Clearance angle/back bevel

[David Ragan]

As i sit here watchinf The Shield reruns, have read multlpe times Soupijg up Block Plane by Newman-
i have multiple plane choices, but have ground cambers into blades..... Then it occurred to me i could jyst buy multiple (not infinite) blades for same plane.... Wow
so-seems like a no brainer to put a back bevel on a bevel up plane----up to a point, right? When does decreasing the clearance become a problem?
Tear out is issue, right?
i mean, a back bevel on bevel up plane will give better edge retention (greater sharpening angle)
Do i have basic idea?

[Winton Applegate]

a back bevel on a bevel up plane
In a word : Nah dude, nah.
Well that was more than a word but never, never, ever, neverever back bevel a bevel up blade.

up to a point, right?
No
In my view even the ruler trick is a mistakarooooo.
There are differences of opinion on that. Mine vs everybody else's so I'm told.
No ruler, no back bevel just F L A T.

When does decreasing the clearance become a problem?
Some say 7° is absolute stink'O
I am more comfortable saying 10°
But
Thinking microscopically now
that is on a very small level (not in a microscopic range of thought).
The wear bevel cuts into that/those numbers so that is approximately why the very low angle planes (talking the bed angle where the blade lays in the plane) . . . is 12°.

Then throw in hand sharpening and the unconscious raising the back of the blade off the stone to get the wire edge off (don't do that) and we are already pushing the clearance without adding more intentionally.
Now
You may say "Well my plane beds at 20°".
There is nothing to be gained by back beveling the bevel up blade.

Back beveling is useful on BEVEL DOWN planes to steepen the cutting angle but as was proven here months ago that is only really beneficial if you are not expert with setting the chip breaker AND you are working really difficult and extra hard wood; the wood from Australia, or purple heart, bubinga etc.

[Winton Applegate]

Oh my gosh . . . there's more
I missed answering

Tear out is issue, right?
No
Tear out with the bevel up is controlled by steeping the main bevel.
Now
You may, (and I was afraid of this in the beginning) be conflageratin'
back bevel
with
secondary bevel
A secondary bevel on the MAIN BEVEL will steepen the EFFECTIVE bevel; in other words be the equivalent of changing the main bevel to a steeper one.
So, unless maybe if you were a competition monster plane guy, it is usually smarter to buy shallow bevel blades, 25° etc (as opposed to 45° or 55° blades) and then use a secondary bevel to steepen them up for when you are getting tear out.


i mean, a back bevel on bevel up plane will give better edge retention (greater sharpening angle)

Forget that. You are applying bevel down thinking to the bevel up.
That only is really an issue around 25° sharpening angle and you will be changing the angle if you are getting tear out or the edge is getting dinged up not because you CHOSE to increase your edge retention.
The best method of improving edge retention is to refrain from planing the edge wearing woods such as teak, some of the purple hearts, pretty much all of the bubingas . . .
I am sure there are zillions that I am blissfully unaware of.


Do i have basic idea?
No you'er clueless and doomed to perish in a scary fire ball decent to the ground.

But keep at it and do carry an auxiliary parachute.
You know me, can't keep from interjecting some humor.

[Winton Applegate]

back bevel on a bevel up plane----up to a point, right? When does decreasing the clearance become a problem?
Hey since I am on such a roll here.

This may be what you are getting at so allow me to reword your question and then answer it.

[SECONDARY bevel] on a bevel up plane----up to a point, right? When does [increasing] the [main bevel angle] become a problem?

It never really does. You can have a square end on the blade's edge end and as long as it is very "sharp" (polished and the two surfaces come together at a very well honed edge) then the plane will cut.
This is called a "negative angle" edge.

The draw back is as the bevel angle increases, on the bevel up plane, the force it takes to push the plane through the wood increases ESPECIALLY for taking heavy cuts.

So use the shallowest bevel you can but as steep as necessary.

PS: practically speaking if you got to an effective cutting angle, bed angle plus sharpening angle, up to 90° then things should go south fast
but
I have a scraper plane (https://www.lie-nielsen.com/product/scraping-planes/large-scraping-plane?node=4075) that uses a negative angle and is intended to work with that.
In actual practice I find
to put it in technical lingo . . .
it sucks
but anyway there you go.

[Mike Henderson]

When I was in woodworking school, the instructor showed us how to get a lower angle on a block plane. Normally, you sharpen a block plane blade at 25 degrees. The bed is 12 degrees so the cutting angle is 37 degrees.

Suppose you sharpened the blade to 20 degrees - the cutting angle would be 32 degrees. But a 20 degree bevel would be weak. So put a 5 degree back bevel on the 20 degree iron and you're back to a bevel angle of 25 degrees, but the cutting angle is 32 degrees instead of 37 degrees.

