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I have finally decided to add a laser cutting head to Tweakie.

The original plan was to optically couple my existing YAG laser but vibrational issues and differential movement between the laser head ( which is far too long to fit directly to the machine) and Tweakie itself has ruled out this possibility.

The alternative (and much more practical) approach is to use a laser head of a size more suited to the machine and as it happens a 30 Watt CO2 laser tube is just the right size to mount inline with the X axis of the machine.

As a project this is far more involved than it may at first seem, there are many issues to be taken into consideration and I will try to describe, as best I can, my progress success and failure.

This is an ongoing project and it will take some time for me to complete but complete it I will sooner or later.

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1) The head end of my YAG laser. It operates at a wavelength of 1064 nm and although this wavelength is invisible to our eyesight the 99.8% reflecting rear mirror is transparent to the 633 nm wavelength of a HeNe laser. This fact allows a low power, visable, sighting beam to be added easily without the necessity for a beam combiner and itís associated power losses. Apart from itís physical size the biggest disadvantage with using this YAG is itís inefficiency. The light source used to excite the laser is rated at 6,000 Watts and the water flow for the arc lamp, YAG rod and Q switch cooling is mega, not to mention the power consumption of the heat exchanger and RF source needed for the Q switch. As stated earlier the idea of using this with Tweakie has now been abandoned in favour of a much smaller device.

2) This is a 30 Watt CO2 laser tube as packed from the USA. Who knows why these things donít actually get broken when you see what the postal services do with the packages ?. This tube is approx 1/3 the length of the YAG head and operates at the longer wavelength of 10600 nm. Not so easy to add a sighting beam as the rear mirror is completely opaque to the 633 nm of the HeNe therefore a beam combiner will be required.

3) My first part of the project is to provide an area to mount the laser tube to the machine and to this end I have constructed some more framework which will be bolted to the existing frame (electric welding to the existing frame is out of the question at this stage so bolted on it will be).

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4) This is the first time I have used the flux cored / coated MIG welding wire and boy does it spitt. Back to using the plain wire and gas a.s.a.p.

5) The new framework, painted and bolted in place on the rear of the machine.

6) Mounts for the laser tube - these have been designed to provide two pads centred at 120 degrees with the tube held in place against these pads with bungee cord . The 15mm plate was cut to size, the hole milled, then cut in half and finally the slots milled. The black pads are made of neoprene and held in place with adhesive.

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7) The bungee cord lengths have had spring steel loops made and fitted to the ends and cosmetically finished with heat shrink sleeving.

8) Laser tube securely held in itís mountings which have not yet been fixed to the alloy plate which will form the stage for the optics etc. As the wavelength of the photons (if they can be called photons) emitted from CO2 lasers do not travel well through fibre optics the beam steering must all be done with mirrors and for obvious reasons, these must be mounted as rigidly as possible.

9) Mountings for a HeNe tube made in the same way as the CO2 tube mounts. This little fella will eventually be used with a beam combiner for beam positioning.

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IMPORTANT

 

There are dangers associated with this project of which you should be aware.

 

1) Extremely high voltages are involved which, given the right conditions, could cause electrocution.

2) The laser beam will burn and could cause serious personal injury, especially to eyes.

3) Many materials when heated or burned produce fumes, vapours or particles which are extremely toxic.

4) Combustible materials may catch fire when being cut with a laser.

 

Do not attempt this project unless you fully understand the risks involved and are satisfied that you can implement all necessary safety precautions to prevent injury to yourself and others.

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10) The PSU which consists basically of a TV line output transformer capable of providing some 18,000 Volts at 20 mA. The output power can be switched on/off , with a short rise time, from a TTL level signal and the current varied using a 0 - 5 Volt analogue input. Like most things these days, it was manufactured in China and extremely well too. A PSU data sheet can be downloaded from here PSU.pdf.

11) The PSU will be mounted inside a new enclosure so that it can be safely fitted to the framework of my machine. This is the progress so far on the enclosure - now to cut all the holes etc.

12) New enclosure nears completion. The mains input connections and the control signal connections are now made within the enclosure.

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13) Complete with engraved warning label the new PSU enclosure is almost finished, just a couple more components to be added.

