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Internal hole measurement - bearing seat - opinions?

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Dave G:
Hi Pekka, I used to do some jig grinding and very close tolerances can be held. These parts were normally hardened die plates and the holes had to be very close. We normally snuck up on the proper size by measuring with dial bore gauges or intramics but for final size we used plug gages. The only problem with plug gages is they are hardened and if they aren't they may gall when trying to insert in the hole. At home if I have a bearing seat to machine I bore with a precision boring head and before starting I will make a few plug gauges in .001 increments leading up to the finished size. Care must be taken when inserting the plug gauge and alot of feel is involved. Roundness of the hole should be alright if you do your boring last. By this I mean, don't bore a hole to size and then mill material off the part close to the hole as the part will move and the hole will no longer be round. One of the things I like to do when sneaking up on a size is if the finish dia is say .0005 over a nominal size I like to get the part .0005 over the desired size .005 to .010 before reaching size. I make my last few cuts the same amount to keep the tool flex consistant. I also try to design my engines with a thru hole if possible so I can size the holes with my Sunnen hone. You would be amazed at how round a hole that has been honed will be. I served my apprentiseship and was employed in a bearing factory for 30 yrs and we had all the neccessary equiptment to measure holes for size and roundness. I once worked with an old timer that ground all the ball races in gyro bearings that were used in missles for the government. The most precision bearings that we made. He related to me that they would get roundness within spec for the most part but every now and then the ball races would be out of spec. They fought this for months until someone had the notion to watch the local traffic pattern outside the plant. What they found was that every time a large semi truck would roll past the plant is when they would get a bad part. Their fix for this was to pour a separate pad of material to set the grinder on that was isolated from all the rest of the factory and the surrounding area. He told me it took 2 weeks for the grinder to settle down after the improvement and it solved all their problems. Sorry for length of this but I find it quite interesting and I hope you do also. Dave

Pete.:

--- Quote ---Make a go gauge, about 1 thou (0.02mm) undersize. Very gently bring the bored hole until the go gauge only just enters the hole, then super fine cuts until the bearing just enters the seat, or as I do above, scrape and emery/wet-dry to size.
--- End quote ---


This is what I just did to fit a bearing into a sprocket carrier. I actually wanted a shrink fit so I made a gauge 2 thou smaller than the bearing then machined the carrier until I could just get this in. Then I heated the carrier and dropped the bearing in. When it cooled off it was held tight and the bearing is as smooth as silk.

bry1975:
Oops wrong post.

dickda1:
I agree with Bogs' assessment of telescopic gauges.  Measuring twice (bore to gauge then gauge to micrometer) has always been a source of frustration for me.  The slightly under plug gauge is the way I use.
-Dick

John Stevenson:
You still have to set a bore gauge with a micrometer.
Plug gauges are OK if you are working to just a few sizes and even then you have to be able to use another measuring method to get close to finished size before you can use the plug gauges.

Years ago our predecessors used  firm joint calipers for most work and made bigger and better things than we do today.

John S.

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