Micro gas torch (07/09/10)
I had seen photos in catalogs of the beautiful "Meco Midget" gas torch and was so impressed by it I decided to have a go at making one. I've a small supply of different sizes of hypodermic needles which would be ideal for tips.
The supplier I used for the hypodermic needles was Medisave (http://www.medisave.co.uk/). Surprisingly, you can order all sorts of needles and syringes online without any problems. A pack of 100 needles is only £3 or so. I used two sizes - 21 gauge (0.8mm OD, 0.5mm ID, green) and 18 gauge (1.3mm OD, 0.8mm ID, pink). When I bought them, only sharp needles were available so I had to carefully sand down the ends before using them. Blunt "drawing up" needles are available, but they were out of stock at the time.
You can also get all-metal needles, which are better for using as torch tips because the plastic ones tend to melt after a while with the heat that travels back down the needle. One site that was suggested to me was http://www.dispensinglink.com/SS%20Reusable%20Needles.htm, although they are in the US.
Here's some pics of the Meco Midget torch. This is available from several places on the web for around $100. These aren't mine - they're from the web.
Below is my version of the torch. A CAD file of the parts is available here. I also found an interesting patent on another micro torch which shows the internal mechanism - see here. Note that the final design is slightly different from the CAD file since I made small modifications as I was building it.
The body is based on a piece of 1"×½" aluminium bar. Gas enters via two brass nipples which also act as the seats for the needle valves. The needle valves are made from two parts - the needle + stem itself and the aluminium knob. This enables an O-ring to be used to seal the needle (if the valve stem was machined from solid with an O-ring groove, it would be impossible to stretch the O-ring far enough to get it over the main diameter of the valve stem).
The outlet is via a 1/8" stainless-steel tube. A small brass piece is soldered to the end and is turned to the ~1.2° taper required for the Luer fitting on the needle. The needle is then simply a press fit on the end of the tube.
The propane inlet connection was a 3/8" left-hand BSP thread, which gave me an excuse to try left-handed threading on the lathe. I'd never done it before (plenty of RH threads) but it went without a hitch.
The end result is a fine flame which is ideal for delicate soldering work or (as was originally intended) cutting glass tubing by scratching and heating. The valves are rather sensitive, but manageable.
15/05/11: I needed to get a lot of heat into the end of glass tubing for forming a flange, so I made a little ribbon burner. It has 0.4mm diameter holes on a 1mm pitch, and is about 30mm long.
Here's a video showing the flame being adjusted.
Page last updated: 7/07/2012, 01:50:00 AM BST
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