How To Fit A Bearing On A Shaft Or A Bore?

Good advice from above but everyone's machines are different to some degree, even machines of the same make/model will have their own personalities. This is why I try to encourage people to get to know YOUR machine. Only you will know how your machine reacts to a spring cut after just taking off .020" vs. a spring cut of removing .050" pass.

Mike.
 
prasad said:
Thank you guys,

Many points learnt by reading your replies. I list them below.
1. Determine the exact shaft diameter you want to get based on "light interference fit"
2. Take very small cuts
3. Measure after each cut
4. When it is close to desired diameter go more slow in taking cuts.
5. Measure but remember the temperature can cause issues. Wait for cool down if necessary.
6. Never try to insert the bearing by hand - it may not go straight and give you an erroneous feeling that there is more machining needed. In reality the shaft may be ready to take the bearing. Depend on the measurement than you insertion by hand.
7. When it read for final mounting freeze the shaft and heat the bearing. (I am not sure if opposite of this will work for inserting bearing into the bore. I remember reading somewhere that bore shrinks when heated. Would it still shrink if the bore is about 5.5"?)

Thanks
Prasad
Click to expand...

On your Item #7 Actually when heated, holes Dia gets smaller ......... Rings Dia gets bigger. It kind of depends on the direction of least resistance to all the material expanding. Also, I would not heat a bearing very much.
 
Jeff White said:
On your Item #7 Actually when heated, holes Dia gets smaller ......... Rings Dia gets bigger. It kind of depends on the direction of least resistance to all the material expanding.
Click to expand...
This has been a heated discussion many times in the past. Almost all materials increase in length when heated, i.e, a positive thermal expansion coefficient. If what you say is true, a steel shaft in a steel plate which had a tight slip fit would seize up if the assembly were heated. It doesn't happen. Another way of looking at it is to heat a solid plate and bore a hole. The plate had expanded outward as a solid. when the plate cools down, it will shrink and the hole with it.

Bob
 
I read many excellent points, I can only share one or two more. When you are turning your shaft heat builds in the part not a lot but trust me it does. When you have snuck up on your measurement, before you take a final cut shut the lathe down and step away for a sweet tea. give the work time to cool off and measure again. I always do this on close stuff and I sometimes don't need another pass. The second suggestion is use a chip brush or clean paper towel to clean /admire the finish not your hand. The oil in your hand and the heat sink properties can skew your results including an odd cut on your next pass. Just my .02 cents worth. yrmv
 
A tooled finish from a HM lathe is almost never as good as a ground finish. I would get to within say 2 tenths of actual and try and burnish the finish to size. If the fit is a little loose, then try a Loctite bearing mount product or similar…Good Luck, Dave.
 
When fitting bearings I like using a fine (Smooth) file and scotchbrite to polish the shaft/bore. Heat shrinking is also a miracle!
 
You could advance with your compound (instead of the crossfeed) set at various angles to reduce the amount taken off, for example, at 5.7° .001 on the compound will move the tool bit in .0001
 
I find press fit bearings at the smaller diamitors are realy hard to hit. I spent ages boreing some holes for 10mm od bearings, ahhh

Stuart
 
Steel changes size in the following way, there is .0000066 expansion/contraction for each degree inch of diameter. 10º on a 10" shaft equals .00066 inches. 100º equals .0066 inches. When you're talking about a foot, that's a lot, when you're talking about 10mm, not so much.
 
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