Bridgeport Interact 1 Mk2 - VFD ? Am I dreaming?

[88incher]

Hi there,

I have a really very nice Bridgeport interact 1 mk2, unfortunately it came to me with a faulty DC spindle motor board (the Tyristor board was chard!) I've replaced some of the tyristors (that were not working as I would expect) and also some other toasted components. Unfortunately there is still some fault there.

I was mulling the problem over today and thought of maybe converting the machine to a modern VFD spindle motor and driver? As I'd also quite like a little more spindle speed (just a little) Can anyone give me an idea of what may be involved in this sort of conversion?..... It's got a TNC 151B control fitted.

I'm not new to CNC maintenance, so feel free to get techy.

Cheers,

James

[jmelson]

Originally Posted by 88incher Hi there, I have a really very nice Bridgeport interact 1 mk2, unfortunately it came to me with a faulty DC spindle motor board (the Tyristor board was chard!) I've replaced some of the tyristors (that were not working as I would expect) and also some other toasted components. Unfortunately there is still some fault there. I was mulling the problem over today and thought of maybe converting the machine to a modern VFD spindle motor and driver? As I'd also quite like a little more spindle speed (just a little) Can anyone give me an idea of what may be involved in this sort of conversion?..... It's got a TNC 151B control fitted. I'm not new to CNC maintenance, so feel free to get techy. Cheers, James

What kind of head does this machine have? Is it like a Bridgeport 2J (with varispeed drive)
or similar? Maybe with the DC drive they didn't fit a varispeed but it still has the back gear?
OK, is this the same frame motor as used in other 2J heads? If so, then a motor from a Bridgeport 2J head will fit. The "slave" pulley of the varispeed will need to be moved over to
the new motor. If you only have single-phase power, get a 5 Hp VFD, so the rectifier and
capacitors aren't stressed by running off single-phase. That should do it, and most VFDs will
give you rated HP above 60 Hz, so you can spin it as fast as you dare. The one place you may
lose something is at the low-speed end. The DC motor may have more torque at low speeds than a 2 Hp induction motor.

I don't know the Interact well enough, and all the pictures I came up with on the net had the shrouds on, so I can't tell what basic head it has under all that.

Anyway, what I was trying to say above is if you can match the basic machine head to a standard
Bridgeport head, then you can probably get the induction motor for that head and it will fit.

On the other hand, if the speed command to the drive is a standard 0-10 V signal, then you can probably find a commercial DC drive that will work fine. That could possibly be less expensive than a used Bridgeport motor and a VFD. The Bridgeport motors command a fair price on eBay.

Jon

[88incher]

Hi Jon,


Thaks for your reply.... Physicaly fitting the motor won't be a problem, it's more the interfacing with the TNC that I'm not so sure about.

The DC motor currently fitted is a 10HP unit made in Italy, and to be honest this retro fit is also being considered to lessen the expense of any future motor / motor drive problems.


Any one actually done somehting like this before? I can't belive that its that unusual to do.

James

[colin1544]

Hello James may be worth your while to give this chap a call as he is not far from you at Bedford area he is a freelance service engineer and would probably be able to sort your board out his name is Gerard and mobile number is 07900220757 I have not used him but I bought a machine from him and he was very helpful. Cheers Colin.

[Jon18buc]

I believe you motor is DC brushed with field excitation and fits in the rear of the c frame this is a long and thin motor by normal size standards.
For this reason you may have trouble getting a standard 3 phase motor to fit.
Depending on costs i would suggest you have the amplifier repaired by a company called Lektronix Ltd. tel 01922 4555555 they will quote before repair
but I estimate it will be around the £900.00 mark also you need to check the motor out as this may b the reason for the drive overloading and breaking down. I would recommend Lektronix for this or a company called EDMR tel 01604 673758 but as with the drive if the motor is faulty this could cost as much as the drive (if faulty). otherwise I would suggest getting second hand parts. Good luck.

[Kevin77]

I've done it. My drive went bad, and rather than spend the $1500 to fix it, I replaced it with a 5HP AC induction motor and vector drive. The TNC control outputs a +/- 10 volt signal for speed and direction. It also outputs a 24v pulse for M3, M4, and M5. I made an interface board to translate the 24v pulse into a steady 10v command that the drive wants to see.

