14 until the welding is completed the clamping operation preferably takes place when support 16 has been moved to the loading station of fig1 b at the loading station an alignment bar 24 is mounted for setting the proper spacing between the tubes 22 and assuring that the tubes are axially aligned with each other fig3 and fig1 b show the aligning station which includes an alignment bar 24 such as a plate mounted in any suitable manner such as from overhead rail 26 so that support 16 can pass under aligning bar 24 where holders 12 and 14 are laterally movable holders 12 and 14 are manipulated to move in a lateral direction unitl tubes 22 22 contact aligning bar 24 preferably contoured clamps 18 20 on holders 12 14 may be opened sufficiently allowing the tubes 22 22 to be axially moved until the tubes contact aligning bar 24 clamps 18 and 20 would then be reengaged to firmly mount tubes 22 22 their respective holders in such case the tubes would be initially loaded while at aligning bar 24 clamps 18 20 may be of any suitable form such as having complementary grooves associated with grooves in holders 12 14 the clamps may be closed in any suitable manners such by springs or threaded fasteners fig1 c and 4 illustrate the next phase of operation wherein support 16.