Need Help!- Moving ball nut router

[giggler]

Hi,

My next project is gonna be a 8'x4' wood router and light ali. Has anyone done a DIY moving ballnut router?

I've considered following the Shopbot approach for my next router with double X drive and twin racks, one mounted on each side of the machine. I can clearly see how this is put together.

I can't see how to do it with a moving ball nut. For example, does one place a 20mm, 8foot ballscrew down one side of the X axis or under the middle of the table on a connecting plate between both sides of the X slide? If to one side, will that aid warping or stalling when maching on the other, non-driven side?

Should I at great cost consider two X axis ballscrews and mimick that of the Shopbot design, just not using racks? I figure this is a bad idea even if possible as it could lead to terrible happenings if one drive is dead, unlike the rack design where at least a gear has the chance to slip by moving a motor tensioning spring in such situations.

thanks,

dc

[jsheerin]

I have a 4'x4' router, and I'd highly recommend dual X drive mechanisms, or at the least putting the drive in the middle. Definitely don't put a screw on one side and expect very good performance.

[giggler]

jsheerin,

thanks. Is your 4' router duel ballscrew or the more common duel rack? I've been looking at racks but was very worried about selecting the correct pitch and then theres mountings to consider which is why I was looking at ballscrews.

dc

[jsheerin]

Dual acme screws. I think if I did it again, I'd look at rack and pinion closely. I may convert mine eventually, but the screws are okay for now. I designed a rotating nut system to use with my current screws but figured out I would only get an improvement in rapid speed which is not that bad at the moment. I wouldn't really be able to cut any faster without upgrading to servo motors which would be a lot more money.

[giggler]

Yes I'm only going with steppers because I've already got them left over from a previous project and spare drives which I've had sitting around for over a year now.

I've considered one large fixed 8' ballscrew in the centre of my machine dropped below the cutting bed so kind of distributed force and the rotating ballscrew nut idea. Because I'm at the design stage, I didn't want to just go down the 1 centre or to the side ballscrew route without asking peoples experiences.

I'm probably gonna build the base and basically assemble most of axis without drive but make sure theres enough scope to change my final design to either driven from both sides or from under base, centre. Again with either screw or rack but first I must find out suitable racks.

dc

[jsheerin]

Here's an example of a single screw rotating nut:
http://www.cnczone.com/forums/showth...t=rotating+nut
http://www.cnczone.com/forums/showth...603#post628603