Jonny69's inventing shed: Giant Spudmatic gun

[Jonny69]

On another forum I'm being pestered to put some more of my toys online so I'm going to run a series of threads and show you what I've got in my garage. I'll start with the spudmatic gun I made today and move onto some of the older stuff as my bandwidth allows

So, plan is to make a little reservoir out of steel tube that I can pump up with a bike pump and have a ball valve at the other end to let it all out at once. No fire, reliable and repeatable tried and tested method which I used last week on one of the gags at work, for firing a model Polaris missile.

Start with a bit of 75mm tube, this bit is 250mm long:



It needs two endcaps, one with a hole in it. Cut these out with a 1mm blade in the angle grinder, then clean them up with a flap wheel. The hole is cut with a Screwfix holesaw which has lasted just 3 holes in 2mm steel:



(I'm not all pro using engineers blue but the way, the steel I had happened to have it on already)

Through that hole is going a brass tank fitting, a common plumbing fitting for 15mm copper pipe:



Fits through the hole like so:



I've drilled a hole in the side so I can squish through a tyre valve that I got from the local tyre place:





This is the only difficult bit for most people, welding the ends on:



The tank fitting needs to be tightened up before the end is welded on so I cranked it up paggin' tight with some PTFE inside, welded in short stitches and cooled in water each time to stop too much heat getting to the brass:



It's assembled with a lever ball valve tap thing, again, another common plumbing part with compression fittings so no tapping or soldering needed:



And this is how it works, fairly self explanatory:



Testing.

The good news is it works pretty well. The pump is a bit rubbish but 40psi sends a 15mm slug of potato clean over the 3 stories of flats in my building. 100psi sends it right over the block adjacent and 160psi which is pretty much all I can manage with all my weight on the pump goes about 75 metres down the road with a bit of recoil.

I'm chuffed, first toy for the camping trip in June is complete. Better stock up on potatoes