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Electric motor on my Tom Senior Vertical Head

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The Merry Miller16/10/2011 14:58:43
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484 forum posts
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Afternoon all.
 
Well it's just happened, a lightly loaded 6mm endmill in the collet chuck just minding it's own business when all of a sudden smoke started pouring (well not pouring just seeping) from the terminal box on the motor.
Switched off and checked the outside of the motor casing, felt quite warm, nay hot!
It could still run albeit I suspect at a lower speed, lower than 1450rpm.
The centrifugal switch was still switching in and out.
 
I removed the motor and removed the front plate to reveal the charred windings.
I'm just curious to know how a motor could be running perfectly yesterday and give up the ghost today for no apparent reason, I could understand it if I had been hammering the beast but I hadn't, I was just machining a small piece of brass.
 
Comments are invited will be interesting to read.
 
Incidentally the motor was a Brooks Gryphon 1/2 h.p.
 

Len. P.
 
 
 
Nicholas Farr16/10/2011 15:43:20
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3988 forum posts
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Hi Len, cars are very often like that as well. I guess you have probably had some insulation breaking down inside the motor windings for some time without any noticeable difference, but today those enthusiastic little electrons finally made their breakthrough and spoilt your day.
 
Sorry to hear of your dilemma.
 
Regards Nick.
Billy Mills16/10/2011 15:56:20
377 forum posts
Sounds like shorted turns. Something rubbing against the windings will wear through the enamel insulation and short a few turns together. The winding then looks like a transformer with a shorted secondary so the shorted windings get very hot even though the current draw from the mains may still be within the fuse rating.
 
These days good re-winders are few and far between, so could be a replacement motor job.
Probably nothing to do with the milling work at all unless the motor had been badly overloaded in the past.
 
Billy.
Clive Hartland16/10/2011 16:07:20
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2929 forum posts
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Motors with centrifugal switches tend to 'arc' the switch, and over time can stick together.
This happened on my sawbench motor and the end result because it was an obsolete type of double ended shaft model meant a rewind. £225 for that but now right as rain.
Without doubt a field coil problem.
A rewind and a new motor, there is not much in the price so take your pick.
 
Clive
The Merry Miller16/10/2011 19:54:19
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The overwhelming list of replacement motors seems to be of the TEC brand, has anybody tried them out. I assume they are made in India or some other country of manufacturing repute!.
 
Len.
 
 
 

Clive Hartland16/10/2011 20:29:29
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2929 forum posts
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I have just looked at a couple of sites with TEC motors and there is one with price reductions based in Sheffield.
Its worth going through some of these sites to see what they are offereing.
 
Clive

Edited By Clive Hartland on 16/10/2011 20:29:51

The Merry Miller16/10/2011 20:49:53
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484 forum posts
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Here's a good one on fleabay.
 
 
http://www.ebay.co.uk/itm/Electric-Motor-Single-Phase-37Kw-1-2HP-1400-rpm-/270615983560?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3f01f835c8
 
Len.
John Stevenson16/10/2011 20:53:13
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5068 forum posts
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Yes, Use loads of them.
 
Doing a conversion at the moment for an ex Myford VM-B milling machine that's missing the spindle, pulleys and motor.
 
Idea is to replace the front bit of the head where the spindle goes with a 1.1Kw TEC 2 pole motor with a custom shaft that will take ER25 collets.
 
Using an inverter this should give me a speed of 1,000 to 6,000 revs which will be ideal for this CNC based machine.
 

 
 
State of play at the moment, Midlands show has gotten in the way.
 
 
John S.
The Merry Miller16/10/2011 21:01:25
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484 forum posts
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A friend of mine is now trying to convince me to take this opportunity to go three phase with an inverter.
I'm looking at what's involved in the switch and the cost implications.
 
Len.
 

John Stevenson16/10/2011 22:38:12
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5068 forum posts
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Len,
Good move to go 3 phase with inverter.
 
John S.
The Merry Miller17/10/2011 14:39:56
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484 forum posts
97 photos
 
 
John S.
 
In your experience how do the bearings on the TEC 1450 rpm motors cope with doubling the armature speed.
 
Len.
 
 
John Stevenson17/10/2011 20:28:42
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5068 forum posts
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Len,
 
Never a problem, the smaller motors have 20mm 6204's which are good for 15,500 grease filled and the larger ones have 25mm 6205's good for 14,000 with grease.
 
These are good quality bearing specs, they have exactly the same bearing for 4 pole 1425 as 2 pole 2,800 so if you double the 4 pole motor speeds you are only running at standard 2 pole revs.
 
John S.

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