Bridgeport J Head Pancake Motor

[awemawson]

My Bridgeport mill doubles as a drill press, and the other day I was drilling a 10 mm hole in a bit of softwood when there was an almighty bang and flash from the control box 

Oddly the motor will run and not make big bangs in high speed, but gives the same dramatic results in low speed

It looks like the control box and contactor have survived but the motor it self is giving me some very odd winding  resistances:

Slow A to B = 55.6 ohms
Slow B to C = 27.8 ohms
Slow C to A = 27.8 ohms

Fast A to B = 13.8 ohms
Fast B to C =  14.3 ohms
Fast C to A - 14.2 ohms

Now as you can gather this is a dual speed motor 2800 / 1450 rpm or there abouts with winding switched by a rotary switch on the side of the motor.

So far I've managed to get it off the machine and onto the bench and opened up the switch cover hoping for loose wires but none to see 

When time permits I'll dig deeper into the motor

So if anyone knows where there is a Bridgeport 'Pancake' motor I'm in the market for one !

[Pete.]

My Bridgeport mill doubles as a drill press, and the other day I was drilling a 10 mm hole in a bit of softwood when there was an almighty bang and flash from the control box 

Oddly the motor will run and not make big bangs in high speed, but gives the same dramatic results in low speed

It looks like the control box and contactor have survived but the motor it self is giving me some very odd winding  resistances:

Slow A to B = 55.6 ohms
Slow B to C = 27.8 ohms
Slow C to A = 27.8 ohms

Fast A to B = 13.8 ohms
Fast B to C =  14.3 ohms
Fast C to A - 14.2 ohms

Now as you can gather this is a dual speed motor 2800 / 1450 rpm or there abouts with winding switched by a rotary switch on the side of the motor.

So far I've managed to get it off the machine and onto the bench and opened up the switch cover hoping for loose wires but none to see 

When time permits I'll dig deeper into the motor

So if anyone knows where there is a Bridgeport 'Pancake' motor I'm in the market for one !

I make that a switching issue. Going by this thread:

There are six windings in the motor. For low speeds the windings are connected in a series loop with power applied to every other connection. So 440 volts is applied across each pair and the individual windings see 220 volts each. For high speed the windings are connected in parallel pairs. One end of each pair goes to a common point the other end receives power. So each winding sees 220 volts.

You should have four times the resistance in the low speed arrangement as in the high speed. Since only one phase combination has that resistance and the other two are showing half what they should, and given that the high speed readings seem to be appropriate, I'd say that the windings are fine but one winding is shorted when the switch is set to low speed. Can only be within the switch IMO.

Might be completely off-track but that's how it seems to me.

[awemawson]

I hope that you are correct Pete, and it was that suspicion that had me take the cover off the switch but I’ve still not got any further into it. String of visitors today as allegedly it my birthday, but I find it hard to believe it’s a year since the last one

[Muzzerboy]

I've got one you can have. It was working fine when I removed it so that I could replace it with a modern 3000rpm 3kW machine and adaptor plate I got from the late JS. I gave it a good clean when I bought the machine, so it's in a decent state all in all. I even have some spare bearings for it, although it ran pretty quietly.

Where are you? I live near Blackpool and work near Leamington Spa. But IIRC, I can send up to 25kg for £7 via Parcel Farce. Let me know if you are interested.

[awemawson]

Yes please thank you very much.

I rebuilt mine 20 years ago from bits of one from John Stevenson so hows that for a coincidence. Someone had sawn the shaft off intending to use the front plate to mount a more modern motor so that was missing and I had to make one. My shaft is two bits grafted together.

I’ll PM you and we can sort something out

Cheers

[awemawson]

I managed to do a bit more investigation with the motor today. Of course the symptoms changed half way through 

Six wires on this "Dahlander' pole switching motor that can be switch configured as two pole or four pole with a complicated switch to do the job. I made up a table  matrix of the six wires and wrote down inter-wire resistance values and it soon became obvious that 'C3' was open circuit - it hadn't been.

Then I removed the rotor to closely examine the exposed windings, and found damage to three wires which my ohm meter tells me are connected to C3 - sadly I cannot remove the stator winding to see the other side - it seems to have been pressed into the 'blind' housing and will require something making up to jack it out, and it is on this far side where the wires go to the outside world.

My guess is that something metallic has been ingested shorting those wires which has weakened the  outer connection which has now broken 

I have been able to test the complicated switch (5 positions  with 12 poles) against the Bridgeport manual, and it checks out (except it looks as though forward and reverse are exchanged)

Conclusion: I still need a new motor !

[Sea.dog]

If that's the only damage evident I'd repair each of the three wires and meter it. What have you to lose?

[awemawson]

Graham, the three wires are not broken they are still continuous just scalped but C3 is not connected to anything other than these wires - no external connection!

I found a reference on the web to the stator being a light press fit but retained by two grub screws. Seems mine only has one grub screw. (I even chopped off the rivets for the label in case #2 was underneath - but no!)

So by warming the aluminium casing, supporting the windings / stator stampings with my fingers, and using a plastic mallet  tapping the casting I have moved the stator 19 mm in an outwards direction. I had to stop as by this time the stampings had warmed up too much for a temperature differential, but by the morning they should have cooled enough to start again.

[Sea.dog]

I couldn't make out whether or not one of them was broken, but I suppose that would be the first thing that you would check. Good to see that you're making some progress Andrew 

[awemawson]

I had a brief further go this morning Graham but couldn't put much enthusiasm into it.

I came down this morning to find our older dog Cleo had died over night - she was ten. So first job was to dig a large hole in the orchard and bury the poor thing. Frankly bashing on the motor housing was just to release a bit of frustration and not very productive.

[pycoed]

Bugger!

