Com turning

[Intimidator#3]

How offten do you turn a com? Is there a set # of Brushes to go through before you retrue the com, or just when power is going away?
Kevin

[[email protected].]

Kevin,

I retrue the comm every time the motor comes apart. I DEFINITELY reccommend that you never run new brushes on an old comm surface.

It may seem that you will get less use over the life of the comm with frequent retrues, but its actually the other way around. If the comm is only slightly worn when you retrue it, only 2 or 3 thousandths will be removed to retrue it, and you will get 5 - 8 rebuilds on a typical armature. On the other hand, I've had occasion to scrap an arm during its first rebuild because the trench in the comm was so deep. Usually, that was on a rental car motor, but several 'racers' have submitted arms that badly worn for reconditioning. Makes ya wonder....

[Intimidator#3]

Monty,

Anouther question for you, I was turning a friends arm sundaynight (I've only turned maybe 12) an it seemed to make a squeeling noise when cut an the slots between the com plates filled in w/ shavings real bad, none of my others have seemed so "soft" could I have been trying to take too much off, or would the shaft on the arm be bent, or any other reason this could have happened? The com seen like softer copper.
thanks
Kevin

[phlirv]

:cool: Are you using a diamond bit? They are the ONLY way to go. It almost sounds like you are trying to use a carbide bit. They have to be sharpened after 2-4 uses. The diamond last for ever and do a beautifull job.
PHIL I.;)

[Intimidator#3]

No Its a Prime Racing Diamond Bit
Kevin

[[email protected].]

Kevin,

I'm almost willing to bet that you have an RJR arm, while the others were ProSlot or Koford. RJR comms are oxygen free copper, which is more difficult to machine. Mr. Root explains that the conductivity should be better - and he isn't wrong. Its just that the difference is VERY slight indeed.

I find that Kerosene or Naptha work well as light cutting fluids for these tough cases. Take a minimal finish cut, wet, and run the lathe a little slower than usual. It should work out.

If that isn't it, you may have damaged the diamond tip. They chip easily, but last almost forever IF you take care to avoid shock like hitting the arm shaft or similar. Never turn anything but a comm with your diamond bit!

[Intimidator#3]

It was an RJR, Ill try using the lighter fluid/naptha an slowing the cut
Thanks again
Kevin

[phlirv]

;) I also use a black permanent marker. Do it on the lathe and cut before it dries! It also showes ( with bi-focals I need all the help) when it still needs another fine cut. I also do the arms often so I take very fine cuts and have some older arms that have had 8-10 cuts and still run well...:p As well as 6 eyes will let me...
PHIL I.

[[email protected].]

Phil,

Paul Ciccarello uses the black marker as well, and he's a lot younger than either of us!

On Chicky's advice, I tried the marker for a while and did learn a few things about feeds & speeds while improving my comm finish, but it takes way too long when you start many days with a few dozen armatures to true.

Kevin,

On the subject of comm finish, please note that you CAN get too shiny a finish, in which case your breakin just takes longer. What you want is something resembling the surface of a compact disk: It will refract light into a mini-rainbow as you move it slightly under a lamp. This is caused by microscopic parralell grooves, and these in turn are what sculpt your brushes as you break the motor in.

[phlirv]

:cool: Learn something new!! I used to make contact lenses and learning NOT to rough cut....Anyway I strived for that mirror finish. I allwas had to take longer to get full contact on new brushed. After trying the water method, back to back, I found that it was worth it!! Now I know why!
Thanks Monty!
ol' 6 eyes PHIL I.:cool: