Boring a Bearing Race

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pete
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Re: Boring a Bearing Race

Post by pete »

To be honest there's still not nearly enough clearly stated information about the part dimensions and it's end use requirements to make any proper suggestions so far. You started out by mentioning boring a bearing race, from that I have to assume the part doesn't have a whole lot of depth and apparently not much wall thickness either. Now your mentioning unhardened 1026 mild steel tube. So was your first post about using that bearing race a method of saving some time and material expense getting a thin walled part, or does it need really need some of the same built in quality's a high grade hardened steel bearing race comes with? What the part is for and what it's meant to do is extremely important for any logical suggestions about what to use and how to end up with a fully finished part to fit those requirements.

If I'm guessing right? This part your trying to make is now starting to sound like it might be an unhardened reducer sleeve to adapt a bearing bore that once used a custom oversized bearing down to fit a standard off the shelf bearing? If in fact that's what it is, then yeah that heavy wall pipe could work. So could boring from solid round stock. For the rough stock held in the chuck and to avoid any possible part deflection from the chuck jaws, I think I'd rather bore from solid stock though.In either case your going to have to maintain the parts concentricity and parallelism to pretty close limits. The whole thing needs to be fully machined and parted off in a single chucking. That pipe or round stock would be done the same for either, cut your rough stock long enough to allow for a good grip in the chuck, plus your finished part length, plus at least .125"-.250" to allow cutting tool clearance so your not crashing into the chuck. You want to keep the overall part length as short as possible while still being long enough to end up with a fully finished part. If I'm right about what your trying to accomplish, then if it were me I'd probably rough the ID and OD within about .010"-.020", leave it over night to cool to room temperature and then finish turn it to your target dimensions. I'd also be sure to make a partial cut off of the part and then chamfer both ends of the OD and the outer ID you can reach, fully cut off and then lightly rechuck the part and chamfer the ID of the side you just cut off. In theory pipe or round stock while being machined is having the same amount removed around it's full circumference so it's "supposed" to stress relieve equally in all directions. With the way the material is rolled and formed there's no way to be 100% sure the stresses are in fact equal throughout the part though. For piece of mind I think I'd still double check the parts ID and OD the next day with a test indicator before finish turning it just in case. If the part did move, the light finish cuts should be more than enough to clean that up. My best guess is it probably would be ok, random guessing doesn't count when machining fairly important part dimensions. But what do you have available for making accurate enough ID and OD measurements in these sizes? Bearing fits are a bit more critical than what caliper measurements can deliver. The reason I'm asking is not many with home shops have adequate and accurate enough ID measurement equipment. Again all of this are just guesses about what your trying to do, and they could just as easily be worthless.
mcman56
Posts: 264
Joined: Thu Apr 17, 2003 2:30 pm
Location: Roseville, CA

Re: Boring a Bearing Race

Post by mcman56 »

pete wrote: Thu Nov 25, 2021 5:10 pm To be honest there's still not nearly enough clearly stated information about the part dimensions and it's end use requirements to make any proper suggestions so far. You started out by mentioning boring a bearing race, from that I have to assume the part doesn't have a whole lot of depth and apparently not much wall thickness either. Now your mentioning unhardened 1026 mild steel tube. So was your first post about using that bearing race a method of saving some time and material expense getting a thin walled part, or does it need really need some of the same built in quality's a high grade hardened steel bearing race comes with? What the part is for and what it's meant to do is extremely important for any logical suggestions about what to use and how to end up with a fully finished part to fit those requirements.

