Bridgeport Series 1 CNC problems

Does anyone have any knowledge of the subject line? A colleague has recently bought a Series 1 CNC with "BOSS". There are
problems with the X axis. When I checked the X axis did not work at all. Replacing the fuse for the axis power allowed working up to 40 ipm traverse. The unit "loses it" in rapid. Axis stops moving after a couple of inches and the stepper whirrs away until the end of the expected distance.
Checked as per the maintenance manual and some parameters (voltage and frequency) are not to spec. X ballscrew whilst "damp" is not oily whilst the ways are.
Mechanical or Electrical?
He is not ready to change the main system for Mach3 or similar, the unit is to be used for a simple one off job.
Any comments from those "in the know"?
Richard
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Richard Edwards wrote:

"Whirrs" as in screams while stalled with the shaft not actually turning? Could be any number of issues from mechanical to drive problems to drive power supply to axis acceleration settings.

Low drive voltage will reduce acceleration capability, potentially causing stalls.

Mechanical drag will increase the problem.

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wrote:

I have checked a hell of a lot of the settings but cannot find any reference anywhere to acceleration settings. Too high a value is one of my concerns.

Drive voltage and current are to spec as I see it.

Totally agree. Now we have the machine "running" I have asked that a program be entered to cycle the table back and forth whilst the way oil is forced into the system. I almost feel like removing the table to check the condition of the lube system. Especially to the nut.

Richard
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Richard Edwards wrote:

So which parameters are not to spec, and how far off are they?

Ball nuts don't require a lot of lubrication since they are recirculating ball bearings with minimal friction. Of course if it's been crashed and damaged, that's another matter entirely. Can you turn them smoothly by hand with the stepper disconnected?
Also, if the problem is just the X axis, try swapping stepper connections between the X and the Y and see whether the issue follows the power supply and drive, or the stepper and axis.

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wrote:
Comments interspersed

Rather than repeat suggest you see my answers to Jon

Not enough time on the visit to check that out

Good option Pete. Actually I did not see rapid checked out on Y or Z. Probably best to see that first. If failures then maybe RCK card problem. If no failure then worth swapping motor outputs. Richard
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On Thu, 19 Mar 2009 22:25:56 +0000, Richard Edwards

Because ball screws have rolling elements instead of sliding elements they require little lube. In fact, too much oil in the ball nut can cause the balls to skid instead of roll, and this skidding will eventually damage the ball screw and/or nut. ERS
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Can you tell if stepper is rotating?
Wes
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Whilst the one thing not checked during my visit today was X axis belt tension, from the sound and action I believe that the stepper motor stalls in rapid.
Richard
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Richard Edwards wrote:

OK, the way the BOSS motor drive worked is it uses a saturable reactor in the low-voltage AC input to each axis to modulate the supply voltage to the drive. When not moving, the reactor is allowed to impose inductance in the circuit, cutting the applied voltage down to about 8 V, I think. When the motor is commanded to move above a crawl, a transistor is turned on, sending current through the control winding of the saturable reactor, driving it into saturation. With the inductor effectively out of the supply circuit, I think the drive now gets about 60 V DC.
Other than a driver transistor popping, a common falure is the reactor control transistor shorts, applying full power to the drive all the time, either blowing a fuse or smoking the whole drive.
It sounds like in this case the reactor control transistor had failed open, or is no longer connected in some way, so the reactor can never be "turned off". That would run the motor on the low voltage setting all the time, not allowing it to move fast.
Jon
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wrote:

Correct that is close to what I measured when not running the axis.

Again I saw this so correct on this machine.

Unfortunately Jon it is not that simple as I discussed above.
I spent 3 or 4 hours with the machine (I have never seen one before). At the end of that at least we had the axis moving upto 40ipm. However "Rapid" always failed, 120ipm according to the manual.
I sort of homed in on the "RCK" card as I did not see the numbers quoted in the manual.(Section 6.5.2) Typically TP3 should be 8.0v it was over 9v tweaking the appropriate pot got it to about 8.3v min The square wave at TP5 should be 4Khz my scope indicated a much lower frequency. (A ?ms period instead of a 250usec period. I do not use the scope much (portable handheld) and did not have the manual with me, so did not play with P10. From memory the frequency was more like 400Hz
All system voltages read OK with a tad of tweaking on 5v, 12v, -12v to get them perfect
The fact that the frequency appears low makes no sense as according to the manual it should be 4khz on rapid and 2khz at 30 ipm. I am confused as this does not relate to 120ipm rapid and 30ipm at 2Khz.
Not sure what to do next <G>
Richard
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    Well ... that depends on *which* BOSS. BOSS-3 through BOSS-6 were as you describe below. BOSS-8 and later (IIRC) use DC servo motors, not the big steppers used by the earlier machines.
    BOSS-1 and BOSS-2 apparently never escaped the factory, and I don't know where BOSS-7 falls in the design spectrum.

