bad ball screw decision

[bob in windsor]

I bought a ball screw off of ebay on impulse and now think I've made a mistake after reading some of the threads here.I've been kicking around an idea for a cnc horizontal slot morticer and bought this ball screw thinking it would be good for an x axis.Its about 20 inches long, 38 mm dia,10mm pitch.I know, I know , its way to big(diameterwise).Anyway, how big of a motor do I need to drive this screw.There wont be a ton of weight as the table will be made of aluminum.As for the pitch, how much accuracy can I expect over a foot of travel?Should I cut my loss now(fifty bucks) and look for smaller screws?

[ViperTX]

Accuracy.....is based on what the ballscrew's thread is rated...things like +_0.003 inches per foot...the 2nd item that affects accuracy is any backlash between the ballscrew & ballnut...

[juzwuz]

Hey...I did the same thing except I bought a 36mm, 43 inch travel, class 2 accuracy ballscrew and once I saw it next to the components for my router, I got this feeling that it was just too big. I actually bought another ballscrew 20mm in diameter that hopefully will be better and I'll have to sell the big one sometime. I started a thread about it and right now there is an interesting discussion about having a fixed screw and a driven ballnut design. Looks kinda complicated for my limited tools and resources to construct.

[bob in windsor]

I'm going to try to find a way to make it work.I have no experience with this at all.I've got good programming and machining skills but this requires more than that.I think it will be a good learning experience.Even if it only ends up being a two axis system,what kind of cash can I expect to spend?I'll need another feed screw, guides, drive motors.Is there a package deal I can buy for the electronic end of things?

[ger21]

I'm assuming this is a woodworking mortiser? Using a router as the spindle? For such a small travel, you should be able to get away with as little as 12mm screws. Why not just use some inexpensive Acme screws?

[ger21]

Originally Posted by bob in windsor Is there a package deal I can buy for the electronic end of things?

Have you looked at www.hobbycnc.com ? I don't think there packages will spin your 38mm screw, though. Our router at work uses about a 30mm screw to move the ~1000 lb head.

[bob in windsor]

Thanks for the replies.