Floating end of ball screw

[packrat]

I'm a newbie here but not to machining. My question is, Why does the floating end of the screw have to be machined?

I mean ,say you have a 16mm dia. screw, why not just use a bearing with that I.D.?

cary

[coop2005]

This is situation dependant, for the vast majority of situations you would want to machine the ends. The screw should have a end machined so that it is captured between bearing inner races on both ends, thus putting a preload on the bearings. Without this preload on the bearings on each end you will introduce backlash as the screw will move slightly with the inner race of the bearings. If your looking for a lower cost way of achieving the same thing you could use a clamping shaft collar and a spacer/washer to allow the ballscrew to react of the bearing inner race.

[MrWild]

The "floating end" not the driven end. All the floating end does is keep the aft-end of the ball screw from whipping. Because of heat/cold cycles the aft end also floats in the ID of the end bearing so it can grow or shrink and not cause problems with the AC bearing on the driven end which do need a preload.

I don't know why people machine the ends except for maybe working with tight spaces and need a smaller/cheaper diameter bearing.

[ger21]

Originally Posted by packrat I mean ,say you have a 16mm dia. screw, why not just use a bearing with that I.D.? cary

Maybe because it's not 16mm. Looking at the technical info from Nook, A ballscrew's diameter is measured from the center of the balls, and the outside (land) diameter is larger. They don't seem to tell you what it is, though.

[garagefela]

Hi there,
Also keep in mind that the ball grooves will no doubt not be concentric to the outside diameter of the screw.

So on the off chance you just maybe, possibly had a bearing that happened to be a snug fit on the outside of a ball screw...... still not the best way to go.

Cheers M

[packrat]

Thanks guys for the replies.

garagefela-- If the screw O.D. is not concentric to the ball groove, how do you set up to turn the end?

I'm in the "thinking" stage of a build. Was trying to make up my mind on whether to use screws from Ebay at whatever length they are or buy a long piece of screw and cut to length I want. Any thoughts guys?

[garagefela]

Originally Posted by packrat Thanks guys for the replies. garagefela-- If the screw O.D. is not concentric to the ball groove, how do you set up to turn the end?

The way that I did mine was to place the screw in a 4 jaw chuck and use and indicator to clock up the base of the grooves.

I placed the indicator in the base of the groove and moved left and right just a bit to ensure I got to the very bottom of the groove and turned the chuck and repeated. Fidddly but do-able.

This is the way that I did it to ensure that the bearing journal was concentric to the ball grooves.

Comments anyone??

Cheers M

[packrat]

garagefela- kind of hard keeping up with the screw pitch wasn't it?

After posting the question I came up with an answer that may work. How about finding a coil spring with a wire diameter slightly bigger than the groove depth. then thread the spring into the ball groove, and hold in a collet. I've got tons of springs, I never throw out anything with out stripping it of all (someday) useful parts, hence the name Packrat!

cary

[tumutbound]

Originally Posted by packrat Thanks guys for the replies. I'm in the "thinking" stage of a build. Was trying to make up my mind on whether to use screws from Ebay at whatever length they are or buy a long piece of screw and cut to length I want. Any thoughts guys?

If you're looking at the eBay seller lineramotionbearings2008 for your ball screws, just tell him (Chai) what size(s) you're looking for and he will give you a quote. It's only a few $$ extra for end machining to your specifications.