DIY 20/40mm heat exchanger

[Tripleaj]

Looking into making a heat exchanger and have a heap of 50mm and 20mm copper pipe available.

Anyone share how or the best way to drill the hole through the 50mm copper elbow to insert the 20mm.

Was going to make a guide and use a hole saw or use a 50mm "T" with a reducer to fit the 20mm.

Any help would be appreciated.

[swifty]

http://www.nzjetboating.com/yabbse/index.php?topic=22263.45

[Jimmy Jet]

Accurately mark out the hole, clamp the elbow down the and drill it undersize with a pistol drill, say 12mm, and take the rest out carefully with a die grinder. By using the pistol drill you can drill perpendicular to the elbow and avoid the drill skating off the radius. You can get really accurate with the die grinder and copper is so soft it will take no time.
Spray a bit of wd40 or kerosene on the carbide burr and it will help prevent the burr clogging in the soft material.
Regardless of the way you weld it up any gap will fill really easily.
Get amoungst it.

[Moab]

Here is a great video about making one of these

http://youtu.be/ZKrPT0_vSug