Thread: What MOD rack size to use?
I'm about to start a second machine build. A 3m x 2m for general materials, wood, polystyrene and occasional plasma. Sort of multipurpose.
I'm going to upgrade from T5 belt to rack and pinion but i'm not sure what is the smallest rack size I can get away with is? This machine will get used maybe once a week but for several hours at a time. I'll be gearing between the stepper and pinion as well.
Any suggestions or examples anyone?
Having just looked at the actual size diagrams in my HPC gears catalogue, I'd probably pick something in the 2-3MOD range.
The smaller you go, the more noticeable any contamination will be, and the larger you go, the more the non-linear motion from straight cut spur gears become.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
Marbles, if you're looking at their catalogue, HPC gears do some nice anti-backlash gears BTW ;-)If you will not be swayed by logic or experience simply pick the idea you
like best, but ask yourself why you sought advice in the first place and,
for a simple life, perhaps consider not doing so in future
Anti-backlash gears don't solve the non-linear issue though. You'd have to use helical rack/gears for that ;-)Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
To avoid contamination, mount the rack, with the teeth pointing down
For a visual comparison:
Stocking more goodies than just Smoothsteppers
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.
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.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
A quick check of the HTC catalogue I've got, lists the torque for a 50t 2 MOD gear at 2.5Nm. I'm pretty sure a decent cut could manage to overcome that, and on high speed machines, I'm sure the accelerations involved could manage to do the same.
And that's before you consider the additional friction they'd introduce into the system, which depending on the machine, may or may not have any significant effect.
That's not to say they wouldn't help, but you have to weigh up the pros/cons of using them.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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