If I'm guessing right? This part your trying to make is now starting to sound like it might be an unhardened reducer sleeve to adapt a bearing bore that once used a custom oversized bearing down to fit a standard off the shelf bearing? If in fact that's what it is, then yeah that heavy wall pipe could work. So could boring from solid round stock. For the rough stock held in the chuck and to avoid any possible part deflection from the chuck jaws, I think I'd rather bore from solid stock though.In either case your going to have to maintain the parts concentricity and parallelism to pretty close limits. The whole thing needs to be fully machined and parted off in a single chucking. That pipe or round stock would be done the same for either, cut your rough stock long enough to allow for a good grip in the chuck, plus your finished part length, plus at least .125"-.250" to allow cutting tool clearance so your not crashing into the chuck. You want to keep the overall part length as short as possible while still being long enough to end up with a fully finished part. If I'm right about what your trying to accomplish, then if it were me I'd probably rough the ID and OD within about .010"-.020", leave it over night to cool to room temperature and then finish turn it to your target dimensions. I'd also be sure to make a partial cut off of the part and then chamfer both ends of the OD and the outer ID you can reach, fully cut off and then lightly rechuck the part and chamfer the ID of the side you just cut off. In theory pipe or round stock while being machined is having the same amount removed around it's full circumference so it's "supposed" to stress relieve equally in all directions. With the way the material is rolled and formed there's no way to be 100% sure the stresses are in fact equal throughout the part though. For piece of mind I think I'd still double check the parts ID and OD the next day with a test indicator before finish turning it just in case. If the part did move, the light finish cuts should be more than enough to clean that up. My best guess is it probably would be ok, random guessing doesn't count when machining fairly important part dimensions. But what do you have available for making accurate enough ID and OD measurements in these sizes? Bearing fits are a bit more critical than what caliper measurements can deliver. The reason I'm asking is not many with home shops have adequate and accurate enough ID measurement equipment. Again all of this are just guesses about what your trying to do, and they could just as easily be worthless.
Correct. I ended up ordering some 8620 solid rod. I have mics that read to 0.0001 and telescope gages plus a dial bore gage that reads to 0.0001. Still, my equipment and skills will eat some tolerance. The ring will only be 4 mm thick. If I target a 0.0005 press fit, will the ring grow a bit when pressed on?

These are the main bearings in a horizontally split single cylinder motorcycle crankshaft. They use dowels to locate and I guess prevent spinning. I bolted the aluminium cases together and tried to get a good bore measurement but was not finding it repeatable. I used the dial bore gage and found that the bore is not very round. It varies from +0.0005 to -0.0015 on the bearing diameter. That seems kind of loose to me. I see that similar engines have issues with bearings rotating in the cases so people uses loctite.
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Rich_Carlstedt
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Re: Boring a Bearing Race

Post by Rich_Carlstedt »

mcman56 wrote: Wed Dec 01, 2021 12:01 pm .................... The ring will only be 4 mm thick. If I target a 0.0005 press fit, will the ring grow a bit when pressed on?..............
Normally the press fit ensures the OD of the bearing from spinning, but your variation shows ( normal ) Aluminum Casting stress relief occurring.
But to your question.....
There is some shrinkage in the bearing OD when pressed into a smaller bore and some bearing specs use that as a preload BUT
All bets are off when you go into a Aluminum Casting/Body for two reasons :

First, The structure (Aluminum) is not as strong as a steel or Cast iron structure and yields at much lower forces.... so you loose the planned interference

Second, The thermo expansion rate of Aluminum is almost twice the rate of steel ( .000011 versus .0000063) so that means the bore of the Aluminum opens up with heat and the "interference fit" is reduced of eliminated ( Loctite solution ?)
For example , say you have a 3 inch OD Bearing in a 3 inch Aluminum bore and you heat it up to 275 degrees (F) . That is 200 degrees above the install temperature. The steel ring will grow ( 3x.0000065"=).00126" and the Aluminum Hole will grow (.000011 x 200= ) .0022"
So if you had a .001" press fit---it's gone when the temp is +200 (F) on the Aluminum body.

Rich
mcman56
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Re: Boring a Bearing Race

Post by mcman56 »

That is exactly what I am finding so odd. However, there are long steel bolts clamping the top and bottom cases together next to the bearing bores so the expansion picture may be a bit complex.
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Bill Shields
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Re: Boring a Bearing Race

Post by Bill Shields »

If it were me...

I would get the sleeve close to size on Id and finish size on od.

put it in the case and clamp together..then finish the inside diameter to desired size to fit bearing. Be sure the new ring does not keep cases from clamping together.

Allowance for the split line gasket or sealant?

You can then locate a short pin to go in the case and sleeve to prevent rotation of the sleeve in the case

Loctite bearing into sleeve.
Too many things going on to bother listing them.
mcman56
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Re: Boring a Bearing Race

Post by mcman56 »

I ended up machining rings from steel. I shot for a couple of tenths under for the ID and over for the OD. I used red loctite and felt a slight resistance when pressing rings on bearings with with a vise. Once assembled everything spins easily and nothing is loose. I have not started the engine yet. Itt was very challenging to hit those kind of tolerances but believe I did.
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Bill Shields
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Re: Boring a Bearing Race

Post by Bill Shields »

There you go... :D
Too many things going on to bother listing them.
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