What MOD rack size to use?

[Norgmonster]

Having recently designed a machine with rack and pinion, where the requirement was speed as opposed to smooth running/accuracy, I would suggest you go with the smallest economical one you can. Nonlinearity will be a real concern with anything larger than 2.

To avoid contamination, mount the rack, with the teeth pointing down

For a visual comparison:

I'm planing a R&P router myself and would like to ask two things?? What do you mean by contamination? And, When you say mount the rack, do you mean something like this?



Sorry if the image is small.