metalworking pillar drill experiences

[routercnc]

In this video I tear the machine down to fit the new stepper motor drive system . . .

[routercnc]

Re-build time. Hope the motor can lift it!

[routercnc]

Let's try that again!

[routercnc]

Trying to fix the backdrive problem . . .

[routercnc]

We're making progress now. Time to fit an electronic brake to the knee motor!

[routercnc]

This time we get the knee DRO fitted and working . . .

[Robin Hewitt]

you are not alone. Here is my friction brake and sprag clutch bearing that stops the knee back driving its' ballscrew. To attach the Z axis DRO reader to the knee I resorted to 3D printing

[routercnc]

Neat work!
Sprag clutches allow free rotation in one direction and transmit drive in the other. Can you explain how this is operating in your setup? Are you letting gravity lower it by letting off the brake and raising it by driving through the sprag clutch?

[Robin Hewitt]

I am not good at explaining things and my drawings are functional rather than informative...

The knee originally had a 6mm pitch, left-hand screw and a 3:2 bevel gear reduction to give 4mm vertical travel per rev.

I fitted a 5mm pitch, right hand ball screw. First it connects to the stepper motor with a toothed belt, then it turns through 90deg using a 1:1 spiral tooth form bevel gear to reduce cogging. Then a 5:4 spur gear reduction. The new gear shaft, goes forwards, where it gets the rather nice 4mm satin chrome dials the mill came with and a Bridgeport style dog clutch and crank. Going backwards it has the sprag bearing keyed on to it. The outside of the sprag bearing has a friction brake. I used bits of timing belt for brake shoes.

When I wind the table up the sprags turn freely and do nothing.

When I wind the table down, or when it tries to wind the table down, the sprags dig in and it resists.

I try to adjust the brake so it feels the same going down as it does for up.

[routercnc]

Time for some better lights . . . plus some bonus 3D printed parts!