- Location
- Bountiful, land of rocks
I had a small machining project come through my shop door the other night from a fellow forum member who is building a rock buggy. He is adding an ORD underdrive to his NP205 and needed the NP205's smaller 80mm input bearing bore machined out to accommodate a 90mm input bearing.
Taking some initial measurements of the bearing and determining a target diameter to bore the case to. The bearing measured 3.5425". For interference fits I generally use a .001" per inch of bore formula but where this didn't need to be a complete press fit and just needed to be snug I figured I would shoot for approx. .0005"-.0008" interference fit. This would give me a target bore of approx. 3.5417". I set my bore gauge to 3.5415" which would be .001" under the bearing diameter but I would try to come in on the high side of that by a few tenths.
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Setting up the case on the mill table. I used a center finder to get it close then swapped in my Blake coaxial tester to dial it in. I was able to get it to about a thou out.
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Swapped over to my 3" Criterion boring head with my new Mesa insert attachment. It has been a while since I bored a precise hole so I took some preliminary measurements to get my feel back on my boring head.
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Landed at .0002" over my target.
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The bearing required a slight tap to fully seat so a perfect fit for the application.
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Final notes as I tracked my numbers. Increasing by .050" at a time to get my feel back for my Criterion boring head. I was landing at approx. .0502" to .051" per pass. I am certain this has to do more with where I lined the marks up on the boring head vs. the boring bars actual accuracy.
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Thanks for looking.
Mike
Good stuff! @ebryson now works at a machine shop as an entry level machinist. He seems to be digging it and is anxious to have skills similar to this. Hopefully he'll check out this thread