PDA

View Full Version : Fracture test of a Harbor Freight file



george wilson
08-09-2012, 5:07 PM
I hate to break brand new tools,but finally I clamped a new 8" HF bastard cur file in a machinist's vise and broke off 1 1/2" from the front end.

For sure,it is hardened all the way through. Nice,very fine grain fracture,with no color or grain variations anywhere.

I hit the file with an 8 oz. machinist's hammer,and it easily snapped off. This caused me some concern because files I have broken off for special use generally have had some resistance to breaking,and frequently took a second or third attempt swinging the hammer harder(or,get a bigger hammer,as they say!)

This makes me wonder if the file was hardened,but not tempered at all. If so,the edges of the teeth could microscopically break away in use on metal,causing the file to seem to get dull too quickly.

When I made rifflers(which are quite small),I'd harden them,then dip in water,and heat till the water sizzled,wait a second,and quench. Old timers called this "Taking the snap out of it),but leaving it plenty hard.

I haven't tried using these files on steel yet,but if you find that they don't hold an edge,I recommend placing them WITHOUT their handle,into an oven at 275º for 1/2 hour. The trouble is: most kitchen ovens can be 75º off. Let them air cool and see if they hold up better.

A better way to temper smallish parts with simple means,is to buy a high temp. Thermometer with a long probe on the back and insert it into a slot on the back of a toaster oven. ONLY rely on what the high temp. thermometer says,NOT on what the toaster's thermometer says. You can get these from Brownell's Gunsmith Supply. A wise investment. They go up to 1000º,or so. Great for producing a beautiful spring temper blue.

I still think the HF files are a good deal,and could easily be heated in an oven if a bit more toughness is needed. You can't easily fix a file that is too soft,like the Mexican Nicholsons. But,too hard isn't a big problem.

Ryan Baker
08-09-2012, 7:14 PM
Good info. Thanks for doing the test George.

Jim Koepke
08-09-2012, 9:25 PM
George,

Thanks for sharing your wealth of knowledge. I find it very handy to know many of the things you have shared.

jtk

Brian Ashton
08-10-2012, 6:02 AM
When I made rifflers(which are quite small),I'd harden them,then dip in water,and heat till the water sizzled,wait a second,and quench. Old timers called this "Taking the snap out of it),but leaving it plenty hard.



Can you be more elaborate on this process... Isn't all taht clear to me but it's sound like a good nugget of info

Jacob Reverb
08-10-2012, 7:00 AM
You can't easily fix a file that is too soft,like the Mexican Nicholsons.

George,

I wanted to ask you about that...whether you had any kind of "fix" for your soft Mexican Nicholsons.

Couldn't you heat them to critical/non-magnetic in a coal forge; quench; and temper to maybe 430°F / pale straw?

I was surprised to hear that 275°F would do anything at all...even soaking.

Thank you for sharing your knowledge with the board. So much of this is being lost!

Jacob.

Jacob Nothstine
08-10-2012, 8:41 AM
George,
Do you have an item number for the file you tested? Would like to pick one up.
http://www.harborfreight.com/catalogsearch/result?q=file

David Weaver
08-10-2012, 10:37 AM
I don't know if george will come back and comment, but on really plain steel like file steel (or japanese white steel #2) that has a lot of carbon, 275 degrees would bring it just off of its max hardness and give it a little bit of toughness. 400 degrees or something like that would be catastrophic for a file that was expected to work steel, it would probably bring it down to 58 hardness or so. 275 should bring a plain carbon file from about 66/67 to 64 or so.

Old file steel probably had a profile very similar to white #2. I doubt the new files have as much carbon in them as the older files, that's just a guess, though, because less carbon (like 0.9% or 1% would make them a little bit easier to harden and temper than files at 1.1 or 1.2%.). The chinese could be making high carbon files, though, you never know.

george wilson
08-10-2012, 10:59 AM
You are correct,David. The slight tempering is just to give a little toughness to the file. It is not a knife,and needs to be harder.

Jacob Reverb
08-10-2012, 1:12 PM
Interesting...thanks for your reply, David.

For some reason I thought files were tempered back about like cold chisels or scrapers but I guess not. Sounds like they're only tempered a bare minimum!

(FWIW, I just looked at a graph in "The New Edge of the Anvil" where they plot Rockwell C hardness against temper temperature in 3 steels with 35; 80 and 120 points of carbon, and was surprised to see it looks like all 3 steels actually get slightly harder from 100° to 200°F, then slowly soften from 200°F to 300°F and then soften a bit faster, and linearly, from about 300 to 1200°...)

Another book talked about some odd method blacksmiths used to temper files with yeast, tallow and bread dough paste to try to keep the carbon in the steel...interesting stuff.

george wilson
08-10-2012, 1:47 PM
I have used a batter made of water,flour,and a bit of yeast for coating tools being heated to prevent decarb. Works fine. Old time recipe.

Disadvantages: Batter won't keep,you have to make it fresh,smells up the shop,smelling like burnt bread.

Advantage: stuff is on hand in a pinch,is cheap. Most of the time I use PBC No Scale. It seems to be the best stuff. If quenching in water,both things fly off of the tool,or can easily be brushed off,leaving a clean,gray surface like a new file.

Stubbs in England used"beer leavings" to coat their files. Old timers managed to use cheap,readily available stuff for a lot of problem solving that modern folk think they have to go and buy.

Jacob Reverb
08-10-2012, 2:34 PM
Thank you, George. I wonder whether that PBC No Scale stuff would be good for forge welding, like borax.