Bridgeport VMC 760 22 retrofit

09 Nov 2021 21:25 #225877 by spincycle

Long time reader of this forum, first time posting. I have to say that the input and knowledge on this forum has always blown me away.

I recently purchased a mid 90's Bridgeport VMC 760 22 for a reasonable price here in Australia. So far I've managed to get it back to my workshop and power it up. It has the original Heidenhain 370 controller and Seimens Simodrive 611 servos/drivers (I believe are analog drive). What an awesome orange and black screen....

So, X Y and Z servos and drives work fine. Toolchanger so far does not operate and most importantly the spindle servo drive appears to of lost its parameters and doesn't move (which may tie in with the tool changing issue, not sure).

I see my options as:
- Fix servo driver issues and run with the original Heidenhain (better resale and least work)
- Keep Seimens 611 servo drives and retrofit something like a Mesa 7i97 and run LinuxCNC (can run more modern tool paths and servicing wil be less daunting. More retrofit work)
- Scrap original servos/drive for something less time bomb and update the controller to______ (same as above, but most amount of work and $$)

I am drawn to linuxcnc for its flexibility. I run a lot of modern toolpaths on my other machine (that runs a Centroid Acorn) and would like to do the same with this.

Does anyone have any insight or experience retrofitting to these analog drives with Mesa or something similar??

My experience with Linuxcnc is limited to an old stepper conversion I did to a turret mill many moons ago. Since then I've built a junkyard Datron-ish router for HSM style aluminium machining. Hence diy cnc isn't entirely new to me, but I wouldn't want to walk blindly into a retrofit like this.

Any insight would be very appreciated!!



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09 Nov 2021 22:29 #225886 by Michael

I have a similar machine a 96 TC22 which I am working on finishing a complete retro (your $$ option). Another member is mid retro on a TC4G, all similar in some respects to your 760

I started down the path of just trying to get the original controls working. Issue with that is you are dealing with proprietary cards and iny case the DX32 control was DOS and needed it's main card replaced. So I could relearn DOS and everything about a 25 year old control or just go with linuxcnc.

If your servos are good and accept +-10v I see no reason to change them. But I would confirm that. Mine had proprietary drives with very little information. So they went bye bye.

We may have the same spindle drive so we can probably get you the parameters. If you do go linuxcnc we can probably get you really close to the whole thing working with sharing our configuration.

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10 Nov 2021 23:05 #226043 by spincycle
Thanks for the information Michael!

Nice to hear that yourself and some other members have undertaken a similar retrofit.

Interesting to hear about the DX32 control. I feel like the the Heidenhain on mine (while still functioning) is a time bomb.

Ideally keeping the current servos would be ideal for my bank account....a new set of 1.5kw servos...ouch. I'll double check the control voltages (-+10v etc) on the Seimens 611 drives.

Possibly a silly question (I've only ever used step/dir controlled DMM, Delta and JMC servos), but if I used say a Mesa 7i97, I would run control voltages from the mesa to the servo drives and then the encoder from the servo motor back to the mesa? Essentially the mesa/linuxcnc is taking care of the feedback loop? (like the spindle?) Or the drives still take care of this? Sorry for the lack of knowledge here!



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11 Nov 2021 05:00 #226061 by Michael
The 7i97 will drive analog +/-10v axis servos and the spindle. You will need more IO then it provides and something like a 7i84 should do great. There is a lot of IO for the tool changer and sensors needed for that.

If you are looking to replace servos I would stay away from the DMM. They are fine in position but they are poor in analog. The drive emulates the motor encoder and has a delay on it which makes tuning a pain. I have some on my machine currently and they will be for sale shortly. Haven't figure out what I am going with yet.

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15 Nov 2021 03:39 #226536 by spincycle
Sorry for the slow reply Michael! Life has got in the way of my cnc world the last few days.

Thats great to know about the DMM servos. Thank you for your advice. I have them on my router with an Acorn controller. I have been very happy with them on this application but it sounds like its not for this next one.

I managed to get my spindle running on the VMC. I am going to give the original controller a go for a short time and then make up my mind about which direction to go!

In the meantime my Mesa 7i96 has arrived for my lathe build which I'm very excited to try :)

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