I've got as far as getting my core blank halves done, but one side appears to have bowed. See image below:
I'm trying to figure the best way to fix this. I'm thinking:
a) Clamp tight and glue together and hope it holds
b) Put some dowels in and clamp and glue to get a stronger bond, though this could affect flex.
c) Clamp and glue together and heat up while clamped to try to remove the residual stresses in the wood, possibly incorporate some misting with water for steam bending.
Anyone else had this problem? If so, how did you rectify it?
Have you tested to see if clamps will pull it shut. If you don't have to crank it up to close the gap, glue should be fine until you heat it in the press.
If your concerned about residual tension, cut one stringer out and bond one section, replace the stringer and bond the remaining section.
All of my core blanks with the insert stringer are bowed like this, so I'll lose 10 cores if it doesn't make the cut.
Yes I will glue on sidewalls afterwards. Clamps should pull it shut, can nearly do it by hand. I'm concerned the residual tension will pull it back apart after it's glued, possibly tearing the centre stringer.
I'm not sure what you mean by "cut one stringer out", could you clarify?
looks like you had some green wood in the core?
did you run the strips though a joiner/planer prior to lamination?
its tough to see what you have going on there.
you have alternating types of wood?
There's no green wood, it's all kiln-dried Paulownia with Tasmanian oak insert stringers. They were run through a thicknesser prior to laminating, however they were then sent to me and may have bowed slightly between being planed and being laminated.
I ended up clamping them together as a trial run, it sat ok with not too much force in the clamps so I glued them together and re-clamped, here's hoping it works...
I was thinking that you could cut the curved section into two sections. Bond on one section - as its half as wide you won't have to crank the clamps. Cut the remains of the stringer from each of the two pieces and replace the stringer. Bond on the remaining quarter.
MM - Nope, it's two separate stacks of wood. In hindsight I should have put an extra centre stringer in and cut it down, then bookmatched. Live and learn.
if you are making skis you want to bookmatch to get the same grain/wood structure and thus the same mechanical properties per ski. i thought that was common knowledge.
Live and learn is right.
I'm making snowboards. The same rule applies in general (so you get the same on each half of the snowboard), however I doubt there's much variation in the wood grain in clear wood with regards to stiffness properties etc. I'd be surprised if anyone could really tell, if there was much of a variation then it would be too hard to produce a consistent product for the manufacturers. If you were using a lower grade of wood then perhaps it may be an issue.
Hi Alex
In the old days when I was making tables from River Red Gum for a living we'd always machine the 2 flitches (2000mm x 500mm x 38mm) for the top with a .75-1 mm gap in the centre in much the same way as your core looks. These were big thick pieces of really tough timber and we never, in the 2.5 years that I worked at the place, had any problems.
It's to do with the gap being in the centre of the join. If the gap is at each end then different story. If the gap is at each end it will slowly open up over time. Especially if it's glued with PVA as the PVA is always a bit elastic and will 'creep' until the join fails from each end.
I reckon you'll have no problems.
C.
