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Author Topic: Bridgeport Interact Mk1 Series2 Conversion  (Read 56451 times)

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Offline SimonRafferty

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Bridgeport Interact Mk1 Series2 Conversion
« on: August 27, 2010, 06:46:49 PM »
A few years ago I (more accurately, my company) bought a nice, clean Interact with a Heidenhain 370 controller dating from around 1994.  It worked pretty well until one day the X-Axis servo drive stopped working.

Finding a replacement for a Control Techniques MIDI Maestro proved a challenge.  I wound up buying one from a 'dealer' of such things for £700 with a generous 7 day warranty.  It worked OK for about six months, then the X and Z axis drives died  :-[

Although I use the machine a lot for prototyping - I just could not justify spending another £1400 on something with no guarantee of it working for long.  I decided to bite the bullet and convert it to Mach3.

Previously I had converted my Lathe to Mach - and I love it - so there was only one choice really.

I have to thank the many people including Hood & JH Choppers who offered advice before I started.

With the heidenhain, I used a Panasonic Toughbook CF18 notebook to run the CAM software.  These are ideal for workshop use as they are coolant and swarf proof and have a good touch-screen built in.  These days you can pick them up for a little over £100.  I decided to use it to control the mill and use a Smoothstepper to interface between USB and the breakout boards.

The Bridgeport had SEM DC Servo motors fitted as standard, operating at about 140v, 25A maximum.  I therefore needed fairly high voltage servo drivers.  I could limit the power and go for Gecko Drives (my preferred option) or buy Dugong Drives from CNCDrives.

I had a chat with the makers of the Gecko, who very kindly suggested that something bigger such as the Dugongs would be a more sensible option.  I ordered 3 x Dugong drives, one of their HDBOB (Heavy Duty Breakout Boards) from CNCDrives and a Smoothstepper from Warp9.

The SEM servo motors use an optical encoder which is only really compatible with heidenhain controllers.  There is a place on eBay who sells converters to allow these to talk to a modern digital drive - but they were way too expensive to be viable.  Instead, I bought AMT103 capacitive encoders from Digikey.  CNCDrives also sells them - but they are 2x the price of Digikey.

I also had a relay board, bought from eBay for something else (made in China and very inexpensive).  It connects to the Parallel port and has 10, 15A relays on board.  I've used these for enable lines, mains power, spindle, coolant, lube pump.  It does the same job as a BOB / Relay board - but for a fraction the cost.

Converting the motors to use the AMT Encoders turned out to be easy.  Once you have stripped out the old encoders from under a cover on the end of the motor, there is a shaft with a M12 thread sticking out.  I just turned up an adaptor with a female M12 thread and an 8mm spiggot on the other end for each motor.  Drilled a 13mm hole in the end cap and screwed the encoders to the outside of the end caps.  Sorry, didn't take any photos - but once you take the end off the motor, the solution is more than obvious!

I stripped out most of the original wiring, labelling as many of the wires that connect to important things like the servo motors as possible.

I fitted the Smoothstepper, Relay Board, HDBOB and three Dugongs, wired them up over a couple of days and remarkably, when I first powered it up - all three axes moved and the spindle ran, first time!

Once all the bits had arrived, it only took a week to have the machine running - but that's where the fun really started!

Offline SimonRafferty

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Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #1 on: August 27, 2010, 07:21:54 PM »
Just for reference, the lead-screws on my Interact move the axis 2.5mm for every revolution of the servo.

The AMT102 encoders are programmable via a little block of switches to a number of steps per revolution ranging from 48 to 2048.  I chose 1000 steps per rev as this allowed the servo to run faster than at the max resolution (a limitation of the AMT102).  The Dugong Drives multiply the resolution by 2 or 4 (programmable) giving me a max resolution of 4000 steps per 2.5mm or 0.000625mm which is plenty!

The Dugong Drives have free configuration software to configure the servos and in particular, set up the PID values.  The documentation is a bit lacking - and didn't give any strategy for determining the values.  I emailed CNCDrives - who were very helpful and sent me a document which explained.  I don't understand why this could not be part of the manual???

The software talks to the drives via a USB lead.  The drives are identified in the software by their serial number, meaning you can plug them all in to your PC at the same time.  I have a 4 port hub inside the mill to which the servo drives and smoothstepper all connect.

One nice feature of the software is that it will run alongside Mach3 on the computer.  This means you can monitor the diagnostics for the drives and change parameters while you are running a program.  To set the PID values, I used a program which just moved the axis concerned back and forth and tweaked the values until the axis moved as fast as possible with near critical damping and no overshoot.

I had a bit of trouble with my X-Axis where it kept tripping the current limit on the drive and tended to move slightly erratically which made configuring the PID difficult.

I wondered if this was what had caused the original X-Axis drive to die twice.  The new drives just light an LED and stop where the old ones started smoking!

To cut a long story short, it turned out to be worn brushes.  New brushes - and it runs fine!  Might be worth a look if your servos are misbehaving?

Everything was fine, I had made some new knobs for the cooker at home :) and was making an adaptor plate to fit a Volvo gearbox into my Land Rover - when smoke started pouring out of the spindle drive!  "Bother!" I said! >:(

Offline SimonRafferty

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Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #2 on: August 27, 2010, 07:26:47 PM »
More Photos:

Offline SimonRafferty

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Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #3 on: August 27, 2010, 08:03:51 PM »
The final part (hopefully) of this story is the spindle drive.

