Acme screw as a R&P?

[Sil_x]

The hob cutter was made by turning down a piece of the lead screw on my lathe and cutting the teeth on my mill. To cut the gear I used my lathe with the hob cutter in the head and the blank on the saddle. Its pretty much like the process that Steve Bedair did on his site Steve Bedair's 9x20 Lathe Site

There are formulas for hobbing gear, I forget what they are at the moment but I remember that my 1.5 inch stock delrin was almost perfect as my blank.

[harryn]

Hi, Thank you for the links and explanations. That is a really interesting approach to making the pinion, and other matching gears for various needs.

[Sil_x]

Here is a vid of my machine
YouTube - minotaur CNC router
I am still trying to get the tool length probe to work so that is the reason for the multiple attempts on the cut

[quazga]

Yeah I know what you mean by having too much fun. Having CNC capability is like going from the Flintstones to the Jetsons! HAHAHA! =D

Great work!

[Sil_x]

I can agree with that.

A few notes on the gear material. After about a month of use the epoxy resin i used has started to chip and crack. I am trying a softer and hopefully more wear resistant urethane casting.

I did hob a few gears out of aluminum for my X axis but even though I tried to get them identical, some raking occurred due to the differences in circumference. They work great on my Y though.

[Mike Everman]

I of course love the screw rack idea. I say of course because I've put some effort into it in the last few years, off and on.
Making pinions out of steel was not particularly difficult when you make a simple tool.
Blanks are put in this fixture and a spiral flute tap used to make two at a time. It is not as perfect as hobbing, where the ratio of tap rotation to pinion rotation would be tightly controlled, but it works well. Plastic would be doable with a hand drill and just two pins in a plate at the right center distance.

You just need to calculate the pitch diameters of screw and pinion, such that the pinion pitch is an even number of teeth (obvious, I know, but if side cutting just one you can feed toward the center until you find a spot where the teeth look good; in this case I've nailed the center distance, and machine two at a time so there is no side load on the tap.)

[Sil_x]

Very nice, I like the simplicity of your fixture!