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Old motor frame size = unobtainium.

challenger

Stainless
Joined
Mar 6, 2003
Location
Hampstead, NC-S.E. Coast
My old wells index model 40 has a spindle motor made by Master Electric Company in Dayton Ohio. The frame is a 7420 which isn't a frame size I can find the specs on. I am wondering if anyone can tell me the modern cross reference for this size frame? It is a 3ph 1/2 hp motor. I'll be replacing it with a new motor because the bearings sound horrible and I think I have a good 3/4 hp motor I can swap after er a couple of modifications. Oh, the fact that I crashed the fan into the motor windings has absolutely no bearing on my decision to not simply replace the bearings and reuse the motor.
I'm an idiot. A very pissod off idiot.
Thanks

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My old wells index model 40 has a spindle motor made by Master Electric Company in Dayton Ohio. The frame is a 7420 which isn't a frame size I can find the specs on. I am wondering if anyone can tell me the modern cross reference for this size frame? It is a 3ph 1/2 hp motor. I'll be replacing it with a new motor because the bearings sound horrible and I think I have a good 3/4 hp motor I can swap after er a couple of modifications. Oh, the fact that I crashed the fan into the motor windings has absolutely no bearing on my decision to not simply replace the bearings and reuse the motor.
I'm an idiot. A very pissod off idiot.
Thanks

Sent from my Pixel 2 using Tapatalk

Consider calling wells for a quote on a new motor

They are really nice people, even though they do this for a living

They were so reasonable and helpful when I owned my Wells CNC, that when I scrapped it, I gave them whatever parts they wanted [basically the head] and strapped them to a pallet that they paid to have shipped back 'home'

They no doubt passed it on to some other WElls owner, like you
 
You're right, "7420" is not a standard (even very old) frame size.

I'm afraid you are going to have to measure a few dimensions. With those dimensions, you can find the closest modern NEMA frame size. To narrow things down, you want a fractional HP (generally two-digit) frame, and the most common examples are 42, 48 and 56, with shaft centerline heights of 2-5/8, 3, and 3-1/2", and shaft diameters of 3/8, 1/2, and 5/8", respectively.

If you know the shaft centerline height of your 7420 frame, that will help narrow things down a lot. The first two digits of three-digit NEMA frame numbers are 4 times the height in inches. I.e., NEMA frames beginning 28x have a centerline height of 7 inches. Since you can always make a mounting pad/spacer, you should look for frames with your current frame's centerline height, or less.
 
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You're right, "7420" is not a standard (even very old) frame size.

I'm afraid you are going to have to measure a few dimensions. With those dimensions, you can find the closest modern NEMA frame size. To narrow things down, you want a fractional HP (generally two-digit) frame, and the most common examples are 42, 48 and 56, with shaft centerline heights of 2-5/8, 3, and 3-1/2", and shaft diameters of 3/8, 1/2, and 5/8", respectively.

If you know the shaft centerline height of your 7420 frame, that will help narrow things down a lot. The first two digits of three-digit NEMA frame numbers are 4 times the height in inches. I.e., NEMA frames beginning 28x have a centerline height of 7 inches. Since you can always make a mounting pad/spacer, you should look for frames with your current frame's centerline height, or less.

You are correct.
I have taken some measurements and compared them to the NEMA charts and this motor is a long way off. Nothing that a bit of mounting plate and pulley sheave modifications won't address.
For giggles I'll call the local motor rewinding shop to see what the cost to rewind and rebuild the motor will run. Last one I had done was a Baldor 5hp single phase compressor motor. It was $400.00 to rebuild and a new one was more than that so I had them do it. This time I really doubt I'll be inclined to do so.
 
I don’t know a lot about electric motors but I have seen at least one instance where a motor with damaged windings that had special rotor and end bells was salvaged by taking the stator or center section with the windings from another used motor of the same physical size HP. and voltage and putting it together with the rotor and end bells of the burned out motor .
You might be lucky enough to find a used motor that could donate the stator and put in a new pair of bearings to get you going again .
 
