Motor Face Runout

[mbailey]

Does anyone know of a way to face the base of the motor to improve runouts, both face and register? Does anyone make a machine for doing this? I'd like to get down to 0.001".

Thanks, Mike

 

[electricpete]

What does base of the motor have to do with runouts?

Do you want to get a flatter base?

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[mbailey]

Sorry Pete, Maybe I should have given a little more detail. This is related to C and D type flanges. NEMA MG-1 section 14.2 defines the tolerances and we are trying to do better. I am interested in a method to machine or grind the mounting base of the motor as an assembled motor in order to obtain the best face and register runouts possible. Something similar to the method of re-facing large pipe flanges, ref.

http://www.cpmt.com/tool_over_ff.php.

Small motors can be put in a lathe and the face and register turned, but larger motors are a new challenge. I was hoping that I could find something that would be easier to handle than putting the motor in a lathe.
thanks, MB

 

[Barry1961]

This may not apply but...........

I have seen various milling setups for use out in the field that would fixture to an existing shaft or hole.

One style was a fairly small spindle on a radial arm that would attach to an existing shaft. Once the spindle arm was attached they could do some precise onsite machine work such as facing, bolt circles and grooves. It was slow since they were not ridged enough to take a large cut but it got they job done. As far as I know these were home made setups.

Barry1961

 

[jraef]

Climax Portable Machine Tool will probably adapt their flange refacer to work for you. I used them in the past for a non-standard application, they are (at least were) very flexible and helpful when you bring them an application like that.

http://www.cpmt.com/tool_over_ff.php

"Venditori de oleum-vipera non vigere excordis populi"

 

[mbailey]

Thanks, I called CPMT and they are currently working on something similar to what we need that may be adaptable to this application. This is a portable milling machine that we could install a grinding spindle and quill to and may be attached to the shaft and the TOE bracket can be resurfaced using a cup grinding wheel to get the results we're looking for. Still need to figure out how to dress the stone, but that's just details. Thanks for comments. MB

 

[Mendit]

You are getting too picky with the .001 runout. In essence you are asking the manufacturer to produce a production machine with the assembled tolerance of NASA project.
Many low thrust vertical motors have single row deep groove bearings, these have axial clearance upwards from 0.010 to 0.025 pending on size. Your expectation here is impossible
Motors with 2 angular contact bearings at the top and a lower single row deep groove will give you the best results .
We have had lots of luck by checking the TIR axis to the face from the shaft, (must be hanging vertical) and mark the runout as you rotate the shaft, spin several times to ensure repeatability. Matchmark, Remove the bracket set up on the lathe or VTL and duplicate the runout. machine off the high spots. Reassemble and recheck. Usally we get with in 0.0015. The bigger the motor the tougher the problem
Small motors can be machined assembled in a lathe.
1 Preload the bearings to take out the looseness
2 Set in lathe in dead centers with the live center in the headstock, keep the shaft still and drive the motor around the shaft, machine the flange face flat.
3 Dont forget to remove the preload from the bearings.
4 Check TIR

 

[mbailey]

Mendit,

I'm assuming that all of your customers are stupid and you know more about motors than they do, Right? I don't think that my tolerances are too tight, I'm just trying to meet a customer's specification with some kind of acceptable capability in our process. This is not a NASA project but one that requires very close tolerances. And with most standard manufacturing practices, I agree that this may be impossible. I've got a shop full of standard manufacturing practices and don't have the equipment that I'm asking for here. Most of us are still in business today because we've given the customer what he asks for. And we all know that customers can be a little ridiculous in what they ask for sometimes. But when your customer asks you to meet a specification and show that you have process capability with Cpk's to prove it, what should your target values be? I know all of us have seen customers requesting tighter tolerances in areas of vibration and efficiencies, this is just another case where they feel it is required. If I want the business (and the 60% GP), I'll have to show the capability or somebody else will.

MB