Introduction: Blow Torch Revamp
I borrowed my dad's blow torch. Having used up the little bit of gas there was left with it I discovered 2 things. Firstly that half the plastic lugs that attached the head to the gas canister were broken off. Secondly that the style of gas canister it used were obsolete. I had to buy a new torch to finish the job. I didn't bin it as I thought it might be possible to adapt it to take the EN417 threaded gas canisters or usable as a burner for a small forge.
Step 1: Investigate
Ok take it apart and see what the options are. The broken plastic clip seemed to be held to the burner head with 2 screws so I removed them. I was surprised how long they were then I discovered that was because they held the 2 parts of the burner head together as well. A new gasket will probably need making for this unexpected joint.
Step 2: Options
I half hoped that an EN417 converter might be available as a spare part. No luck too old (30+) it also seems female EN417 fittings are only available as part of an appliance. Offering a 1/4 to 3/8 bsp Adapter up to the base revealed there was insufficient metal to tap to take a threaded pipe tail. A quick release gas tail looks as if it should fit with out obscuring the fixing holes. Cutting a disc of brass the right size drilling it and silver soldering a gas tail in place is one option. Fixing a brass gas tail to the broken plastic with car body filler and using that as a pattern to cast a fitting in zinc alloy is another.
Step 3: Making a Pattern
I found a chipboard screw thick enough to be a good fit in the brass fitting I had and long enough to pass through it and the plastic and into a section of chip board. It is half of quick release bayonet hose coupler. I filled the screw holes with soft wax to make it easer cleaning them out to hold core pins. I roughly filled the top of the plastic to hold the brass fitting an smoothed around its base to provide a thicker section with car body filler. Once the initial set has taken place the brand I use carves easily with sharp tools before setting hard. A few voids in the stem base needed a little more filling and a wrap with foil saves any further soothing.
Step 4: Mould
I happen to have a delft clay kit for casting small jewellery parts, This item was too big for the standard ring so I made a mould box for it. (I should have thought to do an instructable for that as well.) The process is part way between that described with the kit and the instructions for green sand moulding in:
The charcoal foundry by David Gingery
Place the lower section of the moulding box top side down on a smooth flat surface and fill with clay, work in layers 1/2"~1cm at a time firming each layer in with hard thumb pressure once full give another good firming with just hand pressure and strike level with a straight edge.
Turn it over so it is standing on its bottom, the top surface should be smooth and flat if it isn't press the clay out and start again and get the spread of clay and pressure more even this time. I trimmed the screw I used to hold the pattern together whilst forming it and fitted dowels to the 2 screw holes to act as core print patterns
press the pattern with its core print pins half way into the clay surface.dust with talc and brush/ blow off any surplus. fit the top section of the moulding box. There are locator lugs on each end that mean the 2 halves can only be assembled in one way. Crumble clay over the pattern and press firmly in with your fingers once the pattern is fully covered the clay can be layered and pressed in in the same way as it was with the lower half. Once full and well pressed down strike the top level. lift the top half of the box off the pattern.
Step 5: Vent
The instructions with the clay say push a needle through the clay to form the Entrance and exit vents (runner and riser) I find it better to use metal working drills turned slowly with the fingers to cut them. I used a 6mm~1/4" drill at the highest thickest point for the runner cutting a cone to act as a pouring funnel whilst the drill was still in place, and a 3mm~1/8" at the tip of the gas fitting for the riser. The top section was then set aside.
Step 6: Fit Core Pins
To form tubes in the finished casting means putting cores in that can be removed after the casting has cooled.
In his book on building a lathe David Gingery suggests sooted steel cores can be driven out of a finished casting so I decided to give this a try. I found some plain steel nails the right diameters for the cores I needed cut them to length sooted them all over with a candle and laid them in the voids left in the mould by the dowels. The pins for the mounting holes have the points sawn off and are filed smooth and are positioned so the tops are flush with the top surface of the mounting disc. The nail being used for the gas tube core has the point left in place and is positioned so the point is only just clear of the bore. Blow any particles of clay out of the whole void in the lower section of the box first.
Blow any particles of clay out of the void in the top section of the box and put it back in place
It occurred to me while fettling up the finished casting had I used brass tube of the right bores instead of steel pins I could have just left them in place. With the benefit of hind sight I would use a section of brass tube of a suitable bore instead of a core pin for the gas tube. Then after casting trim its ends down and leave it in place. but still use steel pins for the cores of the fixing holes.
Step 7: Cast
Casting zinc alloy also known as pot metal because you can melt it in a pot on the stove.
Risk from fumes, a lot of warnings are made about this, it is not an issue here. You get zinc oxide fumes when the zinc starts to burn, at 2 to3 times the temperature we are using here. Still work in a well ventilated area preferably out side on a non flammable dry surface. The clay gives off an oily smoke and burns a little.
