Milling in ceramic (Macor)

[hubihubi2]

Hi All,

I am the beginner in milling.
I have to calculate the spindle speed and feed rate for machining special material called Macor (machinable ceramic).
The producer of Macor recommends the following machining parameters:
Cutting speed . . . . . 20-35sfm (6.1-10.7m/min)
Chip load . . . . . . . .002ipt (0.05mm per tooth)
Depth of cut . . . . . . 150-. 200in. (0.38-0.51cm)

I have to convert those parameters to spindle speed [RPM] and to cut feed [mm/min].

I have already calculated the spindle speed according to the following formula:
1. I know from above that recommended cutting speed is in range 6.1-10.7m/min. I would choose middle value, i.e. 8.5m/min,
2. I multiply cutting speed by 1000 = 8500,
3. I multiply tool diameter (e.g. 10mm) by Pi = 31.415 ,
4. Then 8500/31.415 = 270.6[RPM].

Cut feed was calculated as follows:
1. The example tool is flat mill 10mm (diameter), with four flutes,
2. Cut feed [mm/min]= spindle speed RPM x chip load[mm per tooth] x no of flutes,
Cut feed [mm/min]= 270.6RPM x 0.05[mm per tooth] x 4 = 54.12 [mm/min].

I would like to ask whether those calculations are correct?
The feed rate is very slow.

 

[MikeHalloran]

Eyeballing, the numbers seem about right.

It's important to realize that Macor is not ductile, so you are not machining it in the normal sense; you are cracking off very small pieces of it. It does so easily, because it comprises roughly spherical particles about .001" in diameter.
DO NOT reduce the feedrate below .001" per tooth; doing so will just increase tool wear, and not give you a better finish.

Also, rig up a vacuum cleaner to pick up the dust as soon as it's cut off the blank, i.e. running and pointed at the tip of the cutting tool. Macor dust is just the right size to get into the working parts of any machine tool, and hard enough to turn said tool to junk.



Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

What Mike said.

"The feed rate is very slow. " Yes, but in addition to not going too slow per Mike's comments, don't go too fast or you will break out large chunks of the material, and/or shatter the workpiece.