Denford Triac Spindle Problem

[Richard Evans 2Participant @richardevans2]

 

My Denford Triac has lost spindle speed control. It races flat out or drops back to a few hundred rpm at random. It’s a 1995 model with the original electronics adapted for PC/Mach3.

I’m guessing that if it was a spindle tachometer issue it might be more likely to stick to a constant speed,  so maybe its  a failed component on the control board? Obviously that wouldn’t be a great surprise given the age.

I have a little knowledge in this area having refitted the electronics for a Denford Orac lathe, but I just use manual spindle control on that. The Triac is a much more complex machine. I’ve got the circuit diagrams from the Denford forum.

So what next? Options are to try to trace the fault/obtain a replacement board, replace all the electronics myself (a daunting prospect), buy a replacement modern control box if I can find one, or give up on it altogether. A replacement old board seems a bad idea, obviously it too could fail any time.

Anybody got any comments, thoughts suggestions?

Thank you!

 

Richard

 

 

[John HaineParticipant @johnhaine32865]

I believe that the Triac in different versions used either a DC motor or an induction motor + VFD.  Which does yours have?  It sounds like the motor is OK (so not the brushes if it’s a DC type).  Denford used Sprint controllers for DC motors, these are still available (in later versions).  I have a Novamill with DC motor which I got without electronics so I use a KB Electronics controller which works well (though I don’t have spindle speed control from Mach3 yet).  There are also lots of generic DC motor speed controls on eBay and AliE but quality is likely to be variable!  AFAIK it doesn’t have a tacho, the DC controllers set speed essentially by voltage with a series sense resistor to keep speed constant under load.

If it’s a 3-phase induction motor the easiest thing, and recommended, would be to just install a modern VFD.

[Robert Atkinson 2Participant @robertatkinson2]

Having looked at the schemtics and maintence manual and can’t find any reference to a tachometer on the spindle.
The driver board receives the speed command as a 0-10V signal from the main board. One fairly simple test would be to simulate this signal and see how the spinde runs. Just a 9V battery an a potentiometer (any linear pot between 1 and 20 kilohms should be OK.) connected to the input should work. Disconnect the wire to the main board of course. If you get sooth speed control with that look at the mainbaord an software. If the fault is stil present start checking for loose connections in the wiring to the spindle board and motor. Then look at the spindle driver. First suspects would be bad solder joints and failed electrolytic capacitors.

Robert.

[EmgeeParticipant @emgee]

Hi Richard

If you are close to Birmingham this rewinder may help you by checking the motor out, but likely to be the controller if it is the DC motor, running uncontrolled at full speed is a sign the Thyristors are shot, usually caused by stalling the motor and power not being removed in time to prevent damage.

B&T Rewinds (Dave Phelps, 0121 359 8398, dave@bandtrewinds.co.uk) in Birmingham

 

 

[Richard Evans 2Participant @richardevans2]

Thanks all- I’ll take a closer  look and report back but possibly not today.

[David JuppParticipant @davidjupp51506]

I have a Novamill – not the same, but probably similar electronics.

When connecting mine up to a computer (LinuxCNC) I (eventually) found that the 0-10V signal to the DC drive board wasn’t being read correctly – the ground leg of the connection must have been open circuit somewhere on the board, luckily for me there was a spare GND terminal on the connection block, so I simply moved the ground wire across to the spare terminal, which resumed normal service.

My speculation is a dry joint or a faulty trimmer pot on the DC Drive board.  My memory is a bit hazy now but I think moving to the spare terminal may have bypassed a minimum speed trim pot – but I compensated for that in the computer output settings.

[John HaineParticipant @johnhaine32865]

One thing to beware of.  Some models of the Sprint drives have a chassis which is isolated from ground and floats at a rather high ac voltage.  These have a warning on the case not to ground it.  The speed control signal has to go through some kind of isolator (probably optical).

[Richard Evans 2Participant @richardevans2]

I’ve taken a more detailed look at things, which I should have done before my original post. First thing is that I’ve been reminded again of the excellent build quality. There is a tachometer built in to the top of the motor, which is a DC brushed type. The tachometer is a type I’ve not seen before, a spindle commutator with four brushes wired to output wires labelled T1 and T2.

I’ve also discovered that that a small spindle control board has been retro-fitted as part of the parallel port conversion. It’s a DIYCNC Spindle V3, which supplies 0-10V to the Sprint drive. I bought one of these when I was converting my Orac- I didn’t use it at the time, so although I still suspect component failure on the Sprint board, I might as well fit the unused one anyway as a process of elimination.

Couple of photos attached

[John HaineParticipant @johnhaine32865]

<p style=”text-align: left;”>That’s an opto isolated control which suggests that the motor drive unit does have a live chassis. Beware!</p>

[Richard Evans 2Participant @richardevans2]

Thanks John

[John HaineParticipant @johnhaine32865]

This old thread on the mycncuk forum might be useful – specific to Novamill but likely to apply to Triac too.

https://www.mycncuk.com/threads/7992-Denford-Novamill-Mach3-conversion

 

[Robert Atkinson 2Participant @robertatkinson2]

Hmm the TRIAC diagrams I found had AC spindle motors.
How are the brushes on bothe the tachogenerator and the motor?

Rather than risk damaging your spare board if ther is a fault in the motor, you coud try running it off a dC supply and measure the output of the tachogenerator at various speeds.

Robert.

[Richard Evans 2Participant @richardevans2]

Thanks Robert. The tacho brushes show little wear, no dust or other debris. I’ll look at the motor brushes later, but I’d have thought that a problem there would cause a drop in revs, not racing flat out. I don’t have any equipment for tacho/motor testing, and I think it’s beyond my limited expertise anyway.

 

The drawings I’m using are from the Denford Forum, TriacPC-Electrical-Drawings-2.pdf, but I’m only using them to trace wiring as required. For some reason the file has multiple copies of each page which is a bit of a pain.

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