The new and improved Universal Sjostrand bending machine.

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Darryl Young
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Re: The new and improved Universal Sjostrand bending machine

Post by Darryl Young »

I've seen videos where the waist is bent roughly 80%-90% at the beginning, then the lower bout followed by the upper bout, and finally the waist is tightened that last 10%-20% which pulls everything very tight around the form. This appears to work well in the videos (and in the only side I've bent it worked fine).

Is there any concern about "work" or "case" hardening the waist if it is put through two bend cycles? Seems it's fine most of the time from the reported success so just curious if it is a possibility that might rear it's ugly head once in a while. Is case hardening dependent on the type of wood used?
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Jim_H
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Re: The new and improved Universal Sjostrand bending machine

Post by Jim_H »

I've actually thought to do this, although I haven't put any effort into obtaining the materials.

My thought is that with the aluminum on the caul, which eliminates the need for the inside steel slat, you no longer have to worry about damaging your bend when releasing the inside slat.

I need to figure out how thick the aluminum needs to be, and how to fasten it to the form. I was thinking about a combination of some small stainless steel screws and some kind of heat proof adhesive.

Thoughts?
kencierp wrote:To make your forms more like the high volume producers, you can actually cover/enclose them with aluminum. This traps the heat and eliminates the need for the inside slat --- if you pre-bend the waist curve.

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Kevin Sjostrand
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Re: The new and improved Universal Sjostrand bending machine

Post by Kevin Sjostrand »

I took Ken Cierps advice and made a reflector plate for inside the bender. Then I decided it would be nice to be able to clamp this down to the bench too, so I took of the end stands, made some cut outs and took care of that issue.
I think I'm ready to go. No dimmer, not sure I'll need it, but I can wire one in later if necessary. I turned it on, put a thermometer on the form at the waist, and it got to 225 in less than 10 minutes and was still rising, so I can see with the side sandwich on there holding some of the heat in, this should get plenty hot.
Ken H, how hot does yours get?
Oh, and I also ran the wires under the ceramic bases through a hole and under the jig where there is about 2" of space, so especially now with the reflector, I can't see that heat will be an issue down there.

Kevin
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tippie53
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Re: The new and improved Universal Sjostrand bending machine

Post by tippie53 »

the original plans for the bender used them and it will protect your wiring as Ken had pointed out. I used reflective insulation.
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tippie53
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Re: The new and improved Universal Sjostrand bending machine

Post by tippie53 »

Ken had good advice. the only thing I can ad is to have a fire extinguisher handy . I have all my bending equipment at one spot , and while I never had to use it the fire extinguisher is handy , one thing you never mind owning and never having to use.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Kevin Sjostrand
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Re: The new and improved Universal Sjostrand bending machine

Post by Kevin Sjostrand »

Thanks guys, I already have the fire extinguisher in my shop, not sure about a dedicated stand for 360 degree access, but I'll work on it. I can place it on my table saw, but not sure how I'd clamp it, I'll take a looksee there.
I'm excited to try it out............."CRACK".....not, I hope!

Kevin
Ken Hundley
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Re: The new and improved Universal Sjostrand bending machine

Post by Ken Hundley »

Hi Kev: I am not sure how hot mine gets.....I got a grill thermometer to use with it, and promptly lost it. 2 years later, I just found it. I have lightly scorched some zebra (forgot to spritz a side) even wrapped in foil, so it gets hot. I am using a 300 watt bulb in each bout, and a 150 in the waist. I think I will downgrade to 200 all the way across, the 300's are BIG bulbs. They just didn't have any when I went shopping that day. I'll retrofit the thermometer after I revise the whole thing. Actually, now that I think about it, the thermometer needs to go into each form if I want to measure the temperature near the wood, so all I need to do is drill a hole for the probe, and transfer it to each form I am using.
Ken Hundley
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Kevin Sjostrand
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Re: The new and improved Universal Sjostrand bending machine

Post by Kevin Sjostrand »

Yeah, I got one of these inexpensive oven themometers that will sit on top of the SS slat. I realize it will be a little bit hotter at the wood, so I will have to take that in consideration. My bulbs are pretty close to the inside curves of the mold, probably within 4 inches so I figure the wood should heat up pretty fast. I may find that a thermo with a probe is better to insert into the side sandwich, like John sells.

Kevin
Kevin Sjostrand
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Re: The new and improved Universal Sjostrand bending machine

Post by Kevin Sjostrand »

I suppose once you've done this a few times and know how long it takes for the wood to bend with what you're working with, then the thermo is a moot point, and, as you say, it becomes a time formula. I have 500 watts, so I'll see what that does.

Kevin
Jim_H
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Re: The new and improved Universal Sjostrand bending machine

Post by Jim_H »

Really nice Kevin!

One thing I learned when I set up my bending machine. You need access to both sides. It might not be a problem if your bench is low enough and you can reach over to get to the springs, or if it's near the end of your bench.

My benches are pretty high because of my back issues (bending over a low bench is not a good recipe for a comfortable evening in the shop). I originally had mine mounted parallel to the edge of the bench like yours, but found I had a hard time reaching around behind it to attach the springs to the bending cauls. I ended up building a platform for it that would allowed me to extend it out off the end of the bench a bit so I can easily reach around it without my arms touching the hot stuff....

Some people but them on dedicated stands with 360 degree access, but I don't have room for such luxuries. :p
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