Silicon Carbide Grit (Wet or Dry) for Initial Shaping

[Bill Adamsen]

I'm in the process of resurrecting some older chisels I'd acquired. Wet or dry sandpaper on granite has been my sharpening method of choice for about the past 20 years. I started with 220 grit for the major resurfacing (just four chisels, two paring - 1" and 1/4", and two 1/2" mortise chisels) and I went through a quantity of 3 9x12 sheets - which seemed like a ridiculous amount of paper. A prior owner/user had sharpened both front and back of the paring chisels making the amount of cutting down on the front a pretty significant amount of work. I could have done the initial pass to cut the rough bevel with a grinder or sanding belt but always worry about overheating.

I wondered if there was a more aggressive wet or dry sandpaper (80 grit?) or other "hand" method others have used when needing to remove a lot of material from what is going to be a fine chisel?

[Ron Hock]

Silicon carbide is very hard and very sharp buy also very brittle. That's why it cuts so well when fresh but poops out so quickly. Search for "honing film" or "lapping film" (same thing) with peel-and-stick adhesive. Honing films use aluminum oxide grains which are much tougher and last much longer, glued to a Mylar backing which is quite tough and holds up very well to honing pressure, water, etc. Honing films are graded in micron-size particles instead of the ANSI/CAMI (USA), FEPA (European) or JIS (Japanese) grit size standards. I found micron grading to be very straightforward and easy to understand once I understood the basics and looked at a good comparison chart: http://www.hocktools.com/temp/15hGritChart.pdf.

Good luck!

[ian maybury]

+1 that silicon carbide dies very quickly on metal.

A coarser self adhesive paper as Ron says seems to do the business - some have written of having great success working manually on a long strip of 80 grit stuck down on a long strip of granite worktop or the like.

I've had very good results back flattening and cleaning up bevels on the top surface of a WorkSharp using the stock 80 or 120 grit AL Ox discs or 6in x 1/2 in 80 or 180 grit diamond coated lapidary discs - the low 500rpm and small dia mean that heating is manageable provided care is taken to work in very short bursts (few sec) cooling in between in water. Especially when getting close to the edge. It takes a very fine touch to drop on flat every time and avoid dubbing the edge, and gets slow on wide western pattern (non hollow back) chisels unless they start out very close to flat. (e.g. 35mm)

Sanding belts over a flat platen work and are quite a bit faster, but as you suspect overheating is a very real risk that requires very careful handling to avoid. A variable speed drive would be ideal. Derek Cohen has a write up on using a belt sander on his site...

[Mark Stutz]

+1 that silicon carbide dies very quickly on metal.

A coarser self adhesive paper as Ron says seems to do the business - some have written of having great success working manually on a long strip of 80 grit stuck down on a long strip of granite worktop or the like.

I've had very good results back flattening and cleaning up bevels on the top surface of a WorkSharp using the stock 80 or 120 grit AL Ox discs or 6in x 1/2 in 80 or 180 grit diamond coated lapidary discs - the low 500rpm and small dia mean that heating is manageable provided care is taken to work in very short bursts (few sec) cooling in between in water. Especially when getting close to the edge. It takes a very fine touch to drop on flat every time and avoid dubbing the edge, and gets slow on wide western pattern (non hollow back) chisels unless they start out very close to flat. (e.g. 35mm)

I've used the Veritas powered system to flatten backs. I use a foot operated switch so I can use both hands to place the chisel flat on the platen before it starts. Still takes some practice and a sure hand.

[Bill Adamsen]

I wasn't really sure what the material was ... the 3m Imperial Wet or Dry indicates it is Aluminum Oxide. But still, it cuts quickly to start and rapidly dulls. Thanks for pointing out the "honing film" and when I looked that up I discovered lots of resources on using it. I will look into that more deeply. Thanks again!

[Alan Schwabacher]

You can also sprinkle loose silicon carbide grit on the spent paper that is glue to a flat substrate. It seems to cut better than the paper does, and is far cheaper.

[Jim Matthews]

I remember doing the same calculation when I had a stack of irons
and chisels to prep. At $1.80 per tool, it started to add up.

http://www.amazon.com/3M-Wetordry-Sa.../dp/B001449TPS

I would get a Norton coarse stone for this purpose.
They cut fast, are easy to flatten and last near forever.

For a few dollars more, an Atoma 140 will last your lifetime.
It also serves to flatten water or oil stones.
(My preferred method, now.)

I don't like the dust generated by sandpaper methods.
If I use your method, I run the shop filter and wear a mask.

[Al Launier]

I used a multi-grit diamond "stone" to "rough remove" any significant amount of material, then switch to aluminum oxide for semi-rough & finish.

[bill tindall]

Somewhere back in time the myth got started that silicon carbide wet/dry was the material to use for sharpening/flattening. In the coarse grits it is too brittle to use on hardened tool steels. You don't need wet/dry to grind these tools. Aluminum oxide, or better at coarser grits zirconia paper, is the material to use. The lapping films mentioned are very good and very expensive and not necessary for the coarse material removal you are looking for.

Stick some 80 grit zirconia or aluminum oxide paper or a piece of belt on something flat with spray adhesive and grind away. If you have a Klingspor store near-by for $5 you can get a life time supply of belt scraps from their bins.

[ian maybury]

TBH Bill i think you're going to run through significant quatities of almost any paper you care to mention if there's a decent amount of metal to remove. Silicon carbide is pretty commonly available for car repair use (and it cuts very well initially) - which probably explains how it so often gets used.

Another well proven option for flattening chisels is a powder abrasive over a steel lapping plate - i've no experience of it.

The underlying issue in all of this is that the difficulty of the back flattening task depends enormously on the depth and area of metal to be removed. What seems like a great solution on a well finished blade of limited area becomes interminably slow and heavy on material on say a plane iron that's significantly out of flat. Ditto when flattening plane soles as on the other thread.

The backs of Lee valley BU plane irons which are normally very flat indeed (within microns) clean up in minutes over a 1000 grit waterstone. Against that a wide Western chisel that for whatever reason is a bit bowed could require a whole day (as could changing the bevel angle on a thick plane iron), and is instead better attacked on some sort of powered or other much faster cutting option.

It can be quite frustrating if setting up a lot of new tools - no sooner do you think you have the answer to the maiden's prayer but a different scenario shows you that you need yet another level of capability. Once set up it's not such a big deal, as all being equal the worst requirement will be to cut back primary bevels...

[Marc Seguin]

If the paring chisel you mention has a bevel ground on the back as well I'd take that off with a grinder. Hold the chisel at 90* to the wheel/belt and grind back to where the back is flat again. Trying to 'lap' the back steel away until that rear bevel is gone will take ages and be far too much work. You won't need to worry about overheating the chisel if you're shortening it with the grinder since the first pass or two will remove enough steel to get you back to the thicker part.