Ball screws singles/doubles/preloaded???

[replicapro]

Im attempting to comprehend the basics of ball screws. I see there is a huge price difference between preloded and not.

I understand there is pressure between the 2 ball nuts, but what major difference is there?

Also does anyone think buying ball screws by the foot from mcmaster and machining the ends is a good idea, or is it better to get a kit thats pre machined.

Im just a bit confused with all the different options.

[Cold Fusion]

The difference is that with a preloaded setup there is almost no backlash. IE, the slop in between threads is eliminated with the constant pressure of the balls in the axial direction.

Buying the rolled Mcmaster screw is a good enough solution for 95% of people here. It gives a lead error of only .004 per foot. If you go to http://www.homecnc.info Jeff will sell you plans on how to build your own preloaded nut that is MUCH cheaper then buying a complete unit.

Do you own a lathe? If not, call your local machine shops. A job such as this shouldn't cost too much.

[replicapro]

Thats what ill do. I have a sieg mini lathe, I think im going with 5/8th screws so I should be able to feed them through.

[IJ.]

Not sure about the BallScrew CF mentioned but I just finished machining my HiWin BallScrews and it's 60 Rockwell !

Once you get below the Hardening it's quite soft and easy to machine, it's just breaking through that's very difficult.

I ended up using an angle grinder while spinning the ballscrew in the lathe stopping every few minutes to cool the ballscrew with coolant.

All in all a very messy and time consuming job, hope this helps.

[Cold Fusion]

Ground ball screws are Rockwell 60. That means you will probably spend about a week cutting it. Rolled, which you want, are softer and easier to turn.

[buscht]

The ball screws from McMaster are very hard. I think IJ said it very well. I had a machine ship mill 3 of mine and they said that it took 5 hours.

On a short screw ( less than 12" long), you probably don't need a bearing on both ends. That will save some machining time.

I have been trying to purchase some additional ball screws on EBAY that already have the ends machined. Its hard to find a bargain.

One more thing, if you buy the ballscrew and nut from McMaster Carr, notice that its missing an easy way to mount the nut to your machine. You have to buy a mounting flange in addition to the nut. $20 from Nook Industruies, or make your own.

Cold Fusion gave some good advice, but I am not using the preload and don't notice much backlash in the ball nut.

[HuFlungDung]

I would anneal the shaft end a little bit before attempting to machine it. These screws are most likely induction hardened, and it should not be too difficult to "spoil the temper" of it a little bit. Even if you only take it up to 1000F, it will help take the snap out of it.

Only heat the area you want to machine, of course. Oil the shaft and wrap around it with wet rags to prevent the heat from going too far down the shaft.

Use a black hot pressed aluminum oxide insert and it shouldn't take more than a few minutes to get through the tough going.

It is also possible to machine fully hardened steel with Silicon carbide whisker reinforced ceramic, a WG300 insert from Greenleaf. This is an unbelievably tough insert, which we use to rough off and finish hardsurfaced arc welds on shaft buildup areas. The insert flakes a bit when used, but man, for what they are cutting, its incredible really. However, you need at least a 19" lathe to be big and massive enough not to be bending your cross slide, tailstock and compound while this hammering is going on

[HomeCNC]

I have done many of these rolled ball screws with no problem at all. I just spend a little time grinding the end that I want to machine down to the root diameter. After that it turns with a carbide insert bit just fine. I can do a nice bearing end and step down for a thread in a few hours per end.

[mastercnc]

replicapro,

Try this method, Chuck up an end of your ball screw and drill a hole, say .375"ID. Make a stub shaft out of steel that will fit into the end of the ball screw...374ish"OD. Fit the two together and TIG weld the joint. Turn the remaining lenght of your stub shaft to your desired dimensions. Now your ball screw and ends will be true to each other and you won't have to cut into that hardenend case.

M

[IJ.]

Hu: I'm being lazy here but do you have a link or more info on the ceramic inserts?

I have my Lathe retrofit to do soon !

[HuFlungDung]

IJ,

For the whisker-reinforced ceramics, check here:

http://www.greenleafcorporation.com/

For the "regular" Aluminum Oxide hot pressed ceramic, I think just about all the insert manufacturers make a generic version of this. It is relatively inexpensive, but is quite fragile in comparison. These will also machine very hard steels, but the surface cannot have any interruptions in it.

FYI, I have also used a CBN insert, but these are really expensive and interrupted cutting is still hard on them. CBN also has a quite heavy edge hone, whereas the WG300 ceramic whisker inserts are practically sharp.

For roughing, I use the WG300 1/2" dia round insert. These are top clamp style only, but you can rotate the insert and also flip it over. This allows you to get a lot of use out of it for its $40 dollar price (that is just a rough guesstimate). When these inserts get dulled, the pressure builds up and they actually flake off on the top. Quite often, this creates a new sharp cutting edge at the front, sharp enough to continue roughing with.

For finishing, I use the TNMG style WG300 or switch over to the less expensive black aluminum oxide ceramics. Don't use either of these products where the steel is soft, because built up edge will occur, unless you can maintain 1200 or more SFM

If I could, I'd get my teeth replaced with these WG300 suckers

[IJ.]

Thanks Hu !