It has been quite a while since the last post on my Blog... It's not like nothing has been build in the meantime but I just didn't come around to actually write some of that down.
First, a little bit of background info to why I'm building and modding this device:
At the moment I'm involved into a cell biology research project, where I've been chosen to build a prototype device to do some modifications to cell culture inserts. As always, it very easy to get me excited about something like this. And as the DIY factor was quite large in this project I was happy to help out at this point.
To cut a long story short: Cell inserts had to be cut into small pieces while preserving the inserts as dust-free and sterile as possible, because later on the cells will be already in the inserts while they are cut. In addition, the instrument should be operable without maintenance or recurring settings by an operator. These are the reasons why we decided on a laser cutter for this. After a few tests on expensive industrial machines, we decided on a trial with a K40 laser cutter. These are quite common, cheap and also very dangerous machines! So the perfect mix to have some fun with.
A few days after the order, a large box arrived and with it an additional piston based air pump, that we will use later on. The Laser cutter usually comes with everything needed to get it running, but the variety of sellers, versions and options makes it hard to tell if that's always the case.
The device itself is a lot larger than I thought... Takes the full bench in my case. The protective "glass" is covered with a paper and wax type of foil.
A look inside. In the white box beside the exhaust hose is the water pump housed
All of the sheet metal parts on the inside are punched and covered in blue film
Connections and a view in the laser tube cabinet
Hailea ACO 318 air pump
Mechanically the machine itself is build from surprisingly thick, powder coated steel and anodized aluminium parts. The X and Y gantries are reasonably steady and the belt drives are adjusted (at least on this unit) the way they should be. After removing the protective film from all the sheet metal on the inside of the machine, you'll be left with very sharp punched steel edges. Be very careful the first time you touch the edge! On the back of the machine are all the connectors for power, exhaust air, coolant and the coolant pump. The coolant pump has an north American plug. Which in my opinion is one of the most dangerous connectors for mains power out there, but we will get to that later on...
High power laser supply and stepper driver/interface board. The laser power supply also powers the led strip in the cutters enclosure and the driver board.
Emergency off and power switch are wired in series. The blue pcb contains the laser power control interface
slightly better view on the driver board. The usb connector is misplaced and it seems like the enclosure has been designed for another board
A view deep inside the machine. Some empty space where I will place the air pump. Above the empty space is the laser tube compartment, which is closed from all sides (even the inside).
Talking about electronics, in the dedicated compartment are the driver board for the stepper motors, one large power supply for the laser (which also provides the power to the motors and led stripes) an emergency off button and the power controls for the laser tube. The laser tube itself is mounted in the back of the machine and is the common water cooled variant with 40W on the label. There are a few things that I want to change and modify: First and most important step. Making the machine safer! Second, deal with the rather useless part mount. And third, add an air nozzle and pump. I check these points in a rather unordered form as I go along and also fix things that I'm not comfortable with. This is not intended to be a step by step guide and also not any kind of instruction. DO NOT BUY OR USE one of these devices when you are not familiar with electronics and high power lasers! This device is at least in the bought form highly deadly in many ways.
So let's start with the safety issue. The entire machine enclosure is made from sheet metal and therefore should be grounded. This has been done by the manufacturer, however they skipped on important steps while doing so... On this unit the star type grounding lug has been powder coated and therefore was not making any contact to mains earth at all! Ensuring a proper connection to the chassis solved that problem. Please be aware that also all the access doors rely on a metal to metal contact in the hinging for grounding. Fixing this with dedicated grounding wires is the preferred solution. I won't show any pictures of my grounding solution in order to keep people who are unfamiliar with this away from trying this on their own...
The next fix might sound a bit silly to some of you but I'm really a fanboy of the european protective contact socket (or Schutzkontaktsteckdose in german). The UK type plugs are okay for me. I disagree with the fuse in each socket and the rather large form factor, but I personally can't see a problem safety wise. The american plug, on the other hand, always gives me a headache when i see it. I can't seem to understand the reason why it's so popular. Exposed contacts up to the plug housing and minimalistic creepage distance are the largest safety concerns that I have. Of cause I've heard about sockets that have really deep insertion levels till they make contact, but why leave the users health integrity up the manufacturers?
maximal distance with still valid connection. In my opinion far from safe
all doors are removeable
rather useless fan shroud
fan shroud
both old sockets removed and ready to make some space for the new one
the famous german schutzkontaktsteckdose in matching colour
the enlarged hole. Ready to rewire the back end.
Well, enough about my own opinion. The included water pump has such an american plug and the lasercutter housing also has two sockets next to each other. These are activated when the device is switched on and thus protect the laser tube (if the water pump is connected to one of them) from overheating. I removed all the covers from the device (simple spring tensioned pins) and took the entire XY mechanics out of the device. There also was a fan shroud for the exhaust fumes which I removed entirely as it was way to large and restrictive.
Then I removed the sockets, which as it turned out afterwards already had contact with minimal insertion. with a dremel tool, i removed the metal strip between the old sockets and made room for the new large one, which is also earthed.
The water pump also got a new plug, although it will be replaced by a Julabo medical cooling system in the future. Now that the housing was already disassembled, I loosened the screws from the power supply and made room for the air pump. This found its place on the supplied rubber feet with 4 holes in the housing.
sketching up a template for the pump mounting holes
new drilled holes from underneath
air pump finally in place after a long fight with the far right nut...
For this, I drew a template on the inside of the housing and transferred it to the outside. The tightening of the nuts on the inside with the pump in the way was then again a special challenge but also succeeded after a little cursing.... Then I distributed the air hose in the housing and brought the whole wiring and mechanics back to place.
A perfect match size wise!
Since the pump should be controllable via a separate switch, i cut a hole in the control panel and put another switch above the main switch.
The next thing that I did was adding a safety interlock to the lid of the device. The power supply already has a connector for such a switch in place and the enclosure also has openings for cables, but nothing installed by the factory apart from a jumper link to enable the laser all the time... Well you know what I think about stuff like that. So two more holes where drilled (be careful not to drop with metal shavings into the power supply!) and a roller switch got installed.
the air assist switch in place and first powerup
main door interlock to disable the laser during setup times
After this mayor rebuild I was confident enough to plug it in for the first time. And it worked flawlessly! The air hose got connected to a 3d printed nozzle from thingiverse (https://www.thingiverse.com/thing:2939495) and the hose routed to avoid contact with the laser beam. The part mounting mechanism is fixed to one specific height, which make focusing the beam onto our cell inserts quite difficult, so new spacers have been turned on the lathe and installed to our specific needs. The project has been done within 2 days as time was a real issue. The device has already been installed in the medical lab where it will from now on with some minor tweaks, support the research in endothelial cell perfusion. Time will show if our rather unusual and cheap way (at least in the field of medical devices) will be the success needed.
