Drilling Hardened Rasps

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mpcoppin

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Dec 8, 2017
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A friend has a bucket of old rasps sitting around that I can have. I’m thinking of just doing some stock removal on them “as is” because I’ve had really bad luck getting similar rasps to harden after annealing.

The main problem I had the last time I did this was getting holes in the tang. I’m planning to buy a carbide bit for the next one but need help knowing what to buy.

All carbide, carbide tip, straight flute?

My drill is not great (HF Bench Top) and, as you know, rasps aren’t exactly a clean drilling surface so I worry about shattering bits.

Any suggestions (other than a- not working with rasps, or b- putting on big boy pants and learning to heat treat the rasps right)?
 
For small holes in hardened steel, I regularly use a carbide end mill with a slow feed rate. Also, if you are using carbide, the rasp needs to be held firmly and you need a clean/flat surface to drill into. grind that area clean before drilling. I would also recommend wearing protective gear to prevent shards of carbide from entering your squishy bits.

If you want to make life much easier on yourself, temper the rasp first, and temper the area you are going to drill to a dark grey/dull red prior to drilling.
 
What do you have to HT a rasp with? Once the rasp is ground to shape, it "should" harden nicely just by heating red hot an dunking in water - better heated canola oil. I've read some of the modern manuf rasps 'n files are actually low carbon steel with casehardening on surface to make "teeth" hard. Are you sure your rasps are high carbon steel?

A way to test would be to grind all teeth from rasp, make it a "blade shape" for testing if you wish. Once it's very roughly profiled and ground smooth, while in dim lighting heat to "red hot" (check with magnet to be sure it's just past non-magnetic) then dunk in water. That should harden nicely - might even crack. That's ok if it does crack, tells you it's high carbon and will harden with proper HT.

Now, on the carbide bit to use for drilling holes in harden tang - something like this should work for a 3/16" hole:
https://www.ebay.com/itm/222760666272? (at $13 shipped you don't wish to break many).

At $6 shipped these are a bit cheaper, and some folks say a masonry bit will drill harden steel.
https://www.ebay.com/itm/181780327360?

Good luck
 
joedhiggins said:
I regularly use a carbide end mill with a slow feed rate.
Click to expand...
Just a regular 4 or 5 flute square end?

Typically clamp knives down pretty well when drilling. I’ve never tried spot tempering but I should have thought of that back when I was breaking bits on my first attempt.
 
Sure, ball ends work too. Either way. I have a really nice drill press with basically no run-out. not sure if using a press with a lot of run-out in the quill will increase likelihood of snapping mills (seems likely).
 
yeah, cut off a chunk, grind through the surface layer, heat to a brightish orange in a darker room, quench in water. File test, clamp in vise and hit with a hammer (wear eye prot, gloves, heavy jacket, etc.). See if you can get it to break without bending. If none of these things happen, you have a case hardened file. They will be useless for knife making.
 
I was given several farrier rasp at the Blade Show. It was several years after I received the rasp's that I forged a blade out of one. Actually before I forged the blade I did a spark test to see if there was much carbon and it looked like 4th of July. Got the blade rough ground and went to heat treat it. I first went to quench in oil and it was soft as could be. Tried water and still nothing but dead soft. Turns out these rasp's were case hardened. Now if you grind out a knife blade from a case hardened file you most likely will grind off the hard part and have a blade that is to soft. I would recommend doing what joedhiggins suggested.
 
joedhiggins said:
I would recommend learning to heat treat properly, otherwise, why own a kiln?
Click to expand...

Because it was $25 on Craigslist!

It’s only a small (8” square x 3” high) kiln with no temp controls. Tested with cones it gets to about 1600° barely.
 
joedhiggins said:
yeah, cut off a chunk, grind through the surface layer, heat to a brightish orange in a darker room, quench in water. File test, clamp in vise and hit with a hammer (wear eye prot, gloves, heavy jacket, etc.). See if you can get it to break without bending. If none of these things happen, you have a case hardened file. They will be useless for knife making.
Click to expand...

I’ve heated one to about 1500° (bright orange by my eye) multiple times. I’ve tried quenching in canola oil, brine, and plain water. Every time I file test it’s really soft. I’m guessing it’s case hardened & is junk.

I’ll do a test on the new ones before I waste time grinding.
 
mpcoppin said:
A friend has a bucket of old rasps sitting around that I can have. I’m thinking of just doing some stock removal on them “as is” because I’ve had really bad luck getting similar rasps to harden after annealing.

The main problem I had the last time I did this was getting holes in the tang. I’m planning to buy a carbide bit for the next one but need help knowing what to buy.

All carbide, carbide tip, straight flute?

My drill is not great (HF Bench Top) and, as you know, rasps aren’t exactly a clean drilling surface so I worry about shattering bits.

Any suggestions (other than a- not working with rasps, or b- putting on big boy pants and learning to heat treat the rasps right)?
Click to expand...
Look here ...............
https://www.bladeforums.com/threads/sharpening-masonry-drills.1540592/#post-17748361
 
The vast majority of Farriers rasps are a W steel. before I learned this I never could get them to harden in oil, now with water quenching I haven't failed a single one. They will warp to the grooved side if you take to much meat off before heat treat so keep that in mind. Before starting work cut the tang off and water quench it to make sure it will harden.

As a side note I personally have never found one that doesn't harden in water.
 
A fairly large percentage of rasps made in the last 20 years or so are case hardened mild steel. If they won't harden, that is why, and they will be equally unsuitable for stock removal.
 
The guys above speak the truth. Most rasps are case hardened, it’s much cheaper to manufacture. So for all practical purposes thy are not worth messing with. Just buy you some good known steel.
 
JTknives said:
The guys above speak the truth. Most rasps are case hardened, it’s much cheaper to manufacture. So for all practical purposes thy are not worth messing with. Just buy you some good known steel.
Click to expand...

Good file/rasps have some advantage for us who can t HT this steel .Only we must be careful to not overheat when we grinding bevel .....Look in this beauty ............. Puukko is calling me ;)
@mpcoppin you can check file in many ways , no need to HT ....grind one side and check if tip of some knife/blade can scratch that part .... or cut piece and break in half ...........
nsBPCh6.jpg
 
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