Just getting started on the planning stages of a retrofit to a 1985 Bridgeport Boss. This version has servos instead of steppers and the spindle is 2HP with 5 inches of Z travel. The computer boots, but as soon as it is done with all its system checks and goes into the actual run time it gets a little confused. Not a real problem. I bought the machine at a very good price and the mecahical portion of the machine is almost pristine.

I have been using a Sieg KX3 CNC with Mach3 for several years now, have not wanted to spend the money on Mach4 as I was also trying to get some tooling for the lathe and the Hardinge UM horizontal mill. Mach 4 will require getting used to a little different appearance and some changes in the logic of operating the machine. It is not Mach3, so I know there is going to be some learning curve.

My plans are to go with a Ethernet Smooth Stepper as the machine interface. I have been using one, and it has behaved very well for me. How difficult would it be to configure Mach4 so I could use some 20mm industrial push buttons for my Start, Feed Hold, and Stop buttons? I will have a keyboard mounted up where the current keypad for the Boss is mounted, and I would like to get it so I don't need the mouse quite as much as I do with my current setup.

I am also looking at the DG4S-16035 High voltage servo drives and probably the BRKC-180 braking units. from CNC4PC. The current drives are rated 140VDC and I am not sure what the performance would be with a drive limited to 80VDC. And besides, I already have the higher voltage DC supply in my machine...

Any thoughts?

Hi,

How difficult would it be to configure Mach4 so I could use some 20mm industrial push buttons for my Start, Feed Hold, and Stop buttons?

That is dead easy. You say you are using an ESS but do not say what breakout board or boards you are using. You'll need one spare input for each button you wish to use.
Ten buttons, ten inputs.

I am also looking at the DG4S-16035 High voltage servo drives and probably the BRKC-180 braking units. from CNC4PC. The current drives are rated 140VDC and I am not sure what the performance would be with a drive limited to 80VDC. And besides, I already have the higher voltage DC supply in my machine...

You don't say what the servos are? The servos will usually have a recommend max voltage, and that's what you should aim for. If you supply a lesser voltage the servo will still
work but never get to it maximum speed.

As a rough guide, lets say your servos are rated to 2500rpm at 180V, and you have only a 80V supply then the servo will get to about 80/180 x 2500=1111rpm. The torque should remain the same
its just that the servo will not go as fast until or unless you provide a higher voltage.

Craig

Hi,
I use 750W Delta B2 series servos on my machine, and a number of retrofits that I've done.

https://www.fasttobuy.com/flange-80mm-239nm-ac-motor-driver-kits-with-3m-cable-220v-075kw-cnc-servo-motor-for-cnc-router_p28084.html

They have a 160,000  count/rev encoder, 2.4Nm(rated), 7.1Nm(overload),3000rpm(rated), 5000rpm(max). They are AC servos, so all the bells and whistles. Delta
provide free setup and tuning software, which is a must have if you've had little or no exposure to modern servos. They are $438USD per kit (servo, drive and cables).
They do not require a power supply, they hook direct to the 230VAC line, easy.

You might like to consider that replacing the entire servo and drive might be an easier way to go. Many people have tried to get old school DC servos to run using all manner of different
drives and often encounter either compatibility issues or tuning issues. Buying a new and matching servo and drive obviates those sorts of issues.

Before you spend big dollars on the drives and/or braking units you really need to answer the question ' what is the likelihood that this purchase will adequately drive these servos?'
If the answer is not 100% confident then there is a risk that you'll end up with a sub-standard result....and after spending good money would be extremely disappointing.

I do recognise that its likely more expensive to replace the servo and drive, but the certainty of the outcome is appealing. You may also find some other 'twat' who wants to buy
the old servos and defray the extra spent on AC servos, there is a 'twat' born every minute!

Craig

Hi,
those drivers you mentioned require the servo to have an encoder.

Have you checked the encoders on the servos? Are they in fact encoders at all? From 1985 they could be resolvers or even tacho generators. Resolvers
or tacho generators will not work with the drive you've mentioned. You need to check....what you don't want to do is get new drivers at $190 each
only to find that what you thought was an encoder is in fact a tacho generator.

Craig

The servo motors have an encoder on end of them. Don't know the number of counts at the moment. They should still be okay, but might want a few more counts per revolution.

Hi,
are you 100% sure that they are encoders? Resolvers and tacho generators look very similar but will not work as you might imagine.
Also around 1985 optical encoders were in their infancy, they were expensive and fragile. I think it wise to check on their operation before
you spend money on drivers. Remember these things are 38 years old, you need to check.

Craig

Yes they are encoders. BEI 250 line encoders. Might want to go for something with a slightly higher count. In 1985 they were pretty much the norm.

Hi,
kool. 250 line is 1000 count/rev, so at 3000 rpm the signal rate is 50kHz. The drives you listed are max input of 400kHz, so you could put
better encoders but you can't afford to go too far otherwise you'll not be able to signal fast enough. 2500 line or 10,000 count would be too much,
you could not signal the drives fast enough to get the servo to do 3000rpm, although you'd get away with, just, 2000 line.

I'd suggest a max of 200kHz single ended and 500kHz differential. The max signal rate to my servos is 416kHz, and so I had to use differential signalling, I tried
single ended but it started to crap out at 240kHz.

Still makes sense to te3st the encoders, if one or more are shot you really should know about it.

Craig

I am continuing to check things out and examining the wiring. Seems that the Drive Enable for this machine is to pull in the individual drive relays which makes the connection between the motor and the drive amp. Old transistor devices will allow that, the newer stuff with MOSFET and IGBT ouput stages would not tolerate that. I think my drives are not enabling because of the problems inside the computer section of the machine. been working on pulling the motors off so I can set them on the table for testing and not having to worry about what might run into an end stop.

Checking on the encoders - they are 250 counts per revolution, which because of the 2:1 ratio between the motor an the ball screw means I have, in a practical sense, 500 counts per revolution. As the ball screws on this machine are all 5mm pitch I am coming in at just about a thou per count.will work to start, but a 1000 count encoder seems like a better minimum count for this machine.

I have ordered some replacement capacitors for the DPS (Drive Power Supply) board. All the large electrolitic filter caps had blown at some point in the past. The power supply still seems to function ok, but the servos might behave better with cleaner DC power.

Hi,

Yes they are encoders. BEI 250 line encoders.

Checking on the encoders - they are 250 counts per revolution,

Two different quotes from two different posts. Which is correct?. There is a difference between lines and counts. One line results in four counts.

In the first quote you say they are 250 line or 1000 count/rev and in the next quote you say they are 250 count/rev. I can't help but think the last quote is wrong.
All optical encoders have four counts per line, so 250 counts is 62.5lines?? A Half a line?

There are encoders of 256 counts/rev or 64 lines.....but I'm dubious that's is what you've got......but I don't know.

Craig