Chisel Rehabilitation -- How do you set the "finished" edge angle?

[gwagner]

I have a chisel that someone ground from the back side, so I must remove about 3 mm of metal before I get back to the flat on the back of the blade (photo attached). As I grind that much metal the edge angle will change in relation to the stone. So if I start at 30 degrees and grind off 3 mm I'll be at a sharper angle when done. Then I'll have to reset and grind off even more.

Is there a trick or technique for setting the "finished edge angle" from the start when you're rehabilitating a chisel, so that once all the bad material has been ground away I'll be at the 30 degrees I need?

[Ken S]

Welcome to the forum, Gill.

I would set the support bar almost against the grinding wheel in the horizontal position. Place the chisel beneath the support bar so that the support bar is supporting it. You will be doing the first part handheld, but well supported. Hold the chisel straight in, at a right angle or zero degree bevel. Grind until you have removed the back bevel. Once you reach this point, place your chisel in your straight edge jig set for your 30°. Part way through grinding your bevel, check your angle to make sure you are on target. Wolfgang Hess demonstrates this in one of the recent online classes. (I believe the tips class, toward the end.)

Keep your grinding wheel graded coarse and do this on a day when you are not pushed for time.

Keep us posted.

Ken

[gwagner]

Thanks, Ken.

If I understand you correctly, there's still a lot of guesswork going on, at least while getting the chisel close. I came up with a way I think will work. Hard to explain in text so I took some photos. See the steps and photos in the pdf.

Am I missing something, or should this work?

Gill

[tgbto]

I would personally use the side of the stone and the WM-100 to eyeball where the chisel would come clean at the right angle... and then grind for a few days.

A bench grinder or belt sander, even with the chisel held at an approximate angle, would remove most of the material at the apex. You'll finish it clean on your Tormek.

[gwagner]

My fear on using a grinder is the heat issue. I have the coarse diamond stone arriving tomorrow, so I won't have to worry about wear and tear on it. I'll track grinding time and share it here -- and let everyone know whether my trick for setting the angle works!

[Elden]

Remember light pressure on the diamond wheel. I found that issue out first hand on DMT diamond stones quite a few years ago.

[gwagner]

Good to know. Thanks for the heads-up.

[Ken S]

Elden's comment reminded me of a similar lesson I learned with a diamond flattening plate. It would allegedly "flatten every sharpening stone in the shop". That claim is almost true. It worked very well with water stones and India stones. A crystalon stone essentially destroyed it. The crystalon (silicon carbide) was too close to the diamonds in hardness. Diamonds are very useful but can be fragile.
Heat is not an issue with diamond wheels used with water and ACC on a Tormek. Neither are sparks or dust. It is a pleasant, contemplative way to work. Enjoy.

Ken

[gwagner]

My angle-setting trick worked! (See PDF.)

Took me 1.5 hours of grind time on the DC-250 (Diamond Coarse), but I followed everyone's advice and used virtually no pressure. Actually held the jig by the tightening knobs with only VERY slight downward pressure. Moved back and forth at about 30 repetitions per minute. Finished it on the SG-250 at 1,000 grit (since it's also a new stone I didn't need to change angles after changing stones).

The first hour was rather Zen like. But I admit that as I started getting close, time slowed to a crawl!

I would NOT recommend anyone put this much time and energy into a simple wood chisel. I did it for the experience only. I have a few of Dad's old chisels that need some significant rehab, so the sentimental value of doing them will make the investment worthwhile.

[tgbto]

Nice job, congrats on the result, and on your patience !

[gwagner]

Thanks! Not bad for having my machine only one week.

Loved the Diamond stone. Of course as my SG-250 wears down I'll either need to reset my angle after I switch stones, or suck it up and buy the 1,200 grit Diamond. (That's when my lack of patience will cost me money. ;-)

I am having a ball learning this thing. Can't wait to buy my knife and scissors jigs (but gotta wait until after Christmas because I put those jigs on my list.)