[homchz]

My Tree 325 Journeyman seems a tad underpowered.

The other day I was working with Annealed plates about .500 thick and needed to mill them down to .420. The plate is about 4" wide and 18" long. Using a 3 inch Milling Cutter with carbide insert and taking a little over 2" a pass with a .025 DOC it would make about 3/4 of a pass then stop with a spindle fault. I have tried ranges between 500-900 RPM spindle speed and 5-10FPM feed rates, all with the same effect.

I would not think a .025 DOC would be too much for a 3HP machine, and I have milled standard machining steel with no issues at .025 DOC, could it be the Annealed Steel, or should I be looking for issues with the Tree?

Thanks in advance for any info.
Josh

[planar39]

not a fan of tree but i'll offer what i can, you mentioned annealed plates, can i assume this is A-2? with normal a2 i run at 600sfm, with annealed it might be 400-500, (im using a big cnc)
your hp and rigidity is limiting,
not knowing your cutter... for our 3 inch 7 insert, 510 rpm and .004-.006 per tooth
go up from there (equal rpm and feed)

sry im using a mill with more HP so cannot get closer

id suggest a 2" 5 insert and 3 passes, what about another vise? are you seeing chatter? heat issues (chips staying on the part)

or insert grade, we use iskar 8020 for most normal. and 9030 for 4140 or hard milling

if machine error still exists. some motor sensor(axis) is tripping, consult a professional,

try oil on your part, lol im out of ideas, best of luck there

[planar39]

just occured to me, if your making 3/4 pass, dosent this kinda point to motor (?) ratings, i forget the term, damn my lousy maint. schooling.- load? duty?

[homchz]

Thanks for the info, A-2 sounds right but I would have to look at the job slip to be sure. To save time and the fact we were only taking a small amount off the part we ended up surface grinding the plates.

I think you are right that it is a motor issue, I am just not sure if it is because we are overworking a machine that cannot handle it, or if there is an issue with the motor itself. I would have thought a 3HP would handle it, but maybe I am wrong. When we did the formula for what we though we were running is seemed that 3HP would handle it just fine.

I thought of trying a smaller cutter, but did not get around to it, as this is a secondary job in the shop. There was minor chatter but mostly at the ends not in the middle, and the chips are taking all of the heat, and leaving the part just fine.

Thanks for the info on the insert grade too, I'll look to see what we were running.

Josh

[zpsbob]

Other things to consider:
If you've got the 6000 rpm spindle, there's only 2 HP (momentary) and 1.2 HP continuous at 600rpm. Also the 6000 rpm version didn't have the torque needed, more important than HP in this application.
Depending upon version of machine there were a couple different spindle drives used. The last version had an inverter that provided less low end grunt and may have had a problem with parameter settings where the machine will max out at about 50%.

[Michael M]

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