Homebrew PCBs

Hi all,

Is anyone using a Precise spindle?
I got one at an auction. I need more 
info on how to hookup and I also need a VFD.
I am excited to see it run. This would be 
great for PCBs.
The label says
54000 RPM
900HZ
164V
and it is liquid cooled.

Derek B.
High Tech Systems
Denver, Co.

Derek,

These Precise spindles are some of the best for printed circuit 
drilling. I have a four spindle machine that uses Precise SC53 
spindles with the air collet. This machine uses a frequency converter 
for driving the spindles. Sometimes you can find these converters on 
the surplus market but they go for big bucks. I might have a 
schematic of the drive used in my machine if that will help you.

Some of the Excellon machines use a frequency converter made by PTI. 
I have also seen these on the used market for around $150. These 
converters are just a high voltage variable frequency three phase 
motor drive. Perhaps you could get some off-the-shelf industrial 
motor drive to do the job. 

BTW, you can put approximately 7 volts DC momentarily across any one 
of the three windings to stop the spindle in about five seconds. This 
is how the Excellon machines stopped the spindles. These spindles 
have excellent bearings and will spin forever after removing the 
drive voltage so some type of dynamic brake is used for rapid stop 
and tool change.

Tom

Tom,
Thanks for the input that makes me want to finish my
new CNC machine even faster.

I would like to see the schematic you talked about if
you could email it to me. I will be trying to make my own
controller as I can't afford the Precise one at $3,600.

Derek

This is the info I got from Precise:

Hello Derek:

The SC 67 has a 2-phase motor, so you cannot connect it directly to the
three-phase output of a standard high-frequency drive. I think that you have
two options:

1. Purchase a special frequency converter from Precise that is able to
output two-phase directly. The model is the PCF 310, and price is $ 3,600.

or

2. Purchase a standard 3-phase frequency converter from another source (such
as Yaskawa), and you will also need a Scot-T transformer. This transformer
will converter the three phase output from the frequency converter to the
2-phase that the spindle needs. You will have to contact a transformer
manufacturer to have one specially made.

Connection of the motor will depend on which option you decide on. The motor
cable should have four motor leads and a ground (some very old models did
not have a ground lead). If your motor cable does not have a connector, use
an ohm-meter to identify two pairs of motor leads with roughly 0.5 ohm
resistance each. These are the two phases. If your cable has a connector on
it (normally a round, black plastic connector), phase one will be pins 1 and
3, phase two will be pins 8 and 11, and ground is pin #13.

The precise frequency converter will have four pins on an output connector
to connect the four motor leads to.

If you go with option #2, the Scot-T transformer usually only has three
output taps. In this case, you connect one motor lead (pin 1) from phase-one
to an outside tap, the other lead from phase-one (pin 3) and one lead from
phase-two (pin 8) to the center tap, and then the remaining lead from
phase-two (pin 11) to the other outside tap.



Good luck.