basic question for cnc people..

[realstone]

Without getting too technical could someone tell me the general relationship between RPM's on a fingerbit for a hard material (i.e...red dragon, abs. black ) and cut rate.
we have an ancient cnc and had to get new fingerbits made. the new ones seem to glaze up, we tried speeding up the RPM and lowering the rate (ipm) i just wanted to know if that makes sense or not?

[Marmi Natural Stone]

You need to lower your rpms on hard materials. Too many rpms and a slow feed rate can glaze your bits.

[ChrisYaughn]

Slow down the rpms when you slow down the ipm. That helps keep the tool from glazing. Also lots of water

[realstone]

thanks for the input! i will try that on the next run

[ash20ash]

Just like any diamond tool, You want it to "work" a little to get through the material.
I'm gonna guess here on the amps............... MAybe about 20% increase when loaded vs. no load.

I would think the person/company could supply you with the correct setting for both. For normal material that is.

[Nick]

Are you in Vero?

[scott m]

THe easy way to look at it is this.

If you speed the rpms up they diamonds will get rounded over and then protect the matrix and not allow new diamonds to be exposed.....thus glazing and no cutting and eventually snap....

If you slow them down, you are working it real hard, thus not giving the diamonds time to round over. YOu will wear the bit way faster this way, but it will stay sharp.

RPM and IPM need to be adjusted together to keep it working correctly. When in doubt, use a slower rpm as opposed to higher.

[Ger Vanderbas]

Good Question, and good answers folks.

This is a question I often get from fabricators, especially those that come from other cutting industries where the material is more consistent.

Because of the natural formation of the stone there can be subtle, and not so subtle variations in the hardness and density, thus machinability of every stone, and with stone this can change even within the same stone.

The second issue here is the torque/RPM curve of the machine. Each CNC machine has a unique torque profile which is determined by the spindle motor, any transmission involved, and is affected by the workholding and toolholding mechanical factors.

In general there is no BASE formula that is ideal by material, unless you can know all these things, which you can't. There is also no foolproof mathematical formula to know for sure when increasing speeds or decreasing is correct because these varying properties do not always respond precisely the same as "similar" material.

The truest way to find the proper setting here is to find someone with a similar machine, to find the setting that fits best, (alot of people do this by amps, or by sound, but neither of these things are very reliable predictors of ideal speeds) and then begin to compile lists of known safe speeds in groups of materials based on actual results.

From a safe speed, you can determine if your speed increases are going to be worth the decreased life. Generally the gains from safe speed to highest possible speed affect throughput times marginally enough where you may find that the tool life is most important. There is always a sweet spot somewhere, but I think it may not be worth the trouble to find it if you can find good enough speeds and be done with it. Remember, the idea with a CNC is not to be fiddling around with stuff too much and getting the material on and off. Set the tools right, find a good speed, and bang out some footage.
You will then begin to be able to extrapolate a formula from that to give you good enoughs for every material you encounter eventually.

Just writing because I had a minute... Hey everyone! Hope you're all kicking butt...

Ger

[realstone]

thanks again for the input,
Any one who has had the machine we do has already replaced it by now - its an LTEC, its painfully slow but not as painful as doing stuff by hand - IMO. I will definitely slow down the RPM cause we are not getting much too wear as scott has pointed out. Hopefully we can keep this thing going , for a little while longer anyway...

[jonnyrue]

Slowing down the RPM gives the diamonds time to work and keeps them open. Try a router with a softer bonding compound; they don't last as long but sound sweet, don't scream and get the job done without moving your piece around. We took nearly a year to find a finger bit which suited our Bavelloni CNC.