Jerrys' belt drive gearboxs, (working)

[fozzyber]

Well I broke down and started making my own gear box belt drive system, for my old PRT.
xl belts, and bearing pivots...
It sounds like a different machine now, I can't jog over 7-8ips with out stalling I guess b/c of the pk-299 motors loose all of their torque at speed.
but at the lower end of things OMG!!! 2816 oz-in ( 176 in-lbs) !!!!!
Well pics can say more then I can.

[Brady Watson]

It really does make a world of difference. Good job.

Now that you've got way more torque than you'll ever use, you should upgrade a few things before you twist them into a mess or break them.

Get rid of gold strut on X car. Replace with box steel & weld into 3X3's on each end. Weld rails where they meet 3X3 on each end. This will keep the gantry from racking if you get a stall on one side or a motor driver fails - or you hit something.

Replace the 3/8" rack on the entire machine with 1/2" and 1/2" pinions. You're pushing what that 3/8" rack is capable of handling. It makes a tremendous difference in smoothness of movement and cutting over the 3/8".

-B

[donclifton]

What is the gear ratio, looks like a nema 23 motor. I think you math might be a little off.
Don

[fozzyber]

Motors are pk-299, ratio 3.2:1
880x3.2=2816

[donclifton]

Your right, those are some big motors. I have 500oz hold motors on mine with 5:1 gearing and it's way over kill. You rack and pinion takes at least 2/3 of that gearing away.
Thanks
Don

[fozzyber]

I can see that but this was done mostly for resolution than tourque. My cuts look much better now. Next project, is a box for the z,
I don't understand why the z does not have a pivot, I am thinking of designing a z with a pivot. Any thing to watch out for?

[donclifton]

You could always make a Z with ball screws.
Thanks
Don
4axiscnc.com

[Brady Watson]

The pivot is not necessary - in fact is undesirable, as indicated by the PRS way of motor mounting. The pivot allows the mount to introduce a lot of pitch & yaw into the mount and makes pinions wear out faster. Direct mount would be best.

Please be careful that you don't get your fingers or arm in a spot where it shouldn't be. The motor combo you have does not have safety provisions built into it & this can be dangerous. You literally have bone-crushing force at your fingertips...

-B

[fozzyber]

Brady do you have a pic of a PRS z motor mounting?
And yes I will be carefull with "the power'

[Brady Watson]

It's just a flat 1/4" plate that the motor mounts to, with slotted holes to slide the motor in & out of the rack. If you goto the shopbot main site, you can see how they are mounted on the tool. All axes are the same.

-B