My question is about life expectancy on following linear slide setup:
Two parallel 5/16 rods and a slide that uses a pair of small plain ball bearings(5mmx12mmx5mm) on the same axel with the spacer between them instead of a each single grooved roller. The ball bearings will roll on the both side of the rod since the spacer will be shorter than rod diameter.
It's a preloaded design with preload no more than 10-15lb. Speed is 1 foot/sec. It's manually driven device and "high mileage" is not expected.
I understand that radial BB are not made this kind of thrust load but since it's a relatively light load I think that it should work fine.
Try it and see. An alternate idea would be to use thrust bearings to take the side load. There is a web site with a guy making and selling what he calls a Home Brew Linear Bearing. Check it out:
Y ears ago, and maybe still, Sears radial arm saws used small diameter rods along each side of the overarm - and used bearings in which the outer race was concave on the od - then the bearing was adjusted to proper force against the rod and rolled along front to back along the rod just fine. It also supported the weight of the motor, blade, guard and the forces of cutting. Worked well, so maybe one of those types of ball bearings would work in your instance. Ken.
As the width of the spacer approaches the width of the 5/16 rod, the paraxial thrust at the POC will approach infinity by trigonometry, balancing the forces.
Bearing life is proportional to P*V, pressure times velocity. Find a derating factor for off design loads, then keep the spacer thin to prevent multiplying the forces too much.
At a spacer of zero, the load is all radial.
Yeah, but it's not exactly the same, is it, because there's this force, pulling them apart. Now, you can just use a bearing mount type adhesive to glue the outer races together, giving you a 5x12x10 bearing with a groove, because the corners have chamfers. That would roll nicely on a square rod's corner, or on the corner of an angle section.
You put a little pin through them when you are gluing them up to keep them aligned. A firm press fit pin. Then you never pull, always push, to get them off the pin, and then onto your axle. If you pull, they'll separate.
Um, in which direction? The weight of the traveller will load the rollers tending to separate them. If the preload is inward, and more, and then the weight increases they will go from being loaded in to being loaded out, with a wiggle.
For cheap readily available bearings get the 8x15x6mm or whatever it is, which are sold as skate wheel bearings in packs of eight, I think.
8mm is very close to 5/16.
Yours,
Doug Goncz, Replikon Research, Seven Corners, VA Unpublished work Copyright 2003 Doug Goncz Fair use and Usenet distribution without restriction or fee Civil and criminal penalties for circumvention of any embedded encryption
While this is true for plaster molds, he is just dipping them to give them a thin layer for loose sand casting (Lost Foam). Also, his mix has sand in it. (drywall texture).
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