[ynneb]

I am doing a lot of cutting out of shapes.
I am at present using a 12mm bit. I was thinking that a 6mm bit would be better suited for cut outs since it doesnt have to remove as much material as a 12 mm bit. Is this theory right?

Also, can I increase the feed rate because the smaller bit doesnt have to do as much work?

Is an even smaller bit even better? What is the cut off point between increasing cutting efficiency, versus a bit that will wear out much quicker?

Edit: I was thinking that a 6mm bit would have the same cutting surface area as a 12 mm bit and would spin the same too. That is why it should cut faster. Is my thinking right?

Is a 4 blade cutter even better? If so why dont they make them as standard? Is it just a case of economics or is there other reasons for 2 blade cutters

[ger21]

It has a lot to do with the material your cutting, as well as type of bits and diameter of bits. You can cut faster with larger bits, because you'll reach a point where the smaller ones aren't strong enough and will break. They also vibrate more, due to being not as strong. Give me some more info and I'll try to help you out.

[cnczane]

I remember reading that feed and speed are all about getting the heat into the chip and keeping it out of the tool. Hot chips (or sawdust) mean that much less heat to dissipate in your bit and motor.

Feed and speed both affect "how big a chip" and "how hot it is."

Surely, tables are published (Machinists' Handbook?) for different materials and cutters?

[cnczane]

In fact, I saw it here. I'm reposting Rekd's 7-19-2003 response [#62] to flyrc's "Does this look like a CNC machine?" thread [#1015] because of the relevance. If it's not okay, I apologize and expect a PM.

[Begin Rekd]
flyrc,
Running 30 ipm at 2000 rpm = .0038 chip load on a 4 flute or .0075 on a 2 flute. That's heavy even for a 1/2" cutter.

You want to run about .0005 or .001 chip load on something that small (I'm being very conservative, calculating for harder material, substitute numbers that work for wood). To calculate the feed rate, use the knowns CL = Chip Load, RPM = Max RPM for cutter, FL = Number of flutes. Calculate the max RPM you can (safely) run your machine. (I generally run mine at 95% of max RPM)

CL x RPM X FL = IPM
or
.0005 x 2000 x 4 = 4 IPM :sleep:

To calculate the chip load for what you're running;

IPM ÷ RPM ÷ FL = CL
or
30 ÷ 2000 ÷ 4 = .0038

Keep in mind that the ply will have glue in it, which may be clogging your cutter as well, shortening it's life.

HTH

Rekd teh Inebriated


--------------------------------------------------------------------------------

Matt
CNCzone Administrator
Mastercam X Beta Test Site
San Diego, Ca
[End Rekd reply]