Coolant Visualizer & Switch for K40 Laser Cutter

My goals for this device were twofold: to allow me to *see* the coolant circulating thru my Laser Cutter, and observe its temperature in real time.

Project Background

Many months ago I bought an off-the-shelf thermal module from, but I had always struggled with how to integrate it into my laser cutting setup. The 12″ cable for the thermistor was hugely limiting as it meant that the thermal module must be very close to the substance it measures.

By combining a $2 secondhand water bottle and a few tube fittings however, I was able to create a device solved that problem and more:

  • Allows visual verification that coolant is flowing
  • Allows real-time feedback on coolant temperature
  • Can prevent laser from firing if coolant exceeds a programmed temperature 

At a high level, the project is pretty straightforward: I epoxied a thermistor and two brass nipples into a bottle cap and gave it a little style.

Early Mock-Up

Before the water bottle concept dawned on me, I played around with mounting the bare PCB thermal component on some 1/8″ birch. This excercise was useful to help figure out hole patters, but the design was ultimately not very useful.

Building The Visualizer

It wasn’t until the “inverted water bottle as visualization & measurement chamber” concept hit me that this project really came to life. By creating a sealed vessel thru which I pump the coolant, it gives me a quick window into my system, and an accessible point into which I can integrate the thermal sensor.

The steps here are super basic—drill a few holes and stick in some fittings. I happened to use 1/4″ID tubing and fittings, but this basic concept can be used with virtually any gauge of tubing you may have.

With the fittings snugly fit into the cap, I mixed up a small batch of 2-part quick-curing epoxy and sealed everything up.

Creating The Device Panel

I’d like to say I nailed this design on the first try, but it took me a lot of trial and error to land on a final design I liked.

Using my frankenstein $366 Chinese K40 Laser Cutter, I mocked up several versions of how this could work. Cut first, design later, right?!

Fortunately, Amazon has screamin’ deals on chipboard and corrugated cardboard which makes quick iterations very cost-effective.

Once I was satisfied with the cardboard mockups, I cut a version out of acrylic and began to assemble the final device.

Final Device

Final Costs

Component Cost Note
Thermostat Switch $12.47
Water Bottle $0.99 Thrift Store
Scrap Acrylic $1.40/lb Approx. 90¢ Used
Prototyping Chipboard & Corrugation $5-ish Chipboard / Cardboard
Surgical Hose – 10′ $16 Local Hardware
Studded Brass Nibs $2.00 Local Hardware
2-Part Epoxy <$3.00
M3x6mm Socket Head Cap Screws (x12) $0.98
M3 Brass Standoffs (x16) $2.46
M3 Brass Inserts (x8) $0.25
Wire & Connectors <$3.00 Various Sources

Full Disclosure This page links to products I’ve bought at full price & use myself. Buying from a link on this page earns me a few pennies to help pay for my cheap-and-completely-okay web hosting.

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