Thread: Metal files 101

I've posted again on Youtube the video showing the big machines cutting files, I hope it'll work better this time :
[ame="http://www.youtube.com/watch?v=xHDiTnwgZp8"]Cutting - YouTube[/ame]

I wrote to Harry Boggs in the US about the file sharpening service he offers and thought I'd share the response here in case others may be interested. Assuming high quality files, even with postage, the cost to sharpen the files would be far cheaper than good quality replacements.

If the files are American pattern files with a bastard, 2nd or smooth cut
they are going to run you .20 per inch. a 10" file would be $2.00 to sharpen.
We use liquid honing to sharpen files. The abrasive blast removes metal from the back side of the file teeth until the edge is reformed.
We have to remove metal to sharpen the edge and we are not deepening the gullet.
Because of this a smaller fine tooth file will take one sharpening while a coarser file would take two sharpenings.
Every sharpened file is block tested and if the file is too worn out or had too many sharpenings we will dip the file red and reject it.
We charge $.20 per file on rejected files because our labor is in this file.
We make the edges sharper than the manufacturer. In most metals the file will cut faster and last about the same as a new file.
In plastics and laminate this edge is far superior.

Harry Boggs

Boggs Tool & File Sharpening Company

Pete

Hi Liogier,
Working this time thanks.
Interesting stuff, if I remember correctly a machine for making files for clock makers was one of the first "machine tools"(although I think that gets claimed about a lot of things)

Stuart

Yesterday I purchased a new version of the file that I've been torturing:


See those tiny scores running down the file, across the ridges? I reckon that they are where the chips out of the ridges will start. All this time I thought that the marks on the old file were from me running it over the edges of threads, but it would seem that they are there to start with, and just begging for trouble. Noel Liogier makes a big deal about this for his rasps. He says that the blank has be really well polished so that when a tooth is kicked up in the stitching process, the edge of the tooth won't have a chip or otherwise in it. Look at all those scores in the unmilled area - how could you get a good clean ridge out of that???

I got an old rusty chain, and some rusty drill bits, and these were put into a 10% Citric Acid bath for 2 hours. The bath water was hot (prolly 70-80 degrees). The chain was then rolled/rubbed in my hands under running water, a very lightly camelia oiled. The drill bits were lightly Mr Brushed with a new fine wire brass brush on the flutes, and the equivalent stainless steel brush was used on the shank, also oiled.



The difference is staggering!



Then I put some drill bits (less rusty) into Cleaning Vinegar for 15 hours. Whilst there was rust removed, and plenty of black flakes at the bottom, they were nowhere near the Citric Acid result, and were cooked for 7 times as long (I have a pic, but won't bother with it).

Right! I'm done with experiments!

CONCLUSIONS:
Regardless of the solution/time used, there was no actual sharpening of the cutting ridges, WHATSOBLOODYEVER.

Mag Wheel Cleaner (5% alkaline solids): not bad for a bit of light cleaning.

Hydrochloric acid (from full strength to pissweak): WOFT, and dangerous to boot.

Cleaning Vinegar: pretty average, some rust removal, but nowhere near as good or efficient as Citric Acid

Citric Acid (10%): fabulous for removing rust, and therefore improving performance, but quite useless for actual sharpening

Timber Wedge edge: great for cleaning crud out of the gullets, and self shaping.


This is pretty much where I thought I would end up (but just how good Citric Acid was for rust was very enlightening). As far as I am concerned the "sharpening" word should be changed to "performance improvement" or just simply "cleaning". I'm not suggesting that those who claim "sharper" are having themselves on, quite the opposite, except that they a simply using a misnomer.

However, if you have a file that is clean, but won't cut properly, then it's time to buy a new one. Perhaps there is a benefit with Nitric Acid (a known steel eater), but I still can't see this working because the file is blunt by material loss so removing more ain't gonna help.

Over and out
FF

Good effort! I thought the use of the coat hanger wire as a "control" was a good idea, but I'm a little puzzled as to why it was not in any way corroded by the HCL acid. My understanding is that even non-oxidised steel will react with the acid, yet this wasn't occurring.

Pete

I still haven't seen a single word written on how you assessed the sharpness of the file, before or after 'sharpening'. Did you try to actually cut anything? Did you examine the teeth under magnification?

Bryan, sharpness was assessed by inspection under 8x magnification, and also enlarging the full-res pics. There was never any change in the tooth geometry. I was picking out certain identifiable areas of perhaps a square millimetre (shape of the chip etc) and there was no change. You can do it yourself, if you wish - download the pics and enlarge them. I can email the high res ones if you like.

I didn't file anything on the way through because that would have only meant going back a couple of steps each time to clean it up. It may well have also given false readings in the geometry if it became more blunt as a result.

