SB2 > D8 fitting problem

[will_08]

Hey guys,

ive been pondering this in my head for ages now and it doesnt make sense to me. at the minute ive attached both SB1 to the base tube BR12. I then tacked D7 and D8 (ive linished the tubes as in the book)

But where D7 is correct ie it finishes 491 from the base line, and ive went on a trial fitted D5, 9 and tr3 which all fit. D8 will not sit right, ive marked 491.5 from the base line and lined the end of D8 with that when i try and butt it up to SB2 its well out.

Thinking the SB1's werent leaning right but from measuring SB2 to Br12 both corners are 151 as per the book.

Other checks ive done U4 and U5 are the same distance from base line. and my diagonals are the same

any advice appreciated Will