Moving Day

Well I decided to shift my blog from my personal site over here so more people can see it. Hopefully this kind of things interests others. The project got pushed to the back burner due to life money and all that other fun stuff. I have purchased some new borosilicate glass tubes with a slightly larger diameter and thinner wall for better heat transfer. I have also decided to stick with the laser heads I have and will try using a more flexible epoxy glue. As it heats and cools it shouldn't crack like the last one. I am still not too sure how this will work but at least this way I won't have to start all over. As for attaching the coolant lines to the acrylic tube I will continue to use the metals rings I made but also find a better glue to seal them to the tube.

I am also working on a CNC table which I will document on hear as soon as I can. It is going to be a 4'x4' table with dual drives. I plan on attaching my laser a router and plasma/Oxy-fuel for the heads. I have wrote my own control system for an automated drill a while back I will modify to control this system. The software was written on linux using a real time kernel. All loop calculations are done in software. I am using a Mesa 4I65 with some custom FPGA code programmed on it to control IO and ADC/DAC's. The drill software was only a single linear axis with a programmable spindle speed so programming the arcs on dual axis is going to be the fun part. Pic of the drill below..















Anyone have expericence writing velocity profilers for more than 1 axis? I think I figured out how to do it but I would like to discuss this with someone who has experience in the field. I would like to program it for 3 axis motion so I can do some 3D routing. I thought about just using a CNC program like EMC but I like the experience I get when trying to do these things on my own.

New CO2 Design

Friday, September 26th, 2008

I just stopped by the pipe place today and picked up all the couplings I need. I also picked up all the tubing as well. Next time I go to work on a plasma table I will cut up the blocks i need for the mounts and start machining them. This project has been on the back burner for a while due to money and life getting in the way but I will get it done one day. My final plan is to have it run for an entire day without over heating or loosing mirror alignment. Then mount it to a CNC table. I have been collecting parts for my CNC table, drew up some plans and have a few controllers lying around which will work great for this….. One Day…..

On a side note I tried adding a little extra CO2 to the mix and the increase in power was noticable. I was removing the gas line and sticking it into a CO2 bottle quickly so I know I was most likely sucking in O2 & N2 at the same time. If I actually properly increase the mix I can just imagine the power I will get….

New Design Idea

Tuesday, July 22nd, 2008

Here is a idea I have to try to make the laser more rigid.

In this design I split the tube so I can have the vacuum in the center and gas inlets on the end. This will help cool the gas as it effectively cuts the distance the gas travels in the tube in half. I also had a couple ideas to convert this to a fast flow laser in the future so I increased the diameter of the gas and vacuum hoses to allow increased flow If I ever want to. The new design is totally removable and the mirror mounts are sturdily mounted to a piece of steel. I don’t know if I will stick with an I beam but you get the idea.

Rebuild... Again

Monday, July 14th, 2008

I have removed the water jacket and removed the epoxy from the heads. To seal the laser tube to the heads I have placed an o-ring on the od of the tube. I then mounted the heads to a 4×4 wood block and strapped them down tight. It’s pretty crappy but It works very well. I have also since acquired a 15Kv/60mA NST. This seems to effectively double the output power but damn the tube gets hot quick. I have finished one head of the cooling jacket but haven’t had time for the other.

Failure....

Wednesday, July 2nd, 2008

Well so much for 3rd times a charm. After I attached the coolant lines and pumped water into the cooling jacket the plasma just stops. That tells me it is transferring through the water, the other give away was water on the rear mirror. Damn…

So I decided on a solution which will work guaranteed, maybe I shouldn’t use that word… should work. I removed the end caps put them back on the lathe and placed an o-ring on the inner diameter against the discharge tube. I will make a separate water insulator totally isolated from the end caps and use o-rings to seal it against the discharge tube. This way there is no connection between the water and end caps other than a piece of glass.

Next...

Monday, June 30th, 2008

Well now that I have actually got this thing to work I need to fix a coulpe things. First of all the flow regulator has to go. I just assembled a pressure regulator from pieces I had lying around and will give that a shot when I get home. The mirror alignment issue is quite annoying. I am going to build a mount from steel and strap the tube down by the mirror insulators. I am also going to try using spring loaded mirror mounts to try to keep a more constant pressure on them and also reduce the sensitivity of the screw adjustment. Third I havn’t pressure tested the system with water yet. I just picked up the final pieces I need to finish that part and will try it soon.

I have called about getting a proper sized transformer for this tube so I will be able to run it at it’s full 60mA capability. I am also trying to source some high voltage rectifier diodes to try running this on DC, I already have a suitable sized filter capacitor bank rated at 30kV for the job aswell.

I have a variac which will allow me to adjust the output. I’m not sure how well adjusting the voltage with a variac will work while still runnning AC. The arc seems to just barly start at 15kV and with a reduced voltage and a zero cross it may not restart. Running DC should be fine although, once the arc is initiaded the DC current should keep the path ionized as the voltage is dropped.

First Light

Today I made a little progess, I actually got the laser to work. It appears to be about 10W so far. The mirrors constantly fall out of alignment and retuning is necessary quite often.

Progress

Sunday, June 29th, 2008

I have finished both laser heads now and have isolated the water jacket and the discharge with epoxy. I will upload a picture of the finished tube soon. During this time I managed to loose one of my mirror insulators, and have started to build a new one :(. I plan on working on it a little more today hopefully finish the insulator, caps and do a pressure test. I will soon find out how well this new epoxy sealing method works, I’ll hope for the best.

