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Service Machinist: Industrial Electric Motor Shop

the man machine

Aluminum
Joined
Feb 6, 2010
Location
Colorado, USA
Hello.

Last January I took a new job at a shop here in town that services electric motors, mostly industrial, some commercial, and related driven elements such as pumps, shakers, blowers, ect. of many different types and applications running a huge spectrum:

The smallest: 1/4hp 5/16" diameter shaft mod

The biggest: 7,500hp Toshiba

The bulk of the work for two machinists is re-sleeve bearing housings, do TIR on rotors weld or metal spray shaft seal and bearing journals or any area needing it, make new shafts, turn/undercut armature commutator surfaces, recondition pump impellers, dyna balancing, and a whole lot more.

So, is there anyone on this site doing / having done this work? I could sure use some pointers if your experience outweighs my three months at this (40 years in general)

Thanks
 

JS

Stainless
Joined
May 5, 2005
Location
Republic of Arizonia
I don't work in a motor shop.
If you have a calibration rotor for the balancing machine.
Check the machine often.
Usually use a half key when balancing.
If the machine has a flexible rotor function it will help when balancing.
Pump impellers can be a PITA to dynamic balance.
 

HuFlungDung

Diamond
Joined
Jan 19, 2005
Location
Canada
What kind of pointers do you need? I still do a fair amount of this stuff, it hasn't really changed that much in 30 years.

Biggest hint I can think of is to get the technique of precision boring down cold. You need tools that can skim off a few tenths. Your lathes need to be set up to bore straight for the length of any bearing surface that you have to bore. You should have a DRO on your X axis that will direct read to .0001" so that you can tell if your tool is moving as much as you think you are adjusting it.

Get tubular inside micrometers to measure your bearing bores with, enough to cover the entire range you have to work on. Generally you need to finish the bores about 3 tenths over (minimum) so that the endbell can be assembled. If your boss will permit more than that, great.

I usually sleeve bores with a sleeve that is about .050" wall thickness. Interference on the sleeve fit about .005" when going into cast iron, about .002" when going into aluminum (tendency for the sleeve to seize in aluminum seems higher, plus aluminum is weaker and you don't want to crack a thin housing with heavy force). Rough machine the sleeve ID to about .100" wall so that if it is going to relax a bit from heavy stock removal, it will do so before you finish the OD.

Some guys try to do a 'one shot' sleeve where they finish machine the sleeve after the endbell is bored, and then loctite the sleeve in with practically no interference. I find that too stressful, as the cascade effect of machining 3 precision surfaces so that they telescope perfectly and don't change dimension so that a 4th surface (the bearing) will fit precisely at the end is liable to fail to pan out too frequently to suit me. It gets to the point where you feel like you've really failed if the finish bore ends up at .001" over because that feels 'too damn loose' to suit fussy guys, which is the type I deal with. And the bearing can never be tight to assemble, as that IS failure. So you always keep machining and polishing until it is either 'right' or 'too loose' :D
 

the man machine

Aluminum
Joined
Feb 6, 2010
Location
Colorado, USA
I don't work in a motor shop.
If you have a calibration rotor for the balancing machine.
Check the machine often.
Usually use a half key when balancing.
If the machine has a flexible rotor function it will help when balancing.
Pump impellers can be a PITA to dynamic balance.

Calibration rotor? That's interesting, so is the flexable rotor function, I was only briefly exposed to the dynamic balancing, the guy training me is doing all of it right now, yes he told me he does use half keys, I know very little about the balancing but I'll e-him a link to this topic so he an look at it, he's not on here. Thanks a bunch
 

the man machine

Aluminum
Joined
Feb 6, 2010
Location
Colorado, USA
Excellent info, very helpful. "Pointers" needed are your thoughts on what I call motor teardown "evaluations" where shaft bearing journal areas are mic'd and end bell housings are checked for out of tolerance conditions. The other machinist and myself use bearing charts printed by Midland and Toyo (?) bearing companies to check these dimentions. We use both tubular and solid-rod type inside mics to get the IDs but we don't read directly off those tools, we use the ID mics to transfer sizes to OD mics and read off those.

We use premade off the shelf sleeves for our bore reasizing, they're made from cast material, I know Knight Mfg. is one place that provides them, and yes like you mentioned .005" is a good intereference fit. These sleeves finish out accurately and are predictable with regards to finish sizing, the tightest are the smaller sizes which require staying inside .0004" once you get up to 5-6" the tolerance becomes .001" ... Not too hard to hit. I made the mistake of using hot rolled mild steel for a sleeve once, that was self-educating punishment. The cast material can be bored to the low and #320'd up to mid tolerance, or just bore right to the lower 25% end and finish out to mid tolerance with ScotchBrite.

