Thread: Metal files 101

This is the same series of pictures (reduced in number), but I have cropped them in before resizing them to fit on the forum. That is to say that they are effectively higher resolution for the purposes of viewing them within the forum (but the uploading process has hit the res, as it usually does, even when the files are within size limits).

I have eliminated the steps where there was no difference: Spotted Gum rubbing; flat, edge and spin brushing; 1:20 hydrochloric acid; Draino solution

You dirty bastard


Douglas Fir rubbing


Mag Wheel cleaner for 15 minutes



Acid 1:10 for 15 minutes I can't see any change here, at all




Nice polished nicks from the spinning brass wire brush after all solutions. I'm wondering if I photographed a different part of the file here - I can't match up any of the blobs and dings in the pattern. I checked the previous pics, and they are all matched up.




The bottom right hand corner is the only part of the file that has some ridges (or part of) that look like they would have when the file was new. They look like they'll cut something, the rest of the file looks like crap.


Is it Mythbusters re the acid sharpening? Was it long enough in the acid bath? What do you think?

At the end of the process, it seems to me that to clean a file:
1. Rub along the cutting ridges with the edge of a wedge of timber, making sure to get into the gullets.
2. Every now and then give it a hit of Mag Wheel cleaner for 5 minutes to dissolve off some stuff that can't be rubbed off. Scrub along the ridges with a Nail Brush, re-wet with Mag Cleaner for another ten minutes.
3. Then give the file a brush over with a FINE to VERY FINE brass wire brush. The wires of the brush must be half the width of the distance between the ridges, to have any hope of getting into the gullets.

The indications are, that on a smooth file, a file card/brush can only possibly do more harm than good. It certainly doesn't do any more cleaning than a piece of Douglas Fir. This may be different on a medium or coarse file where the distance between the ridges is almost double the diameter of the wires.

One step that I didn't photograph was digging out a few really stuck in bits with the point of a drawing compass.

Cheers, FF

Originally Posted by FenceFurniture

Hi Pete, if you are referring to this then Noel may mean the debris that has stuck to the teeth, but that would be for Noel to confirm.

I too struggle with the idea of acid sharpening. Could it be that the file appears to have been sharpened, when all that has really happened is the acid has removed the stuck on stuff that prevents the tooth edge being exposed? That in itself would be worthwhile, as long as the teeth aren't etched.

Impressive job, FF

Yes, this is precisely what I mean (my level of english can be very frustrating sometimes ) : the acid treatments, like all other methods of cleaning, will make the file to FEEL sharper, once all the debris stuck between the ridges have been removed. Actually (and obviously) the edge of the ridges are not sharper after the cleaning process, but the BITE of the file can been really improved by exposing better the ridges.
So the point of the game here is to clean the file without attacking the tip of the teeth.

I can't see how cleaning a file would result in it's thickness becoming less, as measured by this gentleman sharpening files - Page 3 - MIG Welding Forum

I personally feel that cleaning and etching are different discussions.

Pete

I think the acid cleaning method would 'sharpen' a file, but not necessarily in a way that you would like.
Imagine a sawtooth shape, with rounded tips. Now if you removed an equal amount of material from all the surfaces sooner or later you will remove enough that the rounded tips have disappeared. However, you probably also have some pitting, perhaps have acid trapped in the gullets and now need to find a way to neutralise the surface so it doesn't corrode.
If you have a blunt file, I have discovered a light lick with a flap wheel will take off the rounded tips and give you back some cutting power - perhaps not like a new file but better than nothing (I was making up a scraping tool at the time...).
On the idea that prevention is better than cure, I always try to chalk my files before cutting Al or brass (steel is not quite as bad) and that reduces the tendancy of gullets to clog. I'd also recommend a file - I think made by Nicolson - that goes under the name of Magi-cut.

Michael

I've never tried acid bathing a file, so I'll keep an open mind. I'm inclined to believe any improvement is due to the crap being removed from between the teeth. If it does actually sharpen the teeth, surely it would also work on a drill bit, jointer knife or lathe cutting tool?

Originally Posted by Michael G

I'd also recommend a file - I think made by Nicolson - that goes under the name of Magi-cut.

I've had one of those for years. I only use it on non-ferrous metals (which I think is what it's meant for) and it cuts like a dream. I have been keeping an eye out for another one, but haven't seen any. Do they still make them?

