removing a motor shaft?

NickWheeler

NickWheeler

Joined
Dec 3, 1999
Messages
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Hi guys-


So a local guy has a brand new Baldor motor he's going to either sell me cheap, or maybe even give me. I want to use it for another 9" disc set-up.

Only problem is it has a stupid long shaft. Like 10 or 12" from the motor housing.

I know there are several options here, but I think the one I personally like best--- Would be to pull the shaft, cut the shaft off closer to the housing, turn a 9" steel disc on my lathe, weld it onto the shaft, then re-face the disc with the motor shaft in the lathe chuck so that the disc is as true as possible.

No, I'm not worried about ruining the motor for any other purpose in the future. ;)

What I am worried about, is I've never pulled a motor shaft before--- so I have no idea if it's something super simple, or ridiculously complicated. I have tried several different google searches, and the only thing that comes up much is pulling shafts on tiny RC car motors.

So can anybody point me toward some info on this? Or tell me if it's even possible for someone that doesn't work in a motor shop?

Thanks! :)
 
Sounds to me that pulling the shaft out will be the easy part. on just about every electric motor Ive ever torn apart you just remove the 4 long bolts holding the back on, and pull the back cover off, then the motor shaft slips out. be sure to mark the motor housing and the cover so that when you go to put it back together you can line it up as it was before.

Ive never torn apart a baldor, but lots of other motors. on smaller motors like your bench drill, the brushes are sometimes a pain to get lined back up, but on the bigger motors, Ive never had one come out, so they may be held in with a clip. most of the ones Ive pulled apart are old motors for furnaces that were never oiled, and am just trying to free up the motor bearings.
 
The other option is to call Conrey Electric in Portland. They fix all the motors i need repaired at work for me. They sell n service Baldor motors and are great with advice on the phone.

Hope this helps.
 
Why pull the motor apart, why not just cut the shaft shorter with the motor together? If it's too hard for a hacksaw, a grinder with a cut-off wheel will make short work of it. Welding the disc on may not be the best solution either. It's going to be tricky to not warp the disc, and to keep it true to the shaft. And the armature is not usually removable from the shaft, meaning you won't be able to change the bearing on that end of the motor ever again, and you will have to do your welding and machining with the end of the motor housing spinning on the shaft between the armature and the disc. If you are milling the disc on the lathe, a better solution might be setting it up to use a taper-lock bushing to grab the shaft
 
NickWheeler said:
Hi guys-


So a local guy has a brand new Baldor motor he's going to either sell me cheap, or maybe even give me. I want to use it for another 9" disc set-up.

Only problem is it has a stupid long shaft. Like 10 or 12" from the motor housing.

I know there are several options here, but I think the one I personally like best--- Would be to pull the shaft, cut the shaft off closer to the housing, turn a 9" steel disc on my lathe, weld it onto the shaft, then re-face the disc with the motor shaft in the lathe chuck so that the disc is as true as possible.

No, I'm not worried about ruining the motor for any other purpose in the future. ;)

What I am worried about, is I've never pulled a motor shaft before--- so I have no idea if it's something super simple, or ridiculously complicated. I have tried several different google searches, and the only thing that comes up much is pulling shafts on tiny RC car motors.

So can anybody point me toward some info on this? Or tell me if it's even possible for someone that doesn't work in a motor shop?

Thanks! :)
Click to expand...

Three phase motor ?

I just pulled one apart last month for scrapping / curious
As mentioned, It was just pull the 4 long frame screws and it pulls straight apart- the two endcaps pull off
Depends about the bearings whether they stuck to the shaft, or the endcaps.
There are no brushes, nothing to lineup.



With welding I'd be concerned about overheating winding insulation lacquer and warping the shaft.
The whole armature and shaft was a sealed unit like Ricks diagram shows.
No visible windings in that assembly.
You could probably even dunk the whole think in a pail of water for welding.