What you give up is some of the clearance angle. The original clearance angle was 12 degrees, the same as the bed angle. By taking a 5 degree back bevel, you reduce the clearance angle to 7 degrees. The 7 degree clearance angle seemed to work well on the planes we modified that way. If you make the clearance angle too small, the plane will "skate" and it won't cut. I never tried going less than 7 degrees - but 7 degrees worked.

Mike

[Jim Koepke]

Tear out with the bevel up is controlled by steeping the main bevel.

Is it best steeped in a tomato soup or would Earl Grey work? :eek:

jtk

[Winton Applegate]

Is it best steeped in a tomato soup or would Earl Grey work?

Ha, ha, ha
ahhhhh
ha, ha
ahhhh
yah
sorry bout that.
I was battling this weird thing with the font size.
For some reason when I would click the space bar the whole line of text would jump up to a big size I had used earlier. If I misspelled the word it would work ok.
That or I am just stupid.
I meant to say "steepening". That is about as bad.

[Winton Applegate]

The 7 degree clearance angle seemed to work well on the planes we modified that way.
7°
Like I said . . . about the minimum. I bet Larry would argue that is seriously too little clearance to be practical.
But then he has made it very clear to me that he is sure bevel up in general is just pointless so would laugh at the notion.

Mike,
Do you recall the situation that called for that blade modification ?
Was it soft wood or . . . more likely end grain ?
Was it worth the effort?
What wasn't the stock edge doing that it started doing or improved on ?

[Mike Henderson]

7°
Like I said . . . about the minimum. I bet Larry would argue that is seriously too little clearance to be practical.
But then he has made it very clear to me that he is sure bevel up in general is just pointless so would laugh at the notion.

Mike,
Do you recall the situation that called for that blade modification ?
Was it soft wood or . . . more likely end grain ?
Was it worth the effort?
What wasn't the stock edge doing that it started doing or improved on ?
It was just something that was included in the class. It wasn't in response to any poor performance, but just a "tool" that was being given to us to use when we felt it was appropriate.

In doing the modification, we tested on end grain (maybe pine, I don't remember) but it was just something to test on. It did seem to improve the cut compared to the unmodified plane. But that's just subjective. When you expect something to work, it often does (or you think it does).

So again, it was something that was being taught, and the student was to apply it when the student felt it would be appropriate. Since that class, I've never used it.

Mike

[Winton Applegate]

a "tool" . . . to apply it when the student felt it would be appropriate
Interesting tool.
Maybe I need to go back and reread the soup up the block plane article.
Soup
I knew there was a reason to steep the blades. That's if you want to soup up your block plane.
Sorry . . . that was bad.

[Jim Koepke]

In doing the modification, we tested on end grain (maybe pine, I don't remember) but it was just something to test on. It did seem to improve the cut compared to the unmodified plane. But that's just subjective. When you expect something to work, it often does (or you think it does).

When paring end grain, my chisels sharpened at a low angle seem to do better than those sharpened at a higher angle. It wouldn't surprise me to discover planes with a lower angle of attack having similar results. Even if it was due to thinking it will come out better making it come out better.

jtk

[Kees Heiden]

The only reason to use such low angles would be endgrain planing, but endgrain needs more clearance then long grain. So you work yourself into a corner where one degree more or less could make the difference between good and bad. Add to that some wear after a few boards and the situation only gets worse.

Neat trick in theory, but I doubt it would bring much in reality.

[David Ragan]

The Winton.... Love levity.... If i may-u r saying that on a BU plane, even tho the cuttung angle is the same , it is not wise to put BB on it? Seems like from the oft quoted article that the above will have same cutting angle, but sharpening angle but better cutting edge retention due to cutting edge having much greater mass/less acute

[David Ragan]

Mike,

Ah.....Grasshoppers answer
too small clearance angle, the (something happans to dynamics jyst after cut-on trailing side of edge under the plane) and the "back pressure" (Soupnig up block plane article) becomes too great, forcing the blade up out of the wood?? Skidding results?
Master.... Is this the only downside/significance of clearance angle?

[David Ragan]

Interesting tool.
Maybe I need to go back and reread the soup up the block plane article.
Soup

The Winton, yes, most of these responses i read multiple timess iver time so i can digest what The Enlightned Ones (such as you) are saying to me.

Could it be we are not conceptually on same page w back bevel?
ghe Souping article by Newman is great....there is fluff in it but its great

[Winton Applegate]

Though the books say to finish a marathon one must have a dambed good reason and keep it in the for front of your mind.
It's complicated.

