I've touched on this in other posts, but wanted to address it more clearly and specifically here.

When you file, the motion should be both forwards and sideways at the same time, and at a skew to the work.  This files faster, cuts cleaner without gouging, and keeps the file cleaner (not pilling).  The reason this works is because it shears the metal filing off, instead of chopping it off.  This is because the compound motion makes the effective angle of cut much flatter, as if you had a very thin, very sharp, low angle blade.  If you had such a blade, it wouldn't be strong enough, and would nick, bend or dull quickly.  But, the skew and sideways cutting motion effectively gives you such a blade, but at a stronger physical angle.  Because of the skewed cutting angle, the chip clears the work in the direction of the file "valley" between teeth, instead of being rammed into the vee shaped overhang of the tooth, so it doesn't stick.  Stuck chips (pilling) on a file cause gouges as the high pressure forces that chip to scratch the work.

I have one of the most useful and meaningful books I have ever read.  It's a very obscure technical book, and not one you would normally read.  However, it's very worth reading, and this is one of the most valuable lessons in the whole book.  I'm posting photos of it below.

The technique describes how to chisel more effectively, but it applies to spokeshaves, chisels, rasps and files equally.  Rasps and files are really micro chisels.  

I'll let the explanation in the book speak for itself.  The book is cheap on ebay usually, I'd highly recommend getting a copy and reading it.

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Dave

I have been making gunstocks for over 50 yrs now. If you learn to sharpen wood tools properly and use them you learn to skew cut early.
Many times in Fiddleback Maple. I am only shaving .004" per cut with either a spoke shave or a small block plane.
A thin cut like that skewed with a sharp cutter, will not tear the figured wood.
Trust me as soon as the tool gets a little bit dull you will know as it starts to tear

Yes thats a good book for those starting to learn, and even a better refreshing course for us old farts

WCF

That's great info to share, thank you!

Well, I didn't have that book -- but I had my Dad, who had me and my 3 brothers working with metal tools from age 10 up in a locksmith shop.  Many of the older locks in use in that "shitty" (city -- as pronounced by Boston's Mayor White) north of Boston required repairs of any broken brass parts that only our shop could handle and replicate (as we'd been in business since 1899).

He schooled us well on proper filing technique, and was a stickler for ensuring that "no file marks" were visible, even on the inside of a mortise lock (door locks are quite similar in ways, to gun locks) that the owner would never see.

I recall my father's best quote about metal filing...

"Remember kid, the metal take-off tools work much better and faster than the metal-put-back-on tools..."


I guess that's an extension of "Measure twice, cut once" if you think about it.

Cheers!

Old No7