dealing with bends in a true 2x4 strongback

I just built a strongback from rabbetted MDF to 2" x 4". It has couple of little curves to it.

Nick's book is based on a "2x4" strongback and forms that have 2" x 4" holes, so you can true the forms on the strongback by taking advantage of the small difference, and shimming or using cleats. By building a true 2" x 4", I seem to have lost that option. I have no way to move the molds to accomadate the curves.

Did I just screw up the strongback bigtime? If I do it again, might I get it right? Should I try planing the MDF strongback to true (but no longer 2")? Should I toss this MDF strongback and go back to 2x4's, ala Schade?


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RE: dealing with bends in a true 2x4 strongback

I had (have) the same problem only I made my 2x4 strongback our of 1/2 inch plywood.  I ended up wetting the plywood and leaving it out in the sun on a flat surface.  It straighten it out except on the every ends.  The strongback was 12 ft long I just didn't think I would ever find a 2x4 (lumber) any better.

I sanded the strongback with my belt sander, rounded the edges to create space for the forms.  I had to adjust the end forms, but the other forms lined up very well with just slims.

I read somewhere to use 3/4 inch ply the next time.



RE: dealing with bends in a true 2x4 strongback

The quality of the materials may be part of the issue.  My current project, a dory, required a beefier strongback so I built the box from 3/4" furniture grade plywood.  It's very straight but would be too robust for a dainty kayak.  I saw a kayak strongback made of 1/2" ply at a local building expo.  The builder told me he'd made several 'yaks off the same form with no problems.  His was made of Baltic birch ply.

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