Re: CNC Newbie

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dan Mauch" <dmauch@s...>
wrote:

> I would recheck that diameter. .631 sounded large so I went out to

my

> shop and I checked a few of the ballscrews I have laying around

they all

> meaasure ~.615.
> I had converted my mill drill to run off of steppers and I replaced

the

> acme leadscrews with ballscrews on the XY axis. On he Z axis I made
> eccentric bushings to roll the the pinion in closer to the quill

rack

> for less backlash.
> Servos are faster, so much smooother and don't suffeer from stepper
> motor resonance and they are closed loop. Today a servo system

barely

> cost more than a stepper system. I would go with 600 oz in PMDC

servo

> motors using a 2/1 ratio timing belt drive with ballscrews. I can

email

> you some pictures of some slick stepper/servo motor mounts I made

for my

> mill drill if interested.
> Dan
>

Dan, yes the ballscrews were only .615. .631 was the ball cicle
diameter from the data sheet. Did you machine the the ball screws
down to the root diameter of .4800"? I bought some taper bearings
with an 1/2" ID. I was thinking machining to the root diameter and
placing a shaft collar there. It looks like the collar should be able
to take the axial load. The rest of the shaft will be 1/2" OD. I had
some stub shafts that came with the nuts that I have been practing
on. Dam hard shafts. I do not want to anneal with heat, so I have
been using carbide inserts with slow feeds. It looks like it will
work.

I would love to see the pics. You can zip them to me. Where ia a good
place to get the belts and pulleys from? I thought about making my
pulleys using my 8" rotary table, but thought that the accuracy would
not be there. I am still debating servo or stepper.

Who has the best control gear for the PMDC servo's? I am still
debating the Z axis. As we all know of the large backlash in the
quill on these mill/drills. I have another set of NTN, 1/2"
ballscrews that I bought before the Thomson's came along. I was
thinking about slapping one in the dovetail column? As for encoders.
Do I try to get some as part of the motor, or just put one on the
shafts directly?

Jason