Ignoring all that I used the kitchen work top, I do how ever have a box of insulation tiles as used in school chemistry labs, they cost about £1 each in a box of 10 from my local school science supplies store or £7 each from the jewelers supplies, sold for exactly what I'm using them for here. you can heat then to glowing red one side and just about touch them with your bare hand on the other. I've glued mine to cork tiles for secondary insulation and they don't scratch the work top.
Gauge how much metal you need add a bit more, I'm using a pressed one piece stainless steel ladle brought especially for this, I normally use a refractory clay scorifier which is heated with a blow torch from above, and just about takes a lorry wheel weight (and yes they are mostly zinc alloy these days you know if you get a lead one as its a heck of a lot heavier for the size) before you start heating press a few wells into a pot of the clay to cast off the surplus metal, Dress for what you are doing, Leather gloves leather shoes/boots leather apron. NO man made fibers unless it is ceramic cloth. A cup of molten zinc is going to give you 3rd degree burns if you spill it even if it is only at 500 degrees.
To avoid unnecessary movement I used a camp stove as my lower heat source whilst heating from above with a blow torch once molten I skimmed the little bit of slag that formed to one side with a bamboo skewer and keeping the torch on the surface poured the molten zinc into the runner well with a quick steady flow once it came out of the riser I poured the surplus into one of the wells. Put the ladle down, switch off all the gas and let every thing cool, a bucket of dry sand to put the ladle in would have been good but the insulation tiles did their job.
Step 8: Knock It Out
Once it has cooled open the mould box and remove the casting. Push the block of clay out onto a pice of paper and split it apart with your fingers.
Step 9: Recover Clay
Most of the clay can be re used dig the burnt areas out with a small spoon and dispose of in the bin, with a little more care I could probably have saved more than I did
Step 10: Drive Out Core Pins
Now for the hard part. File the top surface of the base so the tops of the pins for the screw holes are visible. Support the casing on a solid base that he pins can pass cleanly through such as a sturdy bench vise or a couple of solid wooden blocks use a punch smaller than the diameter of the pins and drive them out with hammer blows to the punch. these two are comparatively easy the gas tube core is a different mater.
The point of the nail was left in place and only just clear of the end of the pattern with good reason. It is going to mushroom as you hit it to drive it out if it becomes bigger than the body of the shaft it isn't going to go. file off the point just enough that you have a flat surface to hit with the first blow. Support as before and hit the top of the pin as hard as you can with a hammer once moving and almost in to the casting file the top smooth and right down to the casting, now using a punch start tho drive the pin through the casting. if your punch has a tapper stop using it before it is touching the casting you don't want to risk splitting the casting, continue using a nail slightly smaller than the one used as the core pin as a punch until the core pin is free of the casting. Whilst this did work it isn't how I would do it in the future if I could help it, see earlier note on using a brass tube instead of a long core pin.
Step 11: Clean the Casting (fetteling)
Use a file to clean up the shape of the casting and to give a flat under surface to the main disc and smooth edges to the central lug. Also as I didn't pay enough attention when making the pattern I had to file down the sides of the shaft to permit the screw heads to pass. They were also recessed into the base, something I also hadn't allowed for. Fortunately this just required carefully drilling part way through the casting. I also managed to strip one of the threads not having a 4/40 repair set I drilled out and re-tapped the threads to M3 and replaced the original screws with a couple of M3 socket head screws.
Step 12: Gaskets
To make the lower gasket I cut a disc out of a standard manila envelope of about the same diameter as the recess in the base. I pressed this disc firmly into the recess then cut out the oval in the center with a craft knife using the wall of this recess as a guide. This took a couple of goes to get right and I omitted to take a photo of the good gasket eventually produced
I reused the gasket at the top with a smear of gasket sealant on both metal faces, and when fitting the custom made gasket for the new large base joint, again both metal faces were coated with gasket sealant.
The new screws were then fitted and tightened down with an allen key. surplus sealant that oozed out of the joints was scraped away and the residue removed with a rag dampened with methylated spirt. Clearly this gasket sealant is not suitable for use with alcohol as a fuel, so care should be taken when selecting your sealant.
Step 13: Testing
A length of gas hose and a regulator were connected to the new gas tail. Use the correct size hose clip, over sized clips when pulled in too tight can lead to an ovaling of the supply pipe and there by leaks.
The valve on the blow torch head was closed and the assembly placed in a tub of water. The regulator was then attached to a gas cylinder and switched on.the joints were checked for leaks. No leaks being apparent the gas was switched off and the torch head removed from the water and dried.
The gas supply was then reconnected and the torch tested on bottled gas. the flow of gas from a 30 mBar butane regulator is clearly not enough for the torch to function properly. There are 2 possibly 3 alternatives. Propane with a variable pressure regulator. A European butane cylinder with a hand wheel valve and no regulator. Modify a UK bayonet fitting butane regulator to supply a higher pressure and flow rate.(that is an instructable in its self and it isn't as simple as I first thought.)
