I am wanting to bend 1 3/8 round turning of Kiln Dried Red Oak- 1 3/8 over a 24in. length, with the rest left straight . The overall length of the turning is 42 in. back posts for a rocking chair.
The oak I’m using is not rived out, but very straight grained plain sawn .
Also I want to make a steam box form PVC pipe
Thanks for any and all advise
Ron
Replies
Ron -
I trust that the "turning" is a constant cross section and has no beads of coves which would reduce the section to produce weaker points along the length. 1-3/8" is fairly thick to be bending into a vary small radius so I trust it will be a minimal bend .... you might mention the radius you need to bend it to.
Check for grain runout on all the pieces .... Oak is fairly easy to steam bend, but grain runout will produce a weaker finished product as well giving rise to potential failure during bending.
As for the PVC steam box, make a 'V' trough to hold the plastic pipe its full length. Plastic becomes .... well, plastic when it gets hot and will sag considerably if not well supported. Drill holes at or slightly below the center of the pipe perpendicular to the pipe's axis into which you can fit some 1/4" wood dowels to support the work pieces during steaming. Make sure the dowels are a loose fit not only to make them easy to insert, but to provide some space for the steam to escape. Don't want to be building a pressure vessel here! Cap one end only - use a rag stuffed in the end where you insert the work pieces. Easier to get out when it's hot. And it will be hot. Pitch the whole thing so the steam condensate will drain to one end and drill little drain hole for it to escape.
What do you plan to use as a source for your steam? And how are you planning on piping it from the source to the steam box?
Dennis in Bellevue WA
[email protected]
The turnings that I want to bend is the the back post for a shaker rocking chair. I'm not sure the radius of the bend .
The Turnings are 1 3/8 dia. X 41 5/8- the bend starts roughly at the middle 20 13/16 also the turning starts to taper form the middle to the tip ending up at 7/8.
Its not much of a bend , the plan shows a line from the straight section up to the tip of tapper with an 1 3/8 in distance. I guess a 1 3/8 center to center.
The plan I'm using is from John G. Shea Book - The American Shakers And Their Furniture - just a drawing and basic measurements. Check out the pic.
On the Steamer I'm thinking about a 5gal. metal gas can and using like maybe 1 1/2 dia. pvc from the tee in the middle of the 6in pipe- letting the 1 1/2 extend down on to the spout? For the heat source try to find like the burner for like a fish cooker that runs on propane. What do you think?
Edited 5/12/2003 7:04:50 PM ET by I Like Beans
I think the other suggestion about a bending form is spot on. If you have a band saw, lay out the profile/shape of the inside curve of the bend. Route or hand shape a concave groove around the form to 'contain' the turning. An outside clamping form would contact the thinner ends of the turning before getting the piece into its final form and in all likelyhood would break off the little finials on the end.
Gas can is out! You're scaring me here!! (grin). If you steam these one at a time, I don't think you'll need that much water. A large tea kettle should suffice. Sitting on a propane camp stove. I'd use something like an old automotive heater hose clamped into or onto the teakettle's spout and simply jambed into a hole in the PVC steam tube. This doesn't have to be all that refined to make it work. You *want* leaks for the steam to escape anyway.
Work fast once the part is steamed. You only have a short time once you get it out of the steam box. Get a pair of heavy leather gloves. Better, get some welders' gloves to protect your lower arms as well. This isn't quite the same as working next to a spinning saw blade but it's dangerous none the less if you don't realize what you're dealing with.
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Dennis in Bellevue WA
[email protected]
Did you see the pic.? I didn't think that It was bending so much angling over 1 3/8 in. off center. I have bent Osage Orange 1in think way more than that but it was air dried " making bows".
I was intending on using a form and thought I would do like a 45 degree cut out in the center on the form Also would having the side grain on the inside and out side of the bend help?
I found a steamer on the web. anyhow that's what it looked like they had used
check it out- way to expensive for me.
http://www.mikedunbar.comcom/tools.html
The above posters have offered excellent views on the how-to part of your post question, but I honestly think that using kiln dried material is going to give you unsatisfactory results. Kiln drying involves heat, and that heat sets the lignon in the wood. It is pretty tough to "re-program" a piece of wood after it has been kiln dried. That's why most steam bending is done on green/air dried wood.
That said, give yourself a go with a similar square piece first and see the results. It might be okay, but I'm willing to bet that you will see a large number of stress cracks and fractures in the bend area.
Good luck.
Scott
Scott,
All I have ever bent is kiln dried white oak, with no problems. At first I soaked the stock over night in water before steaming, later I eliminated that step with no effect on the bending process. Lon addressed the issue of bending green wood in his seminar by saying that he lives in So Cal and has yet to find a supplier of freshly cut wood, so all of his steam bending has been with kiln dried wood.
