4 Rail with loose bearing problem

[roscoesplevins]

We have a piece of equipment having two bearing sets of 4 rails with a strip of individual balls. Worked fine for years. Has been a pain for the last three ! At each end of 2 rails is a roll pin stop. The strip of bearings is overrunnng the stops at either end. There is no obvious visual damage or lost parts. The factor rep has serviced the unit twice with new rails and bearings to no avail. Any ideas as to what we need to look for?

 

[MikeHalloran]

What changed, 3 or 4 years ago?


Mike Halloran
Pembroke Pines, FL, USA

 

[roscoesplevins]

Only accumulated use. Rails and bearings were replaced by manufacturer's rep. less than one year ago. Lasted, well, didn't last... Nothing looks amiss, nothing looks missing. But bearing carrier jumps over end stops.

 

[mfgenggear]

Inspect the details for wear & damage.is there a bad batch of bearings.
or where bearing mfg changed, is there increase in heavy loads

Mfgenggear

 

[roscoesplevins]

I have the assembly apart and in the office. Rails look new. Bearings and carrier like new. Lots of grease. Stops at each end are straight and solid. Load is very light. Motion is manual and generally very slow. Some fast retract/extend, but never continues to the stop.

Considering adding a sleeve over tops to increase diameter.

 

[mfgenggear]

"But bearing carrier jumps over end stops. "

What does this mean?
may a better description would help.

Mfgenggear

 

[mfgenggear]

also you need a physical inspection of the details, as well as a visual. wear can be present yet it may appear not to be damaged.

Mfgenggear

 

[roscoesplevins]

Each bearing assemby (there are left and right) consists of 4 rails and one bearing strip. The rails are contained in a groove in the stationary member and a similar arrangement in the sliding member. The bearing carrier is a plastic strip with 10 holes, 10 balls. The balls are held in place by tabs on the bearing carrier. Assembled, the rails are parallel to each other in the X / Y / Z planes with the bearing carrier in the center. Bearing moves in X as the sliding member moves. At the end of each rail pair is a vertical stop to keep rails and presumably the carrier in contact. A gib in one sliding member provides adjustment.

As stated, rails, stops, carrier, bearings are all 1 year old. No damage, no wear, no mislocation. No mislocation until the unit is put into motion. The intened motion seems to be the carrier cycles with the sliding member. It appears the carrier will move with the slider, BUT doesn't always return. The balls continue to rotate as expected but the carrier fails to follow the slider. As this continues, the carrier overrides the end stop. End stop is solid but does not extend as far as I would have expected. The stationary and slider stops line up at only one place in the traverse. That would be the only time the bearing cannot override the stop. Otherwise the carrier and balls can flex over the stop and hang up.

My feeling is that something in the assembly or adjustment is causing our problem. Too much or too little tension in the gibb. Too much/too little lubrication. Not really a bearing problem but a machine building or maintenance problem.

Description sufficient?

 

[MikeHalloran]

It smells like there's a tab feature on the carrier that's supposed to engage some part of one of the rails, but it doesn't because the carrier is assembled facing the wrong way.

Just a WAG.

Mike Halloran
Pembroke Pines, FL, USA

 

[mfgenggear]

roscoe

is a picture possible or a drawing?
I believe Mike is right., the mechanism has a fault or assembled wrong.
is there an engineering drawing?

mfgenggear

 

[techgirluk]

hey there,

Have you considered bearings that are maintenance-free and lubrication free for your equipment?

 

[roscoesplevins]

Is my problem solved?
Rather than have another $6000.00 service charge (yes, that's thousand) with little effect I disassembled this sucker myself. As previously stated sll bearings and rails were in excellent condition. The stops were straight and solid. BUT the stops were where our "bearing strip" were overriding. I made sleeves to fit over the stops increasing the diameter. All assembled as expected, slides as expected and at present, stop as expected. There is insufficent time to declare this problem fixed, but the unit is back in service, we didn't wait for the service tech, and we didn't spend $6000.00. No one here has said "thanks" or "good work" but how often does that happen?

 

[Jboggs]

An engineering manager once told a co-worker of mine, "Your recognition is that you get the opportunity to do more good work."