[Kev]

Hi all

Who has the best prices for ballscrews/ballnuts? I checked out Roton and they have better prices than McMaster but these are the only two that I know of. I am looking at a 5/8 X 0.2 sized screw.

Also, do you think that a 5/8 screw will be large enough for a 5-6 ft. X axis?

Thanks,

Kevin

[buckie555]

Kev

I've just recently bought 5/8" ballscrew from mcmaster for my y and z axis' (36" and 12") and 1" for my x axis (58"). I used the thomson saginaw datasheet to do the critical speed calcs for all three. The y and z were fine yielding acceptable rpm well above what my servos are capable of delivering however if I'd gone for 5/8" for the x as well then I would have limited my traversals on that axis to about 140ipm max. I'm using fairly beefy servos and didn't want the ballscrews to be the limiting factor so I chose the 1" which should allow rapids of upto about 480ipm. It all depends on how fast you envisage running and how the screws will be supported. The critical speed increases considerably if the shaft is fixed at both ends (i.e double bearings) rather than being just simply supported (single bearings). If you're after reasonable accuracy you'll need two ballnuts for each axis so that you can preload them against each other. I was surprised at how much backlash each nut has. The specs state 2 - 13 thou, I didn't measure mine but I'd guess they were at the upper end of the scale. Once again it all depends on what your expectations are. Anyway hope this helps.

Buckie

[cncadmin]

http://www.cnczone.com/links.php?s=&...link&linkid=89

[Kev]

Thanks guys for the replies,

Paul,

Roton does seem to have better prices than Mcmaster.

Buckie,

My motors are not very heavy duty. The 140 or so ipm will probably be OK for me. I was glad to see that you calculated the numbers.

I did not realize the backlash was so high. But you are right the nut is a bit loose.

Kevin