Still July, still pluggin’

Calliope #5 progress
–Well gang I’ve been plugging away on the plenum and I’ve made progress despite a setback or two. Yesterday I got the last bushings welded onto the top so now there are 13: 3/8” pipe connections on top. When that was done I started machining the attachment point on the side of the plenum where I’d fasten the vacuum cleaner hose connector. Sure as shit I made a mistake and got two of the holes drilled off by 0.1”. No problem, thinks I, I’ll just flip the part over and do the hole pattern again on the opposite side, then I’ll TIG the wrong holes to seal ‘em up.
So I got the 12 holes positioned correctly on that side, set up the Tapmatic in the drillpress and started tapping. Imagine my surprise when, long about hole #6 I broke a tap! So much for plan B, eh? Well I got desperate and had a go at an improvised solution. I ground down one end of a hex key, making it pointy enough to sit atop the broken tap and as carefully as I could with my rotten eyes I welded the two together. It took a couple of tries as the tap remnant shattered once more, but eventually I had a decent purchase on the thing and I got it out! I put the initial failure of the tap down to using the wrong lubricant. I took a sniff in the oilcan and it smelled more like way oil than Cool Tool, which I prefer for tapping all but the hardest materials.
–Anywayyyy with that predicament solved I bored out the center with a trio of endmills, finishing up with a 1” roughing endmill. I want the hole to be big enough to get adequate air thru, but small enough so that I can cut an O-ring groove in the space between bolt circle and air hole on the aluminum hatch cover that will eventually cap the space when I switch from air to propane.
–Final work on plenum: capping the ends with some 1/8” plate. I got one end plate milled and ground, then tacked in place last night. Today I’ll make up the other end plate but this one will have a hole in it and sport yet another 3/8” weldable pipe bushing which will eventually be the attachment point for a string of pipe that will become the pilot light for the pyrotechnics.
Latest photos are the last 6 in this set:

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