    That sounds about right.

    And a common cause of the stepper driver transistors failing in these machines in a home shop is imbalance in the voltage output from a rotary converter. The transistors are being run at pretty close to the maximum voltage, and an imbalance will cause one or more of the three axes to be running close enough so the inductive kick can zap the transistors.
    If you have to run the thing from a rotary converter, I would suggest that you use two converters -- one for the spindle motor, and the other for the drive electronics. This lets you balance the spindle motor for maximum torque, and the drive electronics to keep the phase voltages from going too high.

    That makes sense. And the CPU ramps the speed up assuming that it is also controlling the voltage, so when it gets to a certain speed it can't ramp any higher and just sits there and buzzes.
    Good Luck,         DoN.
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are
for
"loses
WHOA! I missed this earlier, even though I read it.
The BP BOSS machines I'm familiar with don't HAVE steppers. They have DC motors with shaft encoders. If the "stepper whirrs away until the end of the expected distance", something mechanical has come loose. Try the coupling between motor and lead screw.
LLoyd
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"Lloyd E. Sponenburgh" wrote:

It's not a coupling, stepper motors "whirr" or more accurately "scream" when stalled.
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On 2009-03-21, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

    He didn't say *which* BOSS. BOSS-3 through BOSS-6 (at least) have steppers. BOSS-8 on have DC servo motors. I don't know what the BOSS-7 has, if it even exists. BOSS-1 and BOSS-2 don't appear to exist at all (except perhaps as early prototypes in the factory).
    The BOSS-3 through BOSS-6 have the DEC LSI-11 quad wide CPU module. I don't know what the later ones have, and I would be interested in hearing from you what it does have. Maybe one of the later double-wide LSI-11 CPUs.
    And given what he has been measuring (elsewhere in this thread), I'm pretty sure that he has one of the stepper motor versions.
    Enjoy,         DoN.
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DoN. Nichols writes:

Now I'm getting nostalgic for my youth.
Minimum-wage grad student in charge of $millions worth of computers.
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    You can get most of those computers together for under $1000.00 total by now -- unless you are including some mainframes, where the metal scrap value is higher. :-)
    Enjoy,         DoN.
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"DoN. Nichols" wrote:

He didn't say which BOSS, but his first post indicated "steppers", so we can presume it's an earlier BOSS if we presume he knows the difference between steppers and servos.
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MC68000.
LS
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On 2009-03-21, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

    Intersting. That was what powered my first unix box at home. A Cosmos CMS-16/UNX. 8 MHz MC68000. (And later computers at home with the MC68010 and MC68020.)
    That would certainly get room for more "feet" of memory (measured in length of punched tape used to store the program, and 10 bytes/inch, or 120 bytes/foot. A lot of the LSI-11's address space was taken up with ROMs for the OS, and not much space left to expand. IIRC, the quad-wide LSI-11 could not address more than 32 K words (64 K bytes) total. The MC68000 could access up to 16 MB. So, assuming that the firmware expanded to a full 64 K bytes (added features), and perhaps to 128 K bytes (less efficient coding or more on-screen prompting text), that still leaves most of the 16 MB for part programs. O.K. 512K for the firmware, and another 512K for the memory mapped I/O ports to leave 15 MB for the part program would translate into 131,072 "feet" of memory, or about 24.8 *miles*. I never did bother measuring how much punched tape a 10-1/2" reel could handle, but I would be surprised to see it holding more than a mile of tape. So there would be no need to fill the entire available address space with RAM. :-)
    Oh yes -- and to put it in perspective, my Emco-Maier Compact-5/CNC lathe runs from a single Mostek 6502 -- again 64K bytes maximum address space and a much less capable CPU.
    Thanks,         DoN.
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DoN. Nichols wrote:

I taught myself assembler on a MC68008 machine and thought it was great, a bit later we covered it at college where we were taught 6502 assembler, that was painful going from byte, word, and long word instructions to byte. For some time I would occasionally use Motorola op codes and wonder why it wouldn't assemble. Did some useful coding on the 6502 but it was arcane compared to the MC68000. The article published by Motorola about the designing of the MC68000 made interesting reading.
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