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  1. #21
    Found these on ebay, look ideal for you

    Click image for larger version. 

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  2. Talking of lasers I did this the other night just as a concept idea.

    Used a sheet of 3mm MDF and cut 5 shapes out.

    One had the centre profile deleted.

    Just bolted together to show the idea but in real life these would be glued and dowels fitted to line up.

    Another shot at an angle and with a bit of cleaning up with emery cloth.

    It's noting special, just a drawing of the top of my head but from concept to finish was 20 minutes.

    What for you ask ?

    Pattern for sand casting, in some cases like this cover it's far quicker than using a router as the centre is taken out as a profile as opposed to a pocket.

    Each layer can be made slightly larger than it's predecessor to give a draft angle.
    John S -

  3. #24
    I think the biohazard one looks better, and just as useful...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #25
    It's noting special, just a drawing of the top of my head but from concept to finish was 20 minutes.

    You've got a funny shaped head John

  5. #26
    Okay, I admit it, I destroyed the blooming thing

    It now has a new tube, tube mounts at the correct height, a proper power supply and it doesn't have a millimeter crust of black gunge on the lens. Probably from cutting plywood. Not me, I found bits in the bottom of the case

    I've been doing the laser forums and there's more to this laser malarky than I realised. Back to school again I suppose. I see that Wee Davy Cameron thinks us over 60's should go to university

    It's mostly a cooling thang. You pump water through the tube, perfect temperature is -28 C but you actually have to keep above the room dew point because 20kV and condensation can make life interesting. Room temperature is fine and dandy but if you let it rise much above 30 C you lose vast amounts of power. Bubbles in the tube are a big no-no because you get hot spots. I have to fit a radiator (on it's way from China) and a big fan. I also need a flow detector which cuts off the PSU if the water flow stops, but I can make that.

    As far as I can make out, the best thing you can do with a 40W is cut perspex. It goes through it like a hot knife through butter even when turned right down, but apparently blowing air down through a nozzle mounted over the lens is a good idea. The perspex vapourises. You want to clear it without condensing it or something like that.

    I also plan to attack it with an angle grinder to redesign the fume extraction. The current system has way too much fan for the ducting, plus he hasn't cottoned on to 2 simple facts. Air doesn't like abrupt changes in duct size. Getting the desired flow is as much about where you let the air in as where you take it out.

  6. #27
    Condensation does indeed cause problems and not just due to the HV. We have had it on the optics as well and it dont like it. As you have found out the optics have to stay clean and free from scrathces as well as this causes them to absorb power rather than transmit it, then they go bang. Done that a few times as well, takes ages to clean out the flight tubes and re-align the machine. Cutting assist air, air blowing through the nozzle, is a must as well. It helps to keep the lens clear of crap, cool it and blow away the cut material.

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