Airfield Models - How To

Make a Razor Hole Saw

May 03, 2015

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Airfield Models ( to Make a Razor Hole Saw

Cutting a clean hole in a soft wood is a challenge.  As far as I know, no tools are made commercially that can do this particularly in all the odd sizes we need.

Brad point drill bits work very well in a drill press as long as the bit is sharp and you work very slowly.  Unfortunately, my drill press can only handle bits up to 1/4".  The other problem is that brad point bits come in limited sizes.

I have been making punches and hole saws for a long time.  They work well but sometimes require a bit of tweaking before they work properly.

If you are working with balsa 1/16" thick or thinner or 1/64" plywood then you can make a twist punch.  A twist punch is simply a piece of tubing sharpened on the inside or outside depending on the application.  In either case the punch has no teeth.

A twist punch doesn't work well for thicker woods because the plug jams the punch and prevents it from cutting deeper.


Making the Hole Saw

Use the hardest tubing you have that is the correct size. I use brass tubing because it's what I have on hand.  It doesn't stay sharp very long even when cutting balsa.

I haven't subjected this tool to the kind of use that would warrant buying better quality metal.

Square the ends and clean off whatever that hard crud is on the tube using solvent or steel wool.

Cut shallow slits around the permiter using an emery wheel in a moto tool. Use an emery wheel in a moto tool to cut shallow slots around the perimeter.  Use your judgment to determine how close they can be while not having teeth that are too weak.

The length of the teeth depends on the depth you will be sawing to.

(Alternate ending to this article:)

Paul:  AAAIIIEEEE!!!!!!!  The *%^@*# emery wheel broke!!!  I'm blind!!  I'M BLIND!!!!!!!!

Previous Model building with only 7 fingers

Next Model building with only 7 fingers and one eye

Wear safety goggles when working with moto tools.

Slowly and carefully sharpen the inside using a tapered stone in a moto tool. If you use the hole saw in a drill press then you usually will not have to sharpen the tube.  Use an appropriate stone in a moto tool to deburr the inside.

If you use an unsharpened tube free hand or in a hand held drill or pin vise then the saw will tend to walk.

Use a tapered stone to sharpen the inside of the tube.  It does not have to be razor thin.  You just need it to be sharp enough to cut into the wood quickly so that it won't walk.

Don't jam the stone into the end.  That will cause the end of the tube to bulge or bend teeth.  Work slowly.

Also, do not sharpen all the way to the base of the teeth.  You want the teeth to shave the edges of the plug so it doesn't jam in the saw.

Remove burrs and bulges using a fine flat file around the outside. Use a flat file to clean up the outside of the saw.

If you use the saw in a drill press then it's a good idea to drill a hole in the side of the saw so that you can feed a wire into the saw to knock plugs out.

Test on scrap.  If the cut isn't as clean as you would like then sharpen again. A sharpened saw creates tapered plugs.  If you want plugs that aren't tapered then don't sharpen the inside and use the saw in a drill press.

In use, be sure to back the saw out so dust can clear from the teeth and help prevent clogging.

Always test on scraps before instead of chewing up your masterpiece.

The best way to use this tool is to place the work over a piece of end grain scrap that is sanded flat.  The end grain helps prevent the plug from breaking out too early and ripping away grain with it.



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Copyright 2006 Paul K. Johnson