I want to DIY.. some questions please!

[JAZZCNC]

Hi Dean, Can you recommend some higher quality open bearing for this type of supported rail?

Sorry didn't see this post. Other than Gary at Zapp then no not really because I won't touch them personaly and I only ever come into contact with them when others have all ready bought them. I hate the bloody things because I'm always having to machine them flat and true even then there still left with shite bearings.!!

Said it before many times but If you want real accurecy and longevity then get rid and save for some profiled rails and don't even go the unsupported route because you will regret that path promise you that.!!

[Robin Hewitt]

If you want real accurecy and longevity then get rid and save for some profiled rails and don't even go the unsupported route because you will regret that path promise you that.!!

Ah! Someone with experience of Hiwin rails

I'm drawing up a plasma cutter with a 2 meter axis on the gantry and I want to use one profile rail, probably the 20mm.
My problem is the spec says they come in two flavours...
1: with slop to allow for slight misalignment between 2 rails.
2: with oversize balls to get a tight fit.
Zapp seems to sell only the sloppy variety and I can't afford twist around the long axial because the head sits quite far forwards, about 65mm ahead of the races.
My question is, how much axial twist do I expect?
Should I add a spring roller running on the rail behind to keep it in tension? That wouldn't be hard because I have to screw the rail from behind so there are no visible holes that might carry abrasive crut passed the wipers.