I spent $600 on a motor and drive, less than half of getting my old drive repaired. And I can run it as fast as I want. Any ideas what the spindle bearings are good for? Maybe 4500rpm would be safe?

Sadly, just as I got all that up and running i ran into an axis drive problem that i'm currently trying to diagnose.

Kevin

[jmelson]

Originally Posted by 88incher Hi Jon, Thaks for your reply.... Physicaly fitting the motor won't be a problem, it's more the interfacing with the TNC that I'm not so sure about. The DC motor currently fitted is a 10HP unit made in Italy, and to be honest this retro fit is also being considered to lessen the expense of any future motor / motor drive problems. Any one actually done somehting like this before? I can't belive that its that unusual to do. James

OK, well the 10 HP motor seems to indicate they use an oversize motor to handle the low-speed
torque issue. Does this machine have a back-gear? If so, it may not be a big deal. If it DOESN'T, then anything that reduces low-speed torque is going to be a limitation on your machine, and needs to be carefully considered. A second consideration is how to rig a forced cooling blower to any motor you get. Running regular motors at reduced speed reduces their internal cooling. Rigid tapping a long row of holes at reduced speed and with frequent reversals will cook a standard-duty induction motor pretty quickly without forced cooling.

Jon18buc mentions his machine had a long, thin motor, designed for low angular inertia. This is a motor that is designed to be rapidly reversed. A "short, fat" induction motor will have a lot more inertia that the VFD will have to fight every start, stop and reversal. If you can find a long, thin induction motor for this application, it will work a lot better.

Kevin mentions +/- 10 V control commands. If the controller sends bipolar speed values to the drive, then you need to make sure your VFD can take that, as opposed to only 0 to +10 V. A VFD which can take momentary forward, stop and reverse contact closures should handle the rest.
I don't understand Kevin's comment that the control sent BOTH bipolar speed and separate contacts for forward and reverse, that may be to accommodate different drives.

Jon

[Al_The_Man]

A 10hp DC motor is unusually large for a 1 phase SCR drive, otherwise if smaller the KB/Baldor line would probably accommodate it, fairly cheap on ebay, also to have a wound field, usually means the motor is fatter than normal due to the field space?
Bit if you go with a VFD, most of the higher end ones offer both 1-10v and ±10vdc control, also for spindle applications it may be worth either getting one with a encoder feedback, or at least can have the option added later, this gives you a much better control of speed, especially at low rpm.
A 2 pole motor in the UK will have a base speed of just under 3000rpm, I would be leery of running either 2 pole or 4 pole over 3600~4000 rpm, unless you have a really well balanced motor.
Al.

[Jon18buc]

Hi Kevin.
Well done on fitting the new spindle and drive.
The machine spindle for series II was 40to 4000 rpm. any speed after this you might encounter balance issues with the mechanical parts.
Watch out for motor overheating depending on cutting conditions and motor running time. Usually a seperate cooling fan should be used as at low speed no cooling is offered by the standard fixed fan on the motor shaft.
I have some spare Bosh cards if you need one.

[88incher]

Hi all,

Sorry been away for a day or so..... Thanks very much for the replies....

I shall try both numbers and see how far we get with that.

The spindle motor currently will momentarily spin up but then chucks the OL led on the KTK driver board?

Horrible thing!

All the best,

James

[Interact77]

I had all the same problems with my interact 4 when i purchased it 2 years ago. my advice to you is trash the Heidenhain control and buy one from ajax for around $2500. You can use your existing servos by doing nothing more than changing the encoders. I put a marathon 10HP motor and a Hitachi SJ300 VFD on my interact 4. I run the drive in sensorless vector mode and its works great.

The Ajax/Centroid retrofit is pretty easy to do. And the end result is AWESOME. Its so easy to use and reliable. Worth every penny.

[Kevin77]

I think 5HP is more than plenty for this size mill. The sensorless vector should give you plenty of low speed torque with little heat buildup. How did you replace the encoders on your servos? Were they SEMs? What did you use for servo drives?


Kevin