View Full Version : balscrews from linear motion bearing and rails, question about sizing

Boyan Silyavski
18-08-2013, 11:45 AM
i am upgrading my machine and am building a steel frame machine for a friend.

I have all a bit messed up in my head from so many websites and measures:frog:

My question basically is:

If i am to buy 1605 or 20xx bascrews from Chai

How to choose the ball screws and the bearings and the ball screw supports and the ball screw nut so i can fix all on one plane and at the same time the moving plate that fixes to the bearing blocks and the ball screw nut to be on other plane?

Assuming money is not a problem and the rails could be SBR >20 or Hiwin square >15 and the nuts supports can be purchased from other place

Some simple setup that will leave me with drilling holes and shimming or epoxying, instead of channel machining. I would like a low profile result with the ball screw
between the 2 rails for the z and the gantry and similar with one rail and ball screw for the other axis. Like modular i mean.

Some other question:

Also, from where to see Chai standard end machining? Sb has Sketchup files for sharing of the ball screw assembly ? 1605 or 20xx?

18-08-2013, 05:27 PM
Silyavski I'm struggling to understand exactly what your asking but I will try to help.

If your unsure of the correct screw to buy then to answer correctly would need more information about machine size and use.
Generally for small to medium sized machines (1200x1200) then RM1610 is perfectly fine. Over this then look towards RM2010.
The 10mm pitch works good for most types of cutting inc aluminium but if your wanting better resolution rather than speed then consider 5mm pitch. Or if using timing belts to attach motors then gear 10mm pitch 2:1 and increase torque and resolution at the cost of speed.

Regards choosing the ballscrew for being on same plane I'm not sure what your meaning because the ball-screw ends have to be on the same plane has does the ballnut mount otherwise they won't align and stick.? . . . . I Understand English is not your native language but please try to explain better.?

Boyan Silyavski
18-08-2013, 06:45 PM
I meant if i mount them on the same plane like you say, i would like a plane square plate to screw to the ball screw nut and the 4 carriages/z/ or 2 carriages /XY/ at the same time without further modifications.

Like this below. Look how they channeled deeper for the ball screw nut and shallower for the square rail in order all to get at the same level at the moving plate that holds them together/ the nut and the bearing blocks.

I imagine there should be combination of sizes when there are no channels, the nut moves freely from below and all are on the same plane for the plate? Or no?


18-08-2013, 08:11 PM
Ok yes I see what you mean now.

Right this is where it gets difficult if you use Profiled rails like Hi-win and especially the smaller rails like 15mm . They tend to be Low profile than supported round rail.
To get around this then that channel is required or you have to put raiser blocks on the bearings to lift opposite plate to allow room for the ballscrew.

Supported linear round rail on the other hand stands higher off the plates and you can get away with out the channel if you use the correct mixture of rails.

If you use SBR20 rail then you will clear the ballnut by about 5mm if you use the BK/BF blocks. The bearing and rail stand about 50mm the distance from surface to top of ballnut flat side is 45mm. So you will 5mm clearance.
The sbr16mm rail & bearing is 45mm high so the ballnut flat is flush with opposite plate, it can be done using 16mm rail but it's close with little room for error.

See pic of rough layout of 16mm setup. With 20mm it's just the same except the bearing surface is 5mm higher. The 16mm bearing is 45 high.

The same can work with profiled linear rails but you have to go to 25mm rail or larger for it to work and that isn't practical.

If you go to Chai's ebay site and click on the rails etc he sells all the specs are there for you, including standard end machining.