Edit: yes they do! http://www.fine-tools.com/magicut.htm
and in oz: http://www.justtools.com.au/prod5863.htm

not cheap though.

Originally Posted by Michael G

Imagine a sawtooth shape, with rounded tips. Now if you removed an equal amount of material from all the surfaces sooner or later you will remove enough that the rounded tips have disappeared.

This seems quite plausible to me.

Here's a Wiki link. Doesn't say a whole lot, but there's a good list of all the file types.

Very nice photos FF, did you use a USB microscope to take them?

Unfortunately I'm away at the moment, but I have a USB microscope I think should be able take similar shots. When I get back I'll also conduct the test and if I also get the same results then maybe this does turn out to be a myth. FF I'm curious though that you found the acid treatment had absolutely no effect as that doesn't seem right. Was there any gas or obvious reaction with the metal when it was in the acid? I use the acid in its "as purchased" strength and the reaction is quite significant, so I'm wondering if your acid was too dilute for the exposure time? I think there's no doubt that acid etches steel, but the precise etching geometry is the question. Bryan, yes that's a very good diagram and I agree, that's how I imagine the process.

Reading through other's experiences with this it seems that files cannot simply be "sharpened" indefinitely and the etching is uneven. I think if one were expecting nice little even triangles of hardened metal like the an unworn file, they'd be disappointed. Instead, according to others, the etching is uneven and pretty much follows the wear pattern of the file. I've read multiple claims that it sharpens them to around 80% of a new file's sharpness. Interestingly, those who have used the process extensively claim the "sharpened" file doesn't last as long as a new one before it again becomes blunt. There is at least one company in the US who offers a file sharpening facility they call "liquid honing", however I have no idea precisely how they conduct the process.

Keep up the good work in this investigation guys. From what I've been able to find out so far there's plenty of information on the net as to how to do this, but none as to why it works. So your input is certainly very interesting, undoubtedly worthy of a new thread.

Pete

Originally Posted by Pete F

I can't see how cleaning a file would result in it's thickness becoming less, as measured by this gentleman sharpening files - Page 3 - MIG Welding Forum

I personally feel that cleaning and etching are different discussions.

Pete

I agree Pete, cleaning and etching are different, just as cleaning and sharpening a circular saw blade are different. Quite simply, cleaning is removal of debris (material not from the file), and etching is removal of the original file material itself in order to sharpen. I think that what may confuse some people is that they are both aimed at the same thing - improved performance. I guess you could say that one is maintenance, and one is an overhaul.

I would say that there is a third category in this equation - restoration, and that's where rust removal comes in, using the acid bath. Certainly I can see that this would reduce the thickness, because the file would be thicker than it was originally - it has to be because the steel has taken on oxygen molecules. It would also be heavier (weigh some steel wool, burn it with a match and then weigh it again).

Bryan, I see merit in your diagram, with a caveat: The ratio of the radius to the angle hasn't changed. In other words the segment, or arc of the circle used to form the tip is still in the same proportion. This would serve to make the gullets shallower, by virtue of lower ridges. But I dunno what effect this would have .

Looking closely at the picture of the three files in the Wiki link, it can be seen that the Coarse file has 6 ridges per cm, Medium has 10 per cm, and smooth 13 per cm. If we assume these ridges are all the same proportion (i.e. all the same triangular shape in profile, just different sizes). The coarse file would therefore have higher ridges and deeper gullets than the finer files, and this makes sense as the deeper gullets can hold a bigger chip.





Now, if we etch away at the ridges with acid, there will still be the same number of ridges per cm, but they will be lower in height (by definition of removal of material - look at Bryan's diagram), and therefore the gullets will be shallower, but broader (although the acid may eat the bottom of the gullet too). Certainly the gullets must be broader. What has effectively happened is that the file (say a Medium) has been taken ever so slightly towards a Smooth file in terms of ridge height, but the frequency of the ridges has not increased to compensate. By any definition the file must now take off less material than it would have when is was new (because the ridges are smaller). If this gives added life to the file, then great, but there is no way that it will ever be the same file that it once was.

I'm well aware that I'm getting into minute detail here, but that's often where the answers lie.

I read the thread in the wekder's forum, and two really good things come from it: using French chalk for sticky metals, and it seems that Sulphuric acid at a specific gravity of 1.25 is the go, as Sulphuric eats at steel better than Hydrochloric (Brickie's acid). I confess to not understanding how a stronger solution will do less work than a weak solution. That is completely counter-intuitive.

