Bridgeport Series 1 Limit Switch

[kewl_cat]

I have a BP Series 1 CNC with a Limit Override light that will not go out when I push the button. I can manually click the CR1 relay and the light will dim and let me jog the machine. I can then push the limit override again and I hear a relay in the head click. I can jog it in G-code but it will not do anything when it gets to a feed. I have a feeling that there is a combination of relays that may not be working. Any ideas? The ACC board has a spot on it that is a little brown where it may have gotten hot. The z-axis also stalls when jogging.

[machintek]

The BPT will run in rapid or jog with the spindle off. To do a feed rate it needs to see the spindle on. This is a safety feature to prevent bashing end mills into the side of a part. There are small switches on the side of the spindle motor contactors to tell the control that the spindle is on. There is another switch or each contactor that locks out the other direction contactor preventing both from turning on at the ame time.

Put the machine in jog, setup, z axis and step. press the minus button repeatedly. Each time you do watch the small shaft and dial benath the Z axis motor. made sure that it does not step in the same direction for three steps and then reverse direction for one. This would indicate a shorted final drive transistor (2N6547). There are 3 groups of these on black aliminum heat sinks above the ACC board.
It is also possible that you voltage in is wrong, you have a bad bridge rectifier, your current is set wrong, you have a chip or washer between two diodes on the small board beneath the ACC card, a chip or washer in the motor terminal strip beneath the ACC card, or the wrong transistors, or a high resistance in the Z axis DC fuse (screw in type, tan in color), or your quill needs to be claened with kerosene and use Mobil Vactra number 2 for way oil. I also once had a bad opto coupler on the ZDI to the SMD.
That gives you a bit to check.

George W.
Th

[kewl_cat]

Thanks for your input. I have tried to run g-code with the spindle on but the same results. The machine is wired 230V 3 phase but I have 208 3 phase in my location. I did try jogging the z-axis repeatedly and it does not back up. I did check the bridge rectifiers as described in the manual. I checked the voltage on the x,y,z axis at the fuseholders per the manual and found 37V but it drops as I hold it longer. I checked the output voltage of the 56V power supply and it has about 54V. When I hit the limit switch relay CR1 the voltage drops to about 33V. Also, the manual said to check the current of the x,y,z at the fuseholders. I get no current there. I also checked inside the machine for chips or other stary matter. I also changed all the fuses. Thanks.

[machintek]

The BPT had a special transformer for a 208 VAC machine. If you have a SMS card you will see current and voltage drop slowly. It was an added board to help prevent final drive transistor blowing.
The drive DC fuses (12, 13, 14) should have about 9 to 9.5 volts with the drives on and a static (motors not turning) current of 8.0 to 8.2 amps. When the motors are turning in rapid, the voltage will come up to about 58VDC and the current will drop to about 2 amps. As the motors age, this current will go up and the motor torque will diminish. The magnets are losing their force.
The CR1 relay does not sound like it is puling in. Is the emergency stop button mashed in? Is the machine in extreme limit state? If you mash the limit over ride does the light go out? Have you tried holding the limit over ride button in and jogging the axis? Is the 24 VDC power supply ok?

George W.

[craig96us]

I think I remember having similar symptoms when I hit an X limit switch, and the switch stuck. Maybe one of the limit switch plungers is stuck bottomed out with the switch made...

Simple things...

/Craig

[kewl_cat]

I checked all the limit switches and they are good. Emergency stop not activated. All axis are not in limit state. I push the limit override and the light stays on. I tried holding the override button down and that doesn't help. I have to take the plastic cover off of CR1 and push the contacts over for it to engage and then the limit light goes dim and then I can jog the machine. According to the manual when pin 4 on the relay is at ground then the relay is off. Pin 4 is at ground and when I pull the wire off of pin 4 then the relay kicks. 24V supply checks out good. Will I be able to get this BPT usable with 208V on that 230V transformer or will I have to find one? The voltage at the fuse on the z-axis is about 17V when I try to jog it. Also the z has gone from stalling to just giving a whirrrr sound. I also cleaned the quill.

[machintek]

Pin 10, wire 135 at CR1 goes to the emergency stop switch. From there it goes to wire 39 which is ground for the 24 volts. 24 volts comes in at pin 2, wire 125 supplies 24 volts but there is a voltage dropping resistor R26 between it and wire 40, the actual 24 volt supply. The reason for this is they wanted the relay to barely hold in so it would react faster to a press of the emergency stop button. Try grounding wire 135 to see if CR1 pulls in. If it does, you may have a bad wire to the ESTOP switch or a bad ground or a loose or bad wire.

george W.

[HillBilly]

Make sure someone has not replaced CR1 with a 24V relay it should be 12v due to the dropping resistor.

Darek

[machintek]

Actually, CR1 IS a 24 volt device.

George W.

[HillBilly]

The ones I have seen were 12v and the dropping resistor allowed you to ground the positive side of the relay without shorting the 24v power supply.

Darek

[machintek]

You are correct. The 24 volts branch off through D16 just after that resistor to the limit of travel switches then to the limit override switch (normally closed), and then to ground. When you press the limit override switch, that circuit opens allowing CR1 to pull in since the voltage now is applied to it. I will have to find a machine or parts list and see if CR1 voltage is specified. I owned a BOSS 9 and it had the same circuit and CR1 was a 24 volt device. My service manager Norb Lion (BPT Bristol PA sales service center), explained it to me that this was designed in such a way to barely hold CR1 in and react quickly.

George W.

[machintek]

Sorry R26 and D14 not D16.

GTW