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Looking at the bottom slat on the Fox bender/Bluescreek bender for sides....

I notice in photos around the internet that some people permantly fix the bottom slat to the form, whilst others leave it loose and bend it with the other slats, blanket and wood. Leaving it loose appears to cause the complication of having that bottom slat needing to be "secured" in some way when the pressure is released, to prevent it from springing back and splitting the wood.

Is there any disadvantage in just securing that bottom slat permanently to the form?
I might add that I am dealing with ukulele sides here, which are very thin.... .070" or a bit thicker, which are fairly fragile.

Rod

Rod buddy one of the purposes of the bottom slat when bending sides is to encase the wood in something that will concentrate the heat being applied to the wood. Think of the bottom and top slat as being like a pot when cooking..... baked beans......

Another purpose is to support the wood so that as it starts to bend it will bend evenly in as much as good slats will bend in curves.

So IMHO a permanent slat on the form is fine but I would still use a free floating bottom slat too that can be spring clamped into a tight stack with the wood, blanket, and top slat. Also at times people modify benders in such a manner that encouraged the heat of the stack to be wicked away. A bottom slat probably won't have this issue in that it's contact with the stack only comes into play after the wood is bent.

I have slats directly connected on our fox bender forms...but I also use light bulbs right now. The slats attached to the from creates an oven affect. I can get the box and slat to over 320 degrees. Then as I bend the sides, the fox works a little more like a pipe. That is to say, only the wood touching the form and the areas close by are getting heated. So the process is much slower. You have to lower the cauls very slowly to aviod cracks.

If I was using a heat blanket, I would just make a form with 3 or 4 layers of plywood. Maybe seperated about 1" apart. That should be enough to keep the sides flat while bending.

Joe

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Joe

The biggest "con" I see to attaching the slat to the bending form is the lack of support to the waist when bending. Now The Fox bender is suppose to have a clamp of sorts to help support the waist so maybe this isn't an issue. The second "con" I see to attaching the slat to the bending form is the cost. If using SS slats that might get pretty expensive if you have 3 or 4 different body shapes.

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Thanks. Some good ideas are coming out here.

You can probably see where my concern lies with such a small body as the soprano ukulele and the fragility of the wood.

Watching the video over and over again..... I don't think that I am going to have the luxury of pulling out the bottom slat first. Note that in the video the slat doesn't come out with a tug until the temporary clamp at the left is released. With the thin uke wood and the strength of the spring steel, that is going to break the wood.

The uke wood is only .070" thick, and about 2-3/8" wide. Fragile.

Lets look with photos at my particular problem....

First, the form:
Actually I have one lucky thing going for me here, as it isn't a standard soprano ukulele shape that I am building, but more like the shape of a dreadnought guitar, with a broad waist, and hardly any curve up to the upper bout from the waist. The whole thing is just 9-1/2" long though.



This by the way is John Hall's bender. You can see that the uke form is pretty tiny when it is in there.



And I am going to have to reposition the retainers for the ends of the springs for the two cauls. But that is easily done.



Rather than pull that lower slat out, I think that I am going to have to devise a way to retain it until after the upper slats, blanket and wood have been released. Two pieces of bent coat hanger wire bent into a tight U shape will do the trick here, as the ends can go through the form tubes. In other words, release the lower caul a little, hold the lower slat down, and insert the two "staples" to hold it down.



And the same at the upper bout end



The waist may be a little more problematic though. In this photo the waist caul has been lifted about 1/8". There's a heck of a lot of upward pressure on the steel already as it tries to unspring itself. Only trial and error will tell me how far it can be released before the spring steel rises enough to break the wood. But at this stage I don't even want to waste my test side pieces on what will probably be be a destruction test.



At the moment the only thing that I can think of doing is to drill holes in the uprights (which will fall just outside the waist caul), and find a way of holding down the lower slat (whilst raising the waist caul) in order to insert a couple of rods, or even nails would do it. But it would be awkward.

What I have thought of doing however, is to have the lower slat full width, but the upper slats narrower. A uke side is less than 2-1/2" wide! That way, the four retaining "nails" could be pushed in to hold the lower slat down even before releasing the waist caul.

Do you think that might work?

Rod

This won't be a popular solution around here...but I am sure it will work:

I would consider using aluminum flashing for the slats on this uke. It comes in 6" wide rolls that are about 100 feet long. I think I paid $6 for the roll. I now have used it successfully to bend the sides of archtops including a sharp venetian cutaway. The reason I suggest this to you for the bottom slat is that it does not spring back very much. The wood sides after being bent will hold the aluminum down on its own. I did a test with .060 mahogany sides about 2.5" wide in the bender. I had no trouble removing the top slats without the bottom slat springing back up. At one point I did double up the aluminum slat and taped them together with aluminum tape found in the HVAC section of HomeDepot. I double them up because bending the cutaway needed extra support of the wood to keep it from fracturing. The double layer worked just fine. But we bent dread sides with single layer slats no issue. Its only super tight cutaways that gave me trouble. The inside radius of the cutaway was under 2".

I also use little clips to hold the material down like your picture. In fact I use them while the machine is still hot. I place them over the top slat. It keeps the slats flat when your bending skinny sides. (3" or less in a 6" FB). But when it comes time to remove the sides, I just pull the clips off.

The aluminum flashing is easy to cut, so you can make shorter lengths for your ukes. And above all, it doesn't spring back a lot. The other cool think is, one you take the slat out of the form, it almost lays flat again. It wan't until I had bent about 5 or 6 sharp cutaways, that the material got a little more difficult staighten out. But it is cheap. Just cut more after 5 times using it...

Good luck,

Joe

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Joe

would work but once again aluminum is thermally wasteful.

[quote="MichaelP
would work but once again aluminum is thermally wasteful.[/quote]

This I did learn the hard way! I wonder on the small pieces if that would be as much of an issue? Also, with a heat blanket, this might not be as much of an issue as with the bulbs.

Joe

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Joe

I use a permanent aluminum slat attached to my mould, and have bent dread 000 size sides that were highly figured with no problem. I have considered doing it the other way (no fixed slat) for an L-00 size coming up in the near future. I have had no problems as of yet, but that is just me, and don't know if it would work for a uke. I take my time and try to have a feel for the plasticity of the wood, which is harder to do with the steel upper slat, but you get used to it. The fixed slat works for me, so far, but I do see the cons of it as so many above have pointed out.

I'll add that I use a heating blanket, and as hot as that thing gets, I don't have any trouble with heat being pulled away by the bender, but I don't do cutaways either! (yet)

(back to my hole, now, I'm putting on some bloodwood binding from Uncle Bob!)

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Brad Tucker

This I did learn the hard way! I wonder on the small pieces if that would be as much of an issue? Also, with a heat blanket, this might not be as much of an issue as with the bulbs.

Joe[/quote]

Actually it is more of an issue in terms of efficient use of wattage with a blanket. The blanket radiates from both sides. Spring steel or stainless steel dissipates the generated heat much much slower than aluminum. Therefore it take less wattage into the blanket to get to 300 degrees and hold there with the lest amount of additional watts. With aluminum dissipating the heat so quick the blanket has to use more power to maintain a constant temp.