Veritas Mk II Power Sharpening - Chisel Lapping Help Needed

[Steve Friedman]

Hi,

I have been using the Veritas Mk II Power Sharpener for over a year and love it for everything except flattening the backs of chisels that require a lot of steel removed. Heat is an obvious problem, even using a magnet as a heat sink. The bigger problem is that holding the blade at different angles seems to produce different results.

For example, I used an 80 grit disc on a gnarly Witherby chisel, with the cutting edge held into the rotation direction (leading cut?) until the scratch pattern was perfectly uniform (checked under a magnifier). I then coated the back with a red sharpie and went to work on a 120 grit platter at a different angle - this time pointed at the center of the platter. The 120 grit scratch pattern and sharpie ink showed several high and low spots. It wasn't just one are - it was showing a slight belly in the blade and some twist as well. By the way, I was using a brand new platter for this. I suppose it's possible that this is all due to uneven finger pressure, but I have at least 4 fingers on top of the blade when I do this.

Even more frustrating is that when I check the flatness against a DMT stone, my Veritas lapping plate, or sandpaper on glass, it's even more out of flat. I suppose I could just flatten by hand instead of machines, but would love to make this thing work.

So, my question is whether this can all be user error? I try to press down only hard enough to keep the blade from flying off the moving disc. If it is user error, has anyone come upo with a clever jig to use with the Mark II to help keep the blades perfectly flat? I don't have as much problem with plane blades because I can use a wooden jig to hold them. Buy chisels don't have holes in them to attach to the jig.

Thanks in advance,

Steve

[Rob Lee]

Hi Steve -

The short answer is - it's just not designed for lapping that way. Maintaining flatness on a large surface will be difficult, as each point of the diameter of the platter will have a different velocity - which means a different cut rate.... the part of the blade nearest the center will abrade more slowly than the part near the rim...

For a holder (hand or power lapping) - use a block of wood with a few flat head screws sunk flush, and then backed out by just enough to act as small "dogs" to grip the side of the blade... works really well.

Cheers -

Rob

[Gary Curtis]

On the same machine I had problems only with large Mortise Chisels. And the cause — I think — was that I was hand holding. Lee Valley doesn't make a tool holder for unusual blades. Knives, for instance. You asked several questions. As to heat build up, I have a water spray bottle near at hand. This gets quite messy, so erect a cardboard shield around the circumference of your work area. It doesn't harm the abrasives.

Over the 5 years I've had the machine, some posters on this forum have submitted photos of homemade tool holders. Usually of wood blocks. Threaded screws and wing nuts grip the tool. It isn't rocket science. You won't make headway if you can't present the tool at a preset angle and maintain that angle religiously. For kitchen knives I just made some 17° wood wedges to guide the blade. If I were ambitious, I'd mount a little roller in the wedge. But I just try press on the forward edge of the knife instead of bearing d

[Jim Koepke]

I also have the Mk.II Power sharpening system.

In addition to what Rob Lee posted there are a few other things that come to mind.

It is real easy to mess up a flat back on a powered abrasive system. I have had a few slips of the hand that put some nasty spots on the backs of smaller chisels.

A bubble between the abrasive and the disk can cause a lot of problems. So can a bit of swarf build up.

One thing that seems to help is to keep the piece being worked moving.

I have used the Mk.II for flattening backs. Since then I have acquired a large hunk of granite. With a 4' strip of 80 grit paper I can warm up a chisel or plane blade without much effort. It can also get the back flat faster than with a powered system. After this, a blade will get a quick shot on a finer grit on the Mk.II. Then it is usually on to the stones.

Only a few of my blades are what even comes close to perfectly flat on the back. If a small area from the bevel edge to edge is good, that is good enough for me. Every blade in my shop gets its back worked every time the bevel gets worked. As this process progresses, all of my blades get better backsides. It is nice to have a perfect polished back for the full length of a chisel, but it doesn't do anything much better than a chisel that only has a polished area for a 1/16" from the bevel on the back.

jtk

[Steve Friedman]

Thanks everyone.

Jim - I've seen the video of you using that granite slab and am in the process of "borrowing" your idea. I am just waiting for the roll of 80 grit paper. I already have a 3" x 36" piece of glass that I will mount to 3/4" MDF. But I do love that granite slab! In fact, I just found out about a granite place near me that sells odd pieces. If the glass doesn't work, that may be my next stop.

Rob - Part of the problem is that you have spoiled me. Since getting the 1 x 42 belt sander/grinder and the Mark II, I virtually stopped sharpening by hand. The The Mark II is great for flattening wider blades, but is tricky with narrow and mortise chisels. I'm happy with that and will accept the fact that I just need to flatten those by hand.

Steve