Sunday, June 9, 2013

Flat Top Tele - Under Pressure

It's the terror of knowing
What this world is about
Watching some good friends
Screaming, "Let me out!"

When I first contemplated bending the sides, I thought a steam box would be the way to go.  By adding enough steam, wood becomes very pliable.  It was clear that I would not be able to make those tight bends at the neck joint with just a bending iron.  So, I built a steam box.

Filling up a box with enough steam to make wood bendable also creates a lot of heat and pressure.  Despite careful monitoring of temperature, a pressure vessel failure remains a concern.  In the event of such a failure, a wooden box can be designed to give some warning signs before its weakest point fails, while a PVC pipe is more likely to send random pieces flying.  So, instead of  using a PVC pipe, I decided to make a 4-foot long wood box from treated 2x's.

The first step was cutting the top and bottom from a 2x10 and the sides from a 2x6.  Next, I drilled a set of holes in the sides for some oak dowels.  The dowels are to support the wood to be bent, allowing the steam to make its way into the wood evenly from all sides.  I attached both side panels to the bottom panel with some wood screws, and started installing the dowels.

I drilled the holes snug enough that it took a hammer to drive the dowels through the holes, to ensure good seals.

With all of the dowels installed, it was time to attach the top with some more wood screws and trim the dowels flush.

With the four panels assembled, I could see some daylight getting through the joints.  To fill in the gaps, I added some foam weather seal.

Moving on the end panels, I made a hole in the fixed end to accept a brass fitting.  The fitting attaches to my steam source, a Wagner Power Steamer.

The other end panel is the weak point by design, attached with a pair of hinges and adjustable with a pair of hook and eye sets.  The hooks can be bent to fine-tune the seal.  Since water vapor under pressure can exceed the boiling point of water, I needed a thermometer with a range higher than 212 degrees Fahrenheit.  Fortunately for my wife, that meant buying a new meat thermometer with a top reading of 220 degrees Fahrenheit for this project.

With steam comes condensate.  To let the condensed water drip out, I drilled three drain holes at the end furthest from the steam inlet, and attached some flat pieces to the bottom panel.  The piece at the drain end is shorter than the other end, to make sure the water makes it to the drain.

Next came some testing.  I put in a 3-foot long piece of 1-1/2-inch wide by 1/4-inch thick pine furring strip, plugged in the steam machine, and waited.  I did not expect to be able to bend this piece much.  What I wanted was to get an idea of how much heat, steam and pressure would be generated in the box, how well it was sealed, and how it would be to remove the wood when opening the box.

After 45 minutes, the thermometer reading was 185.  At 55 minutes, condensate was dripping from the bottom panel screw holes and the box was getting somewhat warm.  After an hour and 10 minutes, the temperature had leveled out at 210.  I pulled the plug at an hour and 15 minutes, and waited 5 minutes before opening the door.  Upon opening the door, there was no noticeable blast of heat or pressure.  The sample piece of furring was warm and somewhat damp, but not overly wet.  The good news was that the wood was somewhat more pliable than a dry piece of furring strip.

So, at the end of the day, I declared this test a good learning experience and a partial success.  I made some notes about sealing up the screws holding the bottom and side panels together, so I could hopefully get the box to heat up quicker and reach a high temperature of 220 degrees Fahrenheit.  Next time, I'll be giving it a try with a piece of that 1/8-inch laminated oak kick board and a bending form.

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