dsmyers

I'd like to fabricate a longer boom for a tandem stoker stem I currently own. It's a Control Tech stem made up of two pieces. One clamps to the captain's seat post and provides a ~5 inch female extension, and the other is a 28.6 mm (OD) boom that slides into the first piece and provides a quill-style handle bar clamp. I was thinking I would just replace the boom with a 28.6 OD length of 4130 and clamp a threadless stem to it. So, I have two questions:

1) Can anyone recommend the appropriate wall thickness? I was thinking 2.1 mm (0.083 in from Dillsburg Aero works).
2) I'll need to have the new boom powedercoated or painted to avoid corrosion. How much is this going to affect the fit? If I use something that already has a 28.6 mm OD, will it no longer fit once painted/powdercoated?

Thanks,
Daniel

unterhausen

can you just make it a fixed length? My tandem stem is the seat lug off of a wrecked bike with a tube to clamp the bars. Come to think of it, I should make a nicer looking one.

Clamp tubing:
1.375" .058 for 31.8 bars
1.125" .058 for 25.4 bars
1.125" .049 for 26.0 bars
Extension tubing:
1.125" .049

unterhausen

powdercoating does have a significant thickness, but I'm not sure how thick it really is.