Just thought I'd add a note here.  I've also built a few Lehman assy's  When 
I needed to loosen one side or another of the vertical pipe risers I was 
troubled by some looseness.  I fixed this by carefully cleaning the threads 
in the flange and pipe, then used conventional plumbing flux and solder to 
solder them firmly in place.  Make sure it's right before doing this!!  
Pehaps an epoxy compound would work as well.   It worked great.  Indeed  I 
also found that 1/2 inch pipe is adequate.  Good Luck,  Mike
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