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I've tried bending four sides as practice using the method used in Todd Stock's videos. I still am doing something wrong because I'm getting alot of spring back. Bent top to bottom. The bottom was with new blanket as the first blanket had a bad spot in it. Any suggestions as to what I might be doing wrong?

Here's a view of the last one which I pulled out of the bender this morning.

Chris buddy it would be helpful if you let us know a few more things. What thickness were the sides? What kind of wood is this? What is the make-up of your stack with the blanket, slats, wood, foil/craft paper etc?

Here is a toot that may help you too: http://luthiersforum.3element.com/forum/forum_posts.asp?TID=11104&KW=tutorial#forumTop

When I bend a side my blanket is rarely on for more then 4-5 minutes. I start at the waist slowly cranking that down except for the last 1/2" or so. Next I do the lower bout followed by the upper bout and then I finish by cranking down the waist the remaining 1/2".

I let the side cool completely in the bender and once completely cool (at least one hour) I turn on the blanket again for about 4 minutes and then leave it to cool as long as I can, over night is fine if that is available to wait that long. So each side is cooked twice. The second cooking helps reduce any spring back if that is going to happen.

Do you wet it before the second heating?

Mike

The wood is flat sawn mahognany at .085" thick. My stack from the bottom up is; slat,blanket(5 watt sq."), foil, damp craft paper, side, damp craft paper, foil and slat. I been following Todd's videos but can't figure out where I'm going wrong. On the last bend the tempreature got up to 360 and I tried using gloves when starting to bend the lower bout to see if I could get a feel for the wood turning plastic as Mario has suggested in other discussions. Maybe it's the re cook I'm missing.

If I read this correctly, you have your blanket in between your slats?
My stack from the bottom up is slat, spritzed mahogony, slat, then blanket. For mahogany I can't see a need for all the other additives (foil and craft paper)
I would not recommend putting your blanket in between your slat.

Ray

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Guitar Building = Continuous Improvement Process

This is where and how I learned to bend my first set. I also lost about half my finger prints that day...

http://www.bluescreekguitars.com/tutorial10.php

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Guitar Building = Continuous Improvement Process

i had a very similar experience when bending my first sets of sides. i practiced using some QS white oak and it took me 4 tries to get it right. you can follow that here. viewtopic.php?f=10102&t=14134&st=0&sk=t&sd=a&hilit=bending
a bit long, but it was a great help as i was walked through the entire process by our friends here on the OLF. you might find it a help.

maybe you could give us some more info? how much moisture? how long are you cooking the sides? what temp?

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sweat the small stuff.

Not to be short but if you watch Todd Stocks you tube videos that's in the Video and Picture Tutorial section the times and tempreatures are the same. Start timer at 40 min., Temp gets to 230-250 and steam is coming off package set waist down to about 3/8" from mold, bend lower bout, upper bout, set waist and let cook till all steam is gone and temp. get to about 320-350 and then back off temp to about 310 and cook till timer runs out which is about 20 min. or so. The timer was set for 40 min. at start.
It could be the blanket in the slats I guess.

I can't comment on Todd's method because I don't do it that way.

But what you have not said yet, so I have to ask, is how long are you waiting for the side to cool before taking it out of the bender. The cooking times that you are mentioning are long enough to make lasagna and you have not cracked a side so they are getting bent. If you are not letting it cool all the way spring back is likely to happen with a warm pliable side. The cooling process is very important to set the bend.

If you checked out the toot that I offered the second bake is to help reduce spring back and "set" the bend. I have seen noticeable differences in sides when I don't do the second bake.

Again - my blanket is only on for 4-5 minutes and that is how long it takes to bend a side for me and many others who I learned from.

Ray craft paper or foil will explain it's purpose to you when you bend something beyond mahogany or even when you bend highly figured mahogany.

Craft paper helps hold some moisture, just a bit, to generate steam and is helpful in bending sides. In addition, when you bend Koa without craft paper the wood can react with the metal, including foil, and turn the sides green.

Foil also helps keep the moisture in again aiding in the generation of steam. Both craft paper and foil can help keep your wood and slats unstained.

I generally lightly spritz my sides prior to bending.

Oh yeah - I forgot to ask. And pardon all the questions - we are trying to help you out and as such we can't know all of the relevant factors if we don't hear them from you.

What kind of blanket/where did it come from? Also the slats, same question as for the blanket. Where in the stack are you sampling the temp? Your thermometer - have you calibrated it against a known source to see if what it reads is indeed what you have? And lastly you have a Fox style bender - what does the bending form look like i.e. is it solid, open with supports, what ever?

Thanks.

Okay, Here is some pictures of my bending gear. First off I have let all the sides cool over night of at least 12 hours probably more like 16 hours. I have an omega blanket at 5 watts. per sq. inch. and the slats came from McMaster-carr and are SS spring steel at .019" thickness and 6"X36". The temp thermometer is a Cen-tech with a K thermocouple. Harbor Freight router speed control. Mold and bender I built. I have yet to read through the two links that have been stated here but I will for sure as I did give them a quick look. I appreciate the responces so far and thanks to all for responding on this 4th. Oh yeah, I put the thermocouple between the paper and the under side of the wood at the peak of the lower bout about 1 inch in.

Thanks Chris that helps a lot.

Well your blanket, controller, timer, and thermometer all should be fine - slats too. The stack that you use sounds fine too to me although I put the blanket over the wood with a slat in between but I have done it your way too successfully.

