Rockford Ball screw preload ajustment

I have a set of Rockford .750 x .200 double nut ajustable preload ball screws.


These are new, but when I go to preload them they get rough. There very smooth all the way upto zero backlash but once I start adding preload they get a roughness to them. Oil doesnt help or hurt them.

I took the nuts apart and cleaned and inspected them to find nothing looking wrong. The balls though only measure .1237 which I thought odd.

DOes this sound like the balls might just be to small ?

You can watch down in the threads and when the setup gets rough you can see the balls try to stack when they go to the return tube.


Jess

Quote:

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Originally Posted by LUCKY13

I have a set of Rockford .750 x .200 double nut ajustable preload ball screws.


These are new, but when I go to preload them they get rough. There very smooth all the way upto zero backlash but once I start adding preload they get a roughness to them. Oil doesnt help or hurt them.

I took the nuts apart and cleaned and inspected them to find nothing looking wrong. The balls though only measure .1237 which I thought odd.

DOes this sound like the balls might just be to small ?

You can watch down in the threads and when the setup gets rough you can see the balls try to stack when they go to the return tube.


Jess

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Jess,

Most rolled ballscrews (with the notable exception of Nook XPR screws, which are glass-smooth) are not particularly smooth when new. They will smooth out as they wear in. They also need to be well lubricated. They can be quite rough when dry. But do not get carried away with the pre-load either, as that will cause rapid wear. You should tighten them only until the torque required to turn them increases slightly. Really, the best way to adjust them is the measure the pre-load, which should be on the order of 125-150 pounds for a 5/8" screw. You can do this by attaching a "fish scale" to one end of the screw, and seeing how much force is required to move the screw within the nut. This will only work in one direction, as with preloaded nuts one direction is rigid, the other will move, by further compressing the springs, once the preload force is exceeded.

Regards,
Ray L.

These are really quit smooth, except for when the balls try to stack in the entrance of the return tube. I worked with them last night and I can effect them with the little bit of movement I can get with the return tube itself. WHen not jamming up they are smooth though, although nothing like the ground THK screws I have here.


By what your saying it sound like this is almost normal for this type screw to have roughness. If thats the case I cant see how anyone would even use them because I see this effecting surface finish.


The roughness I am getting will lock the screw up from turning ( just using hand force to turn the screw) . If this was hooked to a servo turning it I dont think it would lock up but I am sure the axis would be jerking around quit a bit.


It seems to me that the balls are just way to small. I may be wrong on this, but something is not right. WIthout preload there is a lot of backlash on the screw. I can measure as much as .006, which seems like a lot to me. As soon as I get any preload on the screw it gets rough. The low limit on preload is .200 of a turn, the high limit is .500 of a turn. I cant even get .100 of a turn before it starts trying to lock up. If I took it any tighter it would be a real problem. BTW this is with oil for lube. BUt for the heck of it I tried grease, and very light weight oil without any help or effect at all.




Jess

Quote:

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Originally Posted by LUCKY13

These are really quit smooth, except for when the balls try to stack in the entrance of the return tube. I worked with them last night and I can effect them with the little bit of movement I can get with the return tube itself. WHen not jamming up they are smooth though, although nothing like the ground THK screws I have here.


By what your saying it sound like this is almost normal for this type screw to have roughness. If thats the case I cant see how anyone would even use them because I see this effecting surface finish.


The roughness I am getting will lock the screw up from turning ( just using hand force to turn the screw) . If this was hooked to a servo turning it I dont think it would lock up but I am sure the axis would be jerking around quit a bit.


It seems to me that the balls are just way to small. I may be wrong on this, but something is not right. WIthout preload there is a lot of backlash on the screw. I can measure as much as .006, which seems like a lot to me. As soon as I get any preload on the screw it gets rough. The low limit on preload is .200 of a turn, the high limit is .500 of a turn. I cant even get .100 of a turn before it starts trying to lock up. If I took it any tighter it would be a real problem. BTW this is with oil for lube. BUt for the heck of it I tried grease, and very light weight oil without any help or effect at all.




Jess

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Six thou of backash is pretty typical for rolled screws and nuts. With double nuts, the amount of backlash with no preload is totally irrelevent, within reasonable limits. Set the pre-load as loose as you can, and use a drill or something the run them end-to-end for a while. I think you'll find they loosen up, and get a lot smoother and quieter, pretty quickly. I assume these are black? The black coating is rough, but will wear down pretty quickly, making things a lot smoother and quieter. Once they're smoothed out, flush them out thoroughly, and re-oil them.

BTW - You shouldn't use grease on ballscrews - only oil. Grease will collect a lot more crud that can jam up the balls. A good thick oil, like way oil is good.

Regards,
Ray L.

Thanks for the info,

yea the grease was just something I tried and they have been took apart and cleaned,reoiled sense.



Your right about the black. Although I took a sponge soaked in paint thinner and run the screw back & fourth with a drill until the black was gone. That was the first thing I thought when I tried the setup was you could see the black wearing away and the little pieces of black I though was causing the binding. ANyway with a section of screw looking like SS and as smooth as could be I get the same results.


YOu can simple watch the balls try to stack up at the return tube. If I keep the preload light it is smooth as could be ( not as quite as my THK ground screws,but smooth). And when I give enougjh preload to get the locking up I can loosen the return tube and move it a little to get it working smooth again. ITs got something to do with how the balls enter the return tube.


These screws & nuts where bought from IH before AAron sold the place. They have been stored until now when I brought them out of there plastic they where shipped in. They where suppost to be a higher grade ( accuracy) than normal but I dont know that Rockford even offers such a thing. This has be wandering what AAron was offering in a package like this. I bought the setup from a guy that never got to finish his mill. He got them from AAron.


I have to call Rockford back tommarrow to see what they say but its not looking good. I may have to send them in to Rockford. But I might try bigger balls first. It just seems the balls are so small that they are hitting the little tab on the return tube because they set to far down in the thread. I wish I had a video camera so I could show what is happening.


Jess

Quote:

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Originally Posted by HimyKabibble

Six thou of backash is pretty typical for rolled screws and nuts. With double nuts, the amount of backlash with no preload is totally irrelevent, within reasonable limits. Set the pre-load as loose as you can, and use a drill or something the run them end-to-end for a while. I think you'll find they loosen up, and get a lot smoother and quieter, pretty quickly. I assume these are black? The black coating is rough, but will wear down pretty quickly, making things a lot smoother and quieter. Once they're smoothed out, flush them out thoroughly, and re-oil them.

BTW - You shouldn't use grease on ballscrews - only oil. Grease will collect a lot more crud that can jam up the balls. A good thick oil, like way oil is good.

Regards,
Ray L.

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