Laminating the stem

[GregH]

I'll soon be laminating the stem for a Wm Garden Tom Cat. For a previous boat, an Ian Oughtred Acorn Skiff, I bent the laminations around the OUTSIDE of a convex form. While encountering no problems, and producing a fine stem, I was wondering if there's any advantage to bending the laminations INTO a concave form. Also, I'm thinking about using polyurethane glue instead of the thickened epoxy used previuosly. The wood will be white oak. Comments appreciated.

Greg

[Bruce Hooke]

In my limited experience, bending around the outside of a form is a lot easier than bending to an inside form. With an outside form you can clamp down one end and then slowly work your way to the other end, clamping down the laminations as you go. With an inside form you have to try to use long clamps to pull the laminations into place but you can't just use one long clamp because you risk breaking the laminations so you are jumping between clamps trying to tighten them evenly without wasting too much time. If the lamintes are small and thin enough that you can just shove them down against the form then this is less of an issue, but still, you might well need to have a second set of hands handy to apply some clamps while you hold the lamintes in place. Also, with an outside form the bending force is working with you to try to hold the lamintes tight against the form between the clamps, whereas the reverse it true of an inside form.

[osborni]

Well, since the outside of the stem is normally the controlled surface on the plans, making the mold to THAT curve will yield a more accurate profile.

If you make the inside mold, you are counting on getting the thickness of the material and the change in the mold radii correct to yeild a fair stem.

Though in reality, unless you are building a 40' boat, a few 1/8ths here and there won't make much of a difference.

The other advantage is that you might not need as much wood to overhang the mold. When bending AROUND a mold, you need to leave a few feet on either end to get the curves right (in my experience - I'm no expert) When you bend wood INTO a mold, the wood only needs to be a little longer then the finished piece.

[osborni]

Well, there ya go. two different answers to the same question! smile.gif

[Stephen Hutchins]

One advantage of an inside form is to prevent the outside laminate from blowing out as is sometimes the case with tight bends. The best results are got by using two forms, both inside and outside. But that's a bit overkill if your only building one of something.