STEAM BENDING IN A POLYETHYLENE TUBE - part 1

There have been a few references on these Forums recently to steam bending using polyethylene tubing instead of a steam box, so Fitz and I thought we would relate our initial experiences with the method.

Fitz and I had both seen the Louis Sauzedde video on steam bending using a polyethylene tube (an industrial product that is used to make polyethylene bags), and both of us thought the method was worth a try. https://www.youtube.com/watch?v=--iPQIwSEJM&app=desktop Fitz did some research and obtained 500 feet of 3 inch 6 mil polyethylene tubing which we shared. The six mil tubing seems stiff, but when heated, it becomes very soft and flexible. I used some of my share of the tubing to steam and bend two ash inwales for the 15’ Old Town 50 pounder that I am restoring. He used some of his to bend the Honduran mahogany outwales on a 1960’s vintage 18 foot Old Town OTCA that he was restoring.

I’ll describe how we went about things, in hopes that it may help others who may wish to try the technique. It will take two posts, because we have a few pictures. If you are tempted to try this process, do look at the Sauzedde video.
My inwales were successfully bent and I expect I will use the process again, but things didn't go too smoothly for me on this first attempt – in good part because the steam source I used, a Wagner wall paper remover (which I believe is the same as the steam generator sold by Rockler), did not produce enough steam for this method. Some people on the forums have used them with apparent success when feeding steam to a traditional steam box.



I got the ash for the inwale from Rollin Thurlow and cut it to the proper size and angled shapes. The old damaged inwales I was replacing were still in the canoe – they made an ideal bending jig for the new inwales. The day before bending, I dampened both inwales pretty well as I watered the lawn in the afternoon and evening, and left them in the damp grass overnight.

The next morning I put the first inwale in a length of poly tube and laid it level on the horses on which the canoe was sitting, feeding the steam into one end. This produced two problems. First, most of the steam cooled and condensed before it reached the far end of the tube, so the far end of the new inwale did not get enough hot steam. Second, most of the condensed water stayed trapped in the tube between the two horses instead of draining out. And while the steam cooled as it condensed, the resulting water gathering in the thin tube was very hot, not much cooler than boiling.



So I rearranged things for a second try – I fed the steam hose about half-way down into the tube, and I set the tube and inwale on a fairly steep slant by raising one end, so the lowered far end would get enough heat and condensed water would drain from the end of the tube:



After about 30 minutes of steaming, I pulled the steam outlet back up the poly tube so the raised half of the inwale began to get steam and heat, for about another 40 minutes. Because the wood in the first lower section was already hot, the steam did not condense as much as before, and that wood stayed hot.

I had lots of clamps ready to go on the floor of the canoe, and I had a temporary cross bar clamped at each end in order to induce a bit of over-bend to anticipate and compensate for bend-back:



CONTINUED IN PART 2 - NEXT POST

 

STEAM BENDING IN A POLYETHYLENE TUBE - part 2

CONTINUED:

I stripped the tube off and quickly clamped the new inwale in place onto the old inwale, and let it sit overnight:



The next day, I turned the canoe around, leaving the first new inwale clamped in place. I put the second new inwale (which I had kept overnight again in the damp grass) in a poly tube, and clamped it to the canoe with only two clamps. Clamping it this way gave me the incline I needed to drain the condensed water, without the need for the roller stand and milk crates I had used the previous day – fewer things in the way to trip over. With the tube in place and the inwale partially clamped to the canoe, I started with the steam hose outlet well down into the tube:



As before, I pulled the steam hose outlet back up after a time, to heat the rest of the inwale. When the steaming was complete, I cut the tube from the first part of the new inwale and clamped it in place on the old gunwale while the other end was still roughly clamped. I then released the temporary clamps from the other end, pulled the rest of the tube off and properly clamped the rest of the new gunwale to the old gunwale which was serving as a jig.

Bending the second inwale went much more smoothly than the first – even a little practice makes better, if not perfect. I removed all the clamps a few days later, and the new inwales were bent just about right. They have held their shape for more than six months now with no apparent change when clamped back to the old inwale, and should readily fit into the canoe when the time comes.



FITZ’S EXPERIENCE

Fitz used the poly tubes to bend Honduras mahogany outwales. He soaked the mahogany for a week or so in a 20 foot length of PVC pipe he keeps for the purpose – probably a longer time than necessary, he says. He then steamed only four feet of the end of each outwale.
At first he did not think the method would work because the poly tube was not hot enough, until he realized that his Coleman stove was not pressurized enough. When he pumped the stove up so it was producing more BTUs, he found he had ample steam for the job. Indeed, he found he had to watch not to get burned by the steam leaving the end of the poly tube.



After steaming for about 40 minutes, he removed the poly tube, but not all at once. He and his visiting brother removed only enough of the bag to place a clamp, then worked their way toward the end of the canoe while removing enough of the poly tube to get the next clamp on. This way, the gunwale stayed hot the entire time, with no worries about having to work fast to avoid the rail cooling off. Fitz was doing the work in his driveway and outside temperatures were approximately 35 degrees F. Fitz thinks he could have left the bag in place, but it did bunch up under the clamps, so removal while going along seemed to be the way to go. He found that having a second set of hands (his brother’s) was very useful when it came time to clamp up. (Greg agrees – but he didn’t have another person available, so he made sure that all the clamps were ready at hand when clamping time came, and got things clamped up just in the nick of time.)

