Z-Axis THK - Am I on the right track with these?

[jzurek]

This morning I purchased (2) THK SRS25MUU bearings (one on each rail)

Thk SRS25 Linear Bearings on 425 mm Rails - Nice! - eBay (item 200583609513 end time Mar-10-11 04:08:19 PST)

These seem way overkill for my Z-axis but the price seemed right and THK allows force in all directions so I knew they would work. I'm planning on mounting the rails to a 1/2" thick aluminum plate that will hold my 1-3/4 HP router. The bearing blocks will also be mounted to 1/2" thick aluminium on the gantry. Does anyone see a problem with this design? The bearings are close to 3.75" long so I really don't see a need for 4 of them. I expect that I will use about 7"-10" of vertical travel. Thoughts?

Jeremy

[victoria_jay]

I think it is ok if you are going to use your machine to mill wood and aluminum for this kind of set up. It is not rigid enough to mill steal. Good luck.

[Drools]

Just a side note, not all THK linear rails are designed for loads in all directions.
If I remember correctly only the SHS (caged balls) and HSR (non caged balls) rails/blocks are rated for loads in all directions. However for hobby use I have been told you will probably never even come close to the rated values of THK products so using blocks rated for horizontal use should be ok if used in a vertical application.
Edit:
Correction the SRS can be used in any direction
https://tech.thk.com/en/products/pdf/en_a1_136.pdf#1

[jzurek]

Thanks for the reassurance. I will only be milling wood, composites, and aluminum with this machine at this point. If in the future I plan on redesigning it for steel with coolant I would use heavier mounting plates as well as four bearing blocks. I am having the supplier keep his eyes open for 2 more additional SRS25M bearings just to put on the shelf.