ST Slip Ring Flat Spot

[matt]

I have a new ST-10 3 phase gen head.

Well constructed...including 2 brushes per ring

Unfortunately one of the slip rings have a lower "flat" spot.
If I were to remove copper from the rest of the ring to even it out, it would make one ring smaller than the other. Conservativly estimating around 3 or 4 mm (maybe 1 or 2 16ths of an inch) removed all around.

So I just want to replace the whole slip ring assembly. There does not appear to be any mention of the ring replacement in the archives of this list.

Has anyone done this before? Is it hard?

thanks,
Matt

[Doug]

I don't think you can buy a replacement I would try and machine it out.

Some motor shops will have a special lathe that can do a cut int he machine but it probably will need to be stripped because these things are so small.

You could fabricate your own.
Three ways to do this. Some generic slip rings asemblies used to be made and you machine the rough part to fit.
assemble parts and machine them together after glueing.
Cast a compelet assembly in Bakelite as was the way it was done in the old days

[lendusaquid]

Stationary engine parts Ltd do sell new slip rings. Might be worth email to them.

[Ian]

It is not as easy as I would have like it to be....

Once you have got the rear bearing off (this is the easier one to remove but you will either have to strike it off or use a hydraulic puller), unsolder the slipring fly leads from the rotor copper. Cut and remove the lacquered fabric that holds the flyleads close to the rotor and then put a long reach puller on the slipring assembly. They are pressed on but I am convinced that some adhesive is also used.

Removing the slipring also destroyed it in my case - so maybe you could just hacksaw it off.

The splines on the rotor where the slipring assembly sit will need to be cleaned up before pressing a new one on.

Pressing a new on on is easy if you can line it up square to start with. Use an annular drift to push it all the way home before remaking the soldered connections and wire-ties to the rotor shaft.

The reason that I removed my slipring assembly was that it was not square and caused the brushes to oscillate and mis track the brass rings. After I replaced the assembly the new one was still not square but a little bit better than the original one. The brushes still oscillate and mis track but this does not appear to be a problem in use.

If I had your problem today, I would not, now, replace the slipring assembly unitil I had tried to repair the original.

So what is wrong with one slip ring being slightly smaller than the other ? If you were so worried about the rings being different diameters, you could also remove both brass rings (in situ) and turn up some new ones to slide onto the insulator whilst it is still on the shaft.

I hope this helps.

Regards,
Ian

[matt]

Thanks doug for the tip.

Lendusaquid - I should have realised the Stationary Engine Parts would have spares for the ST heads. Great tip.

Thanks Ian for the tips. You just can't beat experience!!!
In answering your question, I did not want differing size sliprings due to the possibility of uneven wear.

How many hours should we expect from the standard ST slip rings anyway ?

Matt

[Doug]

Years and years if kept clean.

Odds are it would be easier and better to take the assembly to a machinist and have him chuck the rotor and machine it true.

This will sove the problem. You can't expect a pressed on part to fit properly in the first place. All Slip ring assemblies in properly built machines are machined true on the shaft.

Have a look here at a machine being stoned in the field to true up a commutaor assembly

http://www.putfile.com/dougwp/media
http://www.putfile.com/album/114831

depending on how bad and out of round ( and if the machine can be spun this one could not and had to be motored so the process is stonning not cutting ) brush wear and arcing can be significantly increased

[M61hops]

Matt: how wide is the flat spot?  If it is less than the width of the brushes so that it doesn't make them move in their holders or catch on the spot maybe you should just leave the slip ring alone?  Or it wouldn't hurt to have one slip ring smaller as long as there is a reasonable amount of material left after turning it down.  It is a lot of work to replace the ring if you don't have to!  I would even consider sleeving the offending ring with a new ring of brass over it if possible.  Just thought I'd throw in my 2 cents.          Leland

[listeroidsusa1]

Doug is right, the only "right" way to do this is to chuck it in a lathe. It is quick and easy to do so I wouldn't even consider replacing it until its absolutely worn out. Once machined and properly seated it'll run for years. The brush electrical load is small and there will be practically no brush wear if they are properly seated to begin with. The Chinese seem to use a nice piece of copper for the rings but be aware that some of the cheaper models (and many American made models) use copper plated slip rings. If yours are plated and they are turned THEN they would need to be replaced once the copper is gone.

[mobile_bob]

fwiw:

in a pinch one can do the following

find a piece of heavy wall copper drain pipe and is near the size needed
it can then be heated which will expand it and then slip it over the original if it is turned down too small
then chuck it up and turn the new fitted ring in a lathe.

i have done this before on a conversion where i fitted two slip rings over a commutator to convert a generator to an alternator
i used a piece of high density gskt paper for the insulating layer
it worked fabulously

of course this is a last ditch effort if there is no other way of getting a new one, or the old ones cannot be salvaged by turning them down
in a lathe.

bob g