I searched for a replacement spindle drive, but DC drives seem a bit rare.  The original drive is a Control Techniques Mentor 2 - which seem to cost about £2000 for a used replacement from a dealer and I was quoted £900 to fix mine, with a £300 excess if they couldn't fix it!  I decided to look at other options.

Bridgeport Interact Series1 Mk2 of this vintage - ones with a light grey fibreglass case as opposed to the earlier dark grey - use either a 5hp or 10hp DC motor for the spindle drive.

The motor is a 'SepEx' type with separate field and armature windings.  The field windings are 65 ohm and the armature 2 ohm.

I found out that the field windings normally have 8A through them and for a 5Hp (3.75kw) motor, the armature current must not exceed 43A.

The armature appeared to be run at about 180v and 20A - almost within the reach of one of the Dugong Servo drives.  I figured that if I added an encoder to the spindle and limit the voltage to 160v I could run it with Mach using step & direction pulses.

Additionally, this would mean I could run the whole mill on single phase.  I currently use a solid state 3phase converter but it is limited to 5Hp maximum and never really liked running the mill.

I talked to CNCDrive about using a Dugong servo driver on the spindle - and they were surprisingly enthusiastic about trying it.  I decided to give it a go.  I mailed them to order one and decided to order the AMT102 encoder from them, but ask for a discount as I thought they were expensive!

I was surprised that what I got back was a rant about how good value they are - and then silence!  I guess it's a mortal sin to ask a Hungarian for a discount!

Plan B:
It seems CNCDrive do not want my order - so I looked for alternatives.
I found these: http://www.inverterdrive.com/group/DC-Thyristor-Drives/SSD-512-32A-Eurotherm-Shackleton-Rapier-Drives-510/default.aspx


They are just a simple Thyristor based DC motor controller.  They have the normal 0 to 10v speed input and are very simple to interface to.  There is no computer on board as far as I can see and the construction is fairly agricultural.

I bought the 32A version - and it arrived next day (today).  I wired it up - and it works perfectly!

The spindle is as fast as it was on 415v 3 phase and generates bags of torque!  Taking a 1" deep cut with a 1" end mill it to draw 12A moving fast enough that I was worried the tool would snap.

I think on the basis of that, I could have got away with the 16A version.

Finally, the mill is running happily again.  All together the conversion has cost less than the replacement servo drives would have been and I have a much better, more modern and capable machine to show for it!

The next mill I buy, I'll put Mach on it first, before it starts costing me money!

Si

Offline SimonRafferty

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Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #4 on: December 06, 2010, 10:51:05 AM »
Another bit of useful intel!

If you are using the AMT encoders, make SURE you enclose them in water, oil, coolant proof enclosures!

If not, they will start behaving strangely, generating too few or too many pulses per revolution.  Not many pulses but enough to cause problems.

I milled a gearbox casing from two big blocks of Aluminium.  I found that once complete, the shafts in the two halves did not line up perfectly - but at the end of the job, the quill was still perfectly centred on its reference.  The Y encoder had added and lost steps during the cycle and ended up back at the same place.  10 hours of machine time and a cubic foot of aluminium in the bin!

It took a week of head scratching to find out what was going on.  It turned out to be lube oil from the slides dripping on to the motor and getting in to the encoder by capillary action.

I've now re-made the end caps with proper seals and cable glands and had no more problems.  I re-made the gearbox casing and this time it works nicely.

Si

Offline Hood

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Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #5 on: December 06, 2010, 05:22:46 PM »
Dont know how I missed this the first time round.

Looks to be a nice machine, have a series 1 and to be honest its not really much of a mill for the work I do but the series 2  are much more like a real machine :) The Beaver mill I also have is much stouter than the series 1 but still think the series 2 is a sturdier machine although I think its just a 30 taper on them which is a bit weird.

Shame about CNCDrives but at least now you know not to ask in future ;D

Any pics of the machine itself?

Hood
Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #6 on: February 09, 2011, 12:50:09 PM »
Simon,

I recently purchased an Interact I Mk2 at an auction.  It has Heidenhain TNC 2500 controller.  I spent the better part of a day last week getting it to complete the initialization sequence. (I was pleased to get this far as I had no guarantee that it worked at all when I purchased it).  Like the machine that you have upgraded here, I am getting an intermittent X-Axis fault.  Sometimes the overload relay trips, sometimes I get a 'AXIS FAULT' error other times a 'GROSS POSITIONING ERROR'.  Seems to work ok as long as I keep the axis gain knob turned down.  I plan on spending a little time trying to run a program using the original hardware before I gut the whole thing and upgrade, so I would like to get this X-axis issue resolved.  I am hopeful that you can share the details regarding the 'brushes' on your x-axis motor that you discuss in the later posts. Did you replace them?  Where did you get replacements? 

As of right now I will probably follow very closely the steps you have so graciously recorded when I begin my upgrade.  Thank you for taking the time.  If you had to do this project over, would you do anything significantly different?

Also, how much HP do you think that you are getting out of the SSD spindle drive?  The spindle drive is working on my mill now.  It runs smooth at 3500rpm.  It is such an awful amount of electronic components that I don't know if I even want to try to figure out how to interface to it since I would probably just replace it as soon as I have a problem.

Thanks again for taking the time to blog your efforts.

jh
Re: Bridgeport Interact Mk1 Series2 Conversion
« Reply #7 on: November 04, 2013, 07:59:41 AM »
some handy info here, thanks for sharing