Flatten old file to make a marking knife?

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Forum topic by Brett posted 10-18-2011 04:51 PM 2798 views 0 times favorited 11 replies Add to Favorites Watch
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661 posts in 2852 days

10-18-2011 04:51 PM

Maybe I’m biting off more than I can chew, but I picked up an old file a few months ago with the intent of making a marking knife out of it. How can I flatten the ridges on the sides of the file before grinding the cutting edges?

-- More tools, fewer machines.

11 replies so far

View Bertha's profile


13550 posts in 2863 days

#1 posted 10-18-2011 05:05 PM

I can’t tell you the right way to do it, but I’ll tell you what I’d do, lol. I’d grab it in a metal vise, put on some glasses, have a fire extinguisher nearby, and go at it with a pneumatic cutoff wheel. I like the shieldless small pneumatic rotary but I’m not known for my safety practices;)

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View Dennisgrosen's profile


10880 posts in 3285 days

#2 posted 10-18-2011 05:50 PM

first you heat it to red orange glow and let it cool slowly …. to take out the hardness it has (anealing)
when coled its alot softer and you can use another file to shape it as you want

when you have the shape its time to sharpen it before you heat and squince the iron
after that you heat it to around 250 -300 degree celcius an hour to make it a little softer
and isn´t so fragile

there is other blogs about how to make plane irons where these things is explained much better than I can

goood luck


View Lee Barker's profile

Lee Barker

2170 posts in 3020 days

#3 posted 10-18-2011 05:51 PM

Are you set on the file?

Here’s my style: I buy old carving forks at thrift stores. Some have rosewood handles, some mystery wood, some composite. The metal is almost always US and almost always stainless. It takes a nice edge and buffs out grandly.

There is usually plenty of flat run (before the curves of the tines) so I cut it off at a good length and grind carefully my bevels. It works beautifully.

If you wanted to make your own handle, just drive out the rivets and away you go.

But I really like Al’s idea too. Makin’ them sparks is fun!



-- " his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View interpim's profile


1170 posts in 3628 days

#4 posted 10-18-2011 06:12 PM

you definitely want to anneal the file before you try shaping it at all… you’ll go through plenty of grinding wheels before you make any good headway on getting it to where you want it.

-- San Diego, CA

View BTKS's profile


1989 posts in 3634 days

#5 posted 10-18-2011 06:14 PM

Dennis did a good summary of heating, cooling, hardening and tempering. You have just drifted into the land of blacksmithing. Be careful in this mysterious land, it will pull you in and make you a resident before you realize you can’t get back to woodland!!!
If you want a marking knife with inserted blade into the handle you can try some metal from a sawzall blade for the marking blade. My BIL used a hacksaw blade to make his.
The downside of files is the extreme brittle nature of the hardend steel. That’s why a file cuts steel and not another file so well. When you get a nice edge it will likely chip off if it is bumped on something hard. Proper annealing and tempering will solve this but it is a trial and error process if you don’t know exactly what kind of steel you have and the proper temperature or colors you need to use.
However you approach the project, have fun!!! Hope this made sense and is of some help.

-- "Man's ingenuity has outrun his intelligence" (Joseph Wood Krutch)

View paratrooper34's profile


915 posts in 3121 days

#6 posted 10-18-2011 06:33 PM

I am with BTKS on this. You can also try a jigsaw blade. Both of them are hard enough to make a good marking knife blade and hold a good edge, yet not brittle. And they polish up nicely. Good Luck!

-- Mike

View Bill White's profile

Bill White

5095 posts in 4130 days

#7 posted 10-18-2011 07:49 PM

That’s a lot of work for something you can buy for very little money.
Google marking knives.


View Dennisgrosen's profile


10880 posts in 3285 days

#8 posted 10-18-2011 11:08 PM

Bill …. its not a money thing … :-)
but the fun in the chanlange to do something you havn´t try before
finding your limits and get new skills during the journey …... :-)


View Brit's profile


7519 posts in 3012 days

#9 posted 10-18-2011 11:46 PM

I’m with BTKS on this one. It is a lot of work and there is no quarantee of success. I don’t know what condition the file is in, but if it is just blunt, send it to Save Edge or Boggs. When it comes back, stick a new handle on it if necessary and you’ll have another useful tool in your arsenal.

For a marking knife, try making one out of an old jigsaw blade.

Just my opinion.

-- - Andy - Old Chinese proverb says: "If you think something can't be done, don't interrupt man who is doing it."

View rance's profile


4264 posts in 3330 days

#10 posted 10-19-2011 12:16 AM

For a marking knife, I’d suggest starting with some thinner material like a jigsaw blade or bandsaw blade. Use the file to make a hunting knife. You’ll be a long time getting it thin enough for a marking knife. As for grinding, I’d suggest using a belt sander. No matter what you use though, keep a cup of water nearby to keep it cooled off.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View CartersWhittling's profile


453 posts in 2843 days

#11 posted 10-21-2011 01:14 AM

I usually use an angle grinder and grind away most of the material. Just make sure the cool the steel very fequently to keep the temper. I then use a bench grinder to finish shaping the steel. When my friend is over he often has a spray bottle and continually sprays water on the steel while I grind, but if you don’t have anyone to help it takes more time, but with a angle grinder you can get it done fast anyway. A jigsaw blade like Brit mentioned above could be a good idea, I have never tried but it sounds like a good idea.

-- And whatsoever ye do, do it heartily, as to the Lord... Colossians 3:23

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