Re: [CAD_CAM_EDM_DRO] Z-Axis Knee Woes

jbordens wrote:

>Hi folks. I'm retrofitting a G3102 Grizzly Knee Mill, a smaller type
>mill somewhere bigger than a drill mill, but smaller than a full
>bridgeport.
>
>I just finished my Z-axis, after success with X and Y. I decided to
>motorize the knee for various reasons. I'm using Camtronics 600-in-oz
>motors and a 2:1 ratio on the pulleys.
>
>The knee is driven by a shaft that is at 90-degrees to a jackscrew.
>The shaft is connected to the jackscrew via a set of helical spur gears.
>
>Here are my problems:
>
>(1) the motors aren't powerful enough, apparently, to raise the knee.
> They stall and eventually cause my geckos to fault. I'm pretty sure
>I have the "limit" set to Max on the geckos.
>

Assuming that you DO have the current limit set right, then the only
hope is to go to a 3:1 or
even 4:1 ratio to get more torque at the screw. Even with a
counterweight, there is still more
mass on that axis than any other, by a huge amount.

>(2) when lowering the knee, the motor turns and every now again
>there's a 'thump' from the mill, as if the knee is not lowering
>smoothly, but in little increments.
>
>

Yup, this is very common. You want to check that you have properly
lubed the knee ways,
and that the gibs are not too tight (or too loose). This is not a CNC
problem, but a problem
with the machine itself. A new machine should not do that!

Jon