Help! Hardinge CHNC Retrofit

[rpseguin]

Ok.
I have a Hardinge CHNC (serial # CNC 532) and it is very clean and nice and was apparently holding super tight tolerances before the control failed (a blessing I'm sure :-).

Anyhow, I have cleaned it up, and am in the process of getting it ready to work.
My plan:
-use Mach 3 turn to drive it
-I have an Axxus DB1 parallel port breakout board
-I have a 12V MPG (I know 5V is preferable)
-use the still mounted DC servos (ElectroCraft 660) with some GeckoDrive G320 or G340 drives
-pull the resolver/tachs off and put encoders on X and Z. Since I want 0.0001" positioning, and the ballscrews are 0.2" pitch, 500 CPR encoders in quadrature should give me that.
-figure out some inexpensive method for controlling the turret. I'm all ears.
-Get a drive for the DC spindle motor. Not sure how many KW, but it looks like 3+ KW or so. It is a permanent magnet DC servo, 3500 max RPM. Anybody have specs on this and drive recommendations where I can control speed/direction from Mach 3?


I'm open to suggestions on how to best get this thing up and running (turret, spindle, ...).

I've attached a couple of pictures of what it looked like when I got it (NOTE: brown stuff is not rust, but some kind of oil buildup/enamel), after a little bit of elbow grease/WD40/rags/..., and the DC spindle motor.

More pictures are available and I will have followup posts as I make progress.

Thanks!
-Ralph

[rpseguin]

Did a few more things in the past couple of days:

-started adding in the chip shields (hopefully not prematurely).  I still have to figure out how to mount the rollers onto the top bars.  The holes drilled into the chip shield are too small for the threaded rod on the rollers.  Anybody have pictures of their roller wheels/bearings on their chip shields?

-I pulled off the X and Z axis tach and resolvers.  Off to ebay?

Next steps:
-measure up and figure out mounting for axis encoders on the ballscrews.
500 CPR in quadrature should yield 0.0001" positioning with a 5 TPI ballscrew

US Digital  E2?  E5?
http://www.usdigital.com/products/e2/

Looking for info and suggestions on the DC spindle servo motor.

Thanks!

[rpseguin]

I ordered some G320 drives yesterday.
Looking forward to getting those.
Going to order some US Digital E2 500 CPR encoders soon.

For the Mach 3 spindle pulse encoder, can you just uses a regular encoder and use the Z (index) pulse?

[Brian Barker]

The index pulse is to small You need to have a much longer pulse to have it work with Mach 3


Check out cnc4pc.com they have a pick up that will work very well

Thanks
Brian

[rpseguin]

Cool.
Got it.

Just finished talking with someone from Hardinge who says my DC spindle motor is rated at 5HP (size seems right),  so I guess using a geckodrive to drive it as a C axis servo (says servo motor on the plate, but not voltage/wattage/...) isn't in the cards.

Was looking at the ballscrews and pulleys, ...
Both X and Z are geared at 4:1, so the 5 TPI ballscrews are effectively 20 TPI from the motor's perspective.

I am definitely planning on mounting the encoder onto the ballscrew.  So at 5 TPI, to get 0.00005" positioning (0.0001" diameter), I need a 4000 PPR (1000 CPR) encoder.


If I were to use a motor mounted encoder, to get 0.0001" in diameter, or 0.00005" in radius, I need 1000 PPR (0.00005" positioning/radius), or 250 CPR encoders.
Is 250 CPR too low to be good on a DC servo motor with a Geckodrive G320?
Would 500CPR be preferable?

Comments?

[polaraligned]

I don't think you want to mount the encoders onto the ballscrews.
Your servos have a 4:1 reduction and the ballscrews are 5 TPI.
The system may break out into oscillation because of the backlash
between your reduction/ballscrews/motor. 
Your following error will be way more than the Gecko's can handle.
They are great drives but sadly they have one shortcoming, and it
is a big one.   The following error is permanently set at 128 encoder
counts.  Not good. 
There is not a single servo drive currently on the market that takes
step and direction and is capable of driving large servos reliably.  Rutex and
CNC Teknix are both having serious troubles with their drives and are
in the redesign process.
Gecko has the short coming I mention above. 
I am using small 12.5 in-lb Baldor servos with 1000 line encoders
driving a series 1 BP mill with 4:1 reduction between motor and
ballscrew.  I am using Gecko drives and they are probably the best
currently out their until CNC Teknix and Rutex get their drives
redesigned.  I have constant problems with my drives going into
error state due to the small following error.   The only solution is
to keep my drive rates low.  I use 80 IPM rapids when my motor is
perfectly capable of driving my table at almost 200 IPM.
Granite devices is the best drive available if you can deal with a
12.5A peak current for your motor.  http://www.granitedevices.fi/
Most of us need 20A or better for our larger machine tools.

Best luck,
Scott

[rpseguin]

Have you tried with the encoders on the ballscrews?  Is that the way your machine is set up right now?
My CHNC has C0 ground ballscrews on X and Z, so I don't think there will be much backlash on the ballscrew, but I haven't checked them out yet.
I will measure it when I get a chance with a 0.00001" indicator when I get a chance.

128 counts of following error on a 4000 CPR encoder is  128/4000 -->  3.2% of a rotation, or 11.52 degrees.
That seems like quite a bit to me.  I cannot imagine having that much backlash in the system.

One other reason for mounting the encoders on the ballscrews is that it ls already set up for that (the tach and resolver were mounted to the ballscrew).  The Electro Craft E660 motors that are already there don't have any back shaft for mounting encoders on them.  I'd prefer to just leave them sit as they are if I can.  Ie, pulling off the motors, machining and mounting encoders, ... seems like a hassle.
Also the gearbox/pully/encoder compartment is sealed off from coolant, whereas the motor bodies are exposed to it (splash cooling? :-)

If I had the money, I would retrofit with a full up CNC control with full servo closed loop.  As it is, I don't have money :-)
Getting the wife to ok buying parts is a hassle already.

[DennisCNC]

Scott, have you looked at Viper servo drives?

[rpseguin]

BTW- the Hardinge parts guy told me that my spindle motor replacement part cost was $13000.00!!!
Maybe I could sell it back to them for half of that and buy all the parts I need :-)

[rpseguin]

Anybody using Agilent HEDS-9733 optical encoders?
Quality?
Reliability?
Durability?

Mouser has a good deal, but minimum quantity is  100 pieces (group buy??)
http://www.mouser.com/search/ProductDetail.aspx?R=HEDS-9733%23U53virtualkey63050000virtualkey630-HEDS-9733-U53