bearings on threaded shaft

I'm working on a design that requires threaded shafts and wants to use ball bearings that would typically be press fit on a precision shaft. The shafts are made from fully threaded studs (.5") and measure about .492. This project is for a low speed application (10-100 RPM's) with no great precision required. I've seen some use jam nuts and threadlocker to secure bearings for this type of DIY work, but the jam nuts would take up needed space in my design. I'm wondering about using thread locker under and over brass shim stock (.002) to get better concentricity. I've made a prototype using this construction and it seems to work well, but reaching out here for caveats from those who might have more knowledge and experience. My aim here is a salable kit, and price point is critical, but I don't want to sell something that will fall apart.
Thanks!

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Originally Posted by al ladd

I'm working on a design that requires threaded shafts and wants to use ball bearings that would typically be press fit on a precision shaft. The shafts are made from fully threaded studs (.5") and measure about .492. This project is for a low speed application (10-100 RPM's) with no great precision required. I've seen some use jam nuts and threadlocker to secure bearings for this type of DIY work, but the jam nuts would take up needed space in my design. I'm wondering about using thread locker under and over brass shim stock (.002) to get better concentricity. I've made a prototype using this construction and it seems to work well, but reaching out here for caveats from those who might have more knowledge and experience. My aim here is a salable kit, and price point is critical, but I don't want to sell something that will fall apart.
Thanks!

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A friend of mine would clean well and use epoxy, aligning as needed before it sets.

If parts are close-fitting there is a great "glue", probably stronger than thread locker. It has worked extremely well but I have no idea how it will work between the threads and the bearing/shims as it is made for close-fitting parts.
https://www.henkel-adhesives.com/us/...ctite_603.html
https://www.amazon.com/gp/product/B0074NALBO/

It's hard to guess at your design but if you don't need the entire shaft length length threaded for assembly reasons an option might be to add metal for the bearing with welding or brazing then machine it to a press-fit tolerance or a close tolerance and use the retaining compound.

Another option might be to simply have a shaft machined and threaded from scratch with precision cylindrical sections for the bearings, depending again on limitations of the assembly process.

Another option might be to screw on a threaded bushing, glue in place with thread locker, and then use a bearing sized for the bushing, pressed or glued.

JKJ

Quote:

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Originally Posted by al ladd

I'm working on a design that requires threaded shafts and wants to use ball bearings that would typically be press fit on a precision shaft. The shafts are made from fully threaded studs (.5") and measure about .492. This project is for a low speed application (10-100 RPM's) with no great precision required. I've seen some use jam nuts and threadlocker to secure bearings for this type of DIY work, but the jam nuts would take up needed space in my design. I'm wondering about using thread locker under and over brass shim stock (.002) to get better concentricity. I've made a prototype using this construction and it seems to work well, but reaching out here for caveats from those who might have more knowledge and experience. My aim here is a salable kit, and price point is critical, but I don't want to sell something that will fall apart.
Thanks!

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Hi Al,
How much side load (if any) is there on the bearings for your application? If you can provide a photo of your specific shaft/bearing assembly - I may have some useful input to help you.
Thanks,
David

(Mechanical Engineer)

Half inch self adjusting bearings with set screws are available from McMaster-Carr. https://www.mcmaster.com/standard-mounted-bearings

Another possibility to consider would be to knurl the area where the bearing goes. This would increase the diameter or the shaft in the area where the bearing would reside and provide a press fit for it. Advantages would be improved concentricity and easy replacement of the bearing if ever needed.

Is it possible to increase the diameter of threaded shaft (fully threaded steel stud in this case) by knurling? That could be cool if possible to do with tools I have (no lathe I'm afraid)....

Al, yes the knurling would work on a threaded shaft. You didn't mention how long your shaft is or where in it's length the bearing would reside to give better advice. Knurling is typically done on a lathe but small parts have been done on a mill. There are different types of knurling tools. The common, inexpensive ones for lathes apply pressure in one direction which means that the shaft needs to be supported at both ends. There is a type of knurling tool that applies pressure in 2 directions, opposite of each other. You could possibly use this type of tool with your shaft in a drill press but it would take a bit of setting up. My best advice to you is find a local, small machine shop to do it as the cost should be very minimal. You could probably get one of the workers to do it on his lunch time for a few bucks. I'd do it for you for free if you lived closer.

Quote:

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Originally Posted by al ladd

Is it possible to increase the diameter of threaded shaft (fully threaded steel stud in this case) by knurling? That could be cool if possible to do with tools I have (no lathe I'm afraid)....

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Hi Al,

It is possible to increase the diameter of the threaded shaft by knurling. For a 1/2 - 13 threaded shaft/rod - you could possibly increase the OD by 0.003" to 0.005". This is best done on a lathe and the results will depend on technique. I knurled a sample piece of 1/2 - 13 steel threaded rod in a location that would be typical for your application. This particular piece was purchased at the hardware store, so it is not precision and the OD is around 0.477". This is typical for these types or rods. By contrast, quality grade 5 hex head bolts typically measure around 0.490" OD. Knurling threads will not give as much diameter increase as knurling solid round material. Knurled solid round brass can give as much as 0.010" OD increase. For your indicated thread measurement of 0.492" this technique could increase your OD up to a range of 0.495" to 0.497".

There are several potential problems with using this technique. Knurling threads can cause the knurled OD to vary (for a single knurled location). For example, the sample that I knurled (shown in the photos) has a resulting OD that varies by about 0.003" when measurements are taken at different locations on the OD. This is not much, but will tend to decrease concentricity of the shaft at the knurled location where the bearing will be installed. Knurling also basically destroys the threads so that after knurling the 1/2-13 hex nuts will no longer thread onto the shaft. For your application - you would need to install any required 1/2-13 hex nuts onto the shafts before both bearing support locations are knurled.

If I were building this item for my own use and I was resigned to using the threaded rod, I would probably forget about the knurling. I think I would use your technique of wrapping thin brass shim stock followed by thread locker. If it did require servicing in the future, it may be possible to apply some sort of industrial solvent (MEK or equivalent) to soften and/or dissolve the thread locker in order to remove the outermost bearing to allow removal of any threaded parts previously installed onto the threaded shaft.

I think you are on the right track. Let me know when you have a salable kit and I may be one of your first customers.

David

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Thanks to all who replied, and especially David for actually experimenting with options here.

My last attempt to glue shim stock was with JB Weld and elastic band clamped shims cut with some care. This both filled the threads beneath the shim, and resulted in a nicely glued brass bearing surface measuring around .497-.499, with enough irregularity that the bearing feels like a very light press fit, ( a slip fit with a little friction) and I think will be the functional equivalent, for my low speed application, of the fit on precision ground rod that will be used elsewhere on the project.

A straight line knurl might be a good choice, since it would be more like a splined end.

wrap fine wire into the threads and paint with thin epoxy. Sand / file as needed.

What you need is a product called bearing retainer.