Rotating Ball nut

[GEOFFREY]

I think you may find the best straightening device would be something like the one we used to use to straighten motorcycle fork tubes. If you don't know what that looks like, it is a bit like a very large bearing puller, but with only two legs at 180 degrees, each with a hooked end to hook over the item to be corrected. Find the centre of each part of the bend and apply gentle pressure to that point, with the leg hooks positioned to suit. The device does not need the legs to be pivoted. I hope that makes sense. G.

[Jonathan]

That is a major concern because even moving the gantry by hand there is some racking and I've tried to create a fair balance for rigidity vs weight!

I'd be wary of compromising rigidity for weight at all. It's much more important to have a strong machine than a fast machine.

Would I still have problems with my ballscrews being slightly bent if going for then rotating nut?

The rotating nuts would still work well with a bent screw, however it will shorten the life of the ballnuts since you'll be applying a radial force to the nut which is not something they're designed for. How much it shortens the life depends on how much it's bent and the length, since that determines the force the nut has to apply to straighten it as it moves along. It's hard to quantify. How bent are they?

[paulus.v]

To Paulus, That indeed is very interesting and also worrying for my 12Nm motors. I was looking at the 150v drives to start with, but I got a guy in china to spec the drives and power supplies to my motors, like he did on a plasma table I recently built and he recommended a 68v 400w system. He also sold the 150v drives btw... However, I do think myself these would work best and would save having to buy power supplies for every drive.

You need to find your motor specs in order to choose the right drive. My 150V was only a guess! If you have the 68V 8A drives is better to get better steppers for them, up to 5.7 amps per phase and the inductance lower than 4.4mH. Probably will be at half the length of the 12Nm therefore near to half the holding torque and inertia.

I was searching the last two days for Nema34 stepper for my machine and found some weird things. I will post tomorrow on my build log.

[paulus.v]

I have 2 x 12Nm nema 34's for the X (1 for each ballscrew), do you think I would get away with the rotating ballnut I found with my motors?. I know with them being bigger motors that the moment of inertia is greater than say a 4Nm, but I plan to drive them with 68V 8A drives.

From what I have read the 12Nm steppers could be a problem. Having high inductance you need to give higher voltage (maybe 150V) to run them to their specs. The torque will also drop fast with rpm. Probably you wont be able to get it moving reliably at 200ipm with decent acceleration using your 10mm screw pitch at 1:1 but I may be wrong.

Do you know the specs of your steppers?


I attach an interesting read. (1Nm=141oz-in)