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2 plane balancing?

M

moyesboy

Alibre Super User
2 plane balancing?

I have an aluminium cylindrical part 31.5 mm long and 17.5 mm dia running at a max of 36,500 rpm.
Till now these ran OK without a balancing operation, but now we added some machined features and quite a few of them vibrate and quickly damage the bearings (rated for 40,000rpm).
I can get them balanced with balance planes on each end, OK to remove some meterial there. But I don't know what to ask for in terms of g.mm at the running speed. I just want to get the out of balance load well inside what is reasonable for the bearings.
Anyone got any rules of thumb for this?
 
W

wfpelletier

Senior Member
Balancing Quality Limits

This is the best explanation and description of the application of balancing quality limits I have ever seen:

http://www.plant-maintenance.com/articl ... limits.pdf

If you read the whole document (which is about seven pages, and fortunately only contains simple formulas and clear explanations), you will probably know more about how to specify balances than most engineers. This article does have some general rules about specifying balance tolerances that will probably give you the answer to your problem. Most likely you will be able to use one of the standard balancing tolerances specified in ISO 1940/1 to calculate a suitable g*mm specification for your part. (This ISO spec is fully described in the article.)

Hope this helps..

wfpelletier
 
J

jwknecht

Alibre Super User


So, the bearings are rated for 40,000 rpm. If they are rated at 40,000 rpm, does this assume a "perfect" balance condition? I don't think so, because perfect is not possible. So, depending on how good of tech support that you can get from the bearing supplier they "should" be able to tell you what the rating of 40,000 rpm is based on in terms of force caused by inbalance.
 
M

moyesboy

Alibre Super User


Thanks for the help on this.
I worked out the balance tolerance to the required std.
If the part is manufactured to my drawing tolerance then it can be out of balance by a factor of 5 times compared to what the G6.3 std allows.
So I can more than double the cost by balancing the part after manufacture, or more than double the cost by requesting extremely tight manufacturing tolerances (that I can't inspect for anyway)!
so it goes

Maybe I should increase the diameter and thus reduce the speed a bit...
 
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