balscrews from linear motion bearing and rails, question about sizing

[JAZZCNC]

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.