Making a mortise chisel from a file

[Karl Andersson]

I was near the final stretch of a project building some new kitchen cabinets – just the frame and panel doors left to do when I started having trouble with my first mortises. The ¼ in Sorby mortise chisel I have (the only one) has square sides (and is only 1/4 tall at the tip) and it kept digging in to the sides of the poplar frame members. The finish was bad as well, pulling stringy fibers out, and the square sides tended to wander about 1/64th off-line.

I decided I needed an oval bolster mortise chisel (pigsticker), but couldn’t get one by today and I REALLY wanted to get the 20 mortises done this weekend. Last night I re-read Roy Underhill’s Woodright book(the one with blacksmithing in it) and decided to make a pigsticker.

I have been grabbing old files at flea markets whenever I can get them for less than a dollar – some are perfectly useable, others I keep for the tool steel – I’ve always wanted to do some blacksmithing. I looked through my worn out supply and found the only chisel that was close to ¼ inch thick was a “Johnson” coarse double-cut file, and it was just at ¼ inch thick, including the teeth.
It occurred to me that in this stringy wood, I could leave the teeth on and they might actually help smooth the mortises, so on I went.
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The first thing I did was anneal the file – I cooked some steaks last night and embedded the file in the coals after, leaving it there overnight to heat up then slowly cool. Today I tested it by hammering the tang to see if it snapped or bent - it bent, so I assumed the annealing worked.
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I built a forge out of bricks –solid for the floor and walls(with air gaps between the bricks on the floor), and a perforated brick in front for my air supply. For fuel, I used charcoal –mistakenly got the “lump” kind, like chunks of charred wood, but it seemed to work. Briquettes would have had less air gaps and may have burned more evenly. I also filled up a 5-gallon bucket with water for my quench tank. My bellows was a variable-speed leafblower (the lowest speed didn’t send too many embers flying). I lit the coals, then started shaping the blade.
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I clamped the file in an old machinist’s vise and started shaping the blade with a metal cut-off wheel on an angle grinder. First I cut off some length, then made the roughly 25-degree primary bevel I then trimmed about ¼ inch off one edge and re-cut the tang and shoulders to be centered on the new 3/4=-inch width.
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I used the grinder to remove the edge teeth from the remaining side and did a rough flattening on my LV MK II sharpener.
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Then it was time to temper the blade. I may be totally wrong that files are tool steel, but it seemed to work well. With the blower on, I was able to get the coals white-hot. I embedded the file in the coals and within about 10 minutes, it was glowing yellow-hot (just where Roy said to get it). I pulled it out and quenched just the tip and first 2 inches, then used a coarse stone to scrape off the carbon the fire had left and watch the temper colors rise back up the blade slowly. When the straw color got to the tip, I quenched the whole blade for a few minutes. Then I went back to the MK II and smoothed down the primary bevel and the belly. I did a little grinding on the tang to make it more even and pointed and then made a bolster out of the cutoff from the tip of the file.

I drilled and elongated the bolster hole with files, then found a piece of dogwood from my stash and drilled it for a stout (primitive)handle. It went on with a few smacks from a mallet – seems pretty permanent. Then I ground a 30-degree secondary bevel, honed it on my oilstones till it shaved hair, and I was ready to make mortises.

[Karl Andersson]

So, how does it work? FANTASTIC! Yeah, I have seen all the jokes made about the “chisel rasp” available at the BORG, but maybe they just got the file-to-blade formula wrong. First of all, the pigsticker dimensions are much easier to use for mortises – you can chop deeper with each cut and lever more waste (about ¾ inches on top of the blade). The Sorby actually bent once when I was levering too much. An added benefit in the stringy, soft poplar is that there are fewer strings because the blade stays on track, and the file teeth on the sides help scrape them off smoothly. I did a couple mortises (about 5 minutes each for 1 1/2x 2 mortises) and when I was at final depth, I was able to put the tip to the bottom of the mortise and lever the blade back and forth and got very smooth, even sides.
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Maybe I should patent this thing…but then again, it is such an easy thing to do and produces such great results, I figure y’all should just go make one and enjoy. Mr. Lee, we can talk if this gets in the catalogue. Mr.Wilson (George) – you’re right, I don’t know squat about metallurgy, but it worked this time at least – next I want to make some fishtail gouges andchisels from my file pile – any tips would be appreciated.

