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Bent&Perfect S/B Form Alignment Issues
By:mick allen
Date: 1/19/2011, 5:55 pm
In Response To: Re: Strip: Setting up forms (Dan Thaler)

: I'm still curious whether anyone has used
: the spacer and wedge method and whether this will indeed
: straighten the beam when tightened.

I use a different spacer, wedge, & wood strongback technique, but may have a few insights on what you mention:

- Theoretically if the spacers were perfect, the form threaded strongback could be even completely replaced by one or two ¼” diameter cables attached to the endforms & temporarily stretched – initially like forms dangling on a string without any strongback at all. Stretch the cable(s), spread out the forms, and fit the saddle shaped spacers on the wires.. If the wedges were evenly spaced around the centre spacer, jam them in and everything would be perfectly fixed - if the cables had stoppers set at the correct length. Theoretically.
- The two endforms would have to be level w/ ea other in order to keep the stretched cables in alignment that in turn keep all the forms in alignment.
- The present interlocking central spacers and asymmetric wedges would have to be simplified to keep even wedging around the strongback – but easy to replace that odd, double setup with a simple saddle( like all the others) but w/ one end shaped to receive the 2 wedges – but opposite ea other.
- So the bent strongback in your case, might be similar to the cables mentioned above – if the bend is not localized, if the strongback can be easily bent back , if the present asymmetric wedge system has wedges on the correct side to take the bend out, if the strongback has no twist, and if the forms do not need further twisting and realignment after the wedges are driven and the strongback is straightened. If any of those requirements aren’t met, I would anticipate difficulties that put the facility of the method into question.

So, simple in concept, awkward in practice, but just maybe possible. I have the impression that it would take a lot of wedge pressure to take the bend out. The one time that I noticed movement caused by the wedges, I took everything apart including the strongback and found that several inner s/b plies were already broken for some reason (but this was a different approach where wedging stress was more localized).
The aluminum strongback process that you refer to: presupposes a perfectly straight and untwisted strongback, is stiff enough to resist (unnecessary) asymmetric bending forces, requires the use of forms that have very precise and tight fitting cutouts, and doesn’t allow or consider readjustment. Basically a wonderful, quick setup if everything is tight fitting and perfectly straight.

Messages In This Thread

Strip: Setting up forms
Dan Thaler -- 1/12/2011, 12:12 pm
Re: Strip: Setting up forms
ancient kayaker -- 1/12/2011, 2:48 pm
Re: Strip: Setting up forms
Bill Hamm -- 1/12/2011, 3:40 pm
Re: Strip: Setting up forms
Dan Thaler -- 1/12/2011, 4:20 pm
Re: Strip: Setting up forms
Bill Hamm -- 1/12/2011, 4:36 pm
Re: Strip: Setting up forms
Bill Hamm -- 1/13/2011, 12:45 am
Re: Strip: Setting up forms
Les Cheeseman -- 1/13/2011, 2:47 pm
Re: Strip: Setting up forms
Al Edie -- 1/13/2011, 9:06 pm
Re: Strip: Setting up forms *PIC*
Ian Johnson -- 1/13/2011, 9:52 pm
Re: Strip: Setting up forms
Dan Thaler -- 1/14/2011, 5:38 am
Bent&Perfect S/B Form Alignment Issues
mick allen -- 1/19/2011, 5:55 pm