What MOD rack size to use?

[magicniner]

Marbles, if you're looking at their catalogue, HPC gears do some nice anti-backlash gears BTW ;-)

[m_c]

Anti-backlash gears don't solve the non-linear issue though. You'd have to use helical rack/gears for that ;-)

[komatias]

Anti-backlash gears don't solve the non-linear issue though. You'd have to use helical rack/gears for that ;-)

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:

[marbles]

Thanks for all thoughts

I'm beginning to think that if I was just cutting large blocks of foam or using as plasma i'd stick to a belt drive system because of the speed and accuracy. Not entirely sure why more people don't use belt. I'm guessing its just that its less well known as a tech and maybe is not so good over long distances.

However as I do wish to cut timber and make up a 3m x axis R&P and has history so is probably the way to go. How about helical rack/gears and probably 2.0 MOD with a gear ratio to suit?

What ratio required to suit high speed roughing cuts in polystyrene and and also give some repeat accuracy in timber is the next thing to sort out.

[m_c]

The issue with belts over longer distance, is you get into resonance/flex issues. You can minimise it by lots of tension, but then the design of what they're tensioned between becomes critical, and you have to make sure everything under tension is strong enough.

There is that system that is essentially a rack the belt sits/locates in, with the belt looping up and over idler and drive pulleys, which eliminates having a long unsupported belt, however from what I remember it was more expensive than other options.

It's like most things, you have to weigh up the pros/cons of each method, and decide what's the best compromise for you.

[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.

[Clive S]

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?

Contamination means dirt or swarf getting on to the teeth that is why he said mount them with the teeth facing down Like in the image.

[JAZZCNC]

MOD 1 is perfectly fine for R&P machine and most common size used at DIY level. Certainly no need to go above MOD 1.5.
I've got industrial built 10 x 5 Router with very heavy gantry which is running MOD1.5.

[marbles]

MOD 1 is perfectly fine for R&P machine and most common size used at DIY level. Certainly no need to go above MOD 1.5.
I've got industrial built 10 x 5 Router with very heavy gantry which is running MOD1.5.

Totally fine to go with MOD 1 in that case, quite a lot cheaper than 2.0 as well..

[magicniner]

Anti-backlash gears don't solve the non-linear issue though. You'd have to use helical rack/gears for that ;-)

Yes, it's kind of in the name ;-)