Sorry for the long post, but I am really happy with my new chisel. I am ready to crank out the rest of the mortises tomorrow –the blade didn’t dull at all during the first two, and I even cut a mortise in a bone dry piece of white oak to test the hardness – no tearing/ crushing on the wood and no more dulling than could be expected.



Let me know if you have any questions – I’ll be having on eof those smug moments and an accompanying beverage.



Karl

[george wilson]

Yellow hot is WAY,WAY,WAY too hot. You might burn the steel,or get it too hard(especially file steel-it is always on the brittle side). Orange hot is more appropriate for steels like 01,W1,or file steel,which is similar to W1.

After hardening,heat the file up to a dark brown color. Since file steel is high in carbon content,and tends to be too brittle,I recommend the dark brown color rather than a medium brown.

Many years ago(the 60's) I have had turning tools made from old files blow up in my face,so be careful.Your chisel won't do that,but the end of the chisel could snap off down in a mortise that you are trying to keep neat looking,and would not like to dig into.

A good way to eliminate guesswork about how hot to heat steel for hardening,is to take a magnet and attach it to a clothes hanger wire. When the steel gets hot enough that the magnet isn't attracted to it,quench. Try to keep the touching of the magnet to hot steel minimal as you don't want to demagnetize the magnet. An Alnico magnet robbed from an old speaker(a real old one) is a good magnet. Don't try using rubber based magnets for obvious reasons!!

P.S.: If you want a chisel without the teeth,grind the teeth off well below the gullet lines. The cyanide used in hardening files penetrates beyond tooth depth,and if not ground away,can cause your chisel to develop a serrated edge as it dulls because the cyanide areas are harder than the in between ones.

[Karl Andersson]

Geroge,
thanks very much for the tips - it was yellow in the fire, but I may have let it cool a little before quenching_we'll see. If it snaps in a mortise, it will become a relic. wouldn't it have been too hard to file if it was over-tempered? It files and grinds similar to my regular tools.

The charcoal was very diry - if I try to make chisels, i think I'll get MAPP gas or something - or do you think that would burn more because of the extra oxygen? the Chris Pye carving book has much more detail about heating and tempering - i'll pull that out before I go further. Roy's book seems more like "this is how it's done in the Smokies" which is where I was at mentally when I decided to do this.

oh, and if I'd filed the teeth, it wouldn't have the smoothing feature and would have ended up about 1/16th too narrow.

Of course, George, if YOU were to do a book about making and modifying tools, that would be perfect. You could probably do a whole book on making tools from scrap and old metal. I have tremendous respect for your knowledge, I just wish I didn't have to scour the forums to get it to hand.
Karl

[george wilson]

The file may be a newer model,and may not be made of the better tool steel they used to be made of. It could even be a soft steel,case hardened. If you got it yellow and didn't temper it too soft,I'd be concerned that the file was made from a cheaper steel.

If it cuts,go with it. Mortise chisels aren't subjected to as much use as regular chisels anyway.

Remember,Roy is not a blacksmith or metal worker. If you have better reference material,use it. I don't know Pye. W1 steel is not expensive. MSC sells it. It would be worth investing in some before spending effort in making tools. W1 is the bottom rung of tool steel,but it will take a sharper edge than more sophisticated steels. Just won't hold it as long. Straight razors were made from plain carbon steel of high carbon content.

Mapp gas: Your steel will actually absorb some carbon from your charcoal,which is not a bad thing. If you get it too hot,it will lose carbon. That MAY be why you can file your chisel,I can't say from here. Try another just heating to a maximum of orange.

