[AMCjeepCJ]

I am having a difficult time deciding where to post this question on the forums, I highly doubt this is the best spot but after ten minutes of looking I figured I should just post my question and if I need to move it, I'll do so.

I need to figure out a way to calculate how much HP (watts, whatever) I'll need for my spindle motor for a small machine I am finishing up. Currently I am running either a 3hp knee mill CNC to cut these parts or my 24hp VMC. It doesn't register virtually any load at all on the VMC and the kneemill seems to be under no strain either. I will be cutting the exact same thing over and over and over for literally millions of inches and I do not want my larger pieces of equipment tied up on these parts.

I am using a .250" 4 flute carbide cutter .220 deep in 410 and 420 stainless. It will be cutting full width with probably a 0.003" per tooth per revolution chip load or less. (I need to be careful going much less or the material work hardens and breaks the cutter.) I'll be running between 1,000 and 1,200 rpm since the cutters last the longest in that range. It will have coolant and the cutter is cutting completely through a plate. It will be piercing through holes that have already been predrilled so the ONLY thing I'm trying to figure out is what would be the easiest way to calculate my power requirements for the spindle motor if I were to operate at around 16 hours a day? I don't need to cut these parts particularly fast, I need them to run consistently unattended while I'm not right there, so speed isn't as important as cutting reliable.

Unfortunately I know very little when it comes to electric motors so I think my questions would be (and forgive me if I word this wrong):

-How many watts would I need to cut this material or what would be the best method to calculate and/or measure this?
-Say it needs 750 watts minimum, (I have no idea,) would I look for something with 50% more peak power than this? 75% more? 250% more?
-How do I figure out peak power verses the power it can pull 30 minutes to "infinity" at a time?
-I need to run this on single phase because I will not have access to the 3 phase power in my shop for this application, does this matter?
-Is there any benefit to running a cooling jacket around the motor to pull away excess heat buildup for extended run times?
-What benefits would gearing down a higher RPM motor to my 1,000 to 1,200 rpm's give if any?

Thanks in advance, I know what I'm trying to ask but I'm just not sure I know how to word it!

[AMCjeepCJ]

PS

I have a 1hp DC spindle motor on another small CNC and this seemed to work fine if I remember correctly but I cannot currently test on that machine.

[dmalicky]

The low RPM is in your favor: Power is (ft-lb)*RPM/5252. So power will not be very high.

1/4" cutter @ 1200 RPM is about 80 SFM.
If your 410-420 Stainless is 200 BHN (250 at most), this calculator using your params...
https://www.kennametal.com/kennameta...and-power.html
says 15ipm and about 0.9 HP (assuming belt drive), or about 700W at the motor shaft. Consistent with your findings.

A high-quality continuous-duty motor of 1 HP, with good cooling air, should be able to do that 24/7. But I'd get 1.5HP to be safe.

You'll want a "continuous duty" motor; then you don't have to guess what it can do 24/7 or install any special cooling. Also it needs to be TEFC or TENV, so chips don't get inside.

Single phase in the US is generally ok up to about 1.5 HP (15A service). 3 phase motors do run a little smoother, but AFAIK it's only noticeable on lathe parts. A 3 phase motor with VFD is nice for adjusting the RPM, if you need that. Many companies make 1-phase in, 3-phase out VFDs, but AFAIK you'll need 220V service for a 1.5 HP VFD.

For industrial single or 3 phase motors, your choices will be ~1725 RPM or ~3500 RPM. If used with a VFD, the 1725 will be better suited to big speed changes, like 20% to 200% of rated RPM (doesn't sound like you need this). If not using a VFD, or VFD very near 100% RPM (60 Hz), the 3500 RPM will be lighter and less $. Running a motor much slower than its 100% rated speed requires "derating" the motor so it doesn't overheat.

Assuming this is a single purpose machine, I'd suggest either of these.
- If you only have 110V service: 1.5 HP ~3500 RPM 1-phase capacitor-start motor, belt drive (3.2:1) to spindle at 1100 RPM. Tweak rpm with a variable-ratio pulley.
- If you have 220V service and need easier RPM adjustments: 2.0 HP 3-phase motor, 1.5 HP VFD. Belt drive to spindle so 100% motor speed = 1100 RPM spindle; tweak from there.

Good motor manufacturers: Baldor, Reliance, Leeson, Marathon, Emerson, Century, US Motors...

[AMCjeepCJ]

Thank you for all of that information David! Yes, it is a single purpose machine. The reason I'm looking to run single phase is so I can build a few of these machines to run production from my house verses driving 18 miles to our main machine shop. Plus, I need to be able to run these machines occasionally on site at my customers locations and almost none of them have 3 phase like I do at both my places, let alone an easy way to hook up to it. There is also a very good chance I'll be sending a few of these machines home with my employees to run added production out of their garages or basements in their spare time depending on work load.

"1/4" cutter @ 1200 RPM is about 80 SFM.
If your 410-420 Stainless is 200 BHN (250 at most), this calculator using your params...
https://www.kennametal.com/kennameta...and-power.html
says 15ipm and about 0.9 HP (assuming belt drive), or about 700W at the motor shaft. Consistent with your findings. "

"Assuming this is a single purpose machine, I'd suggest either of these.
- If you only have 110V service: 1.5 HP ~3500 RPM 1-phase capacitor-start motor, belt drive (3.2:1) to spindle at 1100 RPM. Tweak rpm with a variable-ratio pulley. "

That was EXACTLY the information I was looking for. Many, many thanks~

[AMCjeepCJ]

BTW, that Kennemetal link is fantastic!

[dmalicky]

You're welcome -- glad it's helpful!