuracy of hand sharpening relates to visual, tactile, auditory ...stimuli that we may not even think about while we are employing them. Learning to respond to all those stimuli requires practice. Show me a mathematical equation that can tell me how to perfectly use all my senses to some theoretical perfect degree. Show me a formula in geometry that can handle an unknown number of microscopic curved surfaces intersecting at random angles in three dimensions. Even if such a formulae existed who among us could perfectly coordinate all of our senses to the prescribed numbers?

I am in complete agreement with Jim regarding the fact that mathematics and geometry are not some complete answer inherently more important than the skill level of the individual who is attempting to make a plane blade perform better.

[Jim Koepke]

Thanks Mike,

This is a much more eloquent way of conveying what I was trying to say.

When one is freehand sharpening there is nothing easier than starting with a hollow ground blade.

jtk

[Pat Barry]

I experimented with hollow grinding using two old A2 BU blades. I ground one at 25 and one at 30 as practice and just to see what kind of results I got. I also hollow ground a few of my Stanley plane blades. Once I felt comfortable hollow grinding on my CBN wheel, I ground all the Stanley blades I use with hollows at 30 degrees, including three PM-V11 blades. I took a suggestion you made on another post regarding grinding BU blades at 25 and hollow ground both of my PM-V11 BU blades at 25. I also reground the blade for my new Veritas Custom #4, with a hollow at 30 degrees..
Hi Mike, I'm still curious how you are measuring the 25 degree and 30 degree hollow bevels. Could you please state your measurement method? Also, in a previous posting I enquired about the dimensions of your hollow bevel and secondary bevel. I'm curious what you are getting on your blades because I think its good information to pass on. .

[Jim Koepke]

I can't speak for how anyone else manages to measure their bevels but this works for me:

338481

Measures from 15º to 45º in 5º increments. A very handy little device.

http://www.leevalley.com/US/wood/page.aspx?p=40957&cat=1,43072

jtk

[Mike Holbrook]

Sorry Pat, I thought I had responded, maybe it was another thread or....

I have a Stuart Batty jig that I use to set my bevel angles on my Stuart Batty tool rest. Batty is a turner maybe not so well known among Neanders. He makes/has made an assortment of sharpening jigs and rests. I think he also makes turning tools. The Batty jig has a flat section for placing on the rest and a curved section that fits against the wheel. I suspect it is measuring at the lowest part of the arc in the angle setter, which would be the highest point on the wheel, but I don't know for sure.

I grind all my Stanley and Custom Veritas plane blades at 30 degrees. I have one BU plane blade I ground at 30 for chuckles, but all the other BU blades I have are ground at 25. I have no idea what actual dimensions are or what dimension might be meaningful? So far I do not intentionally make micro bevels. I hone all my hollow ground blades by resting the two edges of the hollow on my stones or MDF with compound, this arguably makes some small micro bevel but I have no idea how one might be able to measure it.

[Andrey Kharitonkin]

IMO that's "homeopathic skew" - Not enough to objectively achieve anything, but if you believe in it enough it might seem to work anyway.

LOL :D Nice one - "homeopathic skew". And very scientific also! :)

Then there is another bonus - length of cutting edge will be longer - load is spread to longer edge - more planing between sharpening (but equally more to sharpen then, ofc).

So many pluses. I have to try that really soon!

[Pat Barry]

Sorry Pat, I thought I had responded, maybe it was another thread or....

I have a Stuart Batty jig that I use to set my bevel angles on my Stuart Batty tool rest. Batty is a turner maybe not so well known among Neanders. He makes/has made an assortment of sharpening jigs and rests. I think he also makes turning tools. The Batty jig has a flat section for placing on the rest and a curved section that fits against the wheel. I suspect it is measuring at the lowest part of the arc in the angle setter, which would be the highest point on the wheel, but I don't know for sure.

I grind all my Stanley and Custom Veritas plane blades at 30 degrees. I have one BU plane blade I ground at 30 for chuckles, but all the other BU blades I have are ground at 25. I have no idea what actual dimensions are or what dimension might be meaningful? So far I do not intentionally make micro bevels. I hone all my hollow ground blades by resting the two edges of the hollow on my stones or MDF with compound, this arguably makes some small micro bevel but I have no idea how one might be able to measure it.
Thanks Mike. That looks like a nice tool for getting your tool rest set pretty accurately - I have struggled with this setup through trial and error process - its not easy to measure afterward although the gauge Jim showed certainly makes the job easier. If you can maintain the contact while honing as you described then the resulting angle will be as you ground it.I also have difficulty with this freehand.

MATH
Just for the sake of perspective if you are grinding a 25 degree hollow bevel with a 6 inch wheel and you are making that bevel the full thickness of a 3/16" thick plane blade, that hollow would be ~ 7/16 long. The depth of the hollow with that grind would be ~0.008" (assuming I did the math right). With a 30 degree bevel the length of the hollow would be ~3/8" and the depth of the hollow would be 0.006". Of course, I'm not sure you would/do hollow grind the full blade thickness. If not the depth I calculated will be proportional to the length of the grind so the hollow depth might be very small. Then, by honing it you might reduce the depth by about half, so, that hollow is a pretty subtle thing on the finished edge. The big benefits are the reduction in material removal needed to get the edge ready for use of course.