I don't remember seeing how the armature would come off the shaft, seems to me it's on for good as a sealed unit.
I doubt your lathe has a large enough headstock through hole to just chuck it - I remember it was in the 3 or 4 inch range

I suspect it's a mount between centers or steady rest job.
Especially since you will not only turn the outside diameter true, but both sides of the disc face too.
It's the only way I can see getting that all done in one setup so it's all true relative to each other.


Welding it on, seems like it's tempting fate though.
Oh I just caught that Mahoney mentioned you can't change bearings, that's bad.

I have a similar cheap motor with a wonky shaft, longer and end threaded.
I decided that when it's time, I'm going to set the shaft in a pair of V-blocks on the mill and just mill a keyway.
 
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Most of the motors I've had apart went back together without any problem.

You might find you don't have a great place to chuck up on, but there is no harm opening it to see.

I'm not sure how you're going to get it back together with a disk welded on one end, so you'd have to weld it half assembled, which means heat is going to make it to your bearings. Also, most motors don't have the bearings you'd need to tolerate the amount of thrust you'd generate using them as a disk grinder. I think you'd want something like a matched set of deep groove angular contact bearings for that, and most electric motors aren't built that way, so your bearing life won't be great in this application.

If you face just one side of the disk on your lathe, it seems pretty likely you'll end up with a less than perfectly even thickness, which implies out of balance. I think most motor shops can balance that.

If it were me, I'd shorten the shaft with a saw and leave it at that. I'd weld the disk to a 2 or 3" long sleeve. I'd turn the face of the disk and the bore of the sleeve in the same setup and aim for a few tenths clearance to your shaft. That will likely spring into a light press fit once you remove the assembly from the clamping force of the chuck jaws. I'd turn it around and cut the other side of the disk, taking careful measurement and tweaking the setup with a small hammer to get the thickness of the disk relatively even for balance. Add a couple set screws, grind a bit of a flat on the shaft for the set screws, heat the sleeve for assembly etc and I think you'd have a pretty good disk setup.
 
Ten thousandths (tenth of thousandths of am inch)...... Machinist vs Carpenter ;-). I do the same thing sometimes.
 
bladsmth said:
Nathan...a few tenths...or a few ten thousandths?
Click to expand...

Usually, when a machinist or engineer says "tenths", they mean .0001". We generally work in thousandths, so a "tenth" is a tenth of a thousandth, though I can see how that may be a bit unintuitive.

Nick is an engineer with machinist's training. I expect that turning that bore to a few tenths over is within his ability and is the best way to mount his disk to that shaft without much runout.
 
Nick
my suggestion would be to machine your disc with a hole in the back to fit onto the shaft after you cut it to the length you want.add 2 set screws to hold it in place and you should be good to go . male is shaft female is the back of the disc ..
 
Thanks guys.

Rick, thanks for the link. And yes, I would LOVE to have an original Marchand illustration! ;) :p

Sam, yep- it's a 3phase, 2hp 1725 rpm Baldor TEFC, inverter duty motor. Retail on it is like $700-800!

Nathan, your post makes good sense to me and sounds like a solid plan, thank you! :)

I should back up a bit because I didn't explain my "weld on disc" very well. I realize most of you probably envision a disc butted up to the shaft and welded on... But what I was thinking of was a disc with a sleeve welded onto the back, then bored to a light press fit on the shaft.

I'd press the disc on, leaving it about 3/8" from being flush with the end of the shaft, then just put a few solid "tacks" inside that 3/8" deep pocket, joining the disc to shaft more permanently. Not a lot of heat, not much chance for distortion, etc. Or as an alternative (or addition) have a couple of holes drilled in the sleeve (like a set-screw hole) that would give me a couple access points to weld the sleeve to the shaft.

I should have typed that out in my op, sorry fellas.

