orientation of bearing block - vxb linear rail

[multiplex]

I was hoping someone could give me some feedback on use of a linear rail.

here is the part in question. 20mm supported linear rail





I'm currently using these on the Y axis of my gantry router. I recently rebuild the gantry out of aluminum, and estimate the weight to be in the 200 lbs range.

I have the rails inverted, and the bearing hanging from the rail. The weight of the gantry is therefore also hanging.

I have the unit assembled, and it works fine. I'm just wondering about long term use, and if there were any other concerns.

http://www.vxb.com/page/bearings/PRO...ystems/Kit7429

[LaserImage]

This isn't based on anything scientific, but I would think that they would perform best if they are upright, not inverted. My thought is that the weight of the gantry could pull the rail away from the mounting surface if inverted, whereas if they were mounted upright gravity would just push the rail more firmly to the mounting surface. With that much weight, it wouldn't take much to keep an upright mounted rail firmly planted on the mount, but it would take a lot of fasteners to keep it inverted.

Just my .02

Gary

edit: another thought... The bearing blocks may be designed to work upright as well. You have a large area on the bottom that is cutout and has no support. If that were on top then you might lose some efficiency as well as strength.

[multiplex]

yeah i'll have to take another look at how the bearings are distributed inside the block - i they favor a certain orientation.

i've shot VXB an email, so hopefully i'll hear something back.

I've been using this configuration for over a year now, but have probably doubled my gantry weight so it may become a concern.

worst case i need to make a new table to match the new gantry