Furthermore, this file is so badly chipped that not even diamond filing each ridge would do anything. With the naked eye you can see (looking perpendicular to the face) that each ridge has between 5 and maybe 15 chips in it. I think about this like thicknessing - if there is a low spot on the surface (say it's 5% of the surface) then you have to take off 95% of the surface to get the board flat.

Even if it did actually sharpen, by removing material in just the right spots - impossible - the ridges would be significantly smaller than at the start. This results in a file that takes off less material, or at best, clogs quicker because the gullets are shallower. Bite the bullet and buy a new file! If acid sharpening was ever going to work then you have to start with a reasonably uniformly blunt file.

Pete: I think that it's because of the high carbon content of the file steel. Carbon inhibits the acid apparently. Don't know what steel the coat hanger is, but I can't imagine it would be particularly high carbon, so go figure! By the way, there was a coating on the coat hanger wire (prolly galvanising) and that caused a nice big fizz until it was gone - indicating that the acid was ok (although old).


Imagine getting a piece of steel, triangular in profile, each face say 10mm across, and with fairly sharp edges. Do you think that dropping it in Nitric acid will yield a block with sharper edges? I can only see that the whole thing would shrink pretty much uniformly. Perhaps because the edges are thinner, then they may get more effect, but that wouldn't sharpen them, just round them over more.

How about someone else get a blunt non-rusted file, clean it, and then try to acid sharpen it? I betcha there'll be no difference (after cleaning).

The fact the steel coat hangar wire wasn't affected is what doesn't seem to add up. What you proved from that is that the acid doesn't etch steel, yet it's well proven that acid does indeed react with steel.

As far as your conclusions about the acid taking off metal in "just the right spots", I'm afraid I can't agree with that at all. Assuming the acid does indeed etch the metal, why do you feel it wouldn't also remove metal from the gullets, and not just the peaks as you're suggesting? In other words the gullets will also be etched deeper. The end result is that the file as a whole would be thinner. Bryan posted a good diagram of how removing metal from the tooth evenly will result in a sharper tooth, and I feel his theory certainly has merit. It seems you're intermixing wear and damage to the file, and I feel they are entirely different factors. As you mentioned, damage is damage and short of specifically somehow eroding specific areas I can't see much can be done to repair that. However that is quite different to wear resulting in a generally rounder tooth. Furthermore, anecdotal evidence would suggest that when steel corrodes the edges are indeed quite sharp. Just look at any heavily rusted thin piece of steel for that!

Pete

By "just the rights spots" I mean assuming that the wear isn't even (as it can't be). Yes the gullets would be etched as well. I also agree the wear & damage are two different things, but I wonder how often they are separated, paticularly in a cheap & nasty file like the one I tested. Actually not that cheap at $16.75, but definitely nasty.

By comparison, the price to us (in the Group Buy) of a Liogier 200mm Milled Smooth is $28.79, including freight. I'm yet to vizzy one of these but I'd be surprised if they are not significantly better quality (steel & milling). There are a few samples headed my way in Monday's shipment of rasps, so I'll know more about them in a couple of weeks or so.

One last argument, so obvious that I've never thought about it before. If acids can sharpen files, why files makers who dedicate their time and efforts to produce the sharpest possible files, do NEVER use this technique in their production process ?

Originally Posted by Liogier

One last argument, so obvious that I've never thought about it before. If acids can sharpen files, why files makers who dedicate their time and efforts to produce the sharpest possible files, do NEVER use this technique in their production process ?

Good point, although I doubt that Nicholson are trying to make the sharpest files possible any more.

Noel what do you make of detailed first pic in post #125? That's a brand spanking new version of the one I tortured. The scores down the length of the file must surely make it a crap file, prone to chipping.

Originally Posted by FenceFurniture

Noel what do you make of detailed first pic in post #125? That's a brand spanking new version of the one I tortured. The scores down the length of the file must surely make it a crap file, prone to chipping.

Yes this is exactly what I thought when I saw that picture. One can see that all these imperfections on the edges of the ridges probably come from two defects in the production process :

- the defects that repeat themselves at the same position from on ridge to the other mean that the producer should have re-sharpen or change his cutting scissor punch a while ago (this implies also that even were you don't see defects the bite of the ridges is probably not perfect).

- the defects that are randomly distributed probably mean that the surface of the file before cutting the ridges was far from perfectly smooth !

FF, could I trouble you for a bit more info on citric acid?
I'm aware of course that its acid from citrus fruit but can you buy it on its own?
I was very impressed with what vinegar did to a rusty bit of steel, so I'm very interested in the product you say is much better.
Purely for rust removal, you've convinced of the folly in thinking it sharpens files.
Jim

FF, could I trouble you for a bit more info on citric acid?
I'm aware of course that its acid from citrus fruit but can you buy it on its own?
I was very impressed with what vinegar did to a rusty bit of steel, so I'm very interested in the product you say is much better.
Purely for rust removal, you've convinced of the folly in thinking it sharpens files.
Jim