As I mentioned in the previous post, I picked up a “K40” laser cutter off of eBay. I knew when I bought it that it was going to be bad. Well, it arrived and I had the chance to dig through it a bit. In a nutshell, it’s bad. Not just bad, but baaaaaaaad.

What was remarkable to me is that this machine wouldn’t even work out of the box. It took me about four hours just to get it running with the software it came with. This had nothing to do with the software itself, but a list of wiring issues. I can only imagine how frustrating this machine would have been to an average joe who doesn’t know electronics and how to debug them.

This post is about a few things that I found as well as some of the quicker fixes I did for more pressing things. I’ll do more posts in the coming few weeks as I actually upgrade my machine.

Wiring Issues

I ran into a few major wiring issues that prevented the machine from running or were massive safety problems.

# The first issue I came across was a bad endstop switch circuit. Somehow, one of the wires to it had gotten completely severed. I’m not exactly sure how as there weren’t any sharp edges the wire could have rubbed up against. My guess is it shipped like this.

If someone received my particular machine and couldn’t find the issue, they’d be screwed. The firmware on the stock board requires each axis to home to the endstop before executing an engraving/cutting job. A broken endstop switch means the engraver wouldn’t work.

# The second issue I came across was a reversing stepper motor. For the stock control board, this is another fatal problem. If the laser head goes the wrong way, it can’t hit the endstop switch and the routine cannot run. If you are upgrading/fixing one of these machines yourself and find a motor running backwards, you will have to do some wiring changes. Pop out the offending motor cable, and reverse the wiring by swapping the outer two wires in the connector with each other and the inner two wires in the connector with each other. For the folks, like me, who are upgrading the control board to something like RAMPS or a Smoothieboard, you likely won’t have to do any wiring changes; just reverse the connector when you plug it into the board.

# Another issue I ran into was some pretty horrible wire routing. While the factory nicely wrapped everything up with plastic wire wrap, they did so in a way that pulled the laser cathode (negative) voltage wire and the LED lighting wires tight against the chassis lid. With a bit of rubbing, the wire jackets would have been worn away shorting the voltages to the chassis. If this were the laser anode voltage wire, the chassis would be electrified between 20kV and 40kV…not exactly a good thing. I undid the wire routing for the time being and will route it better after I’m done with my upgrades.

# The last problem I found is rather scary. There were soldered wire splices on the 120VAC power wires. From a functional perspective, this isn’t the end of the world. From a safety aspect, this is a large problem. Should something short in the machine or the power supply, those wires would heat up, melt the solder, and fall apart. I don’t know about you, but live 120VAC wires and dripping solder flying every which direction sounds like a bad idea. To bring this machine closer to code, I removed the power wiring and replaced the soldered points with 120VAC crimp connectors.


Sad Chassis and An Odd Bed

I bought this laser cutter pretty much exclusively for the chassis; I can make just about everything else in my apartment-based lab and machine shop. While I certain received a chassis, it is not a thing of glory – it has a terrible powder coat/paint job (I honestly can’t tell which), none of the doors fit on straight, and the control panel is loose and floppy. The acrylic window was also ridiculously cut with none of the corners actually matching…not sure how they managed that, but they did.

I can’t really complain though. When it comes down to it, I have a metal box that keeps the PEW PEW PEW’s inside and not flying into my eyes. I will need to add some weather stripping along the cracks to keep stray laser reflections inside, but that is pretty much it.

The original bed is pretty much useless. It had an odd little spring clamp that would work alright for engraving iPhone cases but nothing larger. The bed itself was rather poorly made and installed as well.

Although, again, when it comes down to it, I was going to replace the bed anyways. I am looking at $20, 20 minutes, and a couple dremel cutoff wheels, not something to really fuss over.

Software and Firmware

To those of you who figured out to use the laser draw software, you are a saint and/or a genius.  I spent around an hour with it and got it to start a couple laser engravings before I got tired of it crashing and starting fires. Not exactly useful.

Since I’m updating the control board with my own, this (…again…) not the end of the world. The new board will utilize GCode and GCode variants that will replace the software interface. The goal of this is to get repeatable and precise cuts while also allowing me to add features as I upgrade the machine.