A mirror finish from filing.

[savarin]

Well almost.
I have mentioned before how I use WD40 on the file when filing aluminium as an aid to prevent the inevitable pinning but thought I would do so again with a couple of pictures showing the finish thats easy to achieve.
I use a file that Nicholson call a MagiCut but in this instance I'm using a cheap Trojan file with the same cut.
This is the file and the job, 3 small brackets that were rough cut with an angle grinder.


This is the result showing the sort of pinning that can occur with a dry file, nowhere as bad as a conventional file but still very annoying.


Now spray the same file with WD40 and you can get an almost mirror finish with a lot of material removal at the same time.


As the file loads up a quick brush with a wire brush along the teeth and your ready to go again.

 

[graham-xrf]

It provokes a little speculative theory in me..
When draw-filing, the angle of the file serrations relative to the work can get low, particularly if you hold the file with one hand in advance of the other. I am not sure what cutting effect this has, but it may be akin to the way a lathe finish is achieved using vertical shear. A better example might be a knife sharpening stroke that drags somewhat along the length, instead of being straight across like a plane-iron.

If the file serrations are in line with the stroke, you should expect near zero cutting, and when 90° across the stroke, that would be maximum chiselling. Interesting is the improving effect of the WD40, though I expect many other substances would also have this effect.

I think this theory assumes a single cut file. Blinding the file serrations to some degree using blackboard chalk also makes the less aggressive cut. I was taught this from back in school days, and I have always thought most folk who ever use a file would already know that.

For my ignorance, what is "inevitable pinning"?
Also, is "Magi-Cut" something trick, or special, or patented, or is it simply Nicholson's name for a single cut file?

 

[savarin]

I have never found the chalk trick to work for me.
Inevitable pinning is my take on what happens when filing aluminium, the file teeth get bits of ally jammed into them which then scores the job. I thought this was called pinning.
Searching for magicut it seems this is also called American cut.
I just tried the wd for some reason after getting fed up with the chalk not working.