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Topics - Monty

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Show"N"Tell ( Your Machines) / My new project
« on: September 20, 2006, 07:40:46 PM »
Here is my newest project. An EmcoTurn140 that I picked up.

Overall I am impressed with the quality of the machine. It seems to be first rate. The machine itself is one of the many trade school orphans that show up from time to time. It seems to have very little use on it at all, in fact it appears to be virtually unused.

There are some peculiarities that are complicating this retrofit. One of them is the spindle motor. It is a Very nice 7.5hp DC shunt motor. Of course the control is very tightly integrated, and "modular" thinking was nowhere in the original designers vocabulary. There is no way I can see to separate the axis controls and the main spindle drive from each other. It is also set up to run on 380V 3p power. I guess that is what they have in Austria. Unfortunately I have 230V 1P to contend with. So I am looking at a controller that will let me run this existing motor at 3.6hp as is, or 5hp with a rewind of the armature. I doubt I will ever need 7.5hp in such a small machine. Anyway I figure that a 5hp DC motor will be better than a 3hp AC sensorless vector. Ever price a 4 pole regenerative 7.5hp DC shunt drive? Guaranteed to give you sticker shock.

The other sticky point is the 5phase Berger Lahr stepper motors. These are truly the red headed stepper childĀ  :D of the stepper world. At the time this machine was made they were the cats meow because there was no such thing as microstepping yet. The machine has a published repeatability of .0001. Now whether that is true or not we will see, but I really don't want to fool with changing out the perfectly good motors on there for newer motors. They are also pretty beefy with a 1000oz in rating. So being a cheap skate I managed several bleary eyed 1am searches of old pdf files to find out that Vexta makes a modern version of this along with a nice little driver board. They are unfortunately very pricey if you buy one new. But fortunately since they are so proprietary and nobody knows what goes with what they were available used on ebay for $99. So I bought three as a gamble. We will see if it works out.

I'll keep you guys posted on the progress. I plan on using Mach 3. I picked up an aloris powerdex turret on ebay that might work nicely. Or I may just use a tool post. Or both! I would like to put live tooling on it using a separate stepper and a harmonic drive with an electric clutch. Should keep me busy this winter.

Will mach 3 support using a vector drive AC spindle for positioning/polar milling?

I have a lathe I would like to implement this on. Planning to use the Grex to drive as yet undecided motor drives and the spindle.

The three strategies I have come up with in order of increasing complexity are:

1.) use the spindle motor with the appropriate vector drive and an encoder on the spindle

2.) use a separate servo motor to drive the spindle in milling mode (disengage main motor and vice versa)

3.) use a stepper or servo/harmonic drive with an electric clutch to drive the spindle in milling mode.

Option 1 gets the KISS award. I am a little concerned that a 3hp spindle motor will not have the low end torque to accomplish polar milling. It may work for positioning but will probably need a brake to hold position. I am limited by having a 230V single phase service to my shop. Otherwise I would just oversize the motor.

Option 2 would work, but the interlock setup is a bit dicey, and the smaller servo will be really zinging along at 2500 main spindle rpm.

Option 3 is the most trouble to implement, but it will work if Mach 3 will do it.

Any opinions? (not related to my mental state, please! ;D)

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