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Hello,

Well my dad decided to start building flat tops after seeing my archtop progress. So he wanted to build a fox bender using bulbs. So the last weekend or so, I helped him build a bender that would suit both his flattops and my archtop. We will share it.....LOL! So as part of the process, I made sure that we made it wide enough to later use a blanket, as I think that is probably the best method.

For now, we have tried the bender using some scrap wood with excellent results. I have a few questions. First our test wood was good old lumber yard pine planed down to 3/16". Using a thin slat, a craftpaper dampend, the wood, another craft paper dampend and a final metal slat, we were able to start bending when the fox bender hit about 200 degrees. We had no problems bending the entire board at about 210-220. It will get up to about 260 degree with the current bulb set up and the control on full. (using three 100 watt clear bulbs). No problems with pine and very little spring back. I would assume pine is easy to bend.

Question, we never saw steam, but had no problems bending. Did the package ever get hot enough? The top tin never got steam if I dropped water on it but it did evaporate quickly and was to hot to touch by hand. I would assume the top will not be as hot as the bottom tin.

Question, the thermometer is being place in one of the tubes that connects the sides together. (1/2" tube right at the edge of the mold/form). Is this ok? does it really matter where the thermometer is place...or is it all relative to the begining tempature?

here is a picture of his bender:




Explination of the bender: We had to make a second caul for the waist line. This caul slips in place specific to this guitar. It is a dread and the waist is almost flat with very little curve. The first side bent did not form as well in this area, so we build a slip in caul that worked great. The other few molds we made seem to work ok with the original shape of the caul.

The mold is 6" wide using two pieces of 3/4" plywood and metal tubes as spacers. It is then covered in metal. In one of the tubes, I slid the thermometer. The fixture itself is about 6 1/4" wide to accomidate a blanket (In case the blanket is a little to wide) in the future.

Any thoughts on the temp or the steam?

Joe

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Joe

First off If using 2 100Wat bulbs I doubt you will get the unit hot enough to get to 300+ you will need for many hardwood as quick as you would really want. Most that use bulbs use 3 150 or 200 watt bulbs with a dimmer for the waist, and bouts I found to be best.

On the waist of a dread not bending well one thing I find to set the waist and bouts well is to add a bit of friendly tension on the waist at the start of warm up. As the wood reaches temp bend the waist ½ to ¾ full, bend the lower bout full, upper bout full the finish the waist. The causes the remaining waist bend to pull tight from the bent bouts and makes a better waist set. I find that if I bend the waist full first then the bouts full I end up with a tad bit of slack either side of the waist that allows the waist to spring out. Many use a spreader system that pulls the slats tight as it is bent.

By the way I did not remember reading where you said you were using slats to sandwich the wood. If I missed that I apologize.

Also get a blanket as soon as possible. The heat the wood evenly as wher with bulbs in a system like you have the heat is only at the contact points between wood and bender.

Thanks Michael.

The package was Aluminum slat/craftpaper damp/wood/craftpaper damp/aluminum slat. Also the mold itself has an aluminum slat nailed on it to match the shape.

There is actually 3 bulbs. The two end bulbs are raised up higher than the middle one. Right now he only had 100 watters. I have some 150's at my house I will have to bring over to him. Your right, the temp will rise much faster. It took about 40 min to hit 260 with the wood bent in place.

Actually, I did follow some of your advice you just mentioned. I bent the waist until it was about 1/2" away from seated. Then bent the sides down. Then followed up with firmly seating the waist. The change in the caul to match the radius was a big help. I think that will be part of my normal process. Make a caul for each guitar.

Thanks!

Joe

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Joe

If nothing else I would move away from aluminum slats as soon as possible. you are disapating heat throuth the slats too fast with aluminum. spring steel or stainless is what you want.

when bending hardwoods you will need temperatures ranging from about 280*F to 325*F. you will need three bulbs of 200w to achieve these temp ranges.

but when a blanket, which provides a more even heat, can be had from omega for $70 and a router speed control from harbor freight for $12 to control temperature why fiddle with the bulbs.

Thanks. One of the reasons we built the jig over 6" wide was so we could eventually switch to a blanket. I am assuming my dad wants to watch the cash on his first build to see if he would build more than one. At some point, the cost can get overbearing if your only building one. I will use the jig too, with ambistions of building serveral guitars a year, but that will have to be seen. So a blanket is low on the priority list if a set of $5 bulbs will do the trick.

Thanks for all the help.

Joe

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Joe

Joe...When using bulbs with 150W and 200W bulbs, the inside of those molds gets very hot. I lined the insides with aluminum flashing to not only protect the wood but also to reflect heat upward and onto the side wood.

I now use both bulbs and a blanket and like the combo. If I were starting over, I would make a bender with 2 blankets.

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JJ
Napa, CA
http://www.DonohueGuitars.com

What if Fender had invented the bender? Would it be called the "Fender bender?"

Joe, You may want to take the sheet metal off the form. Covering the form permanently with sheet metal will slow down the heat transfer to the bending slats and the wood when using light bulbs. This would not be a problem if you were using a blanket.

If you wind up breaking a $70 set of sides with the bulbs there's the cost of your heating blanket right there. The blankets work so well with spring steel slats I'd just go that route from the start. (Or bend with a pipe) After finishing one you can believe your dad will want to do more plus if you start using hide glue the blankets make great parts warmers for braces, bridges, etc.
Good Luck
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks everyone. We bent up a set of dread sides this weekend and it worked great. So I built forms for my archtop today. I bent the first side today out of mahogany. The sides are only 2.5" tall due to it being a 3" archtop. It bent easy and the waist is nice and tight. Even taking it out of the bender after about an hour to inspect the form (for burning), there was almost no spring back. So I clamped it in my mold with no issues. Next is the cutaway side. Yowaza!

I will most likely leave them in the bender over night in the future. Also, while I had the bender at my house, I changed the bulbs to 200/100/150 Big bought to small. I still think it could have used a little more heat...although the mahogany bends with no problems with this setup.

Joe

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Joe