I need to bend some round and half round files to use a rifflers. Can anyone point me in the direction of a website that gives the details of re-tempering the files after I've bent them. If I'm not mistaken the process involves getting the file red hot and then quenching in oil. Then bringing the file up to a specific temperature and or color for a sustained period of time, and then quenching or letting it cool slowly, but I'm not sure which.
You might want to try this question over on rec.crafts.metalworking.
Try this:
Curved files are a tricky bit of heat treating, compared to re-using old files as chisels or punches. Although we're spoiled today by easy access to cheap high quality steels, a "tool steel" (i.e. one that could be hardened) used to be a rare beast. Old files were a good source of it and would often be re-worked into other hand tools.
If you're making curved files, especially for use on metal, start with a brand new and unused file. Contamination of the teeth can cause problems during the annealing and hardening processes, and you'll be likely to find that your file is never as good a cutter afterwards as it used to be.
To anneal files, you'll need a hearth. This is a small box of firebrick, where you can heat them and allow them to cool slowly. best thing is to go to an engineer's shop and buy some firebricks. They're cheap, and they'll always be useful in the future. Every workshop can use a simple hearth.
If you don't have this, make a lash-up. Take the side cheeks out of a coal fire and use them. Use the door of an old oven. Cast a bowl of fire cement (or mix your own from cement and vermiculite - search for woodstove making recipes). Be careful using building materials though
- most of them will spall when heated and fire sharp fragments at you. If you're really stuck, just use a bucket of dry sand, heated over a fire.
Be careful with the old "Leave it in the coal fire overnight" approach. You need clean coal, or well-burned low-sulphur coke. House fuels can cause havoc on good steel.
Then heat your files (big gas torch is good, or a solid-fuel hearth) and get them to a cherry red. DO NOT OVERHEAT ! You really don't want to burn the edges off those teeth. Hold them at this heat for a couple of minutes, then allow them to cool as slowly as possible. This is the time when your firebrick box is useful, or else a sprinkled layer of hot dry sand. Keep the cold air off, and certainly don't let water near them.
Batch heating files may be done by placing half-a-dozen of them together. Turn them over and exchange them whilst heating, to make sure it's even, but keep them close together whilst cooling.
Heating files, either for annealing or later on for hardening, will burn the edges of the teeth. Traditionally they were always coated with an oxygen-excluding paste. Makers had their own favourite recipes, and these could range from inert clays to bread dough. "Moist-bastos", an anti-distortion paste used by car body repairers works too. Personally I use red clay from the garden, which has been a traditional material for it here in Bristol for centuries. If you're making coarse woodworking rasps, you can probably get away without this layer. If you're making engineer's needle files for use on hard steel, then it's essential.
Now you're ready to bend your files. Wrap them in lead sheet (roofing lead) first, to avoid crushing the now-soft teeth. Expect breakages, and don't work in a way where you'll slip if one does snap.
Your files will have been made of homogeneous cast steel, so you'll need to harden them, then temper them.
To harden, heat the files to a cherry red and then quench.
Heating for hardening is much like annealing, with similar uses for a firebrick hearth and a shielding paste. There's less need to hold at the high temperature.
The temperature can also be determined very accurately (this is more critical for hardening) by heating to the Curie point - which is also the point at which a magnet is no longer attracted. Make yourself a magnetic tester by wrapping a small magnet (not too powerful) with a piece of coathanger wire to make a handle.
Don't use a hand-held magnet. You'll burn your hand getting that close to a piece of red hot steel and you'll feel a right eejit when the thing sticks to the workpiece and you've got no way to pull it off.
I'd quench file steel in brine, rather than water or oil, but you could use any of the three. Water risks cracking, but might be worth doing if you're going to be working hard steel. Oil is good for big rasps that'll get a hard life of being leant on. Use all of them in a deep vessel and make a vertical point-down quench.
To make brine, pour salt into a kettle of boiling water until no more will dissolve and there's a little left at the bottom. Then leave it until cold.
Clean up the file and polish as best as possible. You might even use a little hydrochloric acid to clean deep between the teeth.
Tempering makes the steel less brittle, and hopefully doesn't lose too much hardness. This should be very subtle for a file - less so for a hard-working rasp. You might even choose not to temper at all - bad idea for a chisel, but reasonable for a small metalworking file.
Tempering is a matter of careful and gentle heating, to a very exact temperature and then quenching (plain water is good). These temperatures are usually described as surface oxidation colours, which can be seen on a polished surface where they change in colour from progressively lighter to darker colours. A file should be tempered to only a "light pale straw yellow" - basically the first sign of colour that you notice. To get even heating throughout the file, you'll probably find it best to lay the file (one at a time) on a thick steel sheet and then heat evenly from beneath. As it's only 430°F that you need, you might even do this by placing the files briefly into a pre-heated oven.
-- Die Gotterspammerung - Junkmail of the Gods
"hedgeog" wrote
: I need to bend some round and half round files to use a rifflers. Can : anyone point me in the direction of a website that gives the details of : re-tempering the files after I've bent them.
Although theory suggests that re-hardening should be done, I've made limited use of bent rasps without instant deterioration of the cut. Maybe the rasps will serve quite well for most timbers if left untreated.
: If I'm not mistaken the : process involves getting the file red hot and then quenching in oil. Then : bringing the file up to a specific temperature and or color for a sustained : period of time, and then quenching or letting it cool slowly, but I'm not : sure which.
From what I've read, there is more to it than that. The correct process involves, I believe, in heating/cooling the files while encased in clay. Presumably the points could be eroded by exidation during the heating and then be cooled too rapidly during quenching, thus making the metal too hard and therefore very brittle.
Jeff G
-- Jeff Gorman, West Yorkshire, UK Email address is username@ISP username is amgron ISP is clara.co.uk Website
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