Since Mike hasn’t got back yet
I can blather on for a while until then . . .


even tho the cutting angle is the same , it is not wise to put BB on it?
Well yes that is what I said, partly because I am so irrationally militant against all this obsession with violating a simple flat surface on the back of the blade for no practical gain except well, I won’t get into the ruler mine field tho I do enjoy the whole hopeless last stand thing of the lone machine gunner battling away against impossible odds as his gun begins to seize and the last belt of ammo is fed in . . .
. . . all the while the blasted two way is muttering on some rot about the war being over . . .

I suppose it is the case only with the 12° BU but mostly it is because the BD planes have started it all all this need with varying the underside face of the blade, which is the bevel, and really it isn’t all that necessary.
. . . back bevel the hell out of your 20° bedded bevel ups if you must but I don't see why.


(something happans to dynamics jyst after cut-on trailing side of edge under the plane)
yes wood fibers are flexible, more so than say . . . machining steel would be, and then especially when the blade begins to wear some; the wood fiber flex pushes the blade some what up out of the cut
I used to TRY to compensate for this by advancing the blade slightly and pushing down harder.

Now speaking strictly from my learning curve which was exclusively on purple heart and bubbinga , before moving on to walnut and the more friendly woods,
for the former two woods not enough clearance and advancing the blade like that and pushing down harder were HUGE MISTAKES.
Enough clearance (at least 12° minus some wear bevel and sharpening (changing to a fresh blade from the stack of blades) were KEY to producing a flat surface on the wood.
WAY MORE SO THAN USING A LONG JOINTER PLANE.

If I waited and tried the above dodges, advancing blade and pushing harder, I wound up with a convex surface on the wood because the beginning of the cut was deeper than the middle of the cut and IT SEEMED but doesn’t make sense that the end of the cut also was deeper. Using a properly sharp blade there was no problem with convexitude dude.


and the "back pressure" (Soupnig up block plane article) becomes too great, forcing the blade up out of the wood?? Skidding results?
No
not really
back pressure is more along the lines of resistance to forward progress/taking a heavy cut compared with having too much back pressure to take that heavy cut.

Perhaps Kees can correct me, because I am about to be wrong here, but the force causing the blade to rise up out of the wood is called “N” factor or in any case not the same as the back pressure force.

Back pressure would be the force that bends the blade down into the wood deeper.

The force resulting from not enough clearance and the blade getting dull, at least in part, causing the compressed wood fibers to now over come the geometry of the blade and reject it out of the cut would be the force roughly opposite to the back pressure.


Master.... Is this the only downside/significance of clearance angle?

There is the heating effect on the blade. Probably not significant in most cases. With the purple heart, at least some of the planks, I would get a build up on the blade of the “resins” in that particular type of wood. It may have been less if the blades didn’t get as hot from having less clearance and being dull and forced to cut anyway.

Now that is splitting some serious BS though.

Finally, and for me this is the crux :
BACK BEVELING THE FLAT SURFACE OF THE BLADE IS A PAIN IN THE JIG
it is far easier to flatten the back and leave it alone with the occasional polish while working the wire edge.
Back beveling ACCURATELY, meaning not rounding the silly thing, is a useless bother for a bevel up and not all that important, but at least mildly useful, for the bevel down but just as tedious . . .
well . . .
nearly as tedious because it is ok to round it on the bevel down because we are not talking clearance any more but EFFECTIVE cutting angle ( the clearance is on the opposite (bevel side) of the blade next to the wood.

The next to the wood modification would be on the bevel side of the blade and even though it is on the wood side of the blade would be called a secondary bevel.
The back bevel on the bevel down blade would be on the flat face on the NON wood side of the blade and simply because it was being done to the flat face of the blade would be called a back bevel. (being done to as in molested or interfered with)

As a result of trying to type those last few paragraphs I may, now, be completely insane from typing all that and be in need of some serious vacation time.
The big snow storm is coming in now and work has called and said stay home so . . .
. . . by the grace of Bob . . . that vacation time has arrived.

I may not respond again now for a while, if ever, . . .
if there is a fire or world calamity that I need to know about I can be found laying on my side on the carpet, staring blankly and unblinkingly, drooling and slowly gasping for air like a beached fish.
thank you for your questions . . .
Wheeewu

:eek:

[Brian Holcombe]

Suffice to say I agree with Winton. I like to keep the back flat, I avoid things like the ruler trick.

[David Ragan]

In all sincerity-thanks guys👍😀
i read all the above a few times- and will do so again after the effects of the painmeds wear off from my knee surgery
in spite of appearances, i at times like things to be simple