Steam bending Tops & Backs

[Dennis Duross]

Here's a picture of the mold I made some time ago. It's made from 2 x 4's, and is 1.375" high under the bridge. Like I said earlier, I didn't have enough positive experiences with it to continue...

[Robert Freemond]

Dennis, That mold looks great, but it's probably too high if you were to use a steam box, & an oven. My mold is 15/16" H. & I end up with a 3/4" H. Top or Back. If the wood doesn't crack you might just eliminate the oven & get what you need.

[Dennis Duross]

I was actually getting a pretty consistent .75" arch, but after seeing your process I'm guessing that the reason (given that my mold was so much higher than yours) was that my soundboards were not as thoroughly pliable as yours to begin with (your well-reasoned 20-minute spa treatment in the steam box, as opposed to my take-no-prisoners heat-gun blasting process). It took me both more force and a mold with a higher arch to achieve a final arch height of .75".

And probably as a result as well---the thing that caused me to ultimately give up was the fact that although I could get the proper arch height, I couldn't get the plates to flatten back out all along the perimeter so I could actually glue them to the rims without introducing what I suspected was more force than reasonable.

So IF I were to give it another try (and that's a big if) it looks like the steam box is the way to go.

[Robert Freemond]

Well, If you give it another try; I'll be glade to help in any way I can.

[Dennis Duross]

Thanks, Bob. Your success may help push me back in that direction. Notice I never did throw out the mold, and it would certainly be easy enough to lower the arch just by attaching some thin plywood all around the perimeter.

[Graham McDonald]

An alternative to the steam box is sealing the wood in oven bags and cooking then in the oven. Never tried it with hardwoods, but it works OK with spruce.

cheers

graham

[Robert Freemond]

Graham, Is there moister in the Oven Bag ?

[Graham McDonald]

I soaked the soundboard halves, thicknessed to around 7-8mm, overnight and them wrapped them in oven bag material and sealed them up. Into the oven at 250-300F and wait until the bags got all puffed up and the wood was flexible, around 20 minutess. After that much as you have been doing it. I did this a quite a bit in the 90s mostly building Irish bouzoukis, wrote an article on the idea for the GAL in 98 and then a book on bouzoukis/cittens which included a chapter on steambent soundboards. That chapter is available as a download from my website, as I have pretty well stopped steambending soundboards and the current ebook edition of the publication doesn't include it. I suspect the arcane rules and regulations of this forum doesn't allow a link, but if you google my name and 'bouzouki' you should be able to find it.

cheers

graham

[Mark Swanson]

Hello Graham, it's good to hear from you and I hope you are well!
Our rules have changed quite a bit, and if the link is relevant to this discussion (which it certainly is) you can post it.

[Graham McDonald]

Excellent to hear the rules are not as bizarrely restrictive as they used to be.
Anyway here is the link
http://www.mcdonaldstrings.com/Zoukbook ... boards.pdf

I hope it might be of some use. I did have the GAL article available as a download, which gave a bit more background to the evolution of how I did the steambent soundboards, but I must have removed the link in an update. If anyone is interested I can upload it again, or PM me and I can send it. It is an interesting way to construct an arched soundboard, it is more economical in use of timber, but I eventually decided that I enjoyed carving a soundboard from a chunk of wood, and I have shifted more to mandolins anyway. I had originally thought that I might be able to make steambent soundboards thinner and lighter, but I turned out that they have to be the thickness that the builders in the 20s and 30s established. There might be some acoustic advantage in having the fibers of the spruce running along the curve, but I have never figured out how you could measure that in any scientific manner.

I do look at the forum pretty regularly, Mark, and I should contribute a bit more

cheers

graham

[Graham McDonald]

The link to the article on steam bent/moulded soundboards published in American Lutherie in 1998 is on this page http://www.mcdonaldstrings.com/links.html
The pictures in the original publication were in the pre-digital photo age, so I don't know where they have got to.

cheers

graham

[Dennis Duross]

Great info, Graham. I hope you do decide to contribute more in the future.