Steam bending cherry

[Scott-VT]

Does anyone have any advice on steam bending a ¾” x 3” x 3’ cherry board. This will be my first attempt at steaming and I’d appreciate any pointers on what to look for. Thanks.

[Bruce Hooke]

What radius are you trying to achieve? There's a big difference (both in techniques and your chances of success) between trying to bend such a board to a 30" radius and trying to bend it to a 10" radius!

Does the board have really nice, straight grain? If not then the board is very likely to split as you bend it.

[Scott-VT]

The radius is 8" to 10". I have several boards to choose from, so I can find one with nice straight grain to work with. I’m not expecting to have this work the first time. How will the amount of time in the steam box factor into the flexibility of the board. Am I looking at 1 hour, 3 hours…….? Thanks.

[preston]

Cherry's supposed to steam-bend well, but I have no experience with timings. Sacrifice a bit an experiment.

I'd make the final piece longer than 3'.
That is, bend a longer piece, then trim it to length.

Preston

[J. Dillon]

If my ageing menory serves corr ;) ectly I saw cherry bend quite well at the WB show 2 years ago in Maine.
:D
JD

[Bruce Hooke]

The usual rule is 1 hour per inch of thickness, so for a 3/4" board you would be looking at 45 minutes (note: IIRC this rule is for dry wood, if you are dealing with green wood as little as half this time may be enough). One useful technique to judge the right time is to put a few 3' long 3/4" square scraps in the steambox with the main board. Check these pieces occassionally and when the bend well then the real board is probably getting close too being ready. Too much time can be as bad as too little -- it makes the wood more brittle.

8 - 10" is a fairly tight radius so I would try to make up some sort of a backer of light steel with end blocks on it. The idea of such a backer is twofold -- it keeps splinters from starting to lift on the outside of the board, and such splinters can lead to bigger cracks very quickly, and it keeps the outside in compression and forces the board to give mostly be compressing on the inside of the bend rather than by stretching on the outside, which is desirable becaue tension failures are more likely to start cracks than compression failures. However, do note that steel can stain the wet wood so you may want to put something between the steel and the wood.

You will have only 30 seconds or so to get the board pretty well bent into place so you need to have your system all worked out and ready to go. You may well need a fairly robust system for applying the bending force to the board. Come-alongs and such like have been used for this. If you go this route be careful -- you are dealing with a lot of force.

If the bend is right near one end of the board then you should run the board a little long at that end and then cut it off if you want a smooth curve.

Submerging the board in water for a few weeks before trying to bend it might be a good idea. It will bend easier if it is wet. The ideal solution is to get a board that has only been dried to 15% moisture content (this would be more typical of air drying) but if the available lumber yards in your area are not cutting the wood you want it can be hard to get anything other than kiln dried stock. One way of making a tank for the boards is to use PVC pipe with end caps.

[windfall]

I have bent a fair bit of cherry, It bends toerably well, but the species is prone to slightly bouncy/woven grain that produces micro runout even on a piece where the overall run of the grain is pretty straight....this tends to display itself a s "shimmer" on the face of a finished board. very beautiful but won't make the radius you describe. In fact, I think you will be hard pressed to make that bend with even perfect stock at 3/4". A backing strap will definetly help, as will extra length. As folks said, you don't have much time, but likewise if you rush it too fast it will snap. Staedy even movementsand some light "prebending w"will help soften it up. Good luck.

[Doug Canada]

Greetings;

Lee Valley has a lot of Steam Bending information & tools.

This is the best deal, though.
http://www.leevalley.com/wood/page.asp?SID=&ccurrency=1&page=31161&category=1,45866,45867

Doug

[imported_Steven Bauer]

When I made my toboggan I used 1/4" Lexan for the compression strap. Worked great.

http://www.imagestation.com/picture/sraid39/p0bda0c0b8ea82af2db8abdcdbddb7efa/fd07026c.jpg

Bending wood is lots of fun.
smile.gif
Steven

[Mrleft8]

Use a steel bending strap on Cherry and you'll end up with a beautiful blue/black stain that you'll never sand out.
8-10" radius I think I'd laminate instead of steam bending.

[Dave Hadfield]

I also think the radius is too tight. Sorry!

[hoss]

I like Cherry but I have found it very hard to bend. I used to make fenders for the horse drawn carriages I built and have tried to use Cherry. Kiln dried is almost impossible, air dried a little better. A steam box is your best choice, soaking will tend to discolour the wood and I agree don't use iron anywhere near wet Cherry. (stains) I would tend to forget bending and laminate the curve using Cherry veneer, much stronger.

[Bruce Hooke]

I've been steam bending some cherry this week so I thought I would record here a few notes that might be of use to someone who comes across this thread.

The cherry I have been bending is kiln dried and has been sitting in my basement for a few years to boot. So, since my basement is very dry this time of year the cherry is also quite dry. Not ideal certainly but it's what I've got handy. I have been steaming the wood for 30 minutes.

The stock I am bending is 1/2" thick. I am bending it to about a 6" radius. With thicker stock (say 1") the equivalent radius could well be on the order of 48" because the stiffness of a beam varies as the cube of the beam depth.

I am using a steel backing strap with steel end blocks. To protect the cherry I put clear packing tape on the side of the steel that touches the cherry. This has worked quite well -- there has been little or no staining on the cherry.

So far I have bent three pieces and aside from having to tweak the form to adjust for springback, and aside from some small compression failures on the inside of the bend on some pieces, things have been working well so far. I've got 4 more pieces to go so we will see how those work out.

What I have noticed, both this time and in the past, is that the final bend I get once the wood is off the form seems to be pretty close to the bend I manage to get into the wood in the first 10 seconds after it comes out of the steambox. Bend achieved in 20 seconds by cranking down on clamps to bring the wood into full contact with the form often seems to be lost. This, however, may be just my perception -- I haven't tested it carefully...