14) To plan the best beam path between the laser tube and the Z axis I have constructed another frame to hold the little HeNe laser. The OD of the frame end plates are 50mm (the same dia. as the CO2 tube) and it fits snugly into the CO2 tube mountings. Having a visible beam here makes the mirror positioning and adjustments surprisingly easy. The design criteria is to have the beam path run exactly parallel and plane with the X axis of the machine so that it hits the Z axis deflection mirror in exactly the same place no matter where the X axis is positioned along itís travel.

15) This is the wooden (MDF) Ďmock-upí of the beam steering fixture with adjustable mirror mounts, also made from MDF. A few modifications are still to be made and tested before I commit to making all the final parts in aluminium. I doubt that the beam from the C02 tube will be truly concentric with its glass envelope so some means of adjustment of the complete fixture must also be designed in. Incidentally, the mirrors I am using here are just for working out the best beam path they are fine for the 633nm wavelength of the HeNe but they would not be at all suitable for the 10600nm of the CO2 laser.

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16) Component parts of the mock-up mirror mountings.

17) Rear view of the assembled part.

18) Mock-up of the final Z axis deflection mirror mount. This mirror moves with the X axis travel but does not move relative to the Z axis. Of the three mirrors, the first mirror is positioned in line with the laser and adjusted to centre the beam on to the second mirror - the second mirror is adjusted to align the beam path exactly parallel and plane with the horizontal X axis movement of the machine - the final mirror is positioned in line with the centre of the beam and adjusted so that the beam is deflected vertically downwards to hit the table perpendicular in both planes.

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19) Newport adjustable mirror mounts for the final beam steering fixture. These were not cheap but considerably better quality than the Chinese alternative.

20) New bracket made for mounting the Z axis deflection mirror. There will probably be some more machining necessary to get its position Ďjust rightí.

21) Third time lucky for the Z axis deflection mirror mounting. This part has been remade so that a cover can be fitted to protect the mirror from dust etc. The mirror itself has also been mounted a lot lower and the deflected beam now passes through a hole in the base plate.

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22) Now that the geometry and dimensions have been established, the Ďmock-upí beam steering fixture has been replaced by an aluminium box section with the mirrors mounted internally. End plates will eventually be fitted to the box section and this form of construction should protect the mirrors and keep them free of dust and other contamination.

23) It is a bit difficult to visualise but the actual beam path is indicated here by the yellow lines. All three mirrors used are 25mm dia. gold coated silicon

24) This is the focus lens I am intending to use. It is 12mm diameter and made from Zinc Selenide (ZnSe) with a focal distance of approx.40mm.

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25) Underside of the focus lens mounting. The position of the central tube is adjustable and held in place by a pinch bolt within the flange.

26) The focus lens mounting top view. This is probably a lot more complicated than it needs to be but aluminium is such nice stuff to machine it is difficult to know when to stop.

27) The finished lens mount. The lens itself is retained by the central sleeve which has been anodized and dyed black.

28) The EHT power unit has now been fitted to the side of the frame and the enclosure for the CO2 tube has been constructed (front and top not yet fitted). My machine is now starting to look very crowded but I still have the water cooling system and laser control panel to construct and fit. Incidentally none of these additions will prevent the router being used with a spindle as originally constructed.

29) This is my first thoughts for the laser control circuit (click on image to enlarge). It is liable to be changed after I have thought about it a bit more but this is more or less the direction I will be following.

30) And this is the proposed cooling circuit using a circulating pump and a 3 fan forced air radiator.

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31) Gems Sensors flowswitch from the USA. For this I have made stainless / phenolic connectors for my pipework which will be attached to the ends of the sensor using 1/4 NP pipe fittings.

32) 12 Volt, continuously rated, brushless, circulating pump from Taiwan. It has a ceramic shaft, plastic impeller and stainless wear plate with a lifetime expectancy in excess of 40,000 Hours. (Should be better than some of the windshield washer pumps advertised for use with CO2 lasers). Looks big in the photo but this pump is quite small with an overall length of 90mm.

33) This is the position the radiator, circulating pump and flowswitch are fitted to the side framework of my machine. As I have been unable to obtain a stainless steel radiator, at a reasonable price, my second choice is to use a computer CPU cooling type. This is made from brass and will, no doubt, cause conductive contamination of the cooling fluid over a period of time so regular changes of coolant will be required. Just how frequent these changes have to be is, as yet, unknown.

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Safety is no accident.

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