ChrisB, so from what I understand, you ran the stock motor and now are running
the 131:1? If so, which would you recommend, why are you now using the 131,
how hard to run another ratio motor and will the 131 play well with two stock
X and Y motors?
There is no need to ‘match’ the Z motor with the X/Y motors, or if there is, you
need a much faster Z motor than the stock one.
For most cutting, you have relativly few Z movements, so the speed of the Z axis
isn’t that significant, but if you are doing a lot of Z movement, you will find
that it’s speed makes the whole machine slow down.
Bar picked the Z motor he did because he didn’t expect there to be a lot of Z
movement, and he wanted to be sure that the motor had enough torque. Several
people have shifted to faster motors, but nobody has purchased a bunch of them
and done comparisons to find out what the minimum gearing is while driving the
high-friction rigid setup. If you have a Z with less friction, you should be
able to go even lower.
If you think about it, you want the Z axis to end up with around 0.1mm per
encoder step to give you a very comfortable 0.5mm position accuracy.
with a lead screw of 8 rotations/inch, this means you do one rotation every
3.175 mm, so you need somewhere around 320 pulses/rev.
with a 7 segment encoder * 4 pulses/seg, this is 28 pulses/rev
320 pulses/rev / 28 pulses/rev = ~11.5:1 motor/output ratio
so a motor with a 10:1 to 12:1 gearbox would still give you more than enough
accuracy. The question would be if it would have enough power to move the Z axis
(and if you are not sliding a router in it’s housing, the answer is probably
yes)
David Lang