CNC controller enclosure

Laser cut acrylic enclosure

Laser cut acrylic enclosure

I converted my Proxxon MF70 mill to CNC quite a while ago. When I was testing things out I wired up the PSU and controller board and just threw them in a Tupperware container so that nobody got electrocuted. It even had the lid open to allow the cables (including 240V mains supply) in. A temporary hack if ever there was one. You know how temporary hacks are though – they tend to stick around longer than intended.

Close up of the connectors for the axes, e-stop and LED

Close up of the connectors for the axes, e-stop and LED

Well, I finally got round to making a proper acrylic enclosure. I attempted to mill one ages ago, but struggled with the small working area on the MF70 and abandoned it. This one is laser cut. It’s held together with machine screw’s and has two shelves – one for the PSU and one for the TB6560 based stepper controller. I particularly like the rounded piece for the power LED and the hexagonal grid for venting.

I’d be happy to share the design files if anyone is interested, but I doubt anyone has exactly the same setup as me. I also altered things as I went, so I don’t have any “final” versions.

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Laser improvements – coolant monitoring

One of the quickest ways to destroy a CO2 laser tube is to let it overheat. My laser has a very simple system – just a plastic breakfast cereal container of water with a small aquarium pump. It works well enough, but is easy to forget.

My first modification was to power the pump from the laser so that it’s running when the laser is switched on at the mains. That gets around the “oops, I forgot” problem, but doesn’t cover a pipe coming loose or the temperature creeping up. I really wanted to actually check cold(ish) water was flowing through the glass laser tube.

The water and temp sensor

The water and temp sensor

To check the flow, I started with a LM35DZ temperature sensor and a cheap water flow sensor from eBay. For neatness I carefully milled the flow sensor to embed the temperature sensor in it. This was then attached to the output of the laser. I intend to check that enough water is coming out and that it’s below a temperature threshold.

I etched a board with a MSP430G2533 microcontroller that counted the pulses from the flow sensor over a fixed timer period and used the onboard ADC to read the temperature. I set the threshold at 40C and 75% of the normal flow.

PCB with logic error

First PCB with logic error

My initial attempt used a MOSFET to pull the last signal down to GND if things were awry. Unfortunately this fired rather than disabled the laser! This was replaced with a 74LSxxx AND gate so I could force it to 5V and disable the active low signal. Some connectors to match the controller board meant I could drop it in with no rewiring.

The finshed PCB - with a fix for a lifted trace

The finshed PCB – with a fix for a lifted trace

So far it has been working well. (I actually finished this months ago but didn’t document it.) It’s not actually been needed to save my tube yet, but it’s nice to know it’s there. I might later and another sensor on the input and also flag if the difference between the two is too high. I could also add a cheap LCD display but that seems a little over the top.

Coolant monitor in the laser

Coolant monitor in the laser

As it’s a single sided board with some through hole pin headers, when it’s in place you only see the “boring” side of it with not tracks or components. Oh well – there’s no need for it to look pretty. Here it is in place. It’s a drop-in addition on the 6 pin cable to the controller board. It’s powered from the existing 5V line and simply forces the signal to fire the laser high (as it’s active low) when it senses trouble. From teh top you can see:

  • The connector to the sensor
  • A debugging / programming header
  • A currently unused connector for a screen
  • The connectors to patch into existing power and signals

If anyone wants a copy of the PCB layout or code, just ask.