i was wondering if anyone could tell me how much of the rated line class of a blank is reduced if cut off from the butt? the blank in question is a 7 foot fiberglass blank which has a 12-40 lb line rating, i want to cut a foot off. any help would be much appreciated.

That's going to be almost impossible to answer because the "line class" as listed is just the manufacturer's subjective idea as what might be a good range for that blank. Doubtless you're going to lose some power, but about all you could do there is run the CCS ERN figure, then slide it back in a foot and run it again. At least that way you could put a percentage power loss on it. But as far as the line range suggest, you don't have a solid place to start from. You could factor the ERN percentage drop and then apply that to the top end of the line range. That's about the only way I can think to do it.

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Scott, why not just buy a 6' blank that will work for you instead of possibly ruining a perfectly good 7' blank? A 6' fiberglass blank is not that expensive and will save you time, work, and a probable headache.

thanks for the advice, i will get another blank.

Thanks Mr Kirkman, Having just started this rod building caper most of what you said has to go into the ' i have no idea of what your talking about basket', however i shall learn more as time permits. i bought your book bye the way, very helpful it is. i will get another blank or just build the 7' one, i was mainly wondering if there was a simple way of calculating line rating drop. which it seems there isn't! thanks for your help, keep up the good work.