[Mike Holbrook]

Pat, I encountered lathes and lathe tools in my chair classes. I thought about buying a lathe, but now I am in more of a downsizing mode, getting ready for moving to a smaller home. I encountered the Batty tools talking to turners. The Batty tool rest is reasonably priced for such a solid rest and I use the Batty jig for setting the bevels I am grinding all the time, very handy. I thought about buying a better grinder for my CBN wheels but ended up upgrading the jigs I use with my Delta variable speed grinder instead and so far I am happy with the investment.

Regarding the math ;-) I bought a LV Custom #4 fairly recently, which is a little weird since I am downsizing. I am thinking about getting rid of some or all of the Stanley planes I restored over the last year or two. They are great tools, but I am so use to the adjusting system on my BU LV planes I'm not sure I want to be switching back & forth between the two systems. I would like to have some planes with chip breakers for all the reasons David Weaver, Derek...have enumerated over the last several years. I am thinking about buying a couple or three LV Custom planes so I will still have planes with chip breakers. The weight, balance, adjustment system, handles....,on the LV custom planes, is just more familiar and does not interrupt my working habits as much.

Therefore I have been testing the limits of using BU planes for medium and heavy stock removal. If I have LV custom planes with chip breakers I should be able to clean up whatever tear out the BU planes may leave behind. I am also trying to move to the mountains of north GA. I am interested in making rougher/rustic looking furniture for the new home, plane marks, drawknife marks, adze, axe....."evidence" of hand tool work is considered part of the charm up there. I will be very close to an actual saw mill that I understand sells logs, rough lumber at bargain prices, so I am excited to have that kind of wood to work.

It's all about what we are planing to do with the tools, isn't it?

[Patrick Chase]

LOL :D Nice one - "homeopathic skew". And very scientific also! :)

Then there is another bonus - length of cutting edge will be longer - load is spread to longer edge - more planing between sharpening (but equally more to sharpen then, ofc).

So many pluses. I have to try that really soon!

You raise an interesting point about sharpening. Unless you have a crowned stone/plate it takes longer to sharpen a cambered blade than a flat one. That's true regardless of whether you freehand or use a guide, as it stems from the fact that each stroke sharpens/hones the entire edge of a flat blade, but only a small portion of a cambered one.

The difference is very noticeable at least for me, though IMO the benefits of camber more than outweigh that drawback.

[Andrey Kharitonkin]

You raise an interesting point about sharpening. Unless you have a crowned stone/plate it takes longer to sharpen a cambered blade than a flat one. That's true regardless of whether you freehand or use a guide, as it stems from the fact that each stroke sharpens/hones the entire edge of a flat blade, but only a small portion of a cambered one.

The difference is very noticeable at least for me, though IMO the benefits of camber more than outweigh that drawback.

Well, sharpening small portion of cambered blade also means there can be more pressure. So, small portion will be sharp quick! :)

Unfortunately, pressure has to be limited, otherwise edge could get micro cracks, deflected and probably numerous other bad things. But not everybody knows that, probably. I didn't up to some point.

So yes, it supposedly takes longer. Not to mention making sure all small portions are touched and that it keeps the right shape after several sharpening.

[Patrick Chase]

Unfortunately, pressure has to be limited, otherwise edge could get micro cracks, deflected and probably numerous other bad things. But not everybody knows that, probably. I didn't up to some point.

You can also put nasty divots in your soft polishing stones, cut your leather strop, and/or shred your microfinishing film (depending on which you use) that way.

I think that's one of those things that most of us learn the hard way. I certainly did.

[Mike Holbrook]

I do my honing on medium and fine Spyderco ceramic stones, finishing on MDF with green compound. They require minimal or no leveling. I checked out Odate's diamond sharpening plates for making cambered blades at Highland Woodworking. They make relatively small cambers and they are relatively expensive. Two or three grits starts getting to be a sizable investment and I decided there was not enough flexibility in that medium. I went with CBN wheels. It has taken a while to get to the point that I can make just about any camber I might want but I think it has been time well spent. I can make a full width/depth hollow bevel on a new plane iron in under 30 min.with all the accuracy I think I need. I don't expect to have to do that but once in the blades life and once it is done I am able to hone very fast.

I also keep sharpening media around that are more rare with the majority of woodworkers. Many of the green woodworking tools have curved blades that need to be sharpened. I have a couple diamond sharpening rods, one round one eliptical. I also have a round ceramic rod and a small elliptical one. I have an assortment of wood dowels and wooden jigs for honing gouges, with compounds, diamond paste... I am fairly well equipped to deal with curved blades and curved hollow ground blades.

Again, my interest in the cambered BU blades mostly has to do with them being easier to move through wood vs more upright frog angles. I am not sure about tear out yet, but cambered BU blades do seem to work a little better for me that straight blades especially when taking off more wood. I think I may be getting some tear out but I can't tell yet if it is significantly more than what I get with a BD blade. The boards I am using have major tear out from a lousy original planing job.

So far I think I like the ease of use well enough to deal with extra tear out. Earlier this AM, I was switching between my BUS and my custom #4 with chip breaker and slightly less cambered blade. I think the custom plane is better but I am not noticing enough difference to worry about so far. Again I am not picky about small amounts of tear out for the work I do. Certainly YMMV.