A recipe for bending sides!

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Kevin Sjostrand
Posts: 3712
Joined: Sat Feb 09, 2008 8:06 pm
Location: Visalia, CA

A recipe for bending sides!

Post by Kevin Sjostrand »

Okay, so I'm starting a new thread for the actual use of the Sjostrand Light Bulb Fox Style Guitar Side Bending Machine...ahem!

Here is what I did. I was 75% successful with my practice bend last night. That's right, it cracked, but only on the upper bout bend.

Let me also say, I realize I am not reinventing the wheel here, or at least I should not be trying to. However, being who I am, I like to try things for myself with what I have, and truth be known, I often learn that I should have just followed the instructions anway.
So that said, here is what I tried.

First, I went and purchased for $15 a thermo with a probe and an alarm, so I could see what kind of heat I was getting from this bender. The surface thermo for ovens I got was not working out very well on the heat up test run. This thermo worked good, even if it is not perfectly accurate.

I was bending a Santos Mahogany side. I thicknessed it to a nominal .085". I am using two .008" SS slats. My bender has two 150 watt, and one 200 watt bulbs in it.
I took both slats and formed them around the mold with the waist clamp and end clamps in place, thus sealing up the mold chamber. Keep in mind, this mold is the typical open style using tubing to hold it together.
I turned on the count down timer switch which is a 30 min timer, inserted the probe on the thermo inbetween the two slats at the waist, and in 7 minutes the alarm went off on the thermo at 250 degrees. I was amazed it heated up that much that fast.by the way, I did on one heat up let it get to 299 degrees before turning it off, it may have gone higher!
I turn the bulbs off. I proceeded to spritz, pretty heavily, the side and wrapped it in brown Kraft paper and turn the bender back on. When the temp hit 250 again, I unclamped everything and inserted the side between the slats, lined it up, intalled the waist support bar, and brought the waist caul down until the side laid on the upper and lower bouts of the mold. I reinserted the thermo probe into the sandwich of slats and side. By this time the heat had dropped down to 120. I let it heat back up to 150 which took much longer this time, about 10 minutes just to get that far, and I started to bend the waist, a little at a time as the temp rose. By the time it was to 180 degrees. I had the waist caul all the way down and I had heard no cracking. At this point I realized if I was going to get any heat from this thing, the mold had to be sealed up (yes Ken, I heard your voice in my ear right about then.) so I wrapped the bottom slat around the mold, and put the end clamps in place to hold it. Wow, it heated back up to 200 very quickly.

So at this point the waist is bent, the surface of the lower slat is 200 degrees, so I undid the lower bout end clamp, moved it to the position near the waist, and started to slowly bend the lower bout as I HELD the lower slat down over the mold with my other hand to keep the heat in. I would go about an inch and stop and wait about 30 sec, then proceed another inch. Once I got over the bout, I just finished the bend. I heard no cracking! By the way, I heard NO sizzling, and saw NO steam during any of this. So I was wondering.....is the water really necessary?????

I turned my attention to the upper bout. I could see this was going to take longer as there was less contact of the wood sandwich with the mold. I took the same approach, holding the lower slat down over the mold as I tried to work the caul clamp slowly, a little at a time over the upper bout. As I was making the turn...sort of speak over the outside curve, the caul slipped down a bit. In other words, I was not in control of it, and I heard a crack. Arrg! I went ahead and slowly continued the bend. As part of the practice run, I let it "cook" for a few minutes, then turn it off and let it all cool for an hour.

When I took the side out, it had in fact broken in two place on the upper bout...one just before the curve, and one on the curve.
So I wondered, did I go to fast? Was there not enough heat? Was there too much water, not enough water? Did the wood get brittle from a combination of too much heat and not enough water? Am I trying to reinvent the wheel?????

The other thing is that on the bottom of the side, there as almost no staining, but on top, there was quite a bit of staining. Obviously water marks, but also possibly some scortching, not sure. Probably could be scrapped off, but I didn't like the look of it. I've never had that happen when I've bent on a pipe, but I've never bent this kind of wood before.

So....what did I learn from this first attempt??

First, I am going to cover the mold/form with sheet metal. 26 gauge galvanized is what I have so I will use that. I see as Ken has pointed out, that in order to get enough heat going, this is pretty essential. I don't know how guys do it without the form inclosed this way.

Second, I may not wrap this wood in paper, and I am wondering if I should try and bend it dry?

Third, I may have to rethink, remake my bout clamping cauls so there is more contact and more control. I can see how the double dowel set up could be much better for this (like I see in the picture of John Halls bender), and if the dowels can roll, that would be even better.

Fourth, I can see that one must go very slow....the heat is going to contact only a small section of the wood at a time until the waist is bent, and then a small area makes contact over the bouts until you get around them..so slow is quite necessary.

Fifth, I did move the side over the lower bout with my hand with moderate pressure to get more contact with the heated form, and I will do this again, as I could feel a little bit when it wanted to bend.

