Denford Triac VMC Spindle speed issue

[rorydog1]

We are stuck on an issue that we hope one of you gurus may be able to help us with. We have a Denford Triac and when we set the spindle speed in the range of 500-1000 RPM, it will run smoothly then speed up and slow down. You can hear the tone of the machine changing and the speed changes are quite dramatic. When we go above 1400RPM the workshop breakers tripped but the control box fuse was OK.

We have tried running the machine from different power outlets to eliminate workshop wiring. The machine is being fed from a PC running Mach 3 only and the interrupts seem to be around 7-8. We were wondering if there is a setting in the Motors section that may make Mach 3 alter the PWM to the motor, but any help diagnosing this problem would be greatly appreciated.

Rory.

[angel-tech]

The atc actuating cylinder may be fouling the top of the spindle. Sometimes the cylinder doesn't retract enough and it rests on the spindle causing the two to weld together. There should be a gap between the two parts, and look for a change in colour of the top of the spindle which will have heat damage.

[rorydog1]

Thanks for getting back to us so fast. It didn't seem to be the problem. We took the spindle's housing off and there is a big gap, about the thickness of a 5p, between the top of the spindle and the ATC actuator. We spun it up and the gap didn't close but the motor is still speeding up and down.

Behind that is the motor and we see the following wires labeled: T1, T2, K1, K2, A1, A2. A1 and A2 are thicker. There is also an earth wire. The motor is an MT30U4-36 P03461 Ferrite Brush DC Taco 9.5. We have a scope and can connect that up to see if it is the electronics are playing up. I guess T1 and T2 are the taco. How would we wire the scope to the these terminals and what should we check for?

Many thanks for your help,

Rory.

[angel-tech]

check the SGR (spindle go relay) is fully home in the socket. Also take the cap off the motor and check the brushes are fine, and there's no carbon build up.

[rorydog1]

Hi, sorry for the late reply. Thanks for the suggestions. We checked the SGR and that was seated fine. Also, we took the top off of the motor and the brushes looked fine and there was no carbon build up. We are a bit stumped as to what to do next. I guess we have to fault trace from the control box but it looks a bit scary in there. Please find attached a photo of the guts of the control box.

There is a board in the top right hand corner labelled down ramp, min and max speed. It has 6 thin wires and 4 higher current wires attached. It looks more modern as it is all surface mount. The bigger wires are labelled 16, 17 19 N and 2.

There are four transformers and one power supply unit rated 24v dc. At the bottom of the box are the control boards for x, y and z axis. Above these are two homemade boards, one labelled op1 op2 and op3 and the other with 5 small relays. There seems to be a commercial board from DIY CNC.co.uk feeding the home brew stuff. In the main body there is the wiring loom, four power relays the SCR, SRR, ESR, then one called CCR lower down. There are four possible relays in a mount called: CIR CDR CBR DPR COR.

Many thanks for any help you can provide.

[Denford Admin]

Behind that is the motor and we see the following wires labeled: T1, T2, K1, K2, A1, A2. A1 and A2 are thicker

I think you're right, the T1 and T2 wires will be tacho...can you check that they are actually connected back to the drive though...Not all machines use the tacho for motor speed feedback - sometimes it just uses armature feedback. If it is just tacho then check that separately somehow - if it can be removed, run it with a drill and see if the voltage produced it steady.. it may output something like 30v per 1000 RPM, should say on the nameplate eg, 30v/KRPM

If the tacho isn't connected then check the drive command input is steady and that the brushes and commutator are all good.

[Martin]

It looks as though your machine has been upgrade to Mach.

You may need to measure the analogue voltage in to the sprint 1200 drive. You should be getting around 10 volts DC at top speed.

The Tacho should output 9 volt DC per 1000 rpm.

You can disable the tacho if you want to try without it but you would need to reset the drive first.