Making gears with a jigsaw

The best tool for cutting out plywood gears is a a bandsaw, but if you don't have one of those, a jigsaw can be used.

But the problem with jigsaws is that it's hard to see where you are cutting and the bade can flex to the side, even on expensive models.


A solution to the visibility problem is to mount the saw upside down. But rather than mount it on the bottom of a piece of plywood, I'm sliding it into a slot cut into a piece of plywood. That way, the saw is not as far from the workpiece. This gives me more stability.


I could fasten the saw by putting some drywall screws near the edges of the saw's base. But I also want to cover the hole around the blade to keep debris from falling in, so I'm using a piece of wood (about 5 mm thick) with a slot in it, screwed down to clamp the saw's base in place.


A piece of hardwood (oak) with a slot cut near the tip helps to stabilize sideways deflection of the blade. I also put a few drops of oil in the slot to let it slide more easily.

I put a scrap of plywood in front of the saw to bring the height of the "table" up to the same height as the piece of wood holding down the saw.



I'm making another gear for my box joint jig, so I'm, using a printout of one of the templates from the plans. You can also make templates using my free online gear template generator or my gear generator program

I'm gluing it on with glue stick, but I only apply glue where the teeth are, plus a dab in the middle. I put the glue on the paper, not the wood. This makes for less glue residue on the wood later.


Cutting out the gears. I have to firmly hold the workpiece down, and not try to cut any curves, or the workpiece really jumps. I cut on either side of each space between teeth, then two diagonal cuts to remove most of the material. I then graze the bottom of the gap with the front of the blade to flatten it out.


The process can be sped up by drilling a hole in each space between teeth.

It helps to pre-punch the centers before drilling. The point of a brad point drill bit naturally follows the divot, and it's easier to line up the awl than a spinning drill. Use a brad point drill bit. Regular drill bits would make too much of a mess of the wood and the template.


With the drilled holes, just two cuts are needed for each space.


Because the gears on my box joint jig need to run at a right angle, it helps to slightly bevel the bottom edges of the teeth. I could have tilted the jigsaw, but it would be a hassle to keep changing the angles for straight, right, and left tilt.

A strip sander is really good for tweaking the teeth, but if you don't have one, a coarse piece of sandpaper wrapped around a strip of wood does a fairly quick job of it too.


Finally, removing the template. It comes off quite easily because I only used glue stick. People tell me I should use spray adhesive all the time, but I think it's too much hassle, with overspray, plugged up nozzles, etc. Glue stick is very convenient.


And here's the new gear on my jig. This one is 33 teeth. I didn't have a 33-tooth gear yet, so this means I can achieve slightly more spacing combinations.


See also:

How to make gears
(using a bandsaw)
Bandsaw vs CNC.
Which will cut a gear
faster?
Michael Sullivan's
router gear cutting
Home made wooden
router lift, with gears!

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