Just to be sure, and pardon me please again for the nit here - when you let it cool you ARE letting it cool in the bender with all the cauls down correct? I just want to eliminate the possibility that it gets removed from the bender and then is permitted to cool.

I'll probably get flamed for this but I am wondering about the solid form. Since it's pretty clear that you are using more than enough heat perhaps the solid form is wicking away some heat. I do see some scorching on the form but you did not mention any scorching on the wood. The form that I use is not solid and the two sides are connected by cross pieces.

You mentioned that your craft paper is damp, do you spray or wipe the wood lightly too?

There is also a possibility that your wood is tough to bend. Mahogany can be all over the place from easy to bend to tough to bend.

I am still thinking here...........

I was just looking at your test sides and I think that I am seeing a crease at the waste on one of them. This leads me to believe that they are not getting bent completely in the bender. Another way to say this is that the issue may not be spring back if the sides are not completely bent initially. It's very possible with a Fox bender to horse the sides around the form and have the cauls all the way down but the wood itself is still not bent very much. This is what I think that I am seeing with your test sides.

Yes, I leave the side in the mold and do not remove it. I've been reserching this for some time now and watching others having problems and figured I had a good idea what to do but apparently not yet. There is a crease in the 1st and 3rd bends but this was a reasult of the adjustable caul not being set correctly. There is a slot in the mold at the waist to allow the alu. waist bar to clear the mold and the slot in the mold is a bit wider and lower then the bar. It's 1/4" lower and it is wider then the center piece of the adjustable caul. As a result when I ran the caul down onto the mold to set the leaves on the caul the main leaf was 1/4" too low and I didn't notice it. After the first bend and really cranking down on the waist vise it sort of stamped it. That's why it a good idea to practice I guess. I reset the caul but on the third bend I over cranked it again where the other leaves slid and the center pressed it again. Then I got off my A** and put a 1/4" filler strip in the bottom of the mold slot so the Alu. bar would bottom out with the top of the bar being flush with the mold. If you look at the picture of the last side you will see it did scorch a little at each end. Now as a matter of fact on that bend I noticed that there was about an1/16"-1/8" gap at the end of the upper bout where it wasn't flush against the mold so I put some small bungi cords from the upper to lower bout cauls to tighten it up. So I'm guessing the extra pressure may have helped to cause it to scorch. I haven't wet the sides, I just wet the craft paper by running it through water in a pan and then squeezgy off excess water on the side of the bench. There's also a crack lengthwise on the second bend but I did that when seeing if it would just happen to go into the outside mold.

One thing we can all agree on here the bend is not setting. I believe the wood is not at temp long enough and or not being allowed to set long enough. I always leave my sides clamped up over night if I bend in the after noon they stay in th bender over night 16 hours sure seems to be enough. I may have missed it but are you placing the sides in the assembly mold and and clamping them to the the mold or using spreaders to keep them pushed flush against the mold after you remove them from the bender? Some woods if you do not restrain them thy will open up like this over time. I never allow my sides to just set free on the bench after bending for an extended period of time.

I too think the bouts do not seem as if there is proper heat getting to them, thus the bend is not being achieved. If your sandwich opens up in the bouts after your bending caul complete the bend at the bouts and the blanket is not in contact the the heat is not getting to the bouts evenly. this leads to lower heat where the blanket is not in contact. One way or another I suspect heat is the culprit

Chris,

A thought here, maybe it's possible you are cooking the wood straight. What I mean is when you start talking about 360 F, you don't have alot of time before that thing is baked. And with spring steel, especially 2x .019" slats, it's probably very straight.

I recently bent 3 sets of sides, 2 of them I did with my normal method 250-260 for all bends, and 1 at 310. The first 2 went fine, the 3rd set had one bent side with a lot of springback, and the other side ( venetian cutaway) cracked at the cutaway. on both of these I noticed the waist bent fine and about 250. By the time I got to the bouts they weren't relaxing. So I thought maybe I cooked them straight. When I bent a replacement set I used my 250 F method and everything worked fine.

hope that helps.

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Matt Jacobs

"Don't tase me bro"

Hesh, I've read through your tutorial and might try that approch to see what happens. I'm also starting to wonder if SSII is in order. I want to get this down be fore attempting to bend my nice claro sides. No room for error with them.
The sides won't go into the mold with out splitting as in the case of #2. They look just like the picture and still do.
Baking? beats me, I'm just learning this wood bending stuff! But sounds interesting to me.

SSII is a great product but the bend set problem will bot be solved by using SSII. Do you have pictures of your upper and lower bout bending cauls? Somewhere the heat is not setting the bends in the bout. that tels me the heat is getting to the wood in the bouts properly

Michael, You can see the cauls in the picture of the meter they are in the back ground but if you want to get a better look I can get them for you in a few minutes.

Some Mahogany can be a bear to bend and may show considerable springback.

Can you try this with some Indian Rosewood and then report back.

Cheers

Bob

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Bob Connor
Geelong, Australia

Yeah, if you send me some.

Since I switched to two blankets I've had very little springback. I had problems before. I pretty much do it like John Mayes in his videos. I go blanket/spring steel(covered with Al foil)/moist craft paper/ side/ moist paper/spring steel/blanket. Clamp it all together with spring clamps. Start the bend when I see a lot of steam (around 265) Usually finish around 320-330. Thermometer is between the top blanket and steel slat just behind the waist caul. Cook around 300 for 10-15". Cool fully and reheat to