Thread: To steam, or not to steam . . . ?

I tried steaming ARC and frankly, the steam didn't seem to make much difference, compared with just bending with clamps. However, the bends were quite large radius. Also, sometimes ARC has wavy grain that's not the best for bending.
As for spring back, it's generally minimal (I use epoxy for laminating). I forget the exact formula, but spring back reduces quickly as the number of laminations increases. It's only a theoretical formula anyway.

Just remember to use plenty of clamps. Some people say you can never have too many clamps, others say you can never have enough.

Many, many years ago I worked with the timber industry in Papua New Guinea and we processed quite a bit of red cedar. I know nothing of "saurian cedar" but what we extracted and sold was the same species as Australian red cedar - Toona australis, later renamed T ciliata. If you cut or plane a bit, the fresh surface will have a very distinctive and quite pleasant aroma; with appearance, an easy species to indentify.

Many years later, I helped build a boat from red cedar - the timber came from Open Bay, PNG - and it was lovely timber to work. I can confirm that the timber laminates extremely well and steam bends quite well; in both techniques there is some spring back, but it is in the lower range. The boat had 3 mm laminates and the bend around the chines was fairly sharp but I cannot remember the precise radius. I would just try bending a piece and if it seems to be stressing, then make the laminates thinner.

I have never mixed steaming and laminating successfully - ie pre-bending by steaming, and then laminating - as it is really difficult to align the curves accurately.

Originally Posted by GraemeCook

I have never mixed steaming and laminating successfully - ie pre-bending by steaming, and then laminating - as it is really difficult to align the curves accurately.

I would second that. We used to make frames, ribs etc for 16' sailing skiffs out of RCD and NSA (Northern Silver Ash). Both steam and bend well, but as stated above avoid the cranky grain, stick with the straight grain, the more boring the better. We steamed, preformed the layups on cauls, let cool then did the actual glue up cold.

Spring back at times can be very unpredictable even from strips cut from the one board. I feel that the growing stresses and grain orientation in the board and hence strips influences springback more than the steaming method. Generally, though with boring straight grain you can get a great feel and understanding of how the laminations will react after one or two attempts. The tight radius bends understandably give you the most grief.

Vern, page 10 onwards of the PDF at the link attached gives good recommendations.

Timber in Boatbuilding (nsw.gov.au)

Strips of that thickness may respond to the heat gun method. I have used it on WRC but found it difficult to keep the bends even. Since you are going to use forms I would expect your results to be better. Effectiveness is dependant on bound moisture content so kiln dried or timber that has been sitting in hot dry conditions is less likely to respond.

There is more info, including a video, about halfway down this page on the Laughing Loon Kayaks website.

Laughing Loon Shop Tips

Originally Posted by GraemeCook

Many, many years ago I worked with the timber industry in Papua New Guinea and we processed quite a bit of red cedar. I know nothing of "saurian cedar" but what we extracted and sold was the same species as Australian red cedar - Toona australis, later renamed T ciliata. If you cut or plane a bit, the fresh surface will have a very distinctive and quite pleasant aroma; with appearance, an easy species to indentify.

Many years later, I helped build a boat from red cedar - the timber came from Open Bay, PNG - and it was lovely timber to work. I can confirm that the timber laminates extremely well and steam bends quite well; in both techniques there is some spring back, but it is in the lower range. The boat had 3 mm laminates and the bend around the chines was fairly sharp but I cannot remember the precise radius. I would just try bending a piece and if it seems to be stressing, then make the laminates thinner.

I have never mixed steaming and laminating successfully - ie pre-bending by steaming, and then laminating - as it is really difficult to align the curves accurately.

The name Surian Cedar is probably the trade name for the imported stuff. We use a lot for doors at the joinery shop and it's mostly good, but can be a bit furry. I have some that's lighter than Balsa wood.
Rgds,
Crocy.

Originally Posted by labr@

Strips of that thickness may respond to the heat gun method. I have used it on WRC but found it difficult to keep the bends even. Since you are going to use forms I would expect your results to be better. Effectiveness is dependant on bound moisture content so kiln dried or timber that has been sitting in hot dry conditions is less likely to respond.

There is more info, including a video, about halfway down this page on the Laughing Loon Kayaks website.

Laughing Loon Shop Tips

Using kiln dried timber or previously steam bent timber makes the task a lot harder! High moisture content boards, strips, veneers, respond far better to steam bending, and dry bending. Kiln drying heavily, rapidly, and artificially modifies the woods moisture gradient from the heart to the face of a board. Generally, that results in some board degrade and a very definite change in the properties of the wood (lignin), unless carefully managed through a kiln schedule with reconditioning cycles to minimize degrade.

I dislike the heat gun method as it creates differential zones of MC in the wood being bent. The zones that require the highest moisture are generally the driest when using a heat gun imho. Its probably OK for small cross sections. The same issues arise in steam bending if one attempt to hasten the process and not allow sufficient time in the steam chamber. It's a case of more time is better!

As we were making frames that we desired to be light weight and high strength we wanted the wood to retain its natural properties and strength, wet heat is a far far preferable choice over dry heat any day in any application imo.

Mind you though, luthiers and other makers have been using dry heat very successfully, it all comes back to the desired outcomes, application, strength, aesthetics, purpose ....

Then there are the cold forming processes ... if the strips are thin enough, no heat or steam is required just lots of patience and glue!

One last tip, we generally reserved any strips taken from the face of a "dried" board for the core of a lamination in a low stress application, i.e. large radius bends, or low load applications. The face of a board generally has degrade both visible and non-visible - well until you start bending it.

Well another - carefully consider possible undesireable outcomes - some woods ebonize quite rapidly with heat & steam and a little iron from say the inside of a gavlanized pipe steam chamber ... etc DAHIKT.

One can push limits knowing the properties of wood and which techniques offer the best possible outcomes / success.

A mix of veneers in the 0.6 mm to 0.8 mm range, lightly steamed on a wire grate over an open pot of rapidly boiling water. Each veneer was individually steamed then placed in the cauls, lightly clamped, cooled, repeat in the correct lamination sequence. Quite a rapid process if well organized. Approx 110 or 120 mm dia??

For this project, three arches were made, one a spare just in case I messed up turning the recess to accept the conical Hans Weissflog inspired boxes. 2009 AWTEX entry.

Off topic a bit, I've helped a couple of times bending 3x2 spotted gum to make wheels for veteran cars. Steamed for at least 2 hours, then about six of us bending it round a form, another 2 applying clamps and another slowly easing off the compression strap. It was bent through 180+, allowed to cool on the form then removed and clamped to limit spring back for a week, before joining the two halves.

Thanks for all the advice guys Much appreciated.
I don't have enough timber for the challenge to leave any just for testing but I have some very similar stuff I experimented with yesterday. 3 x 4mm strips bent over the smallest radius I need just to see what would happen . . . went for lunch . . . and came back to find all three snapped . Will have to wait for the steam generator after all