Also, don't forget about spring back after removal from the form, so you will need to bend it to a greater angle than you want the finished product. Hence, the need for extra legs to test run the bending.
Dr. BillThey would not call it REsearch if you only had to do it once, that would be just search!
Beans, I took a look at the drawings, and I wonder if the originals were steam bent at all? Some rear chair legs were turned out of a wide piece of stock off two (or more) centre lines. For instance, start with a piece about 36" L X 5" W X 2" T. The bottom has a centre line about which it is turned, and the top similarly has a centre line about which that section is turned.
A template is made that gives the profile of the leg as seen from the side, laid on the wood, pencilled around, and the shape bandsawn out-- perhaps followed by more accurate profiling with a router and pattern cutting bit, or on a spindle moulder (shaper) with a similar planing cutter. Next, saddles are made that attach to the leg blank which allow the two (or more) centres to be mounted on the lathe so that the turning can be accomplished.
I've never had to do it myself, but I've seen it being done-- it's quite hairy watching the top of the leg describing an arc about 8"- 10" diameter as the foot and bottom section of the leg rotate calmly about the centre line as normal, ha, ha. Then you switch about, attach a saddle to the already turned lower section, and turn the top section, so now the foot is flapping about like a demented windmill-- not for the faint-hearted! As I recall, even after the turning there was still some work to do with drawknives, spokeshaves and the like to get the curves sweet.
Anyway, it's just a thought, and if the steam bending route is the way you want to go, a readily available steam source would be to hire or buy an industrial wallpaper steam stripper-- the one with a boiler and pipe to a pad that's worked over the scored or scarified paper to loosen the adhesive. They are designed for this kind of constant steam generation and would save you the bother of engineering your own. Slainte.Website The poster formerly known as Sgian Dubh.
I know this is hard to believe, and I don't recall the piece he made, but I saw a NYW episode a year or 2 ago where Norm did this as you describe. I have not ventured there yet, although I note that it is recommended by many for turning cabriole legs (ankles and feet only).
I thought about the off center turning- not sure about attaching the wood needed to the turned section with out screws. But will check more into it.
I don't see why I cant bend it I'm not talking about bending it much just a slight bend - 1 3/8 distance over from straight on a length of 20 1/2 inches.
Is there a rule of thumb for spring back, should I bend it twice as far, being so slight of a bend?
Does anyone know of someone I could email that has built Shaker Rockers that I could ask about how they made the back post?
Actually that's not really all that much bend. From your sketch, at first, I was concerned about the little finials at the end of the piece. But there wouldn't be any need to stress them if you attached straps or clamps below them.
I don't really have that much experience bending so can't speak to springback. I suspect each piece of wood has its own personality.
The few times I've tried multiple center turning I've found it hard to get a fair blend between the different segments.
...........
Dennis in Bellevue WA
[email protected]
s4s, I'll turn the bun foot of a cabriole leg. It's centred near a corner of a large blank. The blank might be 75 or 90 mm square (about 3" or 4") or maybe even more for a very large leg, but the bun foot is normally in a line pretty much directly below the top square section of the leg, which gives the centre line, and the knee, calf, and ankle are won out of the extra material.
In the past I've made a chisel specifically for the profile of the bun foot out of an old file. Then I remove most of the waste around the bun foot with a bandsaw, mount the leg blank on the lathe, and plunge in carefully with the improvised file 'chisel.'
Yes, that off-centre blank is a bit disconcerting as it burls about rather out of whack above the lathe bed. It's been a few years since I made a traditional bun foot cabriole leg-- about sixteen years now that I think about it, but if I had to do one again, hopefully it would be a bit like riding a bike. I'm not generally very good at turning-- it doesn't interest me much-- but I suppose I could get by at it if pushed, ha, ha. Slainte.Website The poster formerly known as Sgian Dubh.
I'm with you on turning, just not my cup of tea, and I do it out of necessity. Were I building the shaker chairs of the thread starter, and chairs are on my short list of nexts, I think my approach would be to turn the bottom, were it to be straight, and to leave the top oversized by 1.375", then bandsaw the blank, and fair primarily with a spokeshave. I am doing my first set of cabriole legs, and working with a spokeshave, with which I have only limited experience, I find to be quietly pleasing. It is interesting that if you sight the line of the curve, like you would an edge to see if it is straight, your eye quickly picks up any humps or troughs.
