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Thread: Cat wheel

  1. #1
    Associate Engineer
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    Jul 2022
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    Cat wheel

    I built a rather large wheel for my cat to get exercise indoors. Think hamster wheel, but 48" in diameter.
    There is a 1-1/4" thick metal rod in the center of the wheel located on the back. The length of the rod is 4" and is welded to a 10" circular metal plate. The plate has 8 1/4" holes equally spaced around the edge of the plate. There are bolts secured in each of the holes which holds the back of the wheel in place. The back of the wheel is made up of 1/2" mdf wood which I cut into a 48" circle using a router. This large circle of mdf wood has a 1/4" groove running 1/4" away from the outer edge around the whole circle. Inside that groove I have seated + glued a sheet of 1/4" thick wood, 10" wide. That 10" sheet of wood runs the length of the groove around the outermost part of the wheel serving as a "track" for the cat to run on. I cut a 2" ring of mdf wood with a router and another 1/4" groove in the ring to seat + glue it onto the track. The ring helps secure the track in place and is the point where the cat enters in to get on the track.
    The whole finished cat wheel weighs about 60 pounds.
    I purchased a 1/4" flange bearing mount and secured it to a 4"x4" standing post about 4' from the ground using 4 lag bolts. I then mounted the finished cat wheel to the flange bearing mount by sliding the 1/4" rod on the back of the wheel into the 1/4" flange. Once mounted, I tightened the 2 available set screws on the flange to the rod. At that point the cat wheel would turn freely. I thought my project was a success. However, after short use of my 15 pound cat, the wheel has slightly drooped down. I believe the weight of the wheel is too much for the flange bearing mount to sustain. Hence the reason for my post here in this forum. I am hoping someone with engineering skills smarter than mine might be able to offer advice. I either need to modify the existing flange bearing mount to allow the wheel to spin without sagging. Or I need a different solution to mount the wheel to.

  2. #2
    Principle Engineer Cragyon's Avatar
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    A picture is worth a thousand words but I'm guessing that a 1/4" flange bearing mount is probably rated way more than 60 + 15 lbs.

    Hard to tell what the challenge is.

  3. #3
    Technical Fellow jboggs's Avatar
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    I have a hunch. What is the spec on that bearing? Brand name and model number.

  4. #4
    Associate Engineer
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    Thank you Cragyon and jboggs.

    I purchased the flange bearing mount from VXB. Model number Kit7359. In the description it says it has a "UCF207-20" bearing.

  5. #5
    Technical Fellow Kelly_Bramble's Avatar
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    So, a UCF207-20 has a basic static load rating of 15.3kN or 33731 lbs. Basic dynamic load rating is 25.5kN or 56218 lbs.

    The bearing seems adequate for a 15 lb cat at a factor of safety of 22,487...
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  6. #6
    Technical Fellow jboggs's Avatar
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    That bearing is a self-aligning type. All standard pillow block bearings of that size are. Self-aligning means it is designed to allow the shaft to find its own centerline, to align itself with the bearing on the other end of the shaft. This allows the bearings to be mounted on imprecise surfaces and still work together. It is not designed for offset or cantilever loads. Self-aligning bearings must be used in pairs. Look closely at the cross section diagram of the bearing and you will see a spherical surface that allows the bearing cartridge to rotate freely. Without another bearing on the shaft to define that centerline it will do exactly what you are seeing.

    The "other bearing" does not necessarily have to be on the opposite side of the load. It just has to be somewhere on the shaft. The farther apart the two bearings are the stronger the arrangement is. If I understand your design correctly, you have a single bearing supporting a cantilever load that is offset from the center of the bearing by several inches.

    The attached file shows two typical arrangements.
    self aligning bearings.pdf

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