bending carved wood

[butch]

Question: I want to make a curved chair back with a carving in it. Two thoughts - 1st: cut out a board, do the carving then steam and bend. 2nd: laminate then carve into the curve. Any suggestions?

[cowboy1296]

Of course I had no idea what I was doing but the only time I tried to bend a board I broke it. If you have aspire it seems that you could cut your curve into a straight board including the 3-d file. In this picture the stage coach is cut into a flat back on a rocker. My only input was cutting the stage coach, a furniture make built the rocker.

[butch]

That is similar to what I am trying to do. That sure turned out nice, thanks.

[cowboy1296]

Yeah he took my rough work and turned it into something beautiful. His rockers with my 3-d graphics are better looking in person than in the pictures.

[srwtlc]

Depending on what you have for software, and the amount of curve there is, you could model the part or curve to size and then add something like Rick's example to it. Then toolpath with a boundary around the design so it cuts just the design. As long as the arc isn't too great, it should cut decent and if there's not much detail at the edges, like Rick's, it would be better. You can also project a v-carving onto the arc/model. I've not done it, but it should be doable if you can model your back part accurately enough.

[cowboy1296]

I was always concerned about the board being weakened because of the carving and could snap if pressure was put on it. But the carving is above where the back would normally rest.

[cowboy1296]

is something like this what you are trying for

[butch]

Similar, except curved. It goes on a bar stool, and I want to make curved backs but with carvings. Never done it so I was hoping someone had tried this or was doing this. I saw a chair with inlays. They put the inlays in, then steamed and bent. Came out very well, but never saw anything carved and then bent.

[butch]

My first thought was that the thinner board would just break. But not sure.

[butch]

Scott - what I am trying to figure out is if I did it that way, can I somehow hold the curve close enough to carve. I think there will be a slight different curve to each back with no way to pull it into shape close enough to carve. When ever I have bent something - and I have only used glued up strips, they just come off the jig different arcs - probably due to changes in the wood.

[srwtlc]

Butch,

Sure, you'd get varying amounts of spring back wouldn't you. You could cut a form/jig and pull them into it to stay relatively consistent for machining.

Along the lines of Rick's last example, you could cut them from a solid piece and then bandsaw the back to shape afterwords. May not be the appearance you want as far as the wood/grain goes though.

[bleeth]

Springback after releasing bent laminations from a jig generally comes from 2 causes:
1. Wrong glue-The only effective glue I have found for this is epoxy. Personally I have never gotten results nearly as good from any yellow glue. Never tried polyurethane (Gorilla) but did do a couple with Resorcinol and it worked also.
2. Wood too thick and/or too dry.

Most of my experience (but not all) is from Teak. I've bent it into 6" radius and 5" high with 6 layers of 1/8" and had no springback at all. The mild curve of a chairback is relatively simple and when done right should be perfect and repeatable.

Of course, as Shopbotters, the preferred method is to start with a thick enough piece of lumber, cut the outside curve on it, flip it and cut the inside curve, and then cut your relief. Go for it. Screw a couple up. Then when you get it right you'll know how forever.

[joe]

I know little on this subject except what I've read in "Fine Woodworking Magazine. They published a complete 120 page review of techniques used by furniture makers and artists. By luck I found my issue published in 1985. My issue was a third printing that came out in 1987.

One of the techniques was ammonia saturation of 1/4" stock that can be bend into a pretzel like is was a noodle.

For a quick view of this paperback is found here.

"Fine Working, Bending Wood".

Joe Crumley

[Brady Watson]

"Bending Solid Wood to Form" PDF via USDA Forest Products Laboratory (http://www.fpl.fs.fed.us/documnts/usda/ah125.pdf)

& http://www.youtube.com/watch?v=Ub4-DqBSby4

-B

[phil_o]

I made the Civil War era chair referenced in this thread. The curved back was not made by bending, it was cut. This may not be the method you are interested in but it worked very well.
http://forum.vectric.com/viewtopic.php?f=27&t=17965&p=126745&hilit=Phil#p126745

Phil

[waynelocke]

If you use more and thinner plies with an adhesive with a harder glue line than PVA, you can arrive at consistent curves with little is any springback. You might even try it with PVA if the plies are thin enough.

