strange bearing preload thread on ballscrew

[mxpro32]

I've got a strange problem that I can't solve. My ballscrew has bearing preload threading that is 10mm x .8 pitch. I can't find a nut to fit this anywhere. I don't think .8 is even an available pitch for 10 mm threading. If anyone has any ideas, i would really appreciate them. thanks.

[trubleshtr]

M10 X 0.75 mm is a standard fine pitch, do you have a thread gauge?

If you have an extra piece of the ball screw, you could turn it into a tap to cut your own nut in delrin.
You could also have a local machine shop make you a nut if the pitch is indeed
m10 x .8
good luck

[mxpro32]

Yeah, i checked it with a thread guage and its .8 pitch. The .75 guage was pretty close so I am kind of wondering if a .75 pitch nut would work. If not, I will probably have a machine shop make some nuts for me if the price is right. I still can't imagine why Star would make a ballscrew with threads on it that you can't get a nut for. I already have the ballnut mounted and the screw is perfect for my application so I'm looking forward to getting this kink worked out. thanks for your thoughts.

[Swede]

Really dumb observation, please don't take offense, as I've done stuff like this...

0.80mm is VERY close to 0.032", yielding a 32 TPI thread. 10mm is pretty close to 3/8". Are you sure your thread is metric? Fairly close to 3/8" X 32, not a standard pattern, but I've seen stranger, 32 is a pretty typical imperial fine pitch. A 32 TPI imperial nut would zip right on there if your thread pitch is truly 0.80 mm.

[mxpro32]

hmmm, interesting thoughts swede. I assumed the threads were metric because the other dimentions on the ball screw were metric, but measuring it now in standard I got a measurment of .39. .375 is 3/8 and if 32 tpi equals .8 pitch then a 3/8 32tpi might just work even if wasn't intended to use that nut. hopefully the 3/8 nut will have enough clearence to absorb the .015 "oversize" threading. now i need to track down some 3/8 nuts. thanks for the info.

[ESjaavik]

I guess Swede hit the nail there. If it were a European part, the 10mm threads would be M10x1. But since it obviously is not in your case the reason may be that they were end machined to Imperial specifications. I have just hunted down the data myself, as I finally Ebought a screw that fits perfect to my mill, so I can get rid of the flex it currently have. Here is most of what I need to know, it may help you too. There you have the load ratings and all the other things you need to know.

http://www2.rexroth-star.com/INTERNET/WEBDOWNLOAD.NSF/4cacbb0890414ccf41256a0200531057/f8c2452909d79f4041256ba400391ffb/$FILE/RE83301_2009_09_KGTENGL.PDF

Did you ask Bosch-Rexroth if they have a suitable nut?

[mxpro32]

well i got 3 nuts 3/8 32tpi from mcmaster carr and they don't even start to thread. I think the problem is that they are machined nuts and they don't have the standard loose tolerance. Now i'm not quite sure what to do. I am thinking that the m10 x .75 pitch might work, but i don't want to buy more expensive nuts (these cost me 20 bucks with shipping) if they aren't going to work. Other than doing that my only other option is to have them machined, which probably won't be cheap, in which case I would prefer not to waste money buying more nuts that don't work before ultimately having them machined. hmm. what to do. I guess I'll get a quote on the nuts and then decide.

[CerveloRod]

I just got my ballscrews from homeshopcnc.com and they use this from MSCDirect.com, 00330274. It is a 32 tpi locking collar. May want to check your dimensions against it.

Rod

[mxpro32]

I think I just solved my problem. considering that 32 tpi and .8 pitch are only .00024 in. off per thread, and the 10mm male threading is only around 19 thousandths larger than 3/8, I figure that using a 3/8 32tpi die to re-cut the threads should make my nuts fit fine. The die will be here tomorrow so hopefully it works. Cervelrod- is your locking collar the type that has grooves on the outside rather than hex-shaped? I came across some of those style nuts in a m10 x .75 pitch, which i was originally going to try and make work.

[CerveloRod]

Yes the locking collar has notches rather than a hex body. I would not try to re-thread mine, to little material and to fine a thread.

Also on mine a nut would take up a lot of room, the collars are only half the thickness of a hex nut.

let us know how the die works out...

Rod

[snaggletto]

Hey,
A 3/8" thread should read just less than .375" on the major diameter if it is anywhere close to being a proper thread. If you are measuring .390" (~9.9mm) I guarantee it is a 10mm thread. I calculate that there is a difference of only ~.002" between .75mm pitch and .8mm pitch. It should be pretty easy to mistake that, even using a pitch gauge. I'd bet money that it's an M10 x .75 thread. Or it's a homemade thread and the lathe operator didn't know what they were doing.

[mxpro32]

yeah, with my metric calipers the o.d. of the threading measures right at 10mm and with my thread guages, the .8 pitch fits perfectly, whereas the .75 doesn't fit at all. the .002 difference in pitch over 8 threads = 16 thousandths, which is more than enough to make a .75 pitch not fit. the 32 tpi pitch, however, is only 2.4 ten-thousandths different per thread than .8mm pitch. and the O.D of 3/8 threads is only around 19 thousandths smaller than 10mm. so hopefully my 3/8 32 tpi die will shave ~.009 off of each side of the threads maintaining their integrity. thanks for everyones ideas.