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View Full Version : Got HF mini, now a couple of questions...



megavolt
09-04-2004, 03:53 PM
Got all my things ready for conversion: 390 oz. servos, gecko drives, controller, etc.

I purchased a ballscrew (5/8", with ball nut) and am trying to figure out how best to mount this.

From looking at the various pictures I've found, folks seem to do one of 3 things:

1. Make a separate assembly that houses the ballscrew, bearings, etc. It sits beside the mill head and attaches to it. Basically a separate linear-slide assembly.

2. Mount a bearing-block right behind the motor, and a bracket on top of the column holds the rotating ballnut, motor, etc.

3. Mount the ballnut right behind the motor. The bearing block is at the top. Basically the reverse of #2.

Any recommendations on the best method? #3 sounds like you'd need to bore a vertical hole all the way through the head to all the ballscrew passage.

#2 sounds the simplest, but I've not seen hardware for actually rotating the ballsnut. What kind of thrust bearings, etc.?

Also, it looks like most folks build their own bearing blocks... presumably from 2 sandwiched angular bearings. Is this correct?

I greatly appreciate any insight!

John

cncadmin
09-04-2004, 06:12 PM
Man have fun, I'm still trying to get mine done. Couple of thing to look out for.

1)The gibbes are cut and the wrong angle and need to be re-done.
2) The guides are not parallel to each other
3) 5/8 nuts will work but you will need to mill the long bed to be able to fit it
4) you need to gear it 4to1

here are a few pic of my conversion

http://cnczone.com/gallery/data/500/1109_0918.jpg

http://cnczone.com/gallery/data/500/12221.jpg

http://cnczone.com/gallery/data/500/11.jpg

http://cnczone.com/gallery/data/500/1109_0916.jpg

cncadmin
09-04-2004, 06:15 PM
I used the same thrust bearing that the HF uses and I used regular bearing to handle the axial loads.

megavolt
09-04-2004, 06:33 PM
Thanks for the reply and pics!

wow 4:1 reduction? Did you try it direct or 1:2 and not have enough torque? My ballscrew came in a linear slide assembly with a considerably smaller servo motor. Applying 12v to it (the smaller motor) provides enough force to almost lift me off the floor. I was thinking these larger servo's would almost be overkill?

Most of your pics look like the x & Y axis? I was going to tackle those later - get the Z done first and just try to minimize all the backlash I can with the stock acme's. A lot of the x & y backlash seem to be in the handwheel/bearing assembly rather than the acme nut itself. I was thinking of adding a thrust bearing on the outside of those so the nut could be tightened up more without binding.


>1)The gibbes are cut and the wrong angle and need to be re-done.
>2) The guides are not parallel to each other
>3) 5/8 nuts will work but you will need to mill the long bed to be able to fit it
>4) you need to gear it 4to1

cncadmin
09-04-2004, 10:45 PM
The backlash is in the nut as well, it's not pre-loaded. 4 to 1 is needed to provide enough torque. Direct will work as well, but you will be limited in cutting force. The thrust bearings must be on both side to provide loading in both directions of movement.

sendkeys
09-05-2004, 01:17 AM
what is the max rpm on the motors?
and what encoder size?

running direct might take you over the rpm limit.

also running 4 to 1 might kill the max ipm. if you are controlling it with say 45khz mach1

also check out http://www.5bears.com/cnc04.htm basicly how im going to do my bearing block.

cncadmin
09-05-2004, 10:43 AM
I'm using servo motor's so 4 to 1 will give me the speed and resoution I need. If you go direct drive than I guess you would not need thrust bearing.

sendkeys
09-05-2004, 02:08 PM
i didnt mean 4 to 1 wouldnt be a good size, just ment if he had say 200 encoder might be right on. but its say 2000 (like i have) and he looking for 200 ipm wouldnt work out :)

megavolt
09-06-2004, 12:36 PM
No max rpm is noted - but staying within the recommended voltage shouldn't exceed any max rpm. Besides, isn't speed (at least ipm) easily configurable in most software?

I believe my encoders are 250.


what is the max rpm on the motors?
and what encoder size?

running direct might take you over the rpm limit.

also running 4 to 1 might kill the max ipm. if you are controlling it with say 45khz mach1

also check out http://www.5bears.com/cnc04.htm basicly how im going to do my bearing block.

sendkeys
09-06-2004, 03:33 PM
I do what CNCadmin says then :)