However, in that thread they are hardly being empirical about the results: there's a lot of "Try it, it works", but no supporting data. Of course a rusty file won't do as good a job as one that has been cleaned, just like any stuck on debris will reduce performance by concealing the cutting edge. What they haven't done is compare a restored rusty file to the same file when it is new (and that wouldn't be hard to set up). I still think that because the restored file now performs better, the fond memory tells the user that it's "like new". Try a new file straight after that and see what you think!

Originally Posted by jack620

I've had one of those for years. I only use it on non-ferrous metals (which I think is what it's meant for) and it cuts like a dream. I have been keeping an eye out for another one, but haven't seen any. Do they still make them?

Edit: yes they do! Magicut Files for Non-Ferrous Metals and Alloy Steels
and in oz: Nicholson 250mm Magicut File #907918AU

not cheap though.

i have a ten inch one of these. its great i dint know it was not for steel thou.

Originally Posted by Pete F

Very nice photos FF, did you use a USB microscope to take them?

Cheers, Pete. No USB scope, just shot them on max res, and then cropped into the business area to reduce file size, und koncentrate ze mind, like ze pains does!

I have learnt this morning that the ridges are like a factory roof from the 40's. The cutting face is close enough to perpendicular to the file face, and the back of the ridge slopes off at around 30 degrees, meaning that the cutting edge has an angle of about 60 degrees.



This of course explains why the sheen of the file is only seen from one direction. This is the file I processed yesterday:



When you look up the file at the cutting faces, it's got more polished nicks than Long Bay Gaol (might have to explain that one to Liogier)



When you look at this with the naked eye it looks like a bloody galaxy!


Thinking about those ridge faces and how they might wear: logic dictates that either the sharp ride would get rounded or flatened, or as can be seen in my case, chipped. The latter seems the most probable to me given the very briitle nature of case hardened steel. Well those chips re going to have very sharp edges, but they may no longer come into contact with the job. I can't see for the life of me how acid will improve that.

If they are not chipped, but rather worn flat or rounded, then at best, acid etching can only increase this new "secondary bevel". Let's face it, the point of the ridge profile is gone, one way or another, and removing more material cannot possibly restore that.
This still leads me to conclude that an Acid bath may well (and probably will) improve performance, but by virtue of cleaning rather than sharpening.

Pete: Yes I think that the acid stength:time ratio was probably well out of order. Bubbles did form on the surface, but there was no fizz. In the first acid bath (1:20) I could see dots of brown debris held in suspension. This could only have been rust, as all the timber chips from that style of cleaning were thoroughly scrubbed off by this time. Today I'm going to leave a couple of inches in the full strength acid to see what happens.

Cheers, FF

If you have a rusty, dirty old file the best first step IMO is electrolysis. This cleans and derusts better than anything and with zero damage. Then you can see what you're dealing with. I have been surprised each time I've done this how well they've come up. If I did that and it proved too dull I would consider acid, or repurposing, or the bin.

Hi FF,
I think the answer different people with different files, but also there is a lot going on here that I for one dont understand. As you say the bevel angle is about 60 degrees and if my new Nicholson files are anything to go by, they arent all that sharp to begin with. Fish hooks are chemically sharpened so it can be done(of course not the same as a file and a bucket of acid). If you look at the first picture on your last post, notice the "rough sanding marks" that run the length of the file? What are they for?(I can only guess that they are to break up the cutting edge?)

Some pictures
First an old well used sandvik. Then an straight out of the box Nicholson.

Stuart

Originally Posted by Stustoys

If you look at the first picture on your last post, notice the "rough sanding marks" that run the length of the file? What are they for? (I can only guess that they are to break up the cutting edge?)

You mean this pic Stu?


And you mean the lines running across the ridges on the edge of the file (horizontal at the front of the pic)?

I think that they are just from -poor manufacturing, and shouldn't really be there.

Bryan: good post man. Why dincha say so before? How do you set up your electrolysis - how about a piccie? I've heard of electrolysis for Brazilians, but not for Brazilian files.


This morning I tried to make contact with the School of Metallurgy at the Uni of NSW. Apparently they are one of the world's foremost schools. Anyway, all the Profs have finished their semester and headed for siesta, so I sent an email to Professor David Young, asking him if he had any thoughts on this matter. We'll see. I thought it was time we had the opinion of some one who actually knows what he's doing . Prof Young is a corrosives expert apparently, so if he doesn't know.....