Modifying a ballscrew nut

[pstockley]

How feasible is it to modify a ballscrew nut? I have an option to get a really nice 12mm ground ballscrew for my lathe x axis conversion. However, due to serious space constraints I need a nut that has a threaded body instead of a mounting flange. I would need to turn down the flange and thread the body. How hard are these nuts typically?

If it isn't feasible then I guess I will have to spend the big bucks on a custom ground screw from hiwin.

[BobWarfield]

I can't understand why this wouldn't be feasible. There should be enough meat there to accomodate a thread.

You could also turn down the flange to a cylindrical profile that is not much larger in diameter than the nut and work from that depending on how you plan to mount and what the clearances are. I would think your biggest challenge is going to be the mayhem that ensues when you remove the nut from the screw. Someone on these forums made that mistake and posted directions for how to get it all back together again but I don't remember who it was.

Here is another thought. I have seen lathe conversions where the nut was outboard of (behind) the cross slide instead of trying to fit it underneath. You need room behind the lathe, but once there, you have a lot more clearance to work with.

Best,

BW

[HuFlungDung]

I would not mess around with the ballscrew nut in that manner. It is likely case hardened (tough going), and there may be some thin areas where you might cut into in the ball return gallery (ruined).

I agree with Bob about mounting the ballscrew in an outboard position on the back of the cross slide. However, you would perhaps have to machine and drill and tap holes in the back of the carriage and cross slide in order to gain some flat surfaces to mount the parts to.

[widgitmaster]

Originally Posted by BobWarfield Here is another thought. I have seen lathe conversions where the nut was outboard of (behind) the cross slide instead of trying to fit it underneath. You need room behind the lathe, but once there, you have a lot more clearance to work with.

Every machine has the leadscrews located in the middle of the slide mechanisms, if the screw is located off center, then the force is unbalanced, and the moving item will wear unevenly as is trys to "dogtrack" down the given path. then it will do the same in the return direction, except the force will be on the opposite side! Basically not a good idea Bob!

AS for the ballscrew nut, I have successfully modified Thompson Square ballnuts, by milling off the ends to make it shorter, and one had the face where the thread started moved in 1/8" to really compact the nut!
They were hard, but not that tough to mill and turn! I would estimate 38-45 RC hardness!

Try cutting it with a sharp file, if it doesn't cut, it needs to be ground!

Eric

[HuFlungDung]

I was thinking more in terms of "outboard where the taper attachment would usually sit and pull on the cross slide or cross slide screw." No change of center position would be involved.

[Ken_Shea]

Eric,
Not in any real disagreement on your comment about not being a good idea with regard to backside positioning of the ball screw as my first thoughts were similar to yours, however, considering the load that the 20 and 25 series THK rails will handle and the suspected loads a small lathe will impose upon the mechanics, personally I think it is a great place to put the ball screw when centerline space is limited, perhaps even when it is not. If/when my conversion is completed and used I will find out for sure since that is precisely where it is going.

Pstockly, Mine is threaded and I would have prefered it be flanged.

[Geof]

Originally Posted by widgitmaster Every machine has the leadscrews located in the middle of the slide mechanisms....Eric

Haas TL1, and I suppose all the TL series, has the Z axis ball screw behind the machine completely outside the linear guides. Actually the position of the ballscrew relative to the slide mechanisms is more or less irrelevant; it is the location of the ball screw relative to the cutting load that determines what direction and how much the twisting load will be.

[BobWarfield]

Hu, thank you for mentioning the taper attachment example. I think Widgit probably just didn't quite see what I was getting at and that example would have made it a lot more clear had I included it up front.

In terms of avoiding the nasty behavior Widgit mentions, I would take care that the ballscrew is well aligned with the center axis of the cross slide. Dial it in carefully. Aaron discusses doing this when converting mill tables to ballscrews on the Industrial Hobbies site. I think that if you have done so, you will have minimized any tendency for the ballscrew/nut to apply twisting loads to the slide.

Best,

BW