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View Full Version : MM Conversion - Option questions.



Moondog
11-11-2004, 02:55 PM
Hello looking at converting a Mini Mill to CNC and I hope you guys can give me your opinion on the following.

1. When converting the Axis should you also have a handwheel attached for manual use. Or have most people found they never use the manual again?...

When converting the Z axis I see some people mount the Ball Nut in the head casting and some mount it to the side of the head. Are their any advantages/disadvantages of either options?...

thanks

cncadmin
11-11-2004, 03:48 PM
You would defiantly would want to mount the z- from the center verse the side. Otherwise it will cock the head to the side while moving. I plan on putting mu handles back on so that if I have something quick to machine out I can do it by hand.

JRouche
11-11-2004, 10:31 PM
I like the idea of being able to use hand wheels. The problem is the safety factor. I have seen some handles where the hand crank portion swings inward towards the hub of the wheel making it safer. Also I would stick to aluminum for the less weight.

I got confused with the ballnut Q. The way I interpreted it was that some folks put the nut on the outside of the head casting? If that is what you said, nope, put her inside. The idea is to get as close to parallel as possible to the axis of Z. Whether it be a quill center line or the centerline of the slides (dovetail, linear rails, square). JRouche

JFettig
11-11-2004, 11:12 PM
If the gibs are properly adjusted, it should be just fine, I have had no problems, I have my head perfectly squaired up to my table, shimmed back a little because it was leaning forward a little. When I first got my mill, I didnt knwo what I was doing and my gib was loose and the head was leaning to the side a little and I couldnt drill strait down, it would push it down kind of sideways and I broke a few small drills.

-edit- about the hand wheels, I really like this feature, one thing is that if you are using ballscrew on the Z axis, it is easy for the head to raise or lower without you wanting it to. with the gibs loose on my mill I can push it from side to side by hand. This is what would happen if your stepper or servo isnt powered up on the z axis and the depth controlled by software.

Same goes for x and y if the gibs arent tight. One thing that is nice with the steppers is that you can feel the steps, with .2" lead ballscrews, one step would equal out to .001" and it would be rather simple to controll.


Jon

AdminCrew
11-13-2004, 07:31 AM
Lose the handwheels, there isn't a need. You can jog and position with the keyboard easier than turning cranks. I had handwheels on my first machine, but havent had them since. Plus its a safety issue.

Moondog
11-13-2004, 01:50 PM
Thanks guys...

From this discussion it seems that handwheels are not needed. Kaderick... you're right you can just jog to the position alter your Z for depth and jog your cuts... the added benefit would be having the DRO's for accuracy...

Next question: Is it better to run the Servos direct drive or to use pulleys and gear down say: 2:1. On a Mill..speed is not the issue.

RotarySMP
11-13-2004, 02:58 PM
On my lathe I canned the hand wheels and haven't regretted it. Made the enclosure design much easier.

To answer your second question we would need to know what motors you have.

Moondog
11-14-2004, 04:47 AM
Rotary... Haven't yet got the Servos, but I would expect around the 250 oz.in. Most of these retrofits use around 150+ oz.in steppers. So i think servos a little larger shold do the trick.

RotarySMP
11-16-2004, 02:47 AM
That is still not enough information.

When you say servo's are you meaning closed loop servo control or open loop stepper control.

Assuming you mean servo's...
Most common servo's are designed for quite high speed, so you will end up with a much cheaper system running a small servo (say 60 Ozin continuous torque) through a 3:1 reduction timing belt than a 180 ozin servo direct drive.