[Jim Marshall]

This is really an interesting thread, I appreciate the great information from both of you. I have toyed with the idea of making some carving knives from files but just never have gotten around to trying. I have made several knives from different things that seem to work well. Hopefully I can find more information where George has posted, thanks for sharing.

[Jim Koepke]

Looks like a great way to have some fun.

jtk

[jason thigpen]

I have some old USA made nicholsons that were my grandfathers. Dull as can be! I've been thinking about doing something similar to this. I was thinking about some heavy duty marking knives.

[David Posey]

Just a few observations:

From everything I've read from blacksmiths, you DO NOT want to use charcoal briquettes, and you were correct in using lump charcoal. Apparently because of the fillers in them they burn up even faster than regular charcoal, which burns pretty fast, about 2-3 times the rate of regular coal. You could use a torch for treating small blades, but for larger blades I think you're better off with a solid fuel forge unless you build an insulated box around it. Having your heat concentrated in a small area makes it difficult to get a wide blade the same temperature all the way across it.

Also, not to be pedantic, but your terminology seems to be a little off.

Annealing is when you take steel up to critical temperature (where it's non-magnetic) and then allow it to cool very slowly. Burrying it in wood ash works, but I doubt the coals from your steaks got the steel to that temperature (although I've not tried this. Seems to me it takes additional airflow to get a fire that hot.) More likely the file was case hardened as George said and the heat was enough to temper the teeth to the point you were able to file them, and the middle part of the steel was always soft.

Heat treating or hardening is when you heat the steel to critical temperature, and then rapidly quench it.

Tempering is when you heat the steel to a specific temperature to trade some hardness for toughness.

http://threeplanes.net/toolsteel.html

This link has some of the details on what the steel is doing and on how to get the results you want. It also has a few different suggestions for determining when you've reached critical and some gas forge plans. The link talks about O1 instead of W1, which is also cheap, readily available, and pretty easy to work. There's lots of different ways to get where you're going. Good luck with your metal working.

[Kenneth Speed]

Bravo Karl! Very gutsy, good for you.

If you want to learn black smithing, you can but it the mean time you made something that works and got the job done.

Way to go!


Ken

[Karl Andersson]

Thanks everyone for the tips and encouragement- I got the rest of the 20 mortices done today and the chisel worked OK. I did have to sharpen it a few times and I think I only had a sharp tip because the more I sharpened it, the more I had to sharpen it (if you get my drift). the steel started to leave a long wire edge when I tried to reshape the tip - so it looked to me like it was too soft. But I think the saving grace was the shape of the tool - the strong back of the blade doubtless kept it from breaking and maybe concentrated the force of the mallet more efficiently. I suppose I should spring for a real one some day.

It was a lot of fun making the tool then having it work (better than my bought one). I would have used better materials, but I had to do this mid-project, and it only took about an hour to make the chisel and the forge. I don't know where to look to find info on how to tell the quality of steel on "found" objects, but I'll start looking. yes, I've heard to look at the sparks from a grinder but that assumes I have a grinder - or does an angle grinder count? I know I've seen a number of tools made from old files and rasps in books, so maybe there's a source short of finding some Ozark wizard.

[Jim Matthews]

Right or wrong - this is genuinely cool.

I'm keen on the "backyard brick forge" - the appeal of this project is the readily available materials.
My favorite belt knife is made from a file, and it holds a brilliant edge. It's one of the few tools that doesn't rust in my shop, too.

[george wilson]

The steel from an OLD Nicholson MIGHT be more reliable(might be tool steel all the way through). But,most older USA files should have been tool steel,I'd think. So,I am still thinking that white hot might have burned out the carbon. Try another and just go orange this time. Or use the magnet.

Jim,hardened steel doesn't rust as readily as softer steel. In the 18th.C.,some fine shotguns had case hardened barrels in an attempt to minimize rust. Doesn't make the steel stainless though,just helps resist easily rusting.