Archive for April, 2010

Ventilation

April 25, 2010

This thing is pretty much ready to run. I’ve installed two tubes for drawing away fumes. One is attached to a plexiglas hood that sits around the cutting head, the other runs below the table. The blast gate on the lower tube helps regulate the draw in comparison to the top hood. Both tubes combine in the wall behind the back of the table, and the larger 12 inch tube runs up to the ventilation fan. The fan is wired up but what remains is to get a motor speed control, and put a hole through the roof with a roof cap.

Another pic of the table.

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New optics

April 14, 2010


The new optics arrived. Their quality is great. The old optics are shown on the left, and you can see the new parts are a lot less bulky than my previous set. The vernier adjust is going to make height adjustment a lot easier.

Collimation. The first thing I did was adjust the collimator. The beam on lasers like mine spread out like a flashlight. The purpose of the collimator is to reduce beam divergence and to control the beam into a nice cylindrical beam, and is also useful because it allows you to expand the size of the beam (see: link). My collimator has two lenses and the precise distance of the two lenses influences overall expansion. To adjust these collimator, I rotated the laser sideways and pointed the beam at burn paper at a distance of 6 inches. Then I put a beam stop about 80 inches away and tested the diameter of the beam. A nice collimated beam should have the same diameter from a distance away. The collimator has some graduated lines on the side, and my burn card shows the beam size for each line. The graduated line for .5 inches seemed pretty good so I locked that position into place.

Centering the beam. Once the collimator was ready the laser was reoriented so the beam was shot downwards. The vernier adjust portion and cutting head was threaded on to the collimator. The optics assembly has a elbow bend with adjusting screws that allow you to center the beam. It was also useful to put some rusty carbon steel on the table, and used a cheap USB microscope to look at the position of the beam. I also used a bit of tape in the retaining ring of the cutting head, and hit the laser at low power for 0.04 sec duration to put a little hole in the tape. The beam was centered after a six or so iterations.

Height adjustment. After the beam was centered I started working on adjusting the height of the beam. This picture shows the goal of height adjustment. The issue is that the beam forms a waist and the most power of the laser occurs at the minimum waist diameter. The sweet spot of the beam waist can be placed in path of the beam by adjusting the height of the cutting nozzle.

To find the best height for minimum beam diameter, I used the thermally sensitive paper and looked at the beam diameter as a function of height. The first pass I took at this was by crudely changing the height while the shot a short duration laser pulse at burn paper. The smaller the dot on this burn test the better. This was repeated again to by starting at the general height from round one and using relative small turns on the vernier adjust. Up until this point the height adjustment was done without the copper cutting nozzle on the cutting head. I put the nozzle on the system and did more tests with the burn paper. If you look at this pic, you can see very odd things happen to the beam with nozzle on the cutting head. The beam is shifted around at the elbow using the adjusting screws until the crescent shapes around the central portion of the spot made by the beam is removed.

More electrical

April 12, 2010

…installed 7 more quad boxes, 6 in the grinder/storage room.

Passed inspection

April 9, 2010

Comments from the inspector (who thought a contractor installed my system, not me):

‘Man, look how old this breaker box is, those parts must have been expensive’.

‘Lets see, they did…this….and this here…Man, they did this thing right!’.

He was also fascinated with my automation system – not the laser, just the way I connected up all the appliances.

‘I got a cousin, he’s got lights, a fountain, a fish tank…he want me to hook him up with something to run it all — could I use this system? What all this called?!’

We gabbed about X10, his ex-girlfriend that had a laptop just like mine, and how his browser cant run flash. Pointed him to firefox.

Things to do

April 9, 2010

Today is a big day – and one that involves sitting around. The city inspector is supposed to show up and review all the electrical work. Since I have extra time (waiting for the inspector) and will soon have a major green light here’s a list of things I can do once the inspection is out of the way:

Electrical:

  • Install additional quad boxes in work area
  • Install additional quad boxes in storage/grinder room
  • Put the LCD screen on its own circuit (run the tv and welder, and bap! Circuit blows)
  • Install a retractable power cord
  • Install ceiling fan.
  • Mechanical:

  • Anchor drill press, grinders to concrete floor
  • Complete welding table (okay I could have done that anyway)
  • Build concrete work table
  • Make better use of the area underneath the subpanel
  • Install dust collector
  • Ventilation:

  • Install roofcap
  • Mount blower
  • Wire motor, with motor speed control
  • Run ventilation pipe
  • Build a noise suppression box around blower
  • Shoot neighbor who will probably complain about the noise anyway
  • Connect ventilation with welding table or install separate system
  • Laser specs

    April 9, 2010

    just in case you were wondering….and the laser manual.

    Laser beam path length

    April 8, 2010


    Finalizing my plans for purchase of new optics. According to the information from the sales guy at Laser Mechanisms the ideal distance for my new cutting head and collimator will be 350mm. The the cut quality enhancer and circular polarizer are a series of optics and its very hard to measure the length of the entire beam path. The sales rep at Laser Mechanisms gave me this drawing that shows a total length of 8.4 inches. The pic inventories all the distances in the optics chain which includes front brackets, the circular polarizer/cut quality enhancer, and a beam bend. The total is 13.45 inches or 341mm. This is passable because I think I can add another 10mm by adjusting the barrel of the extension out another centimeter.

    Additional beam size information

    April 6, 2010

    We final[ly] had time to ray trace your configuration. We have determined that using a 2.0x beam expander collimator along with a 2.5″ focusing lens will indeed produce a spot size ~150um with a DOF (depth of focus) of 2.2mm. Please note DOF is defined as 2x the Rayleigh Length. This only works however when the collimator is placed 350mm from the laser. It is also important to note that our 2.5x beam expander will not work at this distance. The full expanded beam diameter exceeds our 15mm clear aperture. Let me know if you have any questions.

    Best Regards,
    Gary, Sales Engineer, Laser Mechanisms

    Water temp meter

    April 4, 2010

    Home depot sells an inexpensive indoor/outdoor thermometer which I hacked a little bit to monitor the temperature of the water coming into the laser. I spliced in a brass tube on the line coming in to the laser and used heat shrink tubing to mount the thermometer’s sensor to the tube [link]. The thermometer mounts to the laser frame/support using a laser cut bracket that also has a magnet.