Write up of my Denford Triac milling machine conversion
I have put together this write up of my Triac to Mach3 conversion in a bid to help those wanting to take on a similar conversion, but also the thank those who contributed to the original thread, without their posts I would never have completed this project. From the off I want to be clear that this conversion is by no means the best way to go about this. I was in the fortunate position to inherit the mill, and the main objective was to convert it to run on Mach 3 for as little as possible. This process has taken almost 3 years and much head scratching, but I am pleased to say it now is a functioning CNC mill! The voltages inside the control cabinet are high enough to do some real damage, and some of the methods I have used, particularly the spindle drive, are potentially quite dangerous so please be careful. That said I am assuming most people reading this will be wise enough to work safely. Last thing to say is that most people who contributed to the original conversion were far more knowledgeable than me, this write up may at times be patronisingly simplistic, but hopefully it will be useful to someone who knows as little as I did 3 years ago!
Getting the axis moving
The sequence for moving the axis is; Mach 3 outputs pulses through the parallel port to a breakout board, I opted for a very low end 5 Axis CNC BOB, this then outputs 5V pulses which goes into a custom circuit board, which in turn controls the axis drive boards as per the original conversion.
Getting Mach 3 to output pulses – I had some serious trouble getting this sorted. One important thing to note is that Mach 3 will not run on a 64 bit OS. The software opens and looks like it’s working, but no pulses come out. The following .pdf file was really helpful in getting Mach 3 setup correctly with my cheap BOB.
https://warp9td.com/images/BOB_Vendors/ ... /ST-V2.pdf
Getting power to the axis drive boards - I removed the mill from its housing in a bid to make it fit inside my workshop. In this process I disconnected the E-stops, this resulted in the axis drive boards not receiving any power. To get power to the axis drive boards 24V needs to be supplied to pin A1+ (wire 48) on the ESR (Emergency Stop Relay) to achieve this I took a 24v + line from the 24v PSU (Wire 61) and linked it to 41. Then connected from 46 to 48 (see diagram below). I also had to include an axis limit override button that supplies 24V directly to 48. The axis limit switches are all in series and normally closed so if any is pressed, or an E-stop activated, all axis (and I think spindle) loose power. Without the axis limit override switch the first time I reached the travel limit I had no way to move the axis back! I did add a small E-stop toggle switch on the top of the spindle motor housing, this is simply wired in series with the axis limit switches.
Connecting signal inputs to the existing axis drive boards – I carefully followed Dale Gribble’s excellent photos showing where to add the wires, note that the blue wires are for the Step inputs and Red for the Direction inputs. The only thing I did differently was to put the cables through from the front of the PCB, rather than the back. Once those 6 wires were soldered in and the boards had power I could manually move each axis by connecting the Step wire I had soldered into the axis drive boards to a ground wire in the milling machine control box. (It took 2 years to get to this point!)
Getting the BOB to control the axis – I had to reach out to people with far more electronical know how than me for this one. I hope you can see what is happening on the breadboard and sketch. The transistor (BC547C) emitter leg connects to the Step or Dir wire on the drive board, the collector connects to the Ground (on both mill and BOB). The Base takes its input from the 5v supply on the BOB, through a 2K resistor switched by the Step or Dir output. To clarify the dotted line signifies what is happening internally on the BOB.
Driving the spindle
The Sprint drive board blew up on me, twice, so I built a very simple DC motor drive circuit following this video.
It uses a 10,000W SCR motor controller and a Bridge rectifier (KBPC5010). The motor controller gives a controllable 240V AC output, the bridge rectifier turns that into a controllable 240V DC output and I have limited that to the 140V the motor is rated for by placing a 150K ohm resistor in series with the potentiometer on the SCR. The Pot on the SCR is rated at 500K. At 500k ohms it outputs 0V, and at 0 ohms you get 230v, a 150K resistor inline prevents the SCR reading less than 150K so the maximum output is 140V. A downside to this modification is that the SCR now receives 150K – 650K ohms so there is a large portion of the Pot’s travel that provides no output from the spindle.
The spindle spun at 3100 rpm when I ran it at 140V, and the spec for the mill is 2500rpm so I try not to exceed that. I extended the 2 wires on the pot and mounted it on the left-hand side of the cabinet. I stuck a sheet of paper behind the pot’s knob and used a laser tachometer to record the positions of the knob at various spindle RPM’s. Not an ideal solution by any means, but it does work.
I repurposed the CCR relay to power the SCR. The relay on the BOB is rated at 30VDC so I ran a 24V supply through that and into the switching input on the CCR. This allows Mach 3 to turn the spindle on or off, and I set the speed manually.
General changes and notes
Tool changes – The spring retaining the collet chuck was too strong to allow for easy manual tool change, for this reason I plumbed in a small compressor under the table. This compressor goes directly into the compressed air system from the Triac, I relocated this to the side of the mill. This connects to the line for the tool change cylinder. The valve on the air system allows me to apply and release air into the system, and I’ve added an additional valve in the line from the compressor so I can easily drain the compressor tank. There shouldn’t be any chance of an accidental tool ejection!
Guard – I removed the polycarbonate from the case and fashioned a small but effective screen which simply wedges into an additional aluminium strip I fastened to the front of the Y axis housing. If you want to replicate this make sure the side panels sit high enough that they wont catch on the table as it moves.
Axis lubrication – The oiler has been moved to the rear of the machine and no longer electronically controlled. I use the prime handle periodically to force some oil through the lines. Not sure if that is a good idea, or even if it does much good to be honest.
Small electronics control box – This has been relocated to the top of the mill, not ideal as the machine is now quite top heavy, but after many different locations this seems the best place for the time being.
Homing – After much playing around with the optical limit switches for homing the machine I decided not to bother with them. I only ever do small single items so didn’t require that functionality.
I could use some help with at least 2 things: Firstly, I am not happy with the spindle drive system. The SCR works, but I would far rather the BOB have the ability to control the spindle speed. Any thoughts on how I could use the 1 – 10V output from the BOB to alter the resistance the SCR is receiving?
Secondly, I’m currently using a copy of Mach 3 I found online. I don’t want to use pirated software long term, neither to I really want to spend more on software than the whole project has cost. Can anyone recommend an alternative please?
Thirdly, is there anything I've done that I really shouldn't have?
In the spirit of giving something back in return for all the help I gleaned from this post, all the parts I removed are available for free to anyone who can use them. Please have a look through the pictures and drop me a message if there is anything you could use.
Hope this has helped someone!