[Red F]

Butch,
Things to consider:
1. If you carve your design and then steam bend it, there are some issues that will potentially come up. One is that the surface of the wood would need sanding after the screening process and steaming raises the grain in your carving as well as on the rest of the crest rail. Two was that you're bending stresses would be on even since the thickness of your material is not consistent due to the carving. Three with steam bending the bend that you end up with can be more or less consistent depending on your experience, technique, and whether or not you use a bending strap to do the bend.

2. If you steam been first and then carve your bend will be more consistent and predictable but then you have the problem of machining on an already curved surface. You could bend an oversize piece and then have the ShopBot carve the curve as well as the design all-in-one and true up your part. This would add a considerable amount of machine time to your part however and if you machine away a lot of the wood you may relieve some stress is in the wood which could change the curve.

3. You could stack laminate/glue up enough wood to cut your curve out of solid stock and then carve your detail. That would be fairly simple but would not have the continuous grain of the bending process.

4. You could also do a bent lamination. The nice part about this is your curve will be very repeatable and exactly what you bend or very close. So you get good consistency of parts. The drawback is that when you do your carving you may carve through your layers while it's not a big deal as far as stress you would end up with glue lines throughout your carving. That's not too big of a deal if you're going to paint your surface but anything that shows the wood itself will not penetrate that glue the same as it does with the regular one. Also you will need to use harder glue then your traditional carpenters glue or yellow glue. Personally I prefer Unibond.

I realize I haven't given you any answers but I hope that this helps inform your decision. And if you do go with any type of bending look up Michael Fortune. I've gotten a lot of information from him at conferences and his articles.

I also apologize for the format of this text because I was doing this with my voice recognition on my cell phone. A southern accent with a cold can lead to some funny comments.

[butch]

Thanks for all the help. I'll let you know how it works.

[dlcw]

Springback after releasing bent laminations from a jig generally comes from 2 causes:
1. Wrong glue-The only effective glue I have found for this is epoxy. Personally I have never gotten results nearly as good from any yellow glue. Never tried polyurethane (Gorilla) but did do a couple with Resorcinol and it worked also.
2. Wood too thick and/or too dry.

Most of my experience (but not all) is from Teak. I've bent it into 6" radius and 5" high with 6 layers of 1/8" and had no springback at all. The mild curve of a chairback is relatively simple and when done right should be perfect and repeatable.

Of course, as Shopbotters, the preferred method is to start with a thick enough piece of lumber, cut the outside curve on it, flip it and cut the inside curve, and then cut your relief. Go for it. Screw a couple up. Then when you get it right you'll know how forever.

Plastic resin glue works really well for bent form lamination and veneering operations. I've done many projects over the years with this glue and have not had a springback or veneer lifting problem. I also use it for complicated glue ups where I need lots of working time.

It comes in powder form and you mix it with water. Working time of about 45-50 minutes. Dries as hard as glass so clean up edges with a belt sander (it will tear jointer blades up bad). After belt sanding, you can edge on the jointer.

[myxpykalix]

I didn't go back and reread everything so not sure if this has been said....

If for a chairback the curve is not going to be that radical but you didn't really explain how/what kind of carving you were going to do.
If you are just going to do some vcarving this wouldn't be an issue or if you were going to do say a relief carving of a deer in a dish shape, no big deal, but if you are doing a deep 3d relief carving where it is going to be fairly deep you need to be aware of the warping a board will do when you remove alot of the wood around a carving.
I've done some blanket chest lids out of walnut that folded up like the letter U by the time i was thru with it. Those weren't supposed to bend though!:eek:

I think i would take some thicker material to start with like 1.5" thick and make your curve in vectors and do a 2 sided carving of cutting your curve out of the front, then do your 3d carving on the front, turn it over and cut the same curve out of the back.

These pictures are more to show a deep carving out of thick wood, no bend

[bleeth]

You're right Don, Plastic Resin Glue does work fine. For those who haven't used it:Be careful not too inhale the powder as you're pouring or spooning it out. It's very light and will disperse in the air easily and is quite poisonous.