[adam_m]

I was thinking about going with a linear ball slide Z-axis on my current build ( http://www.cnczone.com/forums/diy_cn...x_5_build.html ) and was curious about some experiences from the users on the forum with regard to usage and durability.

My initial thought is a 20mm unit with 2 pillow blocks per rail and an approximate length of about 20". Something similar to theses (20mm Linear Shaft 55" Long 2 Slide Units 2 Shaft Supports Linear Motion Kit: VXB.com Ball Bearings)

What can I expect with regard to side-play and backlash?

Are there ways to adjust backlash/side-play with this type of bushing?

Are bronze bushings a better choice?

Anything I'm overlooking that might tell me to look elsewhere?

Thanks as always for your input.

Adam,

[awerby]

Those work okay for short spans, if you aren't cutting anything hard. I don't think there's any way to adjust them. But supported rails are a step up from that, and square-section rails with ball trucks are better than them. Backlash is something that involves the interface between a thread and a nut, or between gears; it's not a factor in linear rails. Any looseness in them is called "play" or "slop", not backlash, and it varies by the manufacturer (and perhaps by the day of the week the things were made).

Andrew Werby
www.computersculpture.com

[tahustvedt]

Supported round rail bearings usually have pre-load screws, which can be adjusted to eliminate play.

[adam_m]

Thanks for the reply's.

tahustvedt - Do you have a link to what your referring to, I've never seen one, only those that appear to have no adjustment on them.

Adam,

[soren_dc]

Hi.
Im currently building a router using tbr20 rails an bearing blocks for the y and x axis. they have no play when adjusted propperly i'm sure they will preform well when i have everyhing running.

For the z axis I got a set of rexroth 15mm profile rails and blocks used of ebay. They are rock solid and slide silk smooth. They cost a lot more but the load ratings are about 10 times that of the ball bushings