Comm Cutting question

[digex]

How do I know when my carbide bit needs sharpening or replacing? Where would I get it sharpened? Also, what is happening when after I cut a comm, it's all rough instead of shiny and smooth? Only happened once and when I re-cut it, it was ok, but at first it was rough like sandpaper?

[XXXER]

I am not sure, but my best guess would be send it to the manufacturer, and with the 'rough' comm question, maybe you did not use cutting oil, or you went to fast/slow, made bad passes, i don't know. :D

sorry, i do not know a whole lot about Lathes

[very low budget racer]

umm... can you sharpen carbide bits? get a new one they are no more than 30 dollars.

[SmokeyNDBandit]

Use a good magnifying glass or a scope. I use an old eyepiece from a junk telescope to check the bit tip. You can find a machinist friend who can sharpen for you. I use a fine texture diamond hone called EZ-Hone (or something like that). Looks like a big nail file. Any good knife shop should have one or maybe they can order one for you. Mine was about $15. Carbide bits need a little touch up after 3-5 cuts depending on how deep you're cutting with it. Just a couple of swipes on the three sides to get a sharp point again.

The rough texture sounds like a piece of copper debris got caught between the comm and the bit. After each pass, shut off the motor and brush off or use compressed air to clean the bit. Remember to only skim (don't cut) back and forth even if it means having to do multiple passes. Also turn the wheel nice and slow. Be very patient.

You don't have to drop $30 for a new bit every time it got dull. That could get very expensive very fast.

[Grizzbob]

True, good carbide bits don't have to cost $30, just go to a tool shop & you should be able to find them for about $1.50 apiece.... :)

[jeepinator]

A little cynical here, but it would be far better to fork out the big bucks for a diamond bit. You will never, ever have to worry about it again.
If I were to guess, I would say I have more than 100 cutting sessions on my bit. It works just as good today as when I bought it 5 years ago.
I do not even know what they are going for these days, but I paid $75 I think. Well worth it in my exceedingly humble opinion :p

[SmokeyNDBandit]

Jeepinator - cynics are welcome :) "Bryceum" on a recent comm lathe thread mentioned getting a diamond bit after being proficient with a carbide bit. Both of y'all have very good points.

[digex]

Grizzbob, could you go into a little more detail on the hardware store part? Would I ask for a carbide bit? where would it it most likely be? What section would you find it in? And yes, very low budget racer, you can sharpen the bits, I just don't know how to do it myself.

[Grizzbob]

Well, it's hard to do that if you don't live in my area(Tulsa)...here we have a tool shop called Du-Mor tools that carries just about everything, including lathe bits, but its not a standard hardware store. try looking through your local Yellow Pages for Machine tools, or all tools, I bet you'll find several possibilities. Oh, & I also agree that when you feel proficient enough to take advantage of diamond bits, it's an excellent buy, they do seem to last forever.... :)

[Grizzbob]

Oh, I almost forgot, when you find one & go, bring a bit with you, it'll make it much easier for the shop to help you find a proper replacement. Also, there is a company called McMaster(I think that's their name) that I'm pretty sure sells them, & they might have a web page.... :cool:

[Railman]

Digaex, Did you figure out why it cut rough the 1st time? There are many factors that can cause a rough cut. To name a few: drive motor vibration, armature vibration, bit not cutting at proper point on com, armature moving back and forth in ways, too much rpm,
not using a proper lube, jerky feed rate, dirt or copper in armature ways, armature shimmed in too tightly & not allowing to ride in bottom of way, bit holder cross slide assembly having too much play,
& of course a dull bit. The bit will touch up to better than new if done with a diamond hone. I bought a set of 4 hones at Harbour Freight for about $10. I find a 35x power scope is indespensible for cutting coms & checking the bit...Radio Shack $10 +-. The bit should cut at a point about .002 above the center of the com/arm shaft. Any questions free advice available! LOL, good luck.