Linear rail recommendations

I am designing a lathe-like grooving machine for a customer. It grooved 1-1/2” & 2” plastic pipe on each end. The goal is tovautomatically adjust the cross-slides and tail stock for 4 different lengths and 2 diameters. A pick & place mechanism will remove the finished pipe and put another pipe in the lathe right off the extrusion line.

I’ve been thinking the typical 2 parallel rails with 4 bearing blocks for the tailstock, cross slides and pick&place slides. However I’ve been wondering about simply using one or two bearings on a much larger rail to get the required loading moments.

The advantages I see are built in accuracy because of no need for rail to rail and bearing alignment. Lots less fasteners, holes and complexity of mating parts. Actual cost of rails and bearings looks like a wash. Ball screws are still the same size and the larger rails and bearings make room for a ballscrew assembly along one side without a bunch of spacers and such. The customers maintenence people struggle with precision assembly so replacing bearings and rails after millions of cycles should be easy.

Thoughts, suggestions, recommendations?

We had 4 (that I know of) single track rails. They do not last long- months not years. Adding in a Thompson rail for the second rail has been repair that is still lasting. The Thompson’s are not really rigid but limit the axial movement/stress. We are running one bearing on the Thompson in one case- just as good as two imo. Just a torque limiter.

You can have a compliant mechanism between the master rail's bearings and the secondary rail's bearings. This allows your parallelism to be off a bit, without subjecting your master rail to torque loads.

There is wider rails available for this kind of application, and I have found they're quite good for light loads atleast.

Then there is roller rails available too.

Depending on dynamic sideloads, I think it might work if the pushing element is as close to the rail axis as possible.
One idea might be to have one wide rail, and then the ballscrew pushing above it instead of on the side. That way you balance some of the lifting loads from the shaper action with the downward loads from the pushing action. Spacing of the bearing blocks should be far apart to allow them to have more push-pull load than rotational load ofcourse.

Just read the data sheet for the rails, they give the torque limits.

Also there are several different types of rails. There are rails where the contact angles point inwards towards each other like a face to face angular contact, and then there are the ones that point outwards as much as possible and form a stiffer bearing.

The stiffer block can take much more moment loads (torque is similar) but in a standard 2 rail 4 block setup the stiffer bearing block can't handle as much mounting error.