As most long term members will know, I love large frame 20" bikes, minivelos and BMX... Obviously the holy grail bike in that style is the late 70's to early 80's Mongoose Moosegoose: Of course they are rare now and if you can find them, very expensive! Which made me decide to build my own! With some research I found this drawing: Add in some help from @Rat Rod and @RustyGold and I had enough measurements and angles to go on to start a build. I didn't want to cut up an early BMX to build this first one, in case I made some errors or found some issues along the way, but I do have a few newer BMX frames and complete bikes that are not collect-able or worth much, most of which are cheap bike store bikes or even department store ones, so decided to build one out of these frames and parts. The build will end up heavier and with oversized tubing compared to the originals, but it will give me the information I need and still be a cool bike on its own merit hopefully. The main donor picked from the pile would have been a half decent bike at some point, a roughly 2005~ish Mongoose Menace Pro, but it had some dents in the main tubes and some damage to the chain stay and a sanded down headtube for some reason: Perfect donor to build my "Moosegoose" from! Started by measuring and then cutting the frame up, separated the rear triangle out and removed the bottom bracket but left the seat tube attached, fitted some of the parts to my jig that was set to the right angles and measurements: Needed to extend the chainstays, so cut some tube and sleeves: Thankfully I was able to fudge the 1 degree less seat tube angle by just tilting the seat tube back before tacking them up: Next up was extending some forks and the headtube, I didn't have any Mongoose forks, so decided on some Diamondback ones, they needed a 4" extension: Cleaned and drilled for plug welding a sleeve inside to add strength due to the extra length: Plug welded: Of course I needed a 4" extended headtube to match, so another DiamondBack frame donated its headtube to make that happen: After surgery: Then I could fit the forks and headtube to the jig and set it to the right angle: Then measure for the downtube, cut from some 1.5" diameter tube and hand fish mouth the ends: I went with 1.5" tubing rather than the smaller tubing of the original to help balance out the oversized stays and headtube. Tacked that in place and then I could measure for the seat tube, I still have not found a local supply for the tubing to make my own seat tubes (probably going to end up ordering in Chro-Mo once I get better on the TIG) so an old Repco mountain bike donated to the build too, added a small sleeve of 1" tubing inside the join: New pinch point drilled and cut on top and then tacked it in place too: That was as far as the build got today, but I had to throw some parts at it and some tape lines on the frame to get an idea of how it will look when the top tube is done and the seat stays are raised up: I'm very happy! Measurements and angles all add up, and it looks good. Looking forward to finishing it off, assembling it and going for a ride!