Condolences - just had to cut down an apple tree that wasn't doing well & was planted over the best working terrier I ever had. 'Tis a bugger their lives are so short...

[John Rudd]

Sorry to hear MBF has departed this world.....😢

Hopefully when your enthusiasm returns, the motor damage is repairable and eases the pain of your loss....

[tom osselton]

Sorry to hear about Your dog 10 years just isn’t enough time with them.

[Sea.dog]

Sad news Andrew. But, as they say, life goes on. You've a new baby in the fold to ease the pain.

[vintageandclassicrepairs]

Hi Andrew
Sorry to hear your sad news about Cleo

John

[awemawson]

Thanks for your thoughts chaps - much appreciated. It's very cruel that a dogs life is so much shorter than a human one. The puppy of course was a planned 'continuity' but poor old Cleo should have had at least another couple of years.

[awemawson]

I had another go at trying to remove the motor stator from it's cast blind housing. I'd tried the other day using warming to give differential expansion but it's not easy to not over heat the wiring.

So today I tried with a reverse assembled three leg puller. Now there is VERY little of the stator stampings for the puller to grip, and the claws are awfully close to the windings, so care is needed. Trying to hold the three legs in the correct place AND tighten the puller with my four hands proved impossible, but then I hit on the idea of cutting suitable wooden wedges to hold the legs outwards leaving me a free hand for the spanner.

Eventually I got it in what I considered a safe place and started winding. The result ? Edge of the stampings rounded over and there was NO movement.

. . . hmm . . this is proving a bit of a pain!

[hermetic]

Andrew, could you use a hot air gun, or even a torpedo diesel heater with the stator on a weld positioner turntable to keep the heat even, then even heat for say 5 minutes, and then try the extractor again? you will note that I am assuming you have this kit!
Phil

[Muzzerboy]

I thought you'd be able to push the stator out by removing the end cover as well as the front plate. Can't make out what the stator assembly looks like from the photos. Is there a reason you need to pull rather than push?

I'm back home now and have dug out the motor I took from my original (Taiwanese clone) Bridgeport. Slightly more sausage than pancake and dual voltage rather than dual speed but otherwise looks pretty similar.

If you are still up for it, I'll wrap it up tomorrow and get it off to you Monday.

I'd post some pics but I get the error message "Your attachment couldn't be saved. This might happen because it took too long to upload or the file is bigger than the server will allow." Can't imagine this is a novel problem - what's the fix?

[awemawson]

Hermetic I can get it evenly warm with a propane torch, but as the stator is in intimate contact it warms also, and rapidly you get to the point where they are much the same temperature!

[awemawson]

Murray yes please I am VERY MUCH ‘on’ for your motor please, it’s so frustrating not having the Bridgeport, with it going I could make a better extractor.

The aluminum motor housing is all cast as one piece, the top doesn’t detach sadly so it has to come out downwards.

Given the Bridgeport working I could theoretically drill some strategically placed holes in the top to drive the stator out, but I’m not going to risk that with a hand held drill.

I much look forward to receiving your motor !

[awemawson]

So thanks to Murray I have received a single speed 'Pancake Motor' for my poor old Bridgeport.

It's spindle is 22 mm but my pulley is 19 mm so the first job was to bore it out on the lathe - sorry no pictures.

Then it has a 7 mm key way and my (Imperial) broach set obviously doesn't include 7 mm so the next job was to file up a 7 mm key and grind a shaping cutter to fit in a boring bar to shape a suitable key way in the pulley using the lathe and manual long feed - again sorry no pictures.

Then my Bridgeport mounts the motor on two 1/2" UNC studs, one as a pivot and the second in a slot for belt tightening, so having first offered up the front plate of my original to the mounting holes on Murray's motor (which are plain 10 mm holes) to check absolutely that they have the same mounting centres I drilled and tapped them out to 1/2" UNC to fit my studs - I then placed the motor on the machine to prove all fits - it does!

OK now I need to sort out the electrics - my original motor had a housing for a 5 way switch (fast fwd/slow fwd /off slow rev / fast rev) - this one just has a pressed terminal box - the switch must have been elsewhere on the machine and only sadly needs to be three way being single speed.

RSComponents provided a suitable three phase reversing switch and I drew up a suitable box to house the new switch and replace the terminal box. Cutting it out on the Plasma Cutter proved a bit of a pain - I've still not got it fully configured since my Windows 7 debacle - but at last I ended up with a 'flat box' just needing bending.

Like a twit I failed to realise that my narrowest finger on my folder was wider than the narrow dimension of my box - no problem if you bend the narrow bit first, but if you don't . . . . . 

As an attempt to recover the situation I tried sawing a 'bend here' cut but rather as I expected the result wasn't acceptable. Never mind - cut another 'flat box' on the CNC plasma and do it right this time - which I did 

OK Box and lid bent up, all the right  holes drilled for mounting it on the motor, and to take the switch and the 20 mm entry grommet - time for a trial assembly. It all fits but the wiring is going to be a bit tight but should work oOK.

I've dis-assembled it for painting - (tasteful shade of satin black) and will try and fit it all together tomorrow.

[John Rudd]

Looking good so far....👍

Are you going to repair the original motor?   

[awemawson]

John so far it’s resisted all my efforts to pull the stator from the casting. The fault is probably on this inaccessible side of the stator (upper in use) as apart from those three turns that have scrapes the lower side looks good.

Interestingly the single speed motor has a removable top cover so the stator could be driven out, but the two speed is a single aluminium casting (different makers)

[Muzzerboy]

Good to see this thing getting a second life. Glad it seems to fit OK.

Must say, I like the idea of a CNC plasma cutter. What did you use to create the sheet metal design?

Yes, I assumed yours would also have a removable top cover. Would have made stator removal easier (possible?).