NM-200 - strange behavior?

[kvom]

I was machining some blocks of grey cast iron this weekend, needing a profile.

My first "attempt" was just to do a single cut with a 3/4' HSS 4 flute endmill, DOC=.200", radial cut ~.300". G-Wizard called 450 rpm, 4ipm.

Well this was not a success, Once the endmill hit the material the whole machine started vibrating and the head got knocked out of tram along the x-axis. Time out to retram the head and snug down the bolts extra tight.

Next try is with a 1/2" HSS endmill, DOC .100" full width cut. On the Bridgeport I run this at 700rpm and 5ipm and it cuts like butter. On the Novakon I get red sparks and the fluted melt off in 15 seconds.

My conclusion here is that the RPMs don't seem to be accurate at low speeds, since it appears that the SFM is a lot higher than indicated by mach3. There's also a lot of vibration at lower speeds.

I finally just used a 5/16" carbide at 4000 rpm, 10 ipm, which had no problems, although it took quite a bit longer.

[ihavenofish]

I was machining some blocks of grey cast iron this weekend, needing a profile.

My first "attempt" was just to do a single cut with a 3/4' HSS 4 flute endmill, DOC=.200", radial cut ~.300". G-Wizard called 450 rpm, 4ipm.

Well this was not a success, Once the endmill hit the material the whole machine started vibrating and the head got knocked out of tram along the x-axis. Time out to retram the head and snug down the bolts extra tight.

Next try is with a 1/2" HSS endmill, DOC .100" full width cut. On the Bridgeport I run this at 700rpm and 5ipm and it cuts like butter. On the Novakon I get red sparks and the fluted melt off in 15 seconds.

My conclusion here is that the RPMs don't seem to be accurate at low speeds, since it appears that the SFM is a lot higher than indicated by mach3. There's also a lot of vibration at lower speeds.

I finally just used a 5/16" carbide at 4000 rpm, 10 ipm, which had no problems, although it took quite a bit longer.

O_o

was the spindle running the right direction? i ask cause i did this accidentally recently and had a similar result. vibrations, heat, but was still "cutting" so i was left scrathing my head until i actually saw the spindle wind down.

on the nm200 ive done cast iron with a 1/2" carbide bit at 3500rpm and 20-30ipm and it cut like warm butter.

[kvom]

Spindle direction was correct. I think that the mill just doesn't like slow RPMs.

I don't have any large carbide endmills; the 5/16 worked fine.

[ihavenofish]

Spindle direction was correct. I think that the mill just doesn't like slow RPMs.

I don't have any large carbide endmills; the 5/16 worked fine.

i forget if yours is a series 1 or 2. ive run the 200 at 500rpm with a 7/8" cutter in steel and it was fine.