I stumbled upon this:
I thought it applied here .
This man in Joliet Mt used to build my wagon and buggy wheels.
Thanks Herb, That was great!!!
Wow! Thanks for bringing this to us Herb. The fellow certainly has some nice equipment and knowledge. His ability to record it while he is doing it is also masterful. I was able to make the same size bows for my Yellowstone bus with some less sophisticated fixtures. That made seeing this very interesting. I had several failures doing it my way with Oak. My version "cooked" the wood while it was bending using a sliding door:
Richard, I too enjoyed the video but I donít understand your comments and the first two pictures. The third one looks great. Could you elaborate a little, Iím sure more than just me would be most interested :-)
I'll try. I think the 2 hot plates and coffee cans are self explanatory. The left photo above shows the end of the bow c-clamped down in bent position. The photos below show the wood piece passing through the box before bending. It comes out of a sliding piece of sheet metal at the left of the box. A rubber seal helps contain the steam where the bow comes out. The chain at left has a weight on it that pulls the bow when it is starting to soften. I used chain tighteners to pull the bow most of the way. Some of the bends fractured like the first ones in the video. I simply glued them back together thinking they would be as good as a laminated bow.
These bows have held up well for 18 years and have seen some very severe winds. This was an experiment and I didn't have sufficient steam for an optimum bend. However it got the job done and was an interesting project.
Now I think I see how you bent the bow. The only thing is that I donít see how you contained the length. Maybe you didnít and thatís why a couple fractured.
I must admit that I have never tried to bend significant thickness of wood - one day when I have time. Ha. Ha.
I did not try to constrain the length. That was helpful in the video. I did find the need for a steel bar against the top of the wood that bent with it to help reduce the fracturing. I was not able to find much information on steam bending and this was done in the mid 90's before I had internet.
This shows a fracture on the first bow. As I said I glued these and it has has held well. I rejected one out of three bends and the grain was straighter that some of the bows in the video. The black is from the steel against the oak.
I hope this is of interest. I didn't intend to distract from the video but the more we learn the better chance we have of making things work.
Rich, the fracturing on the outside of the bend is due to the timber stretching. With the stops in place, the outside of the bend maintains the length of the timber blank, and the inside of the bend is compressed to the shorter length. I was fortunate to see a master at work bending wood felloes for T wheels when I was in New Zealand. His equipment worked on the same principle, but being set up for a known length of blank, it was considerably simpler. I was surprised to see him boil the hickory blanks in water rather than use steam, altogether a far easier process to use. the trough for the blanks was a simple piece of household guttering heated by a kindling fire underneath. It only took about 10 minutes to heat it ready for bending.
I suggested that he could use the short, straight offcuts from the end each felloe half as the fuel for his fire. He retorted that that was not going to happen, considering the price of Hickory imports into NZ. Instead, all the straight end pieces were glued on edge to a piece of thick MDF and then the whole was passed through a thicknesser until all the hickory was reduced to shavings. These went to a smallgoods factory for smoking their wares.
Allan from down under.
I steam bent a lot of parts when making my Delivery Car. Most of those parts were Hard Maple which is one of the more difficult wood species to steam bend. The easiest wood to steam bend is white oak. That is not my opinion that is per a chart of wood species that I have somewhere and I think it was from Ralph Ricks (R.I.P.) It is the main reason that wood top bows have historically been made from White Oak. I have Ford top bow drawings and they specify WHITE OAK.
What I find amazing is that nobody seems to know much about the "art" of steam bending which can rather easily be learned from the patent office. I just studied the various machines used to steam bend wheel felloes and the principles are rather simple. It is like bending spaghetti if you have a bundle of it rather than a single strand. If you bend a multi strand "bunch" of it around anything the outer pieces need to get longer and the inner pieces need to shrink up and with no constraints the outer pieces will all break. You need to heat the wood to a point where the resins let up on the grip of the wood fibers and they can then relocate. Once cooled the wood fibers are then held in the new position by the same resin and it is then the same as if it had grown to that shape in the first place. Constraining the overall length of the piece prevents the stretching of the outer fibers and divides the stress up so that inner fibers are pushed closer to each other rather than stretching the outer fibers and the job is done without fracture. The steam itself is simply the means of heating the resin without overheating it and one needs uniform heat everywhere around the wood hence the steam chamber. What the old guys point out is you cannot re-steam a piece of wood without seriously reducing its strength. It turns to pulp like a wet toothpick in your mouth does. You get one shot at each piece of wood and if done right it is very repeatable. One hour per inch is what the older timers used as a gauge of time at 212 degrees. You get the chamber to 212 then shove a piece of wood into it and mark the time. If the piece of wood is 1/2" thick then you need to steam it exactly 1/2 hour. My roof slats were 5/16 thick so I steamed each one about 19-20 minutes. Since that was about how long it took to have it on the bending form I simply put a new piece of wood into the chamber with one hand as I pulled the other piece OUT with the other. You MUST put strain on the piece IMMEDIATELY after you take it out since you only have a matter of 10-15 seconds to get the piece onto the frame and held there for the cooling. Careful design of the jig will allow you to put the correct form to the piece in a very short time with the use of pegs and blocks that locate the piece to its correct shape. There is always "springback" but once you have the form figured out and get going you will find each piece is finally the same as every other piece and that is what counts. It was fun but rather time consuming at 20 minutes per piece.
It is a good thing to have lots of guys over to help put clamps on and you MUST work very very fast.
Definitely worth doing once and I can show you a simple chamber you can make except you wood piece size determines the details you need.
Some great wheel building videos on that Youtube channel as well, thanks for the link!