Pesky Concave blade profile after sharpening

Re: Pesky Concave blade profile after sharpening

Ted in Minneapolis

>Hi,

I always get concave and convex mixed up, do mean the corners are digging in when the center isn't touching?

Just a couple of guesses, but you might be pressing down too hard or maybe you're cranking down too hard when you tighten your jig so that the blade bends a bit and only the center gets sharpened. Then when you unscrew the jig the blade springs back the center is a tad shorter than the corners.

-ted

Coupla questions

Wiley Horne--Glendora, CA

>Doug,

Want to make sure we understand the problem. Are you saying that your blades develop negative camber? That is, if you hold the blade up to the light, with the back of the blade toward you (or the front, doesn't matter), and put a straight edge along the cutting edge of the blade--you see light in the center of the blade?

Secondly, have you put a straight edge onto your stones to see what's up there? If you're flattening these stones on glass that can flex--or anything else that can flex--you can get a convex stone.

Wiley

Re: Pesky Concave blade profile after sharpening

Doug Ball

>yes, by concave, I mean there's a dip in the middle.

It does seem like I'm removing more metal in the central portion of the blade...just not sure why that is happening, nor how to fix it.

Thanks

Re: Coupla questions

Doug Ball

>Thanks Wiley.

You're right, I can see light in the central portion of the blade, so I guess it's negative camber.

The 1000 grit waterstone is so new I've never flattened it. The 4000 and 8000 I've flattened just a few times on a diamond stone. They're not convex when I place a straight-edge over them.

Doug

Re: Coupla questions

Warren in Lancaster, PA

>Is the back of the blade concave?

Re: Coupla questions

Doug Ball

>Warren, the plane backs look absolutely flat.

Re: Coupla questions

Warren in Lancaster, PA

>I wonder if you are sharpening with the blade partly off the side of the stone so that the edge of the stone can slightly dig into the middle of the stone. We usually angle the blade so it is completely on the stone, or if it must over hang the side we keep pressure off the part that straddles the edge to avoid digging in the center of the blade.

Couple of things

Dan Donaldson

>First, just because a stone is new doesn't mean it is really flat. The first thing that I would do is check the stones with a straight edge to see that they are really flat. If there is a crown on the stone, that would give you that problem. Another thing I would check is to see if the back is still flat when it is clamped in the jig, just to make sure that you are not warping it from the clamping pressure.

If those are correct, then I would put the blade in the jig and sharpen it with the absolute minimum pressure on it. That might take awhile, but you need to make sure that you are not applying too much pressure and warping it.

If you put a straight edge on the blade, how much is it off?

Re: Pesky Concave blade profile after sharpening

Peter Evans

>The Veritas jig bends under pressure, hence the blade is going onto the stone with a bend in it. And you see the result. Use less pressure, and better still get an Eclipse type jig, or a Veritas Mk 2.

cheers

Poor man's grinder

Wendell @ Murphy, TX

>Here's my suggestion if you don't want to get a grinder. A long, thick piece of glass and Zinconium (sp?)sander belts. I use this setup with the LV Mk II honing jig when I need to straighten the edge of plane blade or chisel. It works well for me and while it may be somewhat slower than a grinder, I don't have to worry about over heating the edge either.

Wendell

Re: Pesky Concave blade profile after sharpening

Doug Ball

>Peter:

I think you might be onto something here.I did routinely crankdown hard on the Veritas jig. My MkII arrived yesterday, I will see if I can avoid the negative camber. I'll also flatten all the waterstones with a 220 grit drywall screen, as suggested in earlier threads.

Thanks for everyone's input!

Re: Poor man's grinder

Doug Ball

>Wendell:

What grit do you use and how long are we talking about?

Doug

Re: Pesky Concave blade profile after sharpening

William Duffield, on the Cohansey

>I'm sure Ted and Peter have given you the answer to your problem. In fact, this problem (using the original Veritas honing guide on wide plane blades), and it's solution, were reported several years ago (on Badger Pond) by one of our most respected members (R.J., maybe?). I'm sure you will soon find that you also have already solved it by upgrading to the much improved MKII honing guide, which clamps from both sides, instead of applying pressure in the center of the blade. The problem is worse with wider blades, with thinner blades, and with blades which have a slot down the middle for the lever cap screw. I am a bit surprised that you are having the problem with your relatively narrow and relatively thick block plane blades, however, unless you sharpen them after the smoother blade but before reflattening your stone.

Re: Pesky Concave blade profile after sharpening

paul womack

>The problem is worse with wider blades, with thinner blades, and with blades which have a slot down the middle for the lever cap screw. I am a bit surprised that you are having the problem with your relatively narrow and relatively thick block plane blades

Indeed. I would have though that bending a Veritas LA block plane blade in its width would be difficult.

Narrow, thick, no slot.

Now a #4 1/2 blade is the other extreme (in this regard)

BugBear

Re: checking for convexity

paul womack

>They're not convex when I place a straight-edge over them.

Convex can be tricky to detect.

I would suggest placing the stock of a small metal rule (6" for preferance) across the stone, on edge.

Then see if you can rock the rule, by pressing down on the rule just at (or very slightly within) the edge of the stone. If the rule moves - it's convex. If the rule sits firm and square the stone is either flat or concave (and you break out your feeler gauges :-)

A thou or 2 of convexity is hard to see, but if you're aiming at thou or 2 shavings, it's enough to mess you up.

BugBear

My poor man's grinder is

Scott Burr in Ben Lomond CA

>A 1-1/2" thick piece of marble. 9" wide by 3' long. Got it at the local

Stone/ rock supply. It was a cut off, so to speak. I paied next to nothing for it. I use a 100 grit belt to set the blade up square and flat across it. If it's really bad use an 80 grint belt.

Re: Pesky Concave blade profile after sharpening

Doug Ball

>As you predicted, the negative camber is much more pronounced on the LV 4 1/2 and quite subtle on the LA block and LN block rabbet plane blades.

The stones appear truly flat with no hint of a rock under my straightedge. I think the diagnosis of blade flex with the old LV honing guide is the correct one. Muchos gracias. I'm impressed!

Doug