Ron,
I think you are going to have real problems bending round stock that thick. Plan on making several extra legs to get the process right. The general rule is 1 hour of steaming per inch of thickness. I have successfully bent 7/8 inch thick white oak, but that was a beast to get into the forms. I imagine you might need a sculpted form on the inside and outside of the angle so that you do not deform your turning to much (bend a lollypop stick and see how it wrinkles on the concave side). Lon Schleining just gave a talk at the Orange County woodworkers association and he show some amazing stuff that was steam or lamination bent. That was one of his points...just try it! If it does not work try another method. Good luck
Dr. Bill
I Like Beans:
I learned the hard way that a strap that encompasses the entire length of the piece to be bent is sooooo important. Remember that wood bends on the concave side not on the convex. You cannot stretch the wood fibers along the outside----- you must compress the fibers on the inside. Fine Woodworking featured such a bending strap in one of their issues. You'll have to look in their index for issue date.
As you may know, wood should be steamed for approximately one hour per thickness. I use 1 1/2" ABS for my steam box. The more confined the interior of the box, the more efficient the bend. You also must consider spring back. Red oak has a considerable spring back, so indent your form at least one inch beyond your desired final shape. Box temperature should be at least 200 degrees throughout the steaming procedure. A meat thermometer set into the ABS will monitor the heat.
I hope this helps. Good Luck!!!
I was thinking of making a bending form of MDF that would lock the straight section make a wedge the formed the out side curve so that I could drive the curved wedge up tight to get the shape against the inside form.
Do you think I really need a back strap to bend the 2 back post of the chair- It seems not much of a bend to me even adding a 1 inch making it 2 3/8 for the spring back. I'm not planning to put the whole bend in one spot but over 20 inch length- just a slight arc.
You are right about the back strap to keep the grain from lifting and splitting on a tight bend.I made a few wood bows and you are right the back does not stretch the belly is in compression to tight bend the back cracks and the belly crushes just like making to heavy of a draw for the wood you use in bow making
I ordered a elc.Steamer Kettle from Lee Valley I think it said 1500 watts- do you think it will get it hot enough?
I was thinking of bigger pipe so I could bend both post in the jig
The bend that you intend is so gradual, you're probably right, no strap is required. Steam bending seems to be quite unpredictable. I once made a Shaker rocking chair, and had to bend the back supports very gradually over about a 50" span. After the wood was out of the steam box and onto the form, all was well. After I removed it from the form, there was very little bend left. Unfortunately, the best method is trial and error, which, in your case, would probably be impossible.
The steam box should be as small as it possibly can be in order to accomadate your wood. If the diameter of your wood is 1 3/8, 1 1/2 ABS might be too small. The next size in ABS I believe is 4". This would probably do.
My steam source is an old Coleman camp stove, and a five gallon gasoline can. It works great. The problem is that most camp stoves today are heated by propane gas, and fuel (white gas) for my stove is somewhat difficult to find. I'm not sure that propane heat would be adequate for steam generation. I read somewhere that you shouldn't use camp stoves because they are not hot enough. The author may have been talking about propane heat. I have no experience with propane used in this manner.
Finally, although the recommendation is to steam one hour per inch of wood thickness, because you're using kiln dried red oak, you may want to let it steam a bit longer, maybe about 10 minutes.
I hope this helps.
The process isn't all that difficult and I've done it on several chairs like you describe. I bought a new 5 gal gas can from W.W. Granger, used a universal radiator hose from the auto parts store and a handful of plumbing fittings from the home center. The steamer box is made from plywood.
I turned the legs first with all their decorative balls, curves and what-not. The diameter was about 1-1/2" hickory, kiln dried furniture grade stock. I steamed them for about hour or so without soaking them. Presoaking may work a little better I would expect. I did build what is called a "limbering jig". It's simply a way to ask the wood to start bending for you! You just place the hot steamed wood into the jig and gently apply the bend until you reach the curve you need plus a bit more. Then you rush right to another jig fixture to maintain the curve and lash the leg to it.
Now! Wait for it to dry. If you air dry, expect to wait several months until it fully returns to the moisture content you had originally and that will in turn "set" the curve and the leg can be removed. The curve may or may not remain. In all likely hood it will spring back a bit as the wood tries to come back to equilibrium but don't worry, it shouldn't be enough to worry about. You will simply have to deal with it but the chair and your eye will never know the difference...trust me on this!
A faster way to dry the wood is to build a kiln with plywood and a heat lamp. The temp should be regulated to run no higher than 140 degrees F. You can expect to wait about two weeks before the leg will take the curve and become loose on the form. I used 2x6" construction lumber to build my forms with two legs per form.
After that, sand smooth and bore the rung holes. I've seen the system to make the legs from one solid piece and then turn them on the lathe. In my estimation, the steaming method is simpler albeit more time consuming and a little less sure as to the final curve. To build a jig to make the curved leg from solid wood is very time consuming but I guess once it's done you have one for all time. I just don't favor all that mass of lumber turning in front of my face and besides, I cut legs with a duplicator so that sort of precludes the jig idea in my instance.
Louis T.
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