Sixth, I am wondering about not using a slat on top, so I can see the wood and see what it is doing, and again push it down and around the bouts with my hand so I can feel it too.

So I was alittle disappointed, but not surprised that it didn't come out perfect the first time.

If you have done bending with this style of bender, perhaps you could shed more light on what you have done that worked, particulary with different types of wood.
What to do with a blanket won't be helpful, because I, and some others my not be using a blanket.

So for different woods, what have you done that was successful.
Temperatures, water and how much, or no water, wrapped in paper, foil, or no wrapping. Slats under and over, or just under, or.......
If you did not have an inclosed form on the top, then how did you get enough heat build up to successfully bend?
And any other questions that might come up that you would have an answer for.

I appreciate you reading this, and commenting as you feel led.

Again, I am not really trying to discover this process all over again as it has been used and done for decades now successfully, but I see so many pictures of bender, and descriptions of how to do it out there, it is hard to decipher what is going to work the best.

Thanks.
No pictures here, you have all seen broken sides before, right?
The bender pics are in another thread.

Kevin
tippie53
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Re: A recipe for bending sides!

Post by tippie53 »

You are correct in the assumption that you don't need the upper slat on the light bulb configuration. You need a working temp if heat from 275 to 375. One thing that may be to your favor is you can see how dry the wood is , The only advantage to paper on this is for keeping sap and resin off the slat.
Try this and see if it helps . Also remember that time is both the friend and enemy here . Wood has no brain so when it gets hot it will bend . Too dry though and it can crack. So with the slats on the bottom nothing on top , you can try this method. Also you can expect about a 5% failure rate with light bulbs .
Put your hold downs on and get the set aligned to the bender. As the heat gets into the wood you can actually feel it letting go and bending . Lower bout first , Have a sprayer handy and as the wood show sign of drying , give it a light spray to dampen it. once that part is on the pattern go to the upper bout again just enough water to dampen the wood. set the upper bout then do the waist.
Once you are on the pattern ( should be under 5-6 min ) let the unit heat up to dry off the water . Be carful with the thermometer as it can leave a mark on the wood. So place it in an area that you can put a side support on to cover the mark. Let the wood heat to 325 and kill it. let it cool down before removing it. As long as you can get this into the mold and it fits , that is all you need.
It is not uncommon on bulb units to have to hand bend to touch up things, but again ,if it fits the mold you did good. Let us know how you make out .
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Kevin Sjostrand
Posts: 3712
Joined: Sat Feb 09, 2008 8:06 pm
Location: Visalia, CA

Re: A recipe for bending sides!

Post by Kevin Sjostrand »

Thanks John, I think I will try the next one this way, no top slat. I REALLY like seeing what the wood is doing.

Kevin
Ben-Had
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Re: A recipe for bending sides!

Post by Ben-Had »

I invested in a heat blanket. I figured a couple sets of cracked sides (or should I say un-cracked sides) would about pay for it. John's bender (now mine) and blanket = no more cracked sides!!
Tim Benware
tippie53
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Re: A recipe for bending sides!

Post by tippie53 »

the very first time I saw a bender with light bulbs was out at Martin in the old plant . We know this now as GMC. They had one there with the light bulbs. Jeremy trach showed me how to bend and that was the method they used . Good luck and keep us posted.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Darryl Young
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Joined: Fri Jul 30, 2010 6:44 pm
Location: Arkansas

Re: A recipe for bending sides!

Post by Darryl Young »

Kevin, how hot was the wood when you were trying to bend the upper bout?
Slacker......
Kevin Sjostrand
Posts: 3712
Joined: Sat Feb 09, 2008 8:06 pm
Location: Visalia, CA

Re: A recipe for bending sides!

Post by Kevin Sjostrand »

Darryl,
I would say, not hot enough! At that point, the thermo was not in place. I am guessing maybe 200 degrees, but there is so little side to form contact around there that very little of the wood is going to be hot.......so I can see that VERY SLOW is very important. I hope that closing in the form will provide the much needed additional heat.

Kevin
tippie53
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Re: A recipe for bending sides!

Post by tippie53 »

Just a hint
Cloths Iron
Before I found heat blankets I did find that the iron helped a lot . Press the iron on the wood , and you will feel it get pliable and work the hold downs. You can use the steam heat be careful as dry heat will be safer . you don't want steam burns wear a long sleeve shirt.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Darryl Young
Posts: 1668
Joined: Fri Jul 30, 2010 6:44 pm
Location: Arkansas

Re: A recipe for bending sides!

Post by Darryl Young »

I'm not really one to be giving advice on bending.......but that sounds 100 deg too low.
Slacker......
Kevin Sjostrand
Posts: 3712
Joined: Sat Feb 09, 2008 8:06 pm
Location: Visalia, CA

Re: A recipe for bending sides!

Post by Kevin Sjostrand »

I have a small iron in the shop I used for taking apart an end block once, and I thought last night after the CRACK, I could use that to help that upper bout bend.......and I may just try it. Careful not to scorch the wood though.
It doesn't have a steam feature. :>)

Kevin
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