3 * RM1610 ballscrews, 780mm & 660mm

[Jonathan]

Just out of curiosity, is there a rule-of-thumb for whether and when to use 5mm or 10mm pitch ballscrew when constructing an XYZ table (for routing mainly hardwoods)?

It depends on numerous factors. 10mm pitch gets you much better speed and acceleration, but unless you use pulleys (which you really should...) you clearly have half the resolution of a 5mm pitch screw. If the axis is quite long you'll certainly want a 10mm pitch screw, since because the screw pitch is greater the rpm for a given feedrate is less so the screw will not whip until twice the feedrate it would with 5mm pitch. For a short axis, like Z, whipping isn't a problem so 5mm is fine. In most cases on a 'reasonable size' router 10mm pitch with pulleys is the way to go for X and Y and choose the pulley ratio depending on what your're cutting (to favour resolution for speed).

However clearly there will always be exceptions and each case is different, so you need to read up on it, decide and calculate for yourself.

[Karl]

... but unless you use pulleys (which you really should...) ...

So what's the rationale for using pulleys to drive a ballscrew rather than connecting the stepper motor directly inline via a flexible coupling?

[JAZZCNC]

So what's the rationale for using pulleys to drive a ballscrew rather than connecting the stepper motor directly inline via a flexible coupling?

Couple reasons really.
Easy to gear for extra speed or resolution/torque. It also helps reduce resonance that affects the motors.

[Karl]

Couple reasons really.
Easy to gear for extra speed or resolution/torque. It also helps reduce resonance that affects the motors.

Many thanks - I hadn't considered the potential flexibility offered by interchangeable gearing.

That raises the question: What brand/source of pulleys/belts are currently in fashion/recommended?

{Presumably, belt manufacturers/suppliers provide tensioning guidance?}


Thanks

Karl

[JAZZCNC]

That raises the question: What brand/source of pulleys/belts are currently in fashion/recommended?

{Presumably, belt manufacturers/suppliers provide tensioning guidance?}

I always use HTD 5mm pitch 15mm width and a good brand is Gates, medway etc. If you go to any good bearing supplier and tell them you want quality brand not the cheap veriety they should be able to help.

[Karl]

... HTD 5mm pitch 15mm width and a good brand is Gates, medway etc...

Many thanks. Are more pulley teeth better than less? Eg for a gearing ratio of, say, 1:2 is there anything to be gained from using 12:24 teeth pulleys as opposed to 20:40 teeth?

Karl

[JAZZCNC]

Yes it's all about teeth in mesh.!! With small pulleys there are less teeth engaged between belt and pulley, less teeth engaged means less able to handle high loads and reduce the amount of torque that can be transmitted and if wrong will rip teeth off the belt.

Read these and it will explain lots. . http://www.roymech.co.uk/Useful_Tables/Drive/Timing_belts.html


http://www.ondrives.com/data/pdf/pul...belts-tech.pdf