Luthiery Fun #5: Bending the Sides Part 2

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Blog entry by Chinitorama posted 10-05-2010 10:08 AM 6112 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 4: Bending the Sides Part 1 Part 5 of Luthiery Fun series no next part

Here’s a shot of my bookmatched sides ready to be bent:
sides and form

Many luthiers shape an edge on each side with a compound curve before bending. This aids fitting the back and makes it a good idea to label everything before you get started. I’ll shape this edge after bending, but want to ensure the grain is as symmetrical as possible from bass to treble sides of the finished instrument.
Bending begins at the waist and I’ve marked this location approximately 14” from what will be the neck end.

With my bending iron plugged in, the dial is turned to the middle setting. Yellow cedar is pale in colour so I have to be more aware of scorching than if I were using a dark timber such as rosewood. Therefore I’m going to lay off higher heat until I’ve had more practice. Even at a lower setting the heating element inside the pipe gets red hot. It’s hot enough to bend when water pings off the surface rather than sizzles.

The side is given a generous spray of water and held against the hot pipe. Steady gentle pressure is applied until I feel the wood become flexible. This has been described as feeling the wood “relax”. Once the wood starts to give way, I apply more pressure whilst listening for the sound made by moisture evaporating on the hot metal. To avoid scorching, I use the spray bottle to keep the surface touching metal moist and keep the wood moving.

Any kinks can be corrected by selective heating on the opposite face.

I check the bend against a mold made of laminated mdf. When satisfied with the fit, I move on to the lower bout.

More checking against the mold. More bending.

After bending the upper and lower bouts I clamp the side into the mold to let the side cool off and dry out. As you can see, the side has been over bent at the ends. This is to allow for spring back as the wood tries to straighten itself out when removed from the bending iron. I again begin at the waist and realize very quickly that I should have made my mold much deeper. I was impatient and tired of large clouds of mdf dust. The clamps fit but it’s awkward.

I make it work and set the package aside to settle. After a day or two I’ll unclamp the side and touch up any irregularities until the side fits the mold perfectly without the need of clamps.

I must admit I was expecting this stage of the guitar build to be more difficult. Yellow cedar bends easily though, and tests on scrap wood helped me get a feel for the process. Enough of the test pieces snapped for me to recognize when I might be pushing the bend too hard.

All in all, I think things went rather well.


4 comments so far

View Brit's profile


7385 posts in 2867 days

#1 posted 10-05-2010 12:09 PM

Hi Jake,

Thanks for documenting the process. I played guitar for about 27 years, before I had to sell me collection to finance my house restoration. One day when I’ve honed my woodworking skill enough, I hope to build my own accoustic.

I like your home made bending iron, I might have to steal that when the time comes. How long do you have to leave the sides clamped in the form so they retain their shape?

-- - Andy - Old Chinese proverb says: "If you think something can't be done, don't interrupt man who is doing it."

View SPalm's profile


5320 posts in 3906 days

#2 posted 10-05-2010 02:06 PM

That is so cool. I am watching with my mouth open. You make it seem doable.

Thanks for the blog,

-- -- I'm no rocket surgeon

View RonPeters's profile


713 posts in 2905 days

#3 posted 10-06-2010 03:32 AM

Yes, very cool. On a violin we use a bending strap to pull the wood against the iron. It keeps me from burning my fingers! Also helps distribute the heat on the other side.

Thanks for showing your progress and process.

-- “Once more unto the breach, dear friends...” Henry V - Act III, Scene I

View Chinitorama's profile


105 posts in 3323 days

#4 posted 10-07-2010 05:18 PM

Hi all,

Notottoman, a two part mold isn’t needed for this kind of side bending. I have seen them used tho when making laminated sides. Some builders veneer the inside of guitar sides to make them more rigid. This in theory isolates the top making it resonate differently to produce a bigger sound.

Brit, I think it varies as to how long the sides need to sit in the mold. I’m using the approach of leaving them in till I intend to glue them to anything. The bending iron design really works and is used by a lot of luthiers. Like I said in the blog, super cheap and the parts can be taken off and used for other purposes between bends.

My plan is to show building the neck in Episode 6.

Thanks for the interest and support!


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