Help needed - Boxford 260VMC random spindle speed fluctuations / stops machining

[The Boxford Miller]

I’m hopeful that someone on this forum can help me to get my Boxford 260VMC running again.

Since acquiring the machine about three years ago it has run faultlessly using the original Boxford software so I hope to get it working again as it was. I’m not currently considering upgrading the machine to run under Mach 3/4 / LinuxCNC - these options may need to be considered later!

The problem -

After a few minutes of use the spindle speed begins to fluctuate, sometimes dropping by up to 200 rpm from the programmed value and then within a second or so recovering again. After several minutes of spindle speed fluctuations all movement on the X, Y, and Z axes stop, the computer hangs but the spindle continues to spin until the 260VMC is switched off at the wall socket. Once all movement of the X, Y and Z axes has stopped the spindle appears to run without spindle speed fluctuations indefinitely if left. The slotted opto switches / spindle encoder have been checked / cleaned and look good.

Observations -

Two components on the Simplatron / Simplatroll DCVT-2 Isolation card (fixed to the end of the Lenze 534 speed controller) get far too hot to touch. These are (T1) the 0 - 120v 0 -120v 0 - 15v 0 - 15v 3VA transformer and (R15) a Red Brown Brown high power resistor.

The board has been removed from the machine and scorch marks are visible next to the pads for R15 but also, to a lesser extent, the pads for D9 and R10.

Due to the apparent overheating of components on Simplatron isolation board I am thinking that this might be causing the spindle speed fluctuations and will begin replacing components if others on the forum agree.

Questions -

Has anyone experienced the same problem and can they share a solution?

Does anyone have a circuit diagram / component list for the Simplatron DCVT- board and any guidance on what it does / how it works?

Am I right in thinking that the Boxford control boards supply a 0 -10v PWM signal to pin 4 of the isolation card with the mark / space varying for different desired spindle speeds?

Does the Simplatron isolation card then change this PWM signal into a 0 - 10V analogue signal input to Pin 8 of the Lenze 534 speed controller which then adds it 110v?

Are there any suggestions for alternative, straight swap isolation cards I could use to replace the Simplatron DCVT-2 if changing components does not fix the issue.

Many thanks in anticipation.

Mike

[The Boxford Miller]

I’m hopeful that someone on this forum can help me to get my Boxford 260VMC running again.

Since acquiring the machine about three years ago it has run faultlessly using the original Boxford software so I hope to get it working again as it was. I’m not currently considering upgrading the machine to run under Mach 3/4 / LinuxCNC - these options may need to be considered later!

The problem -

After a few minutes of use the spindle speed begins to fluctuate, sometimes dropping by up to 200 rpm from the programmed value and then within a second or so recovering again. After several minutes of spindle speed fluctuations all movement on the X, Y, and Z axes stop, the computer hangs but the spindle continues to spin until the 260VMC is switched off at the wall socket. Once all movement of the X, Y and Z axes has stopped the spindle appears to run without spindle speed fluctuations indefinitely if left. The slotted opto switches / spindle encoder have been checked / cleaned and look good.

Observations -

Two components on the Simplatron / Simplatroll DCVT-2 Isolation card (fixed to the end of the Lenze 534 speed controller) get far too hot to touch. These are (T1) the 0 - 120v 0 -120v 0 - 15v 0 - 15v 3VA transformer and (R15) a Red Brown Brown high power resistor.

The board has been removed from the machine and scorch marks are visible next to the pads for R15 but also, to a lesser extent, the pads for D9 and R10.

Due to the apparent overheating of components on Simplatron isolation board I am thinking that this might be causing the spindle speed fluctuations and will begin replacing components if others on the forum agree.

Questions -

Has anyone experienced the same problem and can they share a solution?

Does anyone have a circuit diagram / component list for the Simplatron DCVT- board and any guidance on what it does / how it works?

Am I right in thinking that the Boxford control boards supply a 0 -10v PWM signal to pin 4 of the isolation card with the mark / space varying for different desired spindle speeds?

Does the Simplatron isolation card then change this PWM signal into a 0 - 10V analogue signal input to Pin 8 of the Lenze 534 speed controller which then adds it 110v?

Are there any suggestions for alternative, straight swap isolation cards I could use to replace the Simplatron DCVT-2 if changing components does not fix the issue.

Many thanks in anticipation.

Mike

[The Boxford Miller]

I post an update as this information might help someone else with the same issue, again hopeful that someone will reply with further suggestions.

I removed the transformer from the Simplatron DCVT-2 Isolation card, it’s a Magnetix 120 -120V to 15-15V. A suitable replacement is a Vigortronix - VTX-120-003-615, 3VA 2 x 15V. The resistance of all four windings on the old transformer were checked against a new one and all were found to be correct. The original was soldered back onto the board.

I replaced the original R15 resistor (220 ohm 1W) with a 210 ohm 3W resistor.

I replaced the Bridge Rectifier (W02F) with a new one.

I replaced the Zener diodes D9 and D10 (BZX85C10V) with new ones.

Result - The components on the Simplatron board are now running much cooler, you can keep a finger on the resistor without it burning. Even though the speed of the spindle was still occasionally fluctuating I managed to cut 0.3mm deep in mild steel with a 5.5mm cutter for about 30 minutes. I thought I had fixed the problem but on the next machining operation the X,Y,Z stopped responding, the spindle continued spinning and the computer flagged - “Machine not responding’.

I changed the sole RIFA capacitor (0.15uF / 150nF) on the internal Lenze 534 board for a new one.

Result - This time I really though I had fixed the issue but after about 40 minutes of cutting the same steel the computer lost contact with the 260VMC (no on screen message this time) and after about 50 minutes X,Y,Z stopped responding and the spindle continued to spin.

I turned the ‘IxR compensation’ trimmer potentiometer on the Lenze 534 clockwise about 1/16 of a turn while cutting steel as above. I did this four times and spindle speed remained fairly consistent rising and falling a maximum of 40 rpm above the 2000rpn that was set.

After 1 hr 50 mins of cutting again I though ‘problem solved’ but just as the Z axis took a plunge cut the machine stopped responding on X,Y,Z but the spindle continued.


Ahhh…..

Any suggestions, please!