I put some numbers into ME Consultant with the presumption of SAE1020. It generally gives a number suitable for a lighter or finishing cut.
3" with 7 inserts, .025" DOC, 2" width, 18" length. It returns 700 RPM, 550 SFM, .006" IPT, .042" IPR, 29.4 IPM and says that would be 2.758 hp. .612 minutes per pass. 8620 would drop to 500SFM.
At the moment I have a Hitachi open-loop VFD on my 6000RPM nominal 3hp 325 instead of the OEM Yaskawa 626-MTIII spindle drive, and it sure lacks power. Squaring the edges of 3/8" mild steel plate with a 3/4" HSS EM shows it as pretty easy to stall.
With luck tomorrow should see the arrival of a new closed-loop spindle drive, a Control Techniques Unidrive SP2203. Here's some info from an email the supplier of the drive sent me:
For the Yaskawa UAASKA-04CA1 motor:
You have a motor with a base speed of 1500 rpm @ nominal AC Volts of 220VAC - all good. It looks like it also has a continuous power rating of 2.2kW all the way to 8000 rpm (which means it has a very high break down torque rating = also good).
The encoder wiring would suggest that you have A, B and C channels (common quadrature encoder type signals) and that the voltage levels are 5VDC (TTL or RS422) . . . either are compatible with 95% of the drives on the market.
I did a little more sleuthing on the internet related to the encoder documentation you referenced - on page 110 and 122 of SIE-S626-2H.pdf there is a clear reference to the PG Encoder w/1024/counts per revolution and also references channels A and B to be used for position information (2-phase quadrature) and the C-phase being used as a once/rev reference signal. This is about the most common plain vanilla interface possible and is very easy to interface with.
Motor Rated Current:
Continuous = 3HP @ 23Amps
30 Minute = 5HP @ 32Amps
1 Minute = 6HP @ 38.4Amps (calculated as 120% of 30 minute rating)
Given all of the above information I would recommend the following . . .
For operation that is generally equivalent the Yaskawa Vector drive.
SP2203-LED Used at the Heavy Duty Rating provides:
* 22.5 Amps Continuous Current at 8kHz switching frequency
* 33.8 Amps @ 1-minute rating at 8kHz switching frequency
Alternately you could set it up for 6kHz switching frequency and get . .
.
* 24.2 Amps Continuous Current
* 36.3 Amps @ 1-minute rating
This is going to get you very close to the Yaskawa specifications and everything will be plug and play in closed loop vector mode. I doubt you will have to change more than 8 - 10 drive parameters from the factory settings in order to set this up. Also - vector technology has come a long way since the Yaskawa drive was designed and I wouldn't be surprised if you got considerably better performance from the SP-UniDrive |
.
I think the supplier uses several hundred thousand dollars of the Unidrives each year in his automation business and he says he's been pleased with them. I'm just hoping for performance that is at least as good as the 20 year old OEM drive. But I'm not expecting an 8000 RPM motor to have torque at low RPM like a Bridgeport running in back gear and a low ratio pulley set.
I'll certainly post how things go with the switch to the new drive (which looks like it is going to weigh about 30 pounds less than the original drive!).
FWIW, my Tree brochure shows the 325 as having .75" drilling capacity in mild steel, and to be able to remove 3 (at 3hp) or 5 (at the 15 minute 5 hp) cubic inches of mild steel/minute in milling.
cheers,
Michael