Fitz did have some condensate accumulate in the poly tube, but it was very hot water, so he left it in the tube for the most part, assuming the hot water would only help the situation. He did drain it when it got too full.

He did have some minor trouble getting steam into the poly tube, because the radiator hose of his steamer rig was larger than the poly tube. The biggest problem he had was getting the poly tube over the end of the radiator hose. (Shades of Apollo 13!)

Fitz notes that it took some six hours to do the four gunwale ends, and that things could go faster if he could figure a way to rig a second stove and steam generator, or some sort of steam splitter so both gunwales at each end could be done together. But he used his down time productively, canvasing another canoe instead of just waiting around while the steam did its job.

SOME LESSONS LEARNED

I learned that I should have much more steam in order to do a whole 15' gunwale at once – the Wagner steamer really didn’t have enough output for this task. The plastic tube, unlike the wooden walls of a traditional steam box, provided no insulation and allowed the steam to cool and condense far too rapidly, even when working indoors. So I now have a turkey fryer propane burner, and am rigging an old gas can as a boiler – like the rigs I have seen in a number of canoe shops and similar to the one shown in the Sauzedde video . I'll have plenty of steam when it comes time to do the outwales, which I will do in poly tubes and which I expect to go much smoother and faster. (When it comes time to bend replacement ribs, I’ll use a traditional steam box where I can heat several ribs at a time - I have a lot of cracked ribs to replace. The poly tubing could do the job, but would not efficiently handle more than one or two ribs at a time.) Fitz agrees that a good deal of steam is needed, which he got when he cranked up his Coleman stove.

I learned that a lot of hot water is generated that must be safely collected (unless you are working on a surface that is not harmed by dripping hot water).

I learned that it’s not just the steam that is hot – the condensed water that collects in the poly tube is also very hot. Fleece-lined leather work gloves (Reny’s in Maine, $6 a pair) proved to be effective for me as long as I didn’t get them too wet.

The Sauzedde video shows the stem being fed into the middle of the poly tube, but doesn’t show how this was accomplished. This could be better than feeding the steam from one end, but I haven’t figured a way to feed steam into the middle of a tube of such thin material without seriously risking a tear. Fitz’s technique of steaming only the last few feet of a gunwale works well with the steam going into the end of the poly tube.

The approaches Fitz and I have taken are certainly not definitive. We both liked using the poly tubes, and expect to use them again. These were just our first experiments using them. We hope that reporting on these experiments will help others work around the problems had, and will provoke thoughts and comments on how things might be done differently.

 

Thanks for the taking the time to write this up. As somebody very new to working with old canoes this technique appeals to me because it looks like something I could do in the middle of winter in my basement workshop. I saw a demonstration of this at the Shell Lake event in Wisconsin this summer. They had one of those Wagner steamers on each end of the tube. This worked well for them because it placed the most heat on each end where the wood needed to bend the most and less in the middle where it didn't need to bend as much. They also kept it in the bag as they bent it but they had a lot of clamps. A whole lot of clamps.

 

I tried bending Sapele with this method but gave up - that timber does not like to bend.
The replacement ash worked a treat though.
I developed the idea further by using the bag / tube for soaking - I just put a few folds and a clip over the end, threaded the gunnel in and filled it with water while leaving it at an angle so the water wouldn't run out. On steaming day I took the clip off, let the water out and clamped it in place then ran the steam down one end as there wasn't much bend to deal with in the middle. I did find the plastic got very soft in the steam and worried that it would loose heat too fast. I solved that by double bagging it.

Sam

 

The way I saw it demo'd was as shown in the pic Feather's posted. Clamps, cheap clamps you get at Harbor Freight especially when they are on sale.

 

I plan to use poly tubes to steam the air dried white oak I am using for new external stems on Morris #158. I have 12 blanks, 1"x1 1/4"x6'. My steam generator is a 10 gallon milk can with a loosely fit plywood plug that has a 2" pvc steam vent / delivery pipe installed. The heat source is a propane pot burner. Should be plenty of steam. I watched the video. Looks straight forward. Hot gloves for sure. I will be bending the stems on a jig. Why remove the plastic? I am thinking I will clamp the newly steamed stem pieces (2 at a time) into my jig with the stem still running, still sheathed in their plastic envelope. I won't need to handle the hot wood. Might make for less rebound if the stem continues while the stem pieces are clamped in place? What do you think? I will report back with pics.

 

Hello:

I have not tried the method for stems in a form. I bent mahogany outwales on an old OTCA with the bag method and it worked really well. I clamped it on as I made the bend, bag and all. I don't see why bag and all would not work in your case as well. You will need a good form to avoid twisting. If you look around on this site, there are likely some photos of good stem forms. Most use some wooden wedges etc. I find getting outside stems on the boat after bending to be a challenge. I find a helper and lots of creative clamping is required. Let us know how you make out.

Fitz.

 

gfatula: Any results to report ? I have two Morris outer stems in my future.

In preparation, I am steaming the ends of the outwales. They have been off the boat for close to twenty years and have relaxed somewhat. I want them to be formed when I permanently attach them to minimize the strain on their fasteners.

I'm using a Wagoner streamer that seems to provide plenty of steam. If the picture attaches, you can see that I have the bag taped closed except for the steam inlet and a drain tube for the condensate. There was enough pressure to inflate the bag so that I could feel the steam along its length. I bent the outwales into position while still in the bag, with the steam off, then cut away the bag before clamping. I'll leave the outwales clamped until I'm ready to canvas.