New Optics have Arrived

I received the new optics for the CO2 laser yesterday and am anxious to try them out. I still have to finish some lathe work on the last mirror insulator and caps. Here is a photo of the new optics. I ordered them from Bruce Sunderland at (www.designreasearchoptics.com) who was very helpful with hobbiest like me who are just playing around with this kind of stuff.

I have also finished the second laser head today, I am impressed how well it turned out. Every one I make turns out a little better and quicker than the first.

I also finished the mirror insulator, I still had to take the OD down a bit and insert the mirror mount o-ring. I chose a 1/8″x1″OD o-ring for this and counter sunk it so it won’t fall out like my last design. The mirror insulators fit to the electrode heads very well and seem like they might maintain their alignment. I really won’t be able to tell until I actually get this thing to work and try removing and replacing the head… I’ll hope for the best tho.

CO2 Laser Tube

This is my first semi-successful laser tube. The first one I created used a similar design but with epoxy to seal everything together. The epoxy couldn’t hold back the cooling jacked pressure from the vacuum in the laser bore and failed allowing water to seep in. One side of the laser tube sealed just fine making me think I mush have not mixed the epoxy evenly. Sorry, no pics.
This design used 2 round pieces of aluminum and plastic which squeezed a piece of rubber to seal the cooling jacket from the laser bore. I built everything on this design to be removable and replaceable. For how often I may have to change a broken laser bore or something it was just extra work I didn’t need to do.















The metal clamp hides the rubber seal in this photo. This design also seems flawed although it works much better than the first… My new laser heads and sealing method will work far better I think as long as I take more time to precisely mix the epoxy.

New Laser Heads

I have just recently finished one of the new laser heads for my CO2 laser. I believe this design will work much better that the last. I used a 2″ piece of aluminum and designed it so it will grab the outside of an acrylic tube and the outside of the laser bore. I decided to again go with using the laser head as the electrodes, as that part seemed to work fairly well on the last design. I decided to also space the mirrors apart from these electrodes using some hard plastic material. The step on the end was to try to keep the mirror insulator centered so I can remove the mirrors without adjusting alignment, I’m not too sure how well this will work. When aligning the mirrors on the old tube I found the slightest adjustment caused a drastic change over the long 1.2m tube.















The hole in the top of the 2nd picture is where epoxy will be inserted to insulate these head tubes from the cooling water. I have bought a epoxy which is supposed to bond glass, metals and acrylic. I have tried gluing scrap material together and the outcome is promising. I drilled the fill hold with a #29 drill so after the epoxy has dried I can re-drill and tap the hold with a 8-32 screw for the electrical connection.
And a pic with showing how it will go together, using a piece of laser bore I accidentally broke.


I also spent some time with this one on the buffing wheel. Just for better looks

CO2 Laser

CO2 Laser

A little info on all the pieces that make this work.

Laser Tube
The laser tube, the piece that looks like a florescent light above is the heart of a CO2 laser. It works by exciting the atoms in the gas using an electrical discharge. The gas is a mix of Co2, Nitrogen, and Helium. The exited nitrogen atoms bump into the CO2 atoms and cause them to transfer their energy. The excited CO2 atoms will fall to their lower energy state by releasing energy in the form of light radiation. This light will bounce off the mirrors placed at either end of the tube and cause other CO2 atoms to release energy. Some of this bouncing light will escape from the partially reflective mirror and viola, you have a laser.

Vacuum Pump
To get the atoms of gas to excite you need to send a current through them. If you were to try to get electricity to flow at atmospheric pressure you would need and incredibly high voltage to get at arc started. You would need this really high voltage because the electrodes are almost a meter apart from each other. If you take out some of the pressure in the tube and then try to start an arc it will initiate much easier. This is why you need a vacuum pump. Even at this low pressure you need apx. 15,000V to get a stable arc.

Above: Cenco vacuum pump attached to a 1/2hp 115V motor.


Power Supply
To get the 15,000V necessary to get an arc across the laser tube you need a power supply. The easiest supply is a neon sign transformer or NST. The nst I have is a 15/30 which means it is 15Kv at 30mA, this is a little undersized for the tube I have built but should work for initial test purposes. I am using AC to excite the tube for simplicity although DC is really the recommended method. More on that later.






Water Cooler


The water cooler is simply to keep the laser tube cool. A CO2 laser will not function very well or at all if the gas becomes to hot. This is why helium is introduced into the laser gas. The helium will help transfer heat to the laser tube walls and then the water will carry it out of the tube. I am using a Miller water cooler for a Tig torch, as I had one lying around.






Mirrors
The mirrors in a laser are responsible to increasing the energy output to achieve a useful beam. For CO2 you have to use special materials because of the wavelength of light it emits. A CO2 laser emits light at 10,600nM which is in the far infrared band. This light is totally invisible to the human eye. Because of this long wavelength materials like glass will not allow light to pass and are essentially opaque. Materials which will transmit CO2 laser light are NaCl (Table Salt) ZnSe (Zinc Selenide) and some other semiconductor materials.

A picture at the output mirror, the partially transparent one. You can see the premix laser gas bottle in the background.