Newbie- Ballscrews, Ballnuts and Backlash

[forrest39]

Sounds like a country song!

Actually looking for opinions or experiences setting up ballscrews without parting with too much dough. In particular I'm considering Roton products:

http://www.roton.com/Mating_Componen...family=7059321

I have seen some fancy arrangements using two ballnuts with a spring washer, but this is for an X2 mill so size is an issue. I'm guessing the preloaded ballnut is the answer.

Can anyone share their experience with using the Roton ballscrew and ballnut described above in either the original configuration (non-preloaded) or an 'upgraded' version?!?! Also if anybody has purchased a preloaded ballnut from Roton lately can you share the cost?

TIA --4ist

[HimyKabibble]

Originally Posted by forrest39 Sounds like a country song! Actually looking for opinions or experiences setting up ballscrews without parting with too much dough. In particular I'm considering Roton products: http://www.roton.com/Mating_Componen...family=7059321 I have seen some fancy arrangements using two ballnuts with a spring washer, but this is for an X2 mill so size is an issue. I'm guessing the preloaded ballnut is the answer. Can anyone share their experience with using the Roton ballscrew and ballnut described above in either the original configuration (non-preloaded) or an 'upgraded' version?!?! Also if anybody has purchased a preloaded ballnut from Roton lately can you share the cost? TIA --4ist

A typical inexpensive "single" ballnut will have on the order of 0.005" of backlash out of the box. You can load it with oversize balls, and get that down to 0.003-0.002" (typical) or even 0.001" (if you're REALLY lucky), but you won't get to zero. Getting zero backlash requires either two nuts with spring pre-load, or a much more expensive zero backlash nut. If you don't mind up to about 0.003" of uncertainty in all your dimensions, and little "divots" in your work every time an axis changes direction a single nut will work fine. But if you need to work to 0.001" tolerance, you NEED a zero backlash nut.

Check out seller "linearmotionbearings2008" on E-Bay. He has some very nice prices on Chinese ballscrews and nuts, including zero backlash nuts, and can also machine the screws to your requirement for a reasonable price (good ballscrews are hardened to Rc60, and are VERY hard to machine!). All reports I've seen on his products here have been quite positive.

Regards,
Ray L.

[pntrbl]

Are ballscrews normally case hardened or Rc60 all the way through?

SP

[HimyKabibble]

Originally Posted by pntrbl Are ballscrews normally case hardened or Rc60 all the way through? SP

By definition, anything that is "case hardened" is not hardened all the way through. However, good ballscrews are hardened all the way through, cheap ones are not. The Nook XPR screws I used are Rc60 through and through, and I found them impossible to machine and obtain a decent surface finish without annealing. I've had cheap rolled screws that were only surface hardened, and very shallow at that, and machined just fine with even cheap carbide tooling.

Regards,
Ray L.

[hab82]

I used Roton Ball Screws and nuts on my X2. In my case I used two ball nuts with spring washers on all three Axis. With the flexability of the X2 I couldn't see the benefit of going to ground Ball Screws. I still see some backlash .0015 but I attribute it more to thrust bearings and flex in the mounting than necessarily to the Screws. I used a tool post grinder to get below the case hardening and then used standard HSS tooling for completing the end machining. I never received a reply from Roton when I inquired about low back lash nuts. I am planning a similar approach for my X3 however I have some other Ideas that I will attempt for end machining.

I definitely felt that upgrading to these screws etc was well worth the effort.

Hubert

[forrest39]

By using two ball nuts, did you loose travel on that axis?
Thanks, -4ist

[hab82]

I actually did some machining on the base to recover and actually extend travel for the Y axis. On the X axis I chose to mount the nuts in the saddle. Here again I machined the saddle to accommodate the nuts. I also needed to grind away part of the underside of the table to give clearance for the nuts. Would I do it that way again I am not sure. It works and I made most of mounts for my X3 with it, although the X2 is primarily used for lighter work now. If I had to do it now it would be much easier since I would use my X3 to do the machining instead of hand tools. I purchased a second saddle from LMS so I could use the X2 to do the machining on the saddle. It would have been cheaper to get it from Grizzly.

I considered getting a kit but I also wanted to develop experience so I ended up DIY. One of these days I plan on changing my Z axis because I do not like the amount of flex. But like I said it works so that mod may never happen. Unless you are firmly committed to the X2, you would find the X3 alot easier and It would be a much more capable machine.

The choice to machine or not was driven by wanting to extend the Y travel and where I wanted to mount the nuts not necessarily the use of two nuts.

