Open type linear bearings, mounted sideways

[garagefela]

Hi everyone,
I have a question regarding round linear bearings of the open type.
I want to mount the rail and bearings horizontally/sideways and was wondering if there are any big problems with doing so.

The picture below (someone elses router) is what I would call being mounted vertically and I want to mount it 90 degrees or sideways from what you see.

Obviously the bearing will want to open out a bit and dust also has an easier time of getting in.

Definately will not use closed bearings as I need the support along the rail length. Anything else that needs considering?

Thanks M

[Jason Ross]

If the load is parallel to the mounting top you should have nearly full load capacity on the bearings. Thomson Industries (Danahermotion) has a load normalizing diagram that you can approximate what your total capacity is. Load capacity really degrades when you try to lift the block off of the shaft. In this case it is about 50% of rating. The pillow block will not be as stiff but seeing that you are only intermittently supporting the shaft I believe shaft deflection will be the dominate source of deflection.
Typically in this style bearing the height of the mounting surface to the center line is held very tight there is also a precision reference edge that on one side that should appear machined. I would keep that side up for ease of installation.

[Geof]

I think the picture below is what you have in mind. I built a machine using this orientation years ago, not CNC it was manually driven with rack and pinion; it worked fine. My reasoning with this orientation was that the split bearings have the best load capacity when the load is vertical down for the conventional upright orientation. The next best capacity is sideways with the lowest being when they are being pulled upwards.

On most machines I think the horizontal load from cutting is probably the largest source of load on the bearings and my idea was that the horizontally opposed arrangment meant that one side or the other was always taking this load in its most efficent direction.

One thing you do have to ensure is that the shafts are parellel because this arrangment has less flexibility to accommodate out of shafts out of alignment in the horizontal plane.

[garagefela]

Thanks for the replies guys,
Jason, Danihermotion calcs show that a bearing of this type is derated to 85% when used sideways and like you said 50% when upside down. Thanks for the tip some good info. Well and truly ok for me.

Geof good to see that you had no probs in this configuration. I had planned to machine the sides of my frame where the rail supports are to A) eliminate the supports being cocked over and B) get both rails parallel.

And finally Benny if you are reading this, I can just see you now, probably putting on your size 8 steel capped boots to kick my clacker into gear.
I am only going slow as I know it irritates you. Honest it's not me!!!!

Cheers all M