Teams who use .25" ID Bearings

If you use bearings with .25" Inner Diameter bearings, what do you use to hold them in place?

I can’t find reasonable or reliable .25" Shaft Stock or Collar Clamps.
The only reasonable option I see is 1/4-20 Bolts. I would love to know what you all use!

McMaster-Carr has 1/4" shaft collars for between $1 and $60 with lots of options. I’ve never had an issue as long as the screws are tightened. If you get a setscrew option, use a mill or Dremel to put a flat on the shaft for the setscrew to grab. Ditto for shafts though you’ll spend a bit more.

I’m trying to figure out what application you’re working on, and what issues you’re actually having–it might be easier to help if we knew more about what you’re trying to do.

I’m making an elevator for the offseason, and I just can’t find a practical solution to holding these bearings in place to some holders I made.

We used TONS of these all around our robot. If you select the right sizes and thread they are not ridiculously expensive but definitely not the most affordable option. The -.002 od lets you slide them into places a 1/4-20 just won’t fit. Here’s some use cases around our bot holding .25 bearings.


So here are the two place I need a way to hold these in place

On the yellow block with 4 bearings I was thinking of a stock shaft there with collars on each side
And at the top I need something about 1.75 - 2 inches long so I can fit a spacer between the two yellow plates, then the outer plate will have a spacer between it and the bearing

I can think of multiple methods to 1) hold a shaft in place and 2) keep a bearing on the shaft. Different tricks work better with different sizes and applications. In no particular order:
–4414’s method of through-plate bolts with spacers and bearings
–screwing a shoulder bolt into a block that’s tapped for it (or otherwise threaded)
–pin on the holder end, shaft collar on the other end (this will work, and it will drive you crazy if you don’t have the right tools to drill the pin hole in a steel shaft).
–Different sorts of shaft collars.
–Hold one end with X and use a screw into the other end to hold a washer–don’t do that for this one as you’re talking about a #5 screw at largest and those are going to be painful to drill and tap for.
–just press-fit the bearing onto the shaft. Use a strong vice or hydraulic press. Press the shaft into the holder.

I will cop to using several of those methods at my day job on various sizes of shaft…

For the 4-bearing block, you’re on the right track. 1/4" shaft, 4 bearings, 2 shaft collars–I’d go with setscrew-type and Dremel a flat for the screw. BUT it’s going to be really tough to put together and take apart–that’s a press-fit most likely, unless you’re using a shoulder bolt. Split the block in two between the middle screw holes so you don’t have to worry about loading the shaft inside the block, then assemble and use the shaft collars to help hold everything together.

For the upper one, see 4414’s method but find the right length of shoulder for that application.

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After searching I think I am going to use the shoulder screws, they look like they’ll work really well

Edit: Looks Like they fit perfect! I used spacers in the 4 bearing block of various sizes. I also used a 2 inch shoulder screw in the bearing block, and 2 2-1/2 shoulder screws for the roller stabilizers at the top. Just in case anyone wanted to also use them :slight_smile:

Shoulder bolts are probably the easiest “right” way to do this for most cases we’ll see in FRC. For a “not as right, but works” method, my team and a number of other teams I know will sometimes use regular partially-threaded bolts for this purpose instead of shoulder bolts. They aren’t suitable for long gaps and cantilevers like you have, but when the bearings are close to the supports (<1") you can often get away with it. Regular bolts are substantially cheaper and easier to find than shoulder bolts, so they’re easier if you can make it work.

Also, make sure to pay attention to the bolt head/nut and what this elevator rail interfaces with. Make sure that it’s not going to crash into a gusset or other frame member that would keep the elevator from completing its travel.

On 95 we used a combination of 1/4-20 bolts and 1/4in ball detent pins.

You can see the OnShape model here.

A quick search for 319’s OnShape model will show another great way of using pins and bolts to secure these types of bearings.

I would strongly encourage you to evaluate a different way of making these features. The large cantilever on the upper bearings, likely driven by the protrusion of the lower bearings, is not a great design practice. If you can reduce that cantilevered length of that element it will be more rigid and stronger. Cantilevered elements lose strength and stiffness with length^3, so if you can reduce the cantilever to half it will be 8x as strong and stiff.

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I am inclined to agree with you. Additionally, as designed, the elevator will be wider than needed because of the design of the inner bearing block. This issue will only multiply depending on how many stages are in the elevator.

Matt, you could consider making the inner bearing block smaller, cutting a window the tube, and placing the block inside the tube. While more complicated, this would be much more compact.

It looks like the bearing retainer block is 3D printed, so you could be able to make the spacers part of the block. This could save on manufacturing time and assembly headaches.

Edit: On further review, the 3D printed block could also house a sort of shoulder shape to hold your cantilevered side screws. This could help reduce the load on your screw and also let you use shorter screws. Maybe refer to this design we made: Delrin Blocks as elevator bearing replacement which have a similar design paradigm (consider the eventual thing we settled on, not the sliding delrin idea).

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Thanks for your replies everyone :slight_smile: I should clarify this is just a basic CAD model to learn the functionality of how the elevator will work, it won’t specifically be made. It’s for some of the students to see how it would work and how to design a better one

3946 used some 1/4" shaft, bearings, hubs, and clamps for our scoosh (gear holder/pusher) in STEAMWORKS. Most of what we used was Actobotics or similar:

I also used a 1/4" shaft as a belt tensioner for a recent project robot. I used steel shaft, bronze flanged bushings and 1/4" shaft collars all sourced from a local hardware store. If you go this route, you will want to polish the shaft where it rotates in the bushing, or at least sand it with some 100+ grit sandpaper…

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