41 replies to this topic

[tazman]

Just about to run out – any suggestions (brand - where can I get it, etc...).

[Zippity]

Mark your comm with a black "Sharpie."

 

The ink is a wonderful lubricant as well as highlighting any shallow spots. 

[Cheater]

Zip is right, in my experience cutting comms.

 

When he says 'mark,' he means to color the entire surface of the comm with the Sharpie.

[gotboostedvr6]

A properly-adjusted comm lathe needs no cutting fluid.

 

However, I do lube the V-blocks to slow their wear.

[Bill from NH]

Sharpies do work. If you want a bottle of fluid, Cobra, the comm lathe people in Utah, sell it. Unless you have a local slot car shop, inquire at a mailorder house such as PCH or Slot Car City.
 
I've cut comms both wet and dry with diamond bits. I prefer using fluids. You're correct about lubricating the "V" blocks. If you don't, the anodizing wears off and they'll soon unusable.

[havlicek]

As per above, no cutting fluid is needed at all, but a Sharpie played against the spinning com does seem to smooth things out and makes seeing the low spots easier. If you see a degradation of the cut, it's time for a new cutter (diamond is much better than either HSS or carbide).

 

Other than that... comm cutting fluid is the answer to a question that didn't need to be asked. 

[Bill from NH]

Do it whatever way works for you and so will I. I've cut comms since the the late '90s and I prefer using a fluid. I would guess using a machining compound with my Unimat in the '70s got me in the habit.

[havlicek]

Do it whatever way works for you and so will I.

 
Doesn't that go without saying?

[MSwiss]

I've cut 10,000 comms in life, give or take a few thousand.

 

I've never using a cutting fluid, but I've also always used a diamond.

 

That said, my machinist expert customer/friend said it could be of value, to use it, if using a carbide or HSS cutting bit.

 

And as mentioned, regularly lubricating the arm supports is very important.

[zipper]

With some harder comms the felt pen may give a little better result.

[Ramcatlarry]

Tap Magic cutting fluid should be available most anywhwere. About $1/ oz from McMaster-Carr. 4 oz can last a long time.

[Bill from NH]

Rick Ortogero, if you still want comm cutting fluid after all this discussion, PCH has it. 
 
R/C guys were arguing 15 years ago whether black, blue, red, or green Sharpies were the better color.  

[glueside]

I have used WD-40 since I originally started cutting comms and still use it when I have to cut comms.

[Dan Miller]

Mike is correct. 

 

Natural diamond, with a good edge, with no fluid, is the way to go.

 

Next would be a sharp polycrystalline man-made diamond. What you buy today, as a diamond tool, is most probably a PCD tool and not natural diamond. The cost of natural diamond commutator tools is $300 now days. For $100 you get PCD which is what comes with today's slot comm lathes. 

 

If using a well-honed carbide tool, it may well benefit from cutting fluid use. High-speed steel tool, as a rock bottom choice and then only quality made, not imported crap steel. You really should pass on carbide or HSS as PCD tools are cheap.

 

Using a marker as an indication of cut is OK. I doubt it lubricates to any substantial degree but the visual assist is good.

 

I see many guys take a ballpoint pen to the commutator slots to remove the burr left from cutting. Do not do this. Narrow down a #11 X-Acto blade and drag it parallel to the side of the slots. You do not want to open up the width of the comm slot, which is what beveling the edge of the slot does. When you run a ball or round shape object down the slot, thinking that you are removing the burrs, you are in effect opening up the width of the slot. That promotes arcing. If I could make an armature with .001" comm slots I would do so.

[gotboostedvr6]

That^

[havlicek]

...again, no cutting fluid and a diamond tool is all you need.  Oh and, running a ball point pen down the slots is certainly not necessary, but I'll take Dan's word for it being potentially damaging.  I wouldn't know, because I've cut well over a thousand coms and never done it (*or used cutting fluid), and never had to, or wanted to.

[Phil Smith]

Milk.

[Phil Smith]

I expected to catch a little grief for the milk comment, but I guess it sounds such a really bad attempt at humor that it didn't warrant a response.

 

But it wasn't a joke! This forum is for professional machinists.  These guys know their chit. https://www.practica...-copper-176234/

[Bill from NH]

I would wonder if its effectiveness was dependent upon the milk's percent of butterfat? i didn't see that these posts addressed that. Then I wonder if Crisco would give you anything, other than fat-in-the-can.

[MSwiss]

That back and forth also suggested diamond tooling.

Who would make a mess turning a slot car comm with milk, when you get a great job with a dry diamond?

[Bill from NH]

I like Jeff Strause's suggestion of using WD-40, for after I run out of Cobra comm cutting fluid. That may be awhile, since there aren't any race tracks in NH that currently run built motors.

[Phil Smith]

I agree about the diamond cutter and not using any fluid. I don't use fluid on my mini lathe unless I'm having trouble. The less mess the better. Chinese carbide inserts are cheap and have multiple cutting tips on each one, so it's not a big deal if they dull quickly, although they seem to stay sharp a long time even without fluid.

 

These are PCD (diamond) inserts for lathe parting tools. They might be adaptable for use in a comm lathe. https://www.ebay.com/itm/252815456004

 

There was a thread on that forum in which several guys posted, swearing by bacon grease for some type of material turning that I don't recall. Like milk, the smell would get unpleasant.

[wbugenis]

The PCD turning tool # E4 from J&M Diamond tool is the best value out there:

 

http://www.diamondto...m/turntool.html

 

If you are "having trouble", you have a problem with your tool or the setup that  cutting fluid won't fix.

[Phil Smith]

Why would you say that? Pro grade lathes pretty much all have flood coolant systems on them.

[CDavis7]

I always liked a black sharpie. It served dual purposes:
1. Provided some lubricant (though I had equally good results without it)
2. Made it easier to determine that there was a full cut without low spots

I always used a diamond bit