A 8" length of 4" diameter aluminium tubing was used as the outside of the muff. Two end plates were cut using the CNC router from 16SWG 6061-T6 aluminium sheet to fit the ends of the 4" tube and with 2" holes asymmetrically placed to position the heat muff clear of the lower cowl.
1.5" lengths of 2" aluminium tubing were welded into the holes. The forward one was positioned inside the muff to allow it to slide forward as far as possible on the exhaust pipe. The rear one is on the outside and once welded slots were cut into it to allow it to be clamped to the exhaust pipe using a worm drive jubilee clamp.
Then the end plates were welded onto the 4" pipe to complete the muff hot air box. Next step is to cut an inlet hole for the fresh air supply and two outlets; one for the cabin heat and one for the carburettor heat. These will have short lengths of 2" aluminium tube welded into place to take the 2" high temperature scat tubing which will be used to plumb everything up.
