Quote Originally Posted by Doddy View Post
I've absolutely no knowledge on the subject of rack and pinion... pretty much no knowledge of most other things to be honest, but... am I missing the plot here... if you're talking of gearing the the pinion, then surely the tooth count of the pinion is essentially the gearing component?, If you go from a (e.g.) 60 tooth pinion to a (e.g.) 20 tooth pinion you'd effect a 3:1 reduction.

Or am I being stoopid?

EDIT: Not trying to answer (or validate) the question, and so this response is clearly off-topic, but just casual curiosity. Also, would think the above could avoid introducing additional backlash in a gear chain

EDIT 2: Just reversed the example tooth count above, having woken up a bit.
Yep you'd be Stoopid, but obviously, I'd say that if you were correct but your not:.

All you would be doing is changing the effective pitch and not applying any ratio for either torque or resolution. For instance, working with a Mod1 rack. 60T pinion would give you an effective pitch of 60 x 3.141 = 188.5mm per/rev and if you used 20T your still at 20*3.141=63mm pitch. Far too large for most machines.
So even with 20T pinion, you'll still want 3:1 for a router or similar. You also don't want to direct drive off the motor for resonance reasons.

Now to the OP, I would just make your own setup using pulleys, etc.
It's often cheaper and comes with the added advantage of easy ratio adjustments but more importantly, it lowers the amount of resonance which affects the motors. Timing belts are also low backlash.
Gearboxes are ok but limiting if you are not sure on ratios and because they are direct drive to the motor they can introduce substantial resonance into the motor. You also need low backlash gearboxes which are more expensive than the run of the mill gearboxes.