On Apr 7, 9:57 pm, Brian Nystrom <brian.nyst...@[EMAIL PROTECTED]
> wrote:
> sa...@[EMAIL PROTECTED]
wrote:
> > On Sun, 6 Apr 2008 21:28:05 -0700 (PDT), Norm <normk...@[EMAIL PROTECTED]
>
wrote:
>
> >> Greetings.
>
> >> I am currently building a skin-on-frame kayak using the standard
> >> (classic) text by Chris Cunningham. I have just reached the stage of
> >> putting in the steam bent ribs. I realise that this stage is tricky,
> >> especially given that he recommends that you get 50% more timber for
> >> breakages.
>
> >> I have a specific question which he does not deal with in his book.
>
> >> Cunningham recommends that you start with timber 5/16 inches thick,
> >> and that you thin the ends (maybe up to a third of the length of each
> >> rib, depending on its length) by 1/16 inch. His instructions tell
you
> >> to take all of the 1/16 inch off one side of the rib. (In addition
to
> >> this, the ends of each rib need to be narrowed in order to fit them
> >> into the mortices in the gunnells).
>
> >> This means that when you bend the rib after steaming you have a
choice
> >> of bending it towards the thinned side or away from the thinned side.
>
> >> It seems to me that it would be more likely to split if you bent it
> >> away from the thinned side. That is, it would be better to have the
> >> thinned side on the inside of the curve.
>
> >> I have not yet broken enough ribs to know the answer to this. Does
> >> anyone have an opinion? Or is this likely to be such a minor matter
> >> that it will make little difference in the long run?
>
> >> Yours
>
> >> Norm
>
> > Bend so that the thinned part is on the inside of the bend. The
thinned side has
> > more exposed endgrain due to the thinning, so you want that side under
> > compression, rather than trying to pull it apart. The longest unbroken
grain is
> > the side that can best deal with being stretched without splintering.
>
> While the above is correct if you're going to use Cunningham's method,
> my personal opinion is that his system just creates more work than
> necessary. Using 1/4" ribs without any tapering works just fine. If
> you've already cut your mortises to 5/16", you're stuck, but it's
> something to consider on your next boat.
>
> One thing that is very useful is his pre-bending jig. While the ribs
> won't hold the shape of the jig, it does make the ends much more pliable
> and easier to insert into the frame.
>
> For other ideas, see my Webshots albums at:
>
> http://community.webshots.com/user/brian_nystrom-reg
Thank you for this comment, and also for the reference to your Webshot
albums.
Regarding the 1/4 inch ribs, I have been trying to follow Cunningham
EXACTLY because I have a history of minor disasters and half finished
boats. However, I have not cut my mortices to 5/16, so I do have the
choice to try thinner ribs. (There have been things that I thought of
changing but I have so far resisted).
I have used his jig. One of the problems I had with the first one I
made was that it broke apart while I was bending the first rib. I
then built another one which was much stronger and which works.
However, just last weekend I was wondering if I could make an
adjustable jig which would be suitable for keeping the different sized
ribs in till they cooled. I notice that your rib jig looks like just
such a piece of equipment. I will have a careful look at your photos
over the next few days.
I am one of those people who do not like to do things quickly and I
feel that I work at my worst when I have to make quick decisions. So
the description by Cunningham of the rib process had me worried from
the start.
Many thanks for your comments.
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