I didn't know that I wouldn't be able to do that and then slide the shaft back into the motor. I readily admit my ignorance (in everything) but in this case, the specifics of motor guts. ;)

I have actually milled quite a few keyways in shafts, that part wasn't a worry to me. The problem is I don't have a keyway broach set and heavy duty arbor press to put the keyway in the steel disc. I'm sure a local machine shop could do that in a jiff, but they're going to charge me an hour shop rate (not that that isn't fair! just I don't want to pay it, LOL).

I have seen a keyway cut in aluminum on a lathe with a boring bar (Sam posted a link to youtube yesterday showing the same thing) but I have never done it.


The last detail here, was the part about facing the disc and shaft as one. Even with the CNC turned discs I have, there was a tiny bit of run-out when they were put on the motor shafts. One of them I ended up resorting to putting 4 set screws on the hub, so I could tighten them down with the aide of a dial indicator (just like you would chuck up a part in a 4 jaw chuck) and got the disc running true.

Is a few thou run-out the end of the world on a 9" disc? No... But when you're trying to take blades up to 1200X on the disc, you want that SOB running AS SMOOTH AS POSSIBLE.

In my little brain--- I thought my proposed idea would be simple, cheap, and leave me with a disc that would run dead nutz on. But I am wrong a lot!!! :eek: :foot: :D


THANKS GUYS!!! :)

edited 50 times for clarity and typ-Os ;)
 
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Nick, re-inventing the wheel is fun, but the round ones roll pretty good as they are.

Just make the press fit disc with set screws in the sleeve. Tighten them down and you are done. That way the motor and/or the disc are not reusable later on. Everything else can be the same as you plan....without the welds.
 
bladsmth said:
I was just kidding.
Click to expand...

...oh...

Well I don't know, you jewelers work in some weird units of measures. Carats and points and millimeters. Who the hell ever heard of any of that stuff...
 
HaHa Stacy, I'm not one to re-invent the wheel.... I'm just cheap. :)

Nathan--- that's frick'n funny! :D I have had people question me several times when I said, "tenths." I'm with steve on that... it's definitely a carpenter vs. machinist language thing.

I'm too much of a hack to really work with tolerances any tighter than 1/8" but I like to talk like I know what I'm doing! :foot: :D


So to veer to the left a little here. Nathan, you mentioned most electric motors not being made for the thrust they'll see in this application. So I'm wondering if I wouldn't be a whole lot smarter to build a set-up with pillow block bearings, a shaft, and pulley. That way I could put a 9" disc on one end of the shaft, and a 6" on the other (I have a PILE of 6" zirconium discs and Mirka Golk Stik-it discs that I got cheap).

I was leaning toward direct drive just because that's what everybody seems to run. How's that for herd mentality? :o LMAO

Any thoughts from the peanut gallery???

Thanks guys :)
 
You've already got a disc, how often have you had to change those bearings ?

Direct is more compact
Shaft drive can give you an extra disc.

depends on what's most important.
 
I've never changed them Sam, but my current set up is an old DC motor+controller that probably needed new bearings when I got it 7 years ago, LOL. So I'm probably not the best judge on that.

Compact was hugely important in the old shop, but not in the new one. I do need to have something to run those small discs on, hopefully before the adhesive in them goes bad.
 
A couple set screws bearing on a flat cut on the motor shaft should be more than sufficient to transmit the torque needed to run a 9" disk sander I have a 14" swing Vega wood lathe that relies on a single setscrew on the shaft to hold on a 5" chuck...that holds huge chunks of wood...That has worked fine for years.

If you really want to use a key, you can cut an internal keyway in your sleeve with a hacksaw and files, (and dare I say it...a keyway chisel) the fit does not need to be perfect, just good enough that the key fits in. If the fit is a bit sloppy when you are done, just load the disc in the direction of rotation when tightening the set screws, or tap a shim in. But the work this takes may make the cost of the hour of shop labor for the guys that have the broach set seem reasonable...
 
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