Hubert

[mactec54]

Kimykabibble

Your Nook Ballscrews XPR are only case hardened just as most ballscrews are, the only ballscrew that are through hardened are made from the stainless steel type materials like 17-4 PH etc, & do not have the same hardness as case hardened ballscrews, your XPR are 58-60 RC, the stainless steel screws are only 40-48RC & both are easy to machine with the right tooling.

Pntrbl
Yes ballscrew are normally case hardened RC58-62 even the best you can buy are only case hardened if they were RC60 all the way through there would be a lot of broken screws

[forrest39]

Originally Posted by hab82 I actually did some machining on the base to recover and actually extend travel for the Y axis. On the X axis I chose to mount the nuts in the saddle. Here again I machined the saddle to accommodate the nuts. I also needed to grind away part of the underside of the table to give clearance for the nuts. Would I do it that way again I am not sure. It works and I made most of mounts for my X3 with it, although the X2 is primarily used for lighter work now. If I had to do it now it would be much easier since I would use my X3 to do the machining instead of hand tools. I purchased a second saddle from LMS so I could use the X2 to do the machining on the saddle. It would have been cheaper to get it from Grizzly. I considered getting a kit but I also wanted to develop experience so I ended up DIY. One of these days I plan on changing my Z axis because I do not like the amount of flex. But like I said it works so that mod may never happen. Unless you are firmly committed to the X2, you would find the X3 alot easier and It would be a much more capable machine. The choice to machine or not was driven by wanting to extend the Y travel and where I wanted to mount the nuts not necessarily the use of two nuts. Hubert

Hubert,
I'm still in the planning phase so X2 vs. X3 ??? Hmm.. A few more bucks up front but perhpas something to consider. Most of the parts and pieces are probably the same as far as electronics and ballnuts and such - maybey just different size.
Thanks for the advice!

-4ist

[HimyKabibble]

Originally Posted by mactec54 Kimykabibble Your Nook Ballscrews XPR are only case hardened just as most ballscrews are, the only ballscrew that are through hardened are made from the stainless steel type materials like 17-4 PH etc, & do not have the same hardness as case hardened ballscrews, your XPR are 58-60 RC, the stainless steel screws are only 40-48RC & both are easy to machine with the right tooling. Pntrbl Yes ballscrew are normally case hardened RC58-62 even the best you can buy are only case hardened if they were RC60 all the way through there would be a lot of broken screws

That was my understanding as well, but I can tell you those suckers are damned hard all the way through, may be not Rc60, but hard just the same. I cut a 1" screw down to 1/2", and was still having a hard time cutting with good carbide insert tools.

Regards,
Ray L.

[hab82]

Forrest
I think you should seriously consider the X3. I got mine from harbor freight as a special order using a 20% off coupon and had it loaded in the pickup for about $860. I had spent nearly that much excluding CNC on my X2 to get extended Z range and stop the gear breakage. While I am still planning to add ballscrews to my X3 (I have the screw and nuts waiting for machining) I made a no mod to Mill conversion with stock screws so I have the X3 running at 30 ipm on X&Y and 20 ipm on Z. All I did was replace the Y and Z cranks with Stepper motors (Clamp on Mtr Mount and split coupler) The X was even easier, The X3 comes ready for an X power Drive. I mounted a Stepper mount to the pre tapped holes and made a coupler to match the end of the screw. X3 screws have a split nut arrangement that allows adjustment for backlash. They recommend .003 inches of backlash that most Machining software can compensate for. I am using the drivers and the same motors that I had on the X2 for x and y. Z took a Nema 34 motor to get the above results. Once I go to Ball Nuts I expect to double or triple the performance. That is the results I had on the X2. The advantage of this initial step is that I have a CNC machine with modest performance to use while I prepare the ball screw conversion. I didn't think it was much harder or expensive than preparing a bunch of Chinese scales to have a DRO on a manual machine. This assumes that the investment in motors and drivers is one time. On my X2 I removed the digital scales once the steppers were up and running as they had higher resolution and less backlash than my homemade DRO. Thus on the X3 I went straight to the steppers.

X3 does not have the same level of problems with losing tram and stiffness that the X2 has as well as more power, and range in all three axis. Plus more room for ball screw and nuts. It also already has a screw for the Z axis instead of rack and pinion.

Hubert

[forrest39]

Hubert,

Thanks very much for that interesting input. I'll take a serious look at that. I'll try to keep this thread on topic and not dwell on X2 vs X3, but I may PM you with questions after I do some homework if that's ok.

Again, thanks!
-4ist