This is a follow-up to my recent Instructable on making a Keyhole Saw Handle from Pipe. I went to look for a new keyhole or compass saw blade and found they do not exist. I could buy a cheap compass saw with a plastic handle. I wanted to see about adapting a standard reciprocating saw blade to the handle I made for the earlier Instructable.
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Step 1: Standard Reciprocating Saw Blades
Makita makes a blade for its reciprocating saws that appears to have a large enough hole in the right place so that the Makita blades would work without modification. But, I could not find a local dealer who sells the Makita blades. So I began to adapt the standard blade configuration.
Here you see a variety pack of reciprocating saw blades. Adapting standard blades also makes a compass or keyhole saw more versatile. You can use a coarse wood blade or a fine wood blade. Or, you can use a blade designed to cut steel, or even masonry.
(The photo is from Home Depot's web site.)
Step 2: The Problem
Blades for a reciprocating saw are made from high carbon steel. Most twist drills will not drill through high carbon steel. On the Internet I read about special drill bits available in the United Kingdom for drilling high carbon steel. They are similar to a masonry bit, except that the carbide tip is sharper and is brazed in place with a very high melting point brazing alloy. These bits are used without lubricants and create so much heat that the very hard steel softens and comes off in hot shards. I have another plan.
I marked the location of the hole in my saw handle.
Step 3: The Dremel
I used an abrasive cutting disc in my Dremel tool to begin cutting through the blade on four sides of the mark for the hole. The cutting disc has been used so that it is smaller, which allows smaller and closer cuts. This is better for making a small 1/4 inch hole in the saw blade.
Step 4: Marks on the Other Side
In addition to some scratch marks made when sliding the blade in and out of the pipe handle, you can see three of the cuts from the other side beginning to poke through the blade. I turned the blade over and finished all four cuts from this side. The blade did not get hot and the Dremel cut the high carbon steel at full speed reasonably well.
Step 5: The Finished Hole
Here you see the finished hole. It does not matter that it is square, nor would it matter if it were just a little over-sized. The handle squeezes the sides of the blade and that is what holds the blade. The hole simply makes a place for the bolt to go through the blade.
Step 6: Options
This blade has parallel edges top and bottom. Reciprocating saw blades are made to cut on the pull stroke rather than the push stroke, like a Japanese handsaw. The photos in this Instructable show me adding an extra hole at the end visible in this photo. That gives me the choice of reversing the blade so it cuts on the push stroke in use. If the blade did not have parallel edges that would not be possible.
I was not pleased when I found I could not easily buy a replacement blade for a keyhole or compass saw, but that actually led to something that gives me many more options for using this saw in terms of materials it will cut and cutting direction.
I should also mention I did see some saw kits with handles that accept a standard reciprocating saw blade. The handles on those saws were not at a near right angle to the blade, but came straight back like an extension of the blade.