If you look at the nook critical speed calculator:
https://www.nookindustries.com/resou...ed-calculator/
I believe the end fixity is "C" for one end fixed and one end with a simple support, which is what is most commonly done. With a root diameter of 21.5mm, a length of 1500mm, and an end fixity of "C" it gives a value of approx 1700 RPM for critical speed. This is not an exact value and what you can get in practice, better or worse, will depend on things like how straight the ballscrew is.
10mm lead...17000 mm/min or 670 IPM
5mm lead....8500 mm/min or 334 IPM
That's just looking at the critical speed.
Hi NIC77
very informative and i thank you , i did run my measurements in the calculator and i measured distance between bearing supports which is 1300mm i got a higher critical speed of 2261 rpm.
like jim said the machine would most likely move around a lot at them speeds and he said his table is the same as mine with 750 watt motors and 2.1 gear ratio and 5mm pitch and he has had to tame it down to 100 IPM
but like you said with 750 watt motors driving 25mm screws at 2.1 ratio it would not matter if i went five or ten millimeter pitch either would be fine,but with a 10mm pitch it would be a beast for shore.
i would like to ask if you know of any reliable ball screw manufacture in taiwan that can custom machine ends to my sizes and ship them to me.
kind regards wayne
To put it in perspective, the video below has rapids of "15m/min and 0,5g". It's not my video, I just really like the build. If you pay attention to the rapids you'll see that they are lightening fast.
https://www.youtube.com/watch?v=J2RuAwibGS4
He's got linear rails and a different kind of machine. So with your ways instead of rails and it being a mill conversion, what Jim says I do not doubt at all. You'd probably have to tone the rapids and acceleration down quite a bit from that.
But in selecting the lead of your ballscrew, might as well choose the best one, even if you have to tone it down from there. The only thing I have been commenting on is the inertia of your motor / ballscrew pairing. The thing is, if you could find some new surplus ballscrews made in Germany or Japan (very doubtful that you will at 1500mm long), then you could easily go with 2505 and be happy.
Really, the fact that you're going to go with 750W servos means that whatever you're going to do (just don't pick 3205) is going to work for you decently enough. Many people will choose a high inductance
stepper motor turning a 5mm lead ballscrew and then wonder why they can't get decent rapids and accelerations. And I think that is the long way of agreeing with what Jim said a few posts ago.
I had a look at the HAAS VMC ballscrew parts list. Looks like 3208 is a common size for them. That's with lengths of around 700mm and if I'm not mistaken (which I might be) 1300W servo motors. The point is, they've matched everything well. For your purposes, you don't need the 32mm diameter.
2510 ballscrews with 2:1 gear reduction from a 750W servo. It wouldn't be OK. It would be a
BEAST! You'd have to tone it down from the max it could do. Yeah, that would work.
Single phase power input, three phase power input, DC power input, it doesn't matter, 750W is 750W, just go with what is convenient at your shop. 2:1 gear reduction, just make sure your servo is capable of 3000 RPM if you want to engage beast mode.
Problem solved.
Jim has more experience with the specifics of what you're doing than I do. I think I'm going to defer to his opinions and give others a chance to talk. I admit that I haven't done a mill conversion myself. I just dabble in math.