View Full Version : Fed up of these damn Dremels

John Stevenson
01-31-2008, 06:32 PM

Well not quite a Dremel but an interesting piece.
The job was straight forward, the bearing journal on the tailstock end but as I finished the job I noticed something queer with it.

Anyone spot it ?


01-31-2008, 06:43 PM
The bearings are magnetized.

01-31-2008, 06:46 PM
It looks like the part where the brushes ride is magnetic.

01-31-2008, 06:49 PM
Are those bearings or a slip ring?

John Stevenson
01-31-2008, 06:50 PM
Missed that, no that's not the answer in fact I can't make out if the turnings are stuck to the brass or if they are laid on the sloping back tray.

01-31-2008, 06:50 PM
Well Sir John,

I see what looks like three slip rings, and this unit also has a commutator.

Something excites something else.


01-31-2008, 07:29 PM
How about showing us a picture of the tailstock end so we might have a clue as to what your talking about.

John Stevenson
01-31-2008, 07:40 PM
Skeeter has it.

The rotor / armature is equiped with AC slip rings and a DC comm.

Never seen one before or at least never noticed them so I wondered if it was either an AC/DC generator or a rotary convertor.

Turns out it's an AC motor with DC control of the rotor.

It's quite old and was the forerunner of the VFD drive.
You feed the rotor 440v 3 phase to the slip rings and the whole brush gear on the comm is able to rotate driven by a pony motor that takes it's voltage from the brushes.

The whole idea is to keep constant speed under varying loads.
As it speeds up it generates more voltage which winds the bush gear back and so drops the voltage.

This one is off a packaging machine and runs the machine via a gearbox at 400 rpm. Apparently they are able to keep to these revs to plus or minus 10.

Just thought it was interesting and had sod all to do with repairing the worn journal.


The Doctor
01-31-2008, 07:41 PM
I notice you're supporting it with wooden block while turning, bad shop practice:D


01-31-2008, 07:41 PM
Its out of a reallly really big dremel?:D

Ok i've been starin at it for 12 minutes and all i can see is it seems to have slip rings as well as a com....

01-31-2008, 07:42 PM
Well bu*ger me i was right!..... just slow:mad:

01-31-2008, 07:45 PM
is it one of those dual motor/generators

'cause it looks similar to the set up on some old japanese bikes that had dual starter generators

all the best.markj

01-31-2008, 07:45 PM
IIRC they are also used on offset printing press lines.

01-31-2008, 07:46 PM
Never seen one before
That is why I assumed they were bearings. I took it that you stuck them on there to keep track or something.

Motor generators are standard equipment on gas turbines. It's how they start them.

01-31-2008, 07:49 PM
I'm still having trouble visualising it, though i vaguly remember being told abou something similar in the past