chain drive

[jonm]

hi
has anyone ever used chain drive for a cnc router,
what accuracy could i expect ?

upgraded my drivers to zapps msd542 (excellent drivers) , 40v power supply with 3nm motors
to much for my 12mm 1 start trapezioid screws

looked at the black toe chain driven router but no mention about accuracy

[irving2008]

yes those motors are massive overkill for a 12mm screw... blacktoe's resolution is ~0.1mm IIRC - i read it somewhere but can't find it again at the moment. Its certainly good enough for wood routing, but nowhere near good enough for metal or precision plastic work. How big's the router and why not change the screws?

[jonm]

irvine
x is 1200 y 800
what size screw would you recomend , would timing belts be a better option
can get 25mm wide belts for £12 each

[irving2008]

1200mm should be OK with a 12mm screw, what pitch is it and whats the problem you are having? In fact on that size of machine the simplicity of a screw drive would be hard to beat with any other arrangement...

[jonm]

irvine 3mm pitch screw maybe i have to much acceleration in mach 3

[irving2008]

what speeds are you trying to achieve and how is screw mounted? What symptoms are you seeing?

[jonm]

around 1500mm/m seems very agressive with direction changes, screw is direct drive from motor, screw through bearing held captive with two thrust bearings , free end through 12mm bearing

[irving2008]

1500mm/min is 500rpm, which shouldnt be a problem, and the fixed/free mounting should be OK for 3 - 4 times that speed. If things seem to be stressing on a direction change then I suggest you turn the acceleration right down and bring it up in stages untill you feel comfortable with it... you should be able to reverse direction without the thing trying to throw itself off the bench and without losing steps. Set it up for a back and forth traverse against a dial gauge (to determine if its missing steps) with say a 200mm movement (gives it time to accelerate) and turn up acceleration until you feel the vibration is getting too much, then back it off a tad. Is the machine bolted/clamped down to the bench or freestanding...if the later you will need to drop the acceleration a bit...

[jonm]

thanks irving
didnt realize the power of those 3nm motors untill i connected them to the msd 542 drivers, parallel , 40v 4amp
ran them 2.5amp and 24v before

[ptjw7uk]

I think the chain drive would be cheaper to impliment lower back lash figures for larger router systems.
Only worry I can see is chain stretch and enough fine resolution from the stepper.
You could always gear the stepper to the chain albeit by increasing the links in the chain(no pun intended)
Peter