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unclejon
09-16-2010, 11:39 AM
I need help accurately boring an aluminum housing to fit the O. D. of a ball bearing.

The I. D. will be a light press fit to maintain location on the shaft. The O. D. needs to "float". The bearing O. D. is 62 mm (2.4409" +0, -.0004). I want to make the housing bore .0005 less than the nominal bearing O. D. This should give just enough "grip" on the O. D. while allowing for expansion of the housing.

My question is how to bore to this tolerance on a BP mill with out going oversize. I know from experience that trying to "sneak up" on it doesn't work for me. Would using some type of abrasive "flap" work for the last thousandth or so?

Thanks in advance for your thoughts.

Jon

ADGO_Racing
09-16-2010, 11:43 AM
Obviously, you aren't being quiet enough when attempting to "sneak up on it. :D

strokersix
09-16-2010, 11:54 AM
Your last two or three cuts should be identical in the .002-.005 inch range, measuring each time. This will allow you to predict the result of the final cut. Also ensures the speeds, feeds, lube, tool condition, surface finish are all OK by the time you go for the last cut.

Don't make your last three cuts .020, .005, .001. Guarantee you'll miss.

lakeside53
09-16-2010, 12:21 PM
I totally agree with the above post. Been there and lost before:(

But.. one more thing. Make sure the measurement of the bore is done at a chosen temperature - I've missed many 10ths (and more!) because the item too hot after machining. I now wait or cool the work before the final couple of cuts. The cheap HF laser pointing temperature measurer works great...

oldtiffie
09-16-2010, 12:40 PM
Your last two or three cuts should be identical in the .002-.005 inch range, measuring each time. This will allow you to predict the result of the final cut. Also ensures the speeds, feeds, lube, tool condition, surface finish are all OK by the time you go for the last cut.

Don't make your last three cuts .020, .005, .001. Guarantee you'll miss.

Agree.

Otherwise known as a "spring" cut - works on a lathe too.

RWO
09-16-2010, 03:01 PM
If you miss, overbore it a bit and install a Tolerance Ring. You end up with a wearproof, tight fitting, spring loaded stainless steel seat for the bearing OD. it makes disassembly easy yet no dimensional changes occur.
http://www.usatolerancerings.com/ringtypes.html http://www.usatolerancerings.com/repair.html


RWO

Forrest Addy
09-16-2010, 04:21 PM
EWO. "Tolerance rings?" New one on me. I wonder what the radial stiffness would be?

Carld
09-16-2010, 04:28 PM
You may want to rethink the slip fit part. If you make the slip fit in the aluminum it will fail early because the aluminum will wear fast. If you make a .0005" to .001" press fit in the aluminum and a slip fit on the shaft and put the bearing in with locktite your aluminum housing will last a long time. The bearing ID and the shaft can tolerate movement much better.

fredwillis
09-16-2010, 04:38 PM
Here is an old trick used for things when you dont even have a measuring tool other than a ruler or something like that. bore it till the bearing goes into the bore with litlle resistance, take .001" or whatever but olny do 1/16" deep counter bore till the bearing wants to go, from there back the boring head up a few thousands (remember backlash so do it right) and bore to the seat.
This does a few thing for you. You know the dial number where it is over bored, you can sneak up on the light press fit slowly knowing that you are very close. Also the shallow counter bore will let you get the bearing started dead strait in the press fit with little hassle.
No kidding you can bore a press fit that way with no mics or calipers. what if you have a 20" bearing and no mic that big. well that's how you do it.
you can put that in your book of tricks.

polepenhollow
09-16-2010, 07:28 PM
Familiarize yourself with the material and tool on rough bores.
Last 3 bores, .005, .005, one free pass, verify dia. move balance, appx .0025 move should be expected.
Verify dia.
On the last bore, remove appx .0025 total. Your size should be there.
+/- .0002

K Lively

EVguru
09-17-2010, 07:27 AM
My experience with bearings mounted in Aluminium housings is from old bike engines. The bearing needs to be a good tight fit in the housing. If it can move, then the housing will fret and you get wear, grey sludge, vibration and all sorts of problems. The shaft should float in the bearing, or the bearing should be a roller type and the thrust loads taken care of at the other end of the shaft.

unclejon
09-18-2010, 09:37 AM
Thanks for all the helpful advice.

Jon

polepenhollow
09-18-2010, 03:48 PM
Further thought on Bearing bores.
I sharpen the tool for the last three passes. Sharp point.
I usually lightly load the spindle for the last few passes. I hold the boring head lightly in one hand as it runs and feeds and apply slight gripping pressure.
That keeps the spindle loaded.
It helps give the bore a better finish by taking slack from the splines and keys in the spindle.
K Liv

jdunmyer
09-18-2010, 08:24 PM
My experience with bearings mounted in Aluminium housings is from old bike engines. The bearing needs to be a good tight fit in the housing. If it can move, then the housing will fret and you get wear, grey sludge, vibration and all sorts of problems. The shaft should float in the bearing, or the bearing should be a roller type and the thrust loads taken care of at the other end of the shaft.


I once rebuilt the alternator from my VW: the rear bearing was seated in a plastic bushing, it had failed and ended up wallowing out the housing. Didn't have the B'port at the time, so set it up in the lathe for boring. After cleaning it up, I turned the OD of a bushing out of a largish plastic pipe fitting. One of those nylon (?) adaptors used between metal pipe and that black plastic stuff. Bored the ID after pressing it into the housing, as it sprung away from the tool otherwise.

The alternator lasted at least as long as it did originally. I figured that the plastic bushing was to allow the bearing OD to float a bit with temperature changes.