When I got to the take-up spool in my construction, I could not find a suitable
material. There was no 2 1/2" pipe, at least that was even half-way
truly round. And, certainly no 68mm pipe. My solution was the following:
I found a good stiff mailing tube, 2.3" OD, for a former. I then purchased
a 12"x12" piece of 1/64" aircraft grade birch plywood from a local model
shop, and a length of 1/8" balsa. Even though the plywood would bend easily
around the former, I soaked it, and the balsa in warm water. (Note:
adding about 1 tbsp of household ammonia to a quart of water will make it
easier to bend and handle.)
I rolled both the ply and the balsa around the former (tube) and let them
dry overnight. This way, the wood is nearly the shape you want, it is dry
and will take little binding to hold it secure on the former while you glue
After putting a piece of waxed (greased) paper over my former, I cut a piece
of the ply to fit around the former, adding about a 1/4" to feather the end
joint. I glued the joint with Pliobond (a contact cement) following directions
on the glue container. I then put waxed paper over the joint, wrapped all
of it to hold it tight while the glue set/dried.
When this inner ply layer was dry/set, I glued the balsa around the ply using
the same cement, bound this "core" layer, and let it dry. When the core was
dry I sanded it lightly. Note: Roll the dried spool over a
flat surface, and look for any hesitation (bumps) or stops (depressions).
Just be careful not to lose its round shape, or decrease its diameter.
The last step is to apply the outer layer of the 1/64" plywood, using the
same technique. My result is a beautiful wooden take-up spool, the correct
diameter, and very solid and strong for it's thin walls. I actually
made two spools. Both with the same technique, but using PVA glue for the
other. Both are strong, but the PVA glue lets the pieces slide around during
assembly, takes a while to dry, and the balsa stays "soggy" for quite a while.
After the project, I think I would do the same even if I could find the correct
diameter PVC pipe. I really enjoyed the task! The attached pictures show
a completed spool, and a close-up cross section of the wall. I am now
lathe-turning the end and middle supports and cheeks.