tiny cnc mill idea

[KTP]

Have any of you made or seen a small mill made from the linear slides like the THK KR series?

I recently came across a couple of these slides and was quite impressed with how compact (and heavy! they are all steel) these slides are. They use rolled or ground ballscrews and already have a motor mount.

My idea was just to throw one upside down on another, so that the X axis slide would be attached to the Y axis slide, then mount another as a Z axis.

I would then mount a Sherline 10,000 rpm spindle to the assembly and bolt a tooling plate to the upside down X axis slide base to act as a milling table.

All in all, it looks like you could put together something like this for under $1000 if you get slides on ebay or the like and have a pretty nifty compact mill with whatever travel you desire (or can find slides for).

If any of you have made one of these already, post a pic please.

[Sparky_NY]

Took a little to find it again but I remembered looking this over recently. I believe it is exactly what you have in mind.

http://www.5bears.com/cnc.htm

[digits]

The 5bears mill is fantastic, but this one might be more like the size you have in mind: http://www.cnczone.com/forums/showthread.php?t=23180

[Switcher]

I'm not sure what your looking for, you might want to look at this mini mill, I think it's the best design, & compact.

http://www.cnczone.com/forums/showthread.php?t=25516


Video:
http://www.cnc-dag50.it/content/view/35/51/



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[juzwuz]

http://www.cnczone.com/forums/search...archid=1607403

I remember wisp made an interesting looking cnc router (twin KR46 for the x-axis, one actuator for the y-axis, and something else for the z-axis). It looked nice. I have a couple of KR46 actuators that I was going to use in a similar design but still haven't gotten around to it. I think the "mill" design you are thinking of would work as well. Hope this helps!

[zephyr9900]

Originally Posted by KTP My idea was just to throw one upside down on another, so that the X axis slide would be attached to the Y axis slide,

KTP, I'm making a small lathe from two KR20's in exactly the same way. Rendering is at http://www.cnczone.com/forums/attach...1&d=1188844117

To mount the slides carriage-to-carriage, I had to use two stacked plates, since the carriages are tapped. One plate screws to each carriage, and the screws to attach the two plates hang over the edge for hex wrench access. I have the two slides assembled, and that is as far as I have gotten yet.

I have since turned the KR assembly upside down conceptually to make a long X axis (gang slide) and am planning to mount them vertically: http://www.cnczone.com/forums/attach...3&d=1192171939

Best regards,

Randy

[KTP]

Yes, thanks guys, mounting the KR series slides to each other was exactly what I was talking about (although the 5bears mill and the other one are very nice..just too much work).

I have a few of the KR-33 slides. I am going to clamp one upside down on my big bedmill and put a dial indicator on it. Then when I run it out the extent of it's travel, I can see how much if any sag there is. Obviously on the final mill the cutter would be applying a force always at the slide but it would be interesting to find out how the mass of the motor when it is 12 inches away from the slide would effect things.

I did see that the permissible moment arm for the KR-33 slide is something like 100 foot-lbs in all dimensions. That is encouraging for mounting the slide upside down to form a milling table.

[zephyr9900]

Originally Posted by KTP I did see that the permissible moment arm for the KR-33 slide is something like 100 foot-lbs in all dimensions.

Yes, the KR's are pretty sturdy, but there will still be deflections if you are cantilevering the load very far (as you are going to test for.) That is one reason why I'm building my "THK lathe" with the bed vertical--it minimizes the overhung load on the slides.

For the Z, you might consider doing what I did with my Sherline mill, and relocate the spindle motor behind the column/Z-slide. It brings the center of gravity of the head to just about where the ways are. http://www.prototrains.com/mill/mill.html has some pictures and description.

Best regards,

Randy

[KTP]

So I mounted one of the KR33 slides upside down to my bedmill as discussed and put a dial indicator on the top of the slide (what is normally the bottom).

When I run the slide out 10 inches I get about 0.001 inch deflection near the end of the slide. If I add 4lbs of weight to the end of the slide when it is out 10 inches, I get another 0.002 inches of deflection.

I am not sure how this 0.003 inch deflection would affect milling operations 10 inches away (where the down force of the cutting bit would be). Obviously because of the 10 inch lever arm, the deflection at the cutter would be much less...

I am curious how much a small mill table such as a sherline or taig deflects on the end near the motor when it is all the way out. Anyone ever tried to measure that?

[zephyr9900]

Originally Posted by KTP I am not sure how this 0.003 inch deflection would affect milling operations 10 inches away

You would need to take measurements at several points along the slide to determine if the deflection was a tilt or bow of the slide. If a tilt, the angular deflection would be the same at the spindle axis. If a bow, and the bearings at the carriage were holding the slide level at that point, there would be no effect on the milling.

Those are some impressively small deflections though. I am not at a point yet to take measurements of my KR20's but in the near future I should have some corresponding data!

Best regards,

Randy