machine lathing

[ayk_driver]

ok im in a machine shop for a class and we use metal lathes... could i possibly use one of the lathes to cut my comms? we can take very little off in one cut so i think it mite work.... what cha think?

[Moo-Shoe]

biggest issue in using a full sized lathe is making sure your comm is lined up correctly... you don't want to cut a taper into your comm even if you're only taking a little bit off at a time...

Other than that, you shouldn't have any major problems using a full sized lathe on your comms.

Practice on an old junker comm first though, just to be safe. :)

[adim_x]

use a 4 jaw chuck, and indicate the comm in, i dont see why it wouldnt work, if you used nice newer lathes i think they would work better than our small cheap comm lathes we buy,

[John Stranahan]

Make a stepped Aluminum or Brass bushing to hold the comm end of the arm in a drill chuck placed in the tailstock. Drill the bushing undersize and ream it to 1/8 inch. Oil it. Turn the other end of the arm with a collet chuck or other true running chuck. I used to cut my mod arms on a bigger lathe. Worked great. Had power feed.

[ayk_driver]

no i wont taper it cuz the machine isnt set up that way.... i think i have an old comm ill have to look... we only have 3 jaw chuck but that should be good rite?

[John Stranahan]

My three jaw chuck indicated very true. That's what I used.

[TyceCCSU@aol.com]

The only problem i see with truing up with a machine shop lathe is the possibility of snaging a comm segment and ripping it completly off the comm. thats why the mini lathes are so great, they have the rubber o ring as a drive mechanism, if you snag something, the lathe stops dead while the motor keeps running.
I see no issues with a full comm up until the point of about .275, anthing less than that you likely to tear that baby into scrap metal

[John Stranahan]

I have seen comms shredded on the little lathes. The cure for this is not to start the cut from the end. Start about 1/16 inch from the end and advance the bit until it just touches the comm. The bit will leave a little ring. This is actually easier to do on the big lathe with a man size feed wheel. Never shredded a comm on the big lathe (or the little lathe).

[ayk_driver]

ok thanx for the help guys........

how think thould i go after multiple cuts like not at one time but over a year say?

[John Stranahan]

After a small comm gets to about .270 the motor starts getting weak. The plastic is about .260. The comm is about .290 inch diameter when new.

[ayk_driver]

how much should i take off for a first cut?

[Railman]

"How much do I take off the first cut?"

As much as you need to. Mark the com with a sharpie or majic marker, & start with the minimum amount that will make a cut. I've cleaned up coms with as little as .002" total cut, but the average is probably more like .005" to .008".
Like I said, just take as little as you can on your first pass, & then see if all the black marker is removed. If not make another light pass untill it's all clean. Be shure to clean out the com slots with an exacto blade after the cut is complete. I like to take a very small amount off the knife tip so as to reduce gouging the bottom of the slot. You will wan't to drag it through the slot with the square (not sharpened edge) edge of the blade. I also like to use a small piece of lexan body scrap to clean slots. It will remove the garbage without damaging the slot. After the slot is cleaned out, take a ball point pen, & lightly drag it across the com slot. This will assure that the slot won't snag a brush, & damage the com. Don't over do this step. It only takes a little pressure. Once your done, just clean arm with motor spray, & shake off excess.
Hope this helps,
Joe

[John Stranahan]

limit your cuts to a maximum .001 inch deep. This guards against removing more copper than neccesary. You can take lighter cuts, if you think the comm will clean up with just a tiny infeed.

[ayk_driver]

ok kewl sounds good guys ill just check with my machine shop teach to see if i can do this....

[popsracer]

One of the most inportant things in cutting a com is trueness
after your done. If it is out of round by even a few thousands, the brushes will bounce and cause arcing.
I your chuck will hold a shaft that small ( some wont) then try it on a old motor first. I wouldn't try to cut without supporting both ends of the com shaft. It is very easy to deflect a small shaft like that while cutting and cause a tapered cut. Check with a dial indicator before cutting. More than .001 out of roundness on the shaft end, then I woulsn't cut on that lathe.
25 + years as a Machinist/Maintenance Mechanic.

[ayk_driver]

yeah they will go that small so me happy to no it will work... keep forgetting to task the teacher :S im such an idiot lol