Grinding an edge straight with a flat bevel

[Cory Gilmer]

Hello all,

After stumbling across this forum numerous times from google searches on various woodworking topics, I decided that it's a very worthwhile forum to join. Forgive me if this is in the wrong section - but I think the handtool guru's would be the most likely to be able to help me here. I've spent the last few months buying some sharpening tools and building a small dedicated sharpening station, and have enjoyed riding the learning curve - it is rewarding to take an edge from beyond dull to threateningly sharp. I have run into a few snags though - my current problem is achieving a truly straight edge on a plane blade from the grinder (or rather a truly flat (planer) bevel. A visual check after grinding certainly makes the edge look straight (even holding it up to a straight-edged tool doesn't reveal gaps along the outer corners), but when I go to honing the problem invariably turns up.
My waterstones start cutting the middle of the edge immediately, and it's a very slow go to stretch the area being honed along the whole edge, corner-to-corner. I've attached a picture to show what I mean. Notice how all 3 blades are honed in the middle but not all the way out to sides of the cutting edge? Also, it's clear that in the middle of the edge the honed area stretches further back from the cutting edge - this is because it was the first part of the cutting edge to be honed, so as I continued on the stones to try to get the whole edge, it keeps working this area back further. Each one of these blades has been honed for a good 10-15 minutes and I'm still probably at least that long again away from getting a hone across the whole edge. Despite being completely new at this, I've read quite a bit and know that this is far too long, and that the thickness of a honed edge should be largely consistent along the whole edge. To me, it seems like the problem is that the surface of my grinded bevel is somehow not in the same plane.
I'm not sure what the solution is. At first I wondered if my stones were dished, but then realized that a dished stone would cut from the outside edge of the blade in towards the center. I'm not cutting freehand - I'm using the Wolverine toolrest from OneWay with the Veritas grinding jig, this limits movement of my edge to being perpendicular to the wheel. And I dress my wheel with one of those little bar-dreesers, so I wouldn't think the cutting profile of the wheel is be the problem either.

Any thoughts would be greatly appreciated! Thanks.
Cory

[Simon Frez-Albrecht]

That is tricky. Have you put a straight edge on your stone? It could be humped in the middle. Also try laying a straight edge on your honed blades there...is there now a hollow where they've been honed? What stones are you using? That could help narrow down the problem.

[Sam Takeuchi]

It's your waterstone. Flatten it and try again. If straight edge shows your blade is straight along the edge, how you grind it or condition of grinding wheel doesn't matter. If it was about other problems, then yeah, these things could come into concern, but since it's not, no. Flatten your stones often.

[Wilbur Pan]

There are only a few possibilities to explain what is going on here.

1. Your waterstone is slightly convex in the middle, as Simon mentioned.

2. Coming off the grinder, you've removed slightly more metal from the sides of your plane blades than from the middle, leaving the profile of the plane blade slightly convex in the middle, despite the fact that you are using a jig. If you slide the tool back and forth, it's easy to spend more time on the corners than the middle, as you could slide the tool over, hover at the corner, then slide it back, and hover on the other corner. I do this as well.

I know you've checked your plane blades, but this effect can occur with very small deviations from straightness that are hard to see with the naked eye, and it can take a while to correct this when it happens, as you've noticed. The good thing is that you don't have to worry about this too much. If your waterstone is flat, and it's taking you too long to get to the edge, use a coarser waterstone than the one you are using. Alternatively, you could use something like 80-120 grit sandpaper on a flat piece of granite, tile, or glass. That's a very quick way of removing metal.

One other thing to try is use your bar dresser on your grinding wheel to make it slightly convex, so that the middle of the grinder wheel is slightly higher than the outsides. This might help reduce the amount of metal being removed at the sides. Joel Moskowitz from Tools For Working Wood does this with very good results.

[Cory Gilmer]

Thanks for the replies fellas. I use an 80 grit 3x white norton stone on my grinder and norton waterstones too (225, 1000, 4000, 8000). I do routinely flatten my waterstones every couple of minutes with a DMT diamond stone so I'm a little perplexed about my problem. I'll have a go re-flattening my stones and see if we make any progress!

Cory

[Jamie Bacon]

I think I'd try going from your grinder to your diamond stone. Something you know is flat, but that won't take all day to bring your edge flat, if that is indeed the problem. Then just progress up the ladder on your different grit stones.

[David Keller NC]

Thanks for the replies fellas. I use an 80 grit 3x white norton stone on my grinder and norton waterstones too (225, 1000, 4000, 8000). I do routinely flatten my waterstones every couple of minutes with a DMT diamond stone so I'm a little perplexed about my problem. I'll have a go re-flattening my stones and see if we make any progress!

Cory

Don't assume your DMT is flat - they're often not flat, at least flat enough to avoid putting a few thousandths dish or hump in your water stone. The only way to be doubly sure is to get a surface plate (the small, made-in-china ones are inexpensive) and some 220 grit SiC wet-dry paper and surface your waterstones with that.

Or - you could just go with what you have. Having a few thousandths camber in your edge is ideal - there are very few circumstances where you want your plane blade ground/honed straight across.

[Tony Shea]

I almost wish I had that profile naturally come up on my plane blades, would save me lots of time in trial and error. Like David said I only have but 2 planes (or should I say blades) that have perfectly flat bevels. My LN #7 jointer and my shooting blade for my LV BU jack. All my other plane blade get cambers, and getting the right camber can often gives me troubles. I've often thought about dropping the $100 on a Toshio Odate diamond crowning plate to get my camber.

Anyways, this is a tough thing to diagnose without actually seeing the equipment. My first guess would be your stones as you are showing a straight edge off your grinder. Assuming you are checking the edge with a known straight edge.

[Chris Friesen]

Or - you could just go with what you have. Having a few thousandths camber in your edge is ideal - there are very few circumstances where you want your plane blade ground/honed straight across.

While what you say is true, unfortunately the OP has the opposite of camber. If the stones are convex the blades will be concave, which is NOT what you want.

[Jim Foster]

Just a thought. When three guys are sitting on a fence sharing a soda, and each one passes the soda to the nearest guy after each sip, the one in the middle gets twice as much by default. If your using a grinding wheel and passing the blade back and forth over the grinding wheel, the middle may be getting more material ground away, leaving a concave hollow grind. You could try just going one way across the grinding wheel, see if it helps. (This may not apply to your challenge)

Also, the resulting hollow grind, needs to be a "Cylinder" type surface, if it's not, when sharpening on the flat stone, certain areas will wear away much faster, one of the blades in your picture looks to have a complex hollow grind that may lend itself to the problem your having.

[Sam Takeuchi]

When three guys are sitting on a fence sharing a soda, and each one passes the soda to the nearest guy after each sip, the one in the middle gets twice as much by default.

Passing man cooties around isn't cool :rolleyes:

[Jim Koepke]

Cory,

Welcome to the Creek.

Always the curious one I wonder where you are located.

One thing you said may be the problem,


To me, it seems like the problem is that the surface of my grinded bevel is somehow not in the same plane.

If you have removed more metal at the edges of the blade on the grinder or if the blade is bowed, this could cause your problem.

I do not think this is a stone flatness problem. My stones do not get flattened often and this doesn't happen to me. My stones do get regular rotations and I do make a point of using the full surface of the stones.

jtk

[David Keller NC]

While what you say is true, unfortunately the OP has the opposite of camber. If the stones are convex the blades will be concave, which is NOT what you want.

Indeed, but there's another explanation - that he's grinding a camber on the blade, and his stones are flat, in which case the center would be honed as shown in his picture. I think the only way to tell for sure is the standard "hold a known straightedge (like a machinist's rule) to the edge, and hold that up to the light". Generally speaking, a couple of thousandths gap will show up as a thin sliver of light, so perhaps he can measure the result and let us know.

[Jim Neeley]

Passing man cooties around isn't cool :rolleyes:

That's why the original quote was about sipping whisky... it kills the coots! LMAI..

[Jim Neeley]

Cory,

Have you tried that "known straight edge" on your stone?

Jim

[James Taglienti]

Did someone say something bout whiskey

[Cory Gilmer]

Thanks for the replies gents. Here's what I've found from looking into your collective suggested investigations:
- after (re)flattening my waters stones I found them to be dead flat with my 24-inch steel veritas straightedge (although I'm wondering whether the surface tension of the water in the stone may adhere to the straightedge and close any gaps that may be between the hard surfaces, preventing the tell-tale light from shining through - should I be drying the stones before checking?)
- my grinder's stone is definitely not concave, if anything it's a bit convex, although this may have developed since grinding the plane irons

Funny, I realize that a camber is ideal, but I'm a little phazed by the fact that I 'm getting it without even trying to (I hadn't gotten that far in my learning yet!). I can tell you when I try for a camber I won't be able to anymore - wish I could claim to have been trying for it. Problem with the profile I'm getting off the grinder now is that I have the Veritas MKII sharpening jig as well (more training wheels), and the wide roller makes it difficult-to-impossible to hone the entire cambered edge without honing away the camber (the roller is so wide that it prevents rocking the edge). If I could hone the camber coming off the grinder I'd be a happy camper, but as it stands with this waterstone jig, the only way to get a hone all along the edge is to hone and hone and hone until the edge is completely honed, but the camber gone. I guess I could get one of the cheap side-clamping jigs with the narrow roller that can rock to allow you to hone a cambered edge - but I'd hate to make the MKII obsolete so early on (I guess it would still be useful for chisels, where cambering isn't used?).

Tony, my understanding was that a somewhat aggressive camber is good on the coarse planes like a scrub or a jack, and should get smaller moving up to a jointer and smaller again on a smoothing plane. Is this wrong? I'm curious because you said you use your jointer without a camber.

I was overwhelmed by getting into woodworking - never mind that. I haven't even got to the wood yet! Amazing how involved something that seem so fundamentally simple can be - but guess thats reality of most things I suppose.

Thanks again everyone.
Cory

[Jessica Pierce-LaRose]

Maybe mines just worn out, but I have the MK II jig, and while I obviously couldn't get the exaggerated camber of a jack plane with it, by applying pressure at the edges, I have no problem getting more than enough camber for my smoothing planes.

[Jim Neeley]

Cory,

I'll tell ya what I get told regularly: Don't let yourself over-analyze it, to the point where you never do it! <g>

[David Keller NC]

Cory - You can get an auxillary roller for your MK II:

http://www.leevalley.com/US/wood/page.aspx?p=54181&cat=1,43072,43078&ap=1

That will allow cambering. And yes, I'd dry off the surface of your stones with a paper towel if you're using the "sliver of light" trick to tell if they're flat.

But - here's a simple way to tell what you're getting on your plane blades - put them in the plane and take a few shavings. You should be able to back the iron off so that you don't get a full-width shaving. On a cambered blade, that will eventually result in a very thin shaving coming from the center of the blade, with nothing on the edges. If your blades are straight across, you shouldn't be able to do that - you'll back the iron off, the shaving will get thinner but still full-width, and finally you'll go from very thin full-width to nothing at all, and no amount of fine adjustment will give you a "center shaving".