4th axis rebuild

This is a small project I “finished” recently, but yet to try out in anger on the CNC.

It started out life as a really cheap 4-axis that came with a 6040 router. I don’t have any before photos, but it was really bad. It was belt drive (which is fine in itself, actually better than what I’ve done) but none of the pulleys ran true and the belt tensioner was a normal bolt with a piece of pipe slipped on it. Genuinely useless.

I hadn’t built anything proper using gears before, so I used it as a little manual machining project to learn off the very talented folk I’ve been working with. So basically everything on the backend is new.

I’ll update with some footage once I get the chance to mount it up on the CNC and turn/index something.


Hi Derryn,
looks fantastic. Am envious, would love to give gear cutting a try but don’t have access to the equipment.

A couple of questions:

  1. Is there any further gearing not visible i.e. in the beige box behind the chuck?
  2. Have you encountered any backlash issues and if yes, how have you addressed them?


I didn’t actually cut the gear teeth. Not that it would have been difficult with a dividing head and gear cutters, but hardening the teeth would have been a bit of a pain. For ~$20 I just bought the gear blanks, then bored for the shafts and broached keyways.

No further reduction, just the 2:1 on the back which is what it originally came with. There’s just a shaft running on two bearings mounted in the front and back plate. Although NEMA23 planetary boxes are easily available at a reasonable price in anything from 4:1 to 100:1. So one of those would simply fit in-front of the motor if needs be.

The gears are simply meshed in pretty tight, but there is a small amount of backlash. Unavoidable with simple spur gears really. I haven’t had the chance to see how much impact that has on the router yet.

I would say just using HTD timing belt would be better for this application, or using an off the shelf precision worm/planetary box. But then this was never about building the best thing, but rather learning a few new skills.


…also v jealous.

That is a very solid setup…what are you intending to making?

No idea what I’m going to use it for at the moment. But they do open up some interesting possibilities.

I’ll probably just carve a bunch of wood to start with to get the hang of the CAM side of it.

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