> Hey guys,

> OK, I'm in the way early stages of building Joe Greenley's Silver. After
> attaching all the forms to the strongback, I was starting to feel like
> maybe my center line was suspect...and I was worried about moving on
> without feeling 100% sure that these forms were lined up right...so I blew
> $110 on a laser level. I've found that my strongback (a boxbeam built of
> 3/4 ply) was bowed in the middle. By about 7/16 of an inch. (I know this
> bowing is not uncommon). I've also confirmed that the floor itself is not
> level.

> Here's my question: is it ok if I don't correct the bowing and instead
> just go ahead and plumb the forms up using the laser level? can I be
> assured that the bowing won't get worse going forward and screw things up?

> p.s. If anyone in the Boston area wants to borrow the laser level, let me
> know! :)

If you use a construction laser level, it needs to shine on something - so holes will only work if you put marked plastic across, plus I think it only gives a horizontal level - ie no vertical orientation. So same as w/ the water level it will not give vertical alignment. And each involves a bit of setup and only good when only minimally stripped - while string is forever - as long as you can see inside. The construction laser I saw threw a line about 1/4in wide - so pretty tough to estimate down to 1/32in - but there're probably others around - maybe it can be focussed.

So spend the BIG bucks (break the bank at 25 cents!) and use two stringlines! My accuracy at 8feet is 1/128in after the string has been untouched for 8 mos(my word of honour)at 16feet you'll get somewhere around half. The string is just twisted nylon at .031 - .033 in. diam. - about 1/32in. Then you can check it absolutely any time you want and easily too, and at any orientation - sideways, upside down, leaning against the wall, on the roof rack - dont matter at all b/c no levels or horizontals are being used.

For stiffness, you could maybe use my method but use 1 1/2in mat'l for spacers and wedges - larger x-section under compression, but a stiff member ( straightness not req'd) is really what is necessary to start. I don't have the experience to judge, but I would be annoyed it my strongback was deflecting appreciably and therefore having to use a ctr support. In any case the form holes HAVE to be oversize - otherwise you can laser or string or pipe to your heart's content but be able to do NOTHING about it b/c you can't shift your forms around.

Basically any stiff spine will work as well as any careful measuring, but string makes it all easy.

see link below

-mick