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  1. #21
    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.
    I don't think I have compromised the rigidity really, the machine will be fairly heavy duty, but I've tried to use aluminium components where I can to help keep the weight down. I agree that the speed isn't as critical as a strong structure.

    Well, I had one ballscrew that was very bent, of course when I bought them they were all packaged up, so it was hard to see that they could have been bent. I've managed to straighten the worse one almost completely, but am awaiting loan of a friends press to enable me to straighten it further. I'm wondering if I could get the ballscrews under tension whilst on the machine by tightening both ends, and hopefully pulling it straight?

  2. #22
    You will have a problem pulling it straight. the only reliable method is to press it out. small amounts at a time, mark and check against a flat surface.
    If the nagging gets really bad......Get a bigger shed:naughty:

  3. #23
    You will have a problem pulling it straight. the only reliable method is to press it out. small amounts at a time, mark and check against a flat surface.
    Sorry I meant once I had pressed it as straight as I can get it, then put it under tension whilst on the machine and in use.

  4. #24
    I' ve come up with an idea to house the bearings for this rotating nut idea:

    Click image for larger version. 

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    If I went with Jonathan's suggestion of 7207 angular contact bearings with an OD = 72mm, then I could probably machine this housing myself on my lathe. Once bored out I should be left with a 6.5mm wall thickness, do you think this will be sufficient? After all, the main force acting on this setup will be axial. I was looking at the 7008 bearings with 68mm OD, which would leave me with more wall thickness, but I can't seem to find anyone selling them?? Failing that, would I get away with deep groove bearings?? There seem to be a much better size selection.

  5. #25
    6.5mm would be suffcient and you could use 7007 bearings, but not 7008 for the reasons given earlier. There's no problem in terms of strength from using the smaller bearings, since compared to the bearings you'd use if spinning the screw the ratings are still far greater. Don't even think about deep groove bearings. They're not designed for axial loads. When you put an axial load on one, the balls are forced to ride up on the side of the ring, which isn't ground to such a good finish, so they wear out very very quickly.

    How much have you found that spindle mount for? I could probably get a block of aluminium and bore it for you for less money...

    Have you thought about how to make the shaft? I'm guessing your lathe is big enough, but bear in mind it needs machining very accurately for the bearings and nut with good concentricity. It also needs thread-cutting for a locknut.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. #26
    Thanks again Jonathan for your good advice!

    How much have you found that spindle mount for? I could probably get a block of aluminium and bore it for you for less money...
    Well, I can get 2 spindle mounts for about 70 shipped, plus taxes if they stop it. I was just trying to estimate how much it was going to cost to have machined from a block and judging from recent work I've had done, ALOT! But if you could do them for less, then obviously that would be a massive bonus! AdCNC has offered to do them for me, so I plan to see him this week and have a nose at his machines while I'm there :)

    Regarding the shaft, I will get this done professionally (i.e not by me) because like you said it needs to be a good fit and screw cut. My Idea is to have a flange at one end to bolt the ballnut to, then a locknut at the other to pull everything together, then the pulley after the thread on a slightly smaller diameter shaft.

  7. #27
    I'll machine them for less than 70, PM on the way...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #28
    Hi friend
    I have a question about rotating bull nut. whet we used this method how to fix screw to table? how install the screw?
    thank's

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