Steam Bending Wood

[drodda]

Does anyone have any ideas on how much over bend you need to acheive a certain radius. I am talking a radius of 58" and 64" not a really tight radius. Is there a perticular way to build the jigs to get close to exact results? I am using Oak and Ash 3/4" x 3" tall stock also. I am wanting to try to build a couple table aprons myself but have very little hands on experience with steam bending. I am trying to get a good starting point to build a jig to bend these around. Any help would be greatly appreciated.

[drodda]

On the same note does anyone have a source where a person could purchase wood already cut to the thicknesses needed to glue laminate the bends? 1/8" thick or there about I'm guessing.

[greg_russell]

Dave,

Regarding getting material, I would check with your hardwood supplier. The one we use has several large resaw bandsaws. We just spec the species and the thickness and they cut it for us.

Greg

[lto]

Dave,

The amount of overbend is not critical, you could go about 5%. On some bends we allow for zero springback, it all depends on the bending set-up and the drying method.

You will do better with air dried wood, as some kiln dried is rather diffucult to bend. Do not use green lumber, although it will bend to shape easier, it will twist and crack more in the final drying.

Either method you choose, laminating or steam bending, will be time consuming. I remain partial to solid wood bending, unfortunately shipping bends of this size in small quantities can end up costing as much as the bends.

http://www.barevillewoodcraft.com/


2530

[cip]

Dave;
If you are interested there is an article in the May issue of American Woodworker on glue up type bending including this formula for spring back:

project radius = radius times (number of plies minus 1) equals the form radius.

example of a 5" rad. with 10 plies

5(10-1) = 45/10 = 4.5 "

[jay_p]

Dave,
Spring-back is more of a consideration if your final piece is going to be a stand alone, unsupported assembly. If it is going to become part of a system as it often is in furniture construction, then other pieces of the assembly will help hold the bent piece in the desired shape.
We use Weldwood plastic resin glue for these types of glue-ups because it provides a more rigid glue line with less creep. This glue also allows for a longer assembly time (though it also has a longer clamping tim)There are also other brands of UF glue. Some people use casein glue.
Aliphatic (yellow) or PVA glues have more creep over time and also have a much shorter assembly time.
Jay

[bleeth]

A note to all new users of plastic resin (urea) glues-The powder is extremely light weight and toxic-avoid breathing it. Carpenters glue is never the suggested glue for bending-Urea and epoxy create a much stiffer part with much less spring-definately give it plenty of time to cure on the form.

[gerald_d]

I have never bent wood, but have bent a lot of steel, and I think that there is something that is not being mentioned here. It is fairly impossible to bend anything right up to its tip, or very end - the last bit always stays straight, irrespective of the force applied. So, start with a piece that is a bit longer, and bend over a mold that is a bit longer, then trim off the straight tips afterwards.

[bleeth]

I do the "fairly impossible" with laminated curves in wood quite regularly Gerald and I'm sure I'm not unique in this regard. It has a lot to do with how you clamp and your type of form.

[jay_p]

Gerald is right about the last bit of the bend. We always oversize our forms and our materials to allow the piece to go beyond the end of the desired bend. Then we trim everything back.
In this chair
2531, we cut all of the form pieces on the ShopBot from .dwg files and then vacuum bagged the laminates. This is my first image upload, so excuse the quality.


Jay

[jay_p]

Gerald,

It is not as comfortable as it could be. The distance from the front of the seat to the back is too great. If the second interation ever gets built (??) it could work quite well. The form is based on the treble clef symbol from musical notation.
On the first try with the largest form, we had a form failure and the whole thing imploded. After that we bagged the veneers separately (with the form itself out of the bag) and bent them to the form.

Jay

[mdebruce]

Jay
Just found this and wanted to say way to go! Nice work!
MDe

[hines]

FYI, I saw a how-to article on steam bending wood in the newest Wood Magazine.

[jay_p]

Thanks MDe. We have done quite a few other unique bending projects. Someday perhaps I will get around to posting others. It's quite a lot of fun.

Jay