Pressing a Bearing

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Jonathans

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Hi, I am wanting to try something new with my bladesmithing and need a little machining expertise. Rather than using small caged ball bearings on either side of the blade of a folding knife, I want to try boring a .5” hole through the blade and pressing a sealed bearing into it. The pivot will then go through the bearing. For a tight, permanent fit, how many thousandths smaller than the bearing should the hole be, and with the blade being .150 thick can I expect the bearing to be perpendicular to the blade on its own or are there measures I need to take to ensure this? Thanks
 
For a bearing that size, you'll want a hole 0.0005 to 0.0008" smaller than the bearing. Try to err on getting to the smaller hole size. Unless you have pin gages, hitting the hole size could be a problem.

You'll want to experiment with your parts and drill bits (and press) to see if you can get an acceptable fit.
 
The rule-of-thumb passed onto me was that for a press fit, you want about 0.001" interference per inch of bore, which matches the above.
 
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That much press fit for a ball bearing may result in a gritty action, bearings are not designed for a strictly press fit as used for other purposes, which, yes, are usually .001" also the same for shrink fits.
 
If you over shoot your dimension there always Loctite.
 
SLK001 said:
For a bearing that size, you'll want a hole 0.0005 to 0.0008" smaller than the bearing. Try to err on getting to the smaller hole size. Unless you have pin gages, hitting the hole size could be a problem.

You'll want to experiment with your parts and drill bits (and press) to see if you can get an acceptable fit.
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Drill bits are not going to give you an acceptable fit, the hole would need to be reamed or bored; reaming is quite chancey when you get down to such small tolerences.
 
Jonathans said:
Hi, I am wanting to try something new with my bladesmithing and need a little machining expertise. Rather than using small caged ball bearings on either side of the blade of a folding knife, I want to try boring a .5” hole through the blade and pressing a sealed bearing into it. The pivot will then go through the bearing. For a tight, permanent fit, how many thousandths smaller than the bearing should the hole be, and with the blade being .150 thick can I expect the bearing to be perpendicular to the blade on its own or are there measures I need to take to ensure this? Thanks
Click to expand...

Given that there will be very light loads on both the housing and shaft side of this bearing, a loose class fit would probably be fine. This amounts to an H8 or H7 fit, which is essentially a line-to-line fit where the ID of the bore is the same size as the OD of the outer bearing race. Since a folder needs smooth action with no grittiness, I agree with Benmychree that tight fits should be avoided and I would not go with the shadetree fits of 0.0005 - 0.001" under myself. If you must have a tolerance, I would go with - 0.0002-0.0004" max. The inner shaft will likely be much looser so that's not a concern.

I also agree with John that you won't get this fit by drilling and probably not by reaming unless you order a special sized reamer to suit your material. It will be far cheaper to bore the hole.

If you can bore the hole to 0.5000" ID then the fit will likely be adequate to support the light loads and should go in square to the bore given your 0.150" width.
 
Yes, agree with Mikey, a metal to metal fit would be a good thing, what calls a line to line fit.
 
Thanks for all the input guys. I was going to drill and ream on the mill, but if boring is the better way to go I’ll be figuring that out. So far all my boring for anything has been on the lathe. I’m thinking I’ll look for an appropriate sized pin gauge as micing an id is tough.
 
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