My old wells index model 40 has a spindle motor made by Master Electric Company in Dayton Ohio. The frame is a 7420 which isn't a frame size I can find the specs on. I am wondering if anyone can tell me the modern cross reference for this size frame? It is a 3ph 1/2 hp motor. I'll be replacing it with a new motor because the bearings sound horrible and I think I have a good 3/4 hp motor I can swap after er a couple of modifications. Oh, the fact that I crashed the fan into the motor windings has absolutely no bearing on my decision to not simply replace the bearings and reuse the motor.
I'm an idiot. A very pissod off idiot.
Thanks

Sent from my Pixel 2 using Tapatalk
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many motors if you can manage to get it apart, changing bearings is relatively easy. some motors getting apart can be a challenge, sometimes rusted solid or they used the high strength loctite never made for taking stuff apart
 
many a motor i flopped upside down clamped on a hardened steel plate with holes in it to guide a drill bit as i drilled 1/2 a hole or slotted the holes.
.
they also sell hardened drill bushings that can be pressed in soft steel to do same thing. and soft steel good enough to guide a hole saw with pilot removed to also cut 1/2 a hole or slot holes
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or use a rotary file in a hand held grinder to slot the holes.
.
most millwrights would have any motor even remotely close to size bolted on in less than 10 minutes. sure if motor over 500 lbs might take a extra 5 minutes
 
to bad this is an old post i was looking at some motors that i have and i have one of them master ser qg-10069 . frame 7420 . style 122213 . 1/2 hp 220 / 440 3 ph. hz 60 / 50 rpm 1140 / 960 . i was told it cam off of a Bridgeport mill
 
My index model 55 has the same motor for the table feed. My motor sounds great tho.

Its my (likely dry) spindle bearings that make a hell of a noise
 
I'd suggest looking in 'Machinery's Handbook". There should be data on old/obsolete motor frames with conversions to current (sorry about the pun) NEMA frame sizes.

Usually the newer NEMA frame sizes are a bit smaller than the older motor frames. If the motor is 'foot mounted', making some 'conversion bars' out of flat stock or square bar stock with the two (2) sets of mounting holes - one for the old motor's mounting bolts to go into the original mounting, & one set tapped for the new motor's feet. I had an ancient 3 phase 2 HP motor on my shop air compressor. It is a Worthington compressor and is direct-coupled to the motor shaft via a 'rag joint' or 'dampener' type coupling (canvas/rubber disc between the coupling flanges). I went to a NEMA frame single phase 2 HP motor. I had room to spare. The centerline height of the new motor was about 1 1/2" lower than the original motor. I made an 'adapter' out of some flat bar and some square bar which brought the new motor up to centerline height. Since this is a direct coupled application, I made the adapter about 0.030" lower than the actual centerline height. This allowed me to 'dial in' the shaft alignment and use shim stock to get the centerline height DNA (dead nuts accurate).

I have a Master gear motor on my Burke Mill. It is a brute of a motor for what it is. Cast iron frame, definitely not made to any current NEMA standard. As it was setup on my Burke mill, even on the factory furnished motor mounting bracket, there was a slight rub of the belt. I made some spacer bars out of something like 3/4" x 2" flat steel bar stock, counterboring them for socket head screws to hold the bars to the bracket without any heads sticking up. I then repositioned the Master motor so things lined up without any belt rubbing issues. My guess is the mill originally had a 3 phase motor on it (the original magnetic starter was still in place), and somewhere along the line, it was refitted with the single phase Master gear motor.

IMO, unless a motor with a special frame has some special application (such as a flange mounting into a machine's headstock or similar), current NEMA frame motors can usually be adapted.

A bit of careful measurements of both the old motor, the existing mounting, and comparing with NEMA frame dimensions is what it takes. I've had to deal with older (ca 1920's) motors that needed replacing on powerplant equipment. These motors were mounted on cast iron or fabricated steel bedplates and some had drive pinions on their shafts. It was a case of designing adapter bars and sometimes having to shrink a bushing into the pinion hubs to work with the slightly smaller shaft diameters.
 








 
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