Thank you for your help, this is good info. I'll get some pics up asap.
 

JS

Stainless
Joined
May 5, 2005
Location
Republic of Arizonia
I have to use an Italian balancing machine occasionally for mine equipment, pumps, fans etc.That digital machine has all sorts of interesting features and considering all the BS it has put me through, its not too bad of a machine.
The calibration rotor is a shaft through a larger piece of mechanical tube all balanced to 1.0 tolerance. The OD of tube at the ends has holes ever 5 or 10 degrees. The holes are for weights to purposely unbalance the rotor by a few grams. So you know what you have and what you put on and the angle the machine will verify and if necessary reset the base line of the machine.
Anyway if the machine is not repeating etc I usually put it on and test , in 8 years only had to reset calibration 2 times.
Usually, it's either a flexible rotor or messed up part that has you chasing your ass. When it's a good set up it takes 3 - 5 readings , corrections and I'm done.

The previous analog machine had slide bearings kind of neat to watch the part move around horizontally on two points while the analog dials were giving you vibe and speed data. You found your critical speeds when you balanced the part.
 

Mike C.

Diamond
Joined
Nov 25, 2004
Location
Birmingham, AL
I did pumps and motors for about 5 years at my first real machinist job (have had a home shop and worked in an aviation museum as a restoration machinist for almost 15years before that), left for four years and worked in a chrome plating/hydraulic shop and went back to the pump shop last October.

Modern digital computer balance systems like the one I use have virtual key compensation. You just input the size of the keyway, diameter of shaft, distance from the machine roller to center of key, round ends or not (open ended impeller keyway), and it calculates out the error. Just started with the balance machine first of the year, but it's not too bad so far. Company that sold us the machine calibrates it every year. Have not had it a year, so we will see how far out it is first of next year.

Not sure what kind of metal spray rig you are running. I'm running a Metco wire gun. Doesn't get the work nearly as hot as a powder spray rig. If you have a lot of repetitive work, you can save a LOT of time spraying by spraying one and turning it to exact size, polish to fit, etc... while hot. Let it cool and you may have to do it again, as it will shrink, of course. Mic it cold and see how much it shrank. Add the amount undersize it came out to the original measurement when hot and now you have a constant to take that size bearing to immediately after spraying. Leave them that amount over and they will cool to exactly on size. When I started spraying, they were getting two shafts a day done, because they had to let them cool before turning. I can do eight shafts a day now, if they are common sizes I have compensated.

Agree with all the above. On sleeving wallowed bearings, I leave the sleeve only about .050 undersize, at most and then finish bore without disturbing the setup, if at all possible. That gives you one .010-.020 pass to figure out where you are, another .010 to stabilize, a .010 to give an honest cut and the third can be adjusted a few thousandths either way to land the bearing fit. I have five machines I use to bore with, depending on how the work is made. I have a 12" squarehead LeBlond for small lathe work, a 20" American Pacemaker for large lathe work, a Cincy #3 vertical for stuff too big or awkward to get in the lathes, a Cincy #2 horizontal for stuff that works better that way than vertical, and a 42" Webster and Bennett vertical turret lathe for stuff too big for anything else.

DROs are nice, but unless you have a tenth reading scale and display, they are not very useful for finishing a bearing. The VTL has a DRO and it is very useful for getting in close, but it only reads in .001 on the radius (can't get closer that .002 on diameter). Last few passes have to be made with a DI on the rail or using the handwheel dials, which can be visibly split into .0025 increments. Most anything big enough to go in that machine will have a bearing housing tolerance of .0007 or so... you can work with that.

The lathes both have crossfeed and compound dials graduated in diameter, put .010 on the dial, it takes .010 off the diameter. Swing the compound to 60 degrees and on a radius reading dial, it will now take half as much, so .010 on the compound means it takes .010 off the diameter. With the diameter reading dials, it goes to half that, so putting .010 in on the dial means it takes .005 off. Each .001 graduation takes .0005 off. Again, eyeballing it to quarters between the division will land you at .00012. You can't skim a .00012 cut, but you can leave the dial under or over by a quarter of the division of the dial and land fits within .0002 pretty danged easily as long as your cuts are the same depth, same speed, same feed, same tool, etc... in other words, DON'T CHANGE ANYTHING on those last three .010 passes to maintain stability.

For boring on the Cincy mills, I have a big Chandler Duplex boring/facing head. The dial on it is graduated in .0005 increments on diameter, so again, you can hit .0003-.0005 pretty easily on those final passes.
 








 
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