CNC vs Manual mill tool sizing

MwTech Inc · Oct 21, 2021

OK. very adept at manual machining from a Bridgeport up to my #4 vertical.

But with a VCM on the way, watching hundreds of videos it seems that everyone uses a 1/2 end mill to cut everything taking a jillion passes.....

It is actually faster/better to make a jillion passes rather than using a large cutter ?

Now, if I have a good size bit of material to remove, I use a 1" or larger and just chew right thru....

maybe I will need to "re-learn" cutting with a VCM???

VCM i'm getting has 7 hp spindle

Remember i'm not competing in the CNC parts market so cycle time does not really matter to me

Garwood · Oct 21, 2021

It's a VMC.

It depends on the machine. An early 80's Hitachi Seiki weighing 10k lbs with a 40 taper spindle is on the lighter end of the scale as VMC's go. If it's in fair shape as far as spindle and ballscrew thrust bearings go, you should be able to take whatever cut you want with a 1/2" endmill within the HP limitations of the spindle motor.

Quality CNC mills are vastly more rigid than manual machines for a given weight and HP in general. And CNC's have excellent flood coolant and you climb cut with them.

You'll figure it out.

My advise though is to forget HSS endmills. Some people will say HSS is good to learn with. I think it's terrible crap. Buy some decent carbide endmills to start with and skip right past that HSS crap.

mhajicek · Oct 21, 2021

A CNC with fast max feed rate and a fast control is generally faster doing dynamic milling, high axial, low radial, many passes with feeds and speeds calculated to account for chip thinning. Especially in harder materials. If your machine is a beast, or slow, you may be faster with a high radial, but that requires much more rigidity and HP.

Steel cutters are fine for plastic, but even there, there are quality carbide cutters that do much better.

7HP isn't a lot for a CNC.

Zeuserdoo · Oct 21, 2021

VCM What?

MwTech Inc said:
OK. very adept at manual machining from a Bridgeport up to my #4 vertical.

But with a VCM on the way, watching hundreds of videos it seems that everyone uses a 1/2 end mill to cut everything taking a jillion passes.....

It is actually faster/better to make a jillion passes rather than using a large cutter ?

Now, if I have a good size bit of material to remove, I use a 1" or larger and just chew right thru....

maybe I will need to "re-learn" cutting with a VCM???

VCM i'm getting has 7 hp spindle

Remember i'm not competing in the CNC parts market so cycle time does not really matter to me

Thoughts to myself while reading this.
"VCM...?"
"VCM...?.....hmm"
"Vertical Cutting Mill?"
"Variable Cut Mill?"
"Very Cutting Milling?"

It took Garwood's post for me to figure out what you were talking about. :crazy:

Garwood · Oct 21, 2021

mhajicek said:
7HP isn't a lot for a CNC.

That's what Haas ran up until about 2010.

His Hitachi probably has a Fanuc 5KW/7.5KW spindle motor. That's the same thing as 30 Haaspower.

mhajicek · Oct 21, 2021

Garwood said:
That's what Haas ran up until about 2010.

His Hitachi probably has a Fanuc 5KW/7.5KW spindle motor. That's the same thing as 30 Haaspower.

No, it's half. A Haas "30 horsepower" is 15 HP continuous.

MwTech Inc · Oct 22, 2021

OK finger fumble......VMC...LOL

Ok get it about the speed and feed thing and the climb milling...

Mtndew · Oct 22, 2021

MwTech Inc said:
It is actually faster/better to make a jillion passes rather than using a large cutter ?

Typically yes, it's a lot faster. But it also depends on the part shape.
You can use the HSM Advisor and play around with the settings to find the difference in MRR between hogging and the Dynamic style paths by using the depth of cut and stepover within that program.
It's a fantastic program and well worth the money once you get rolling with the new cnc.

Advanced CNC Speed And Feed Machinist Calculator - HSMAdvisor

Garwood · Oct 22, 2021

mhajicek said:
No, it's half. A Haas "30 horsepower" is 15 HP continuous.

I believe Haas's claimed 30 HP is actually 300% of the 30 minute rating of the spindle motor and drive they use. The actual continuous rating is more like 7.5HP.

The 5/7.5KW Fanuc motors used in many VMC's in the 1980's throws down a real 7.5HP forever or 10HP for 30 minutes. In real world use you can run them indefinitely at 10HP while cutting because you aren't in the cut that long.

So, in my opinion, having used both and having had both off the machines laying on the bench and taken Haas and fanuc spindle drives apart I would say the 5/7.5 KW Fanuc motor/Drive setup is actually way more powerful than what Haas used for it's first 20 years.

MwTech Inc · Oct 22, 2021

I like what Garwood says.......

CarbideBob · Oct 22, 2021

Zeuserdoo said:
Thoughts to myself while reading this.
"VCM...?"

If you have to aske about a spkel mistake and do not undkesatn you are in the wrong place.
Bob

mhajicek · Oct 22, 2021

Garwood said:
I believe Haas's claimed 30 HP is actually 300% of the 30 minute rating of the spindle motor and drive they use. The actual continuous rating is more like 7.5HP.

The 5/7.5KW Fanuc motors used in many VMC's in the 1980's throws down a real 7.5HP forever or 10HP for 30 minutes. In real world use you can run them indefinitely at 10HP while cutting because you aren't in the cut that long.

So, in my opinion, having used both and having had both off the machines laying on the bench and taken Haas and fanuc spindle drives apart I would say the 5/7.5 KW Fanuc motor/Drive setup is actually way more powerful than what Haas used for it's first 20 years.

I don't think they're stupid enough to leave themselves that wide open to a false advertising lawsuit. Every bit of their documentation, power curves, etc. say 30HP momentary (ten minute, I think), 15HP continuous. To say it's actually half of that, 7.5HP, is a bold claim, and requires proof.

Roughing Ti with a 1/2" 7 flute, 1.25" deep,.020" radial, at 180IPM, would show about 30% on the spindle load meter, give or take. According to this HP calculator:
Tooling Pro

that cut requires 7.515HP at the tool. If the spindle is 90% efficient, that's 8.350HP at the motor, which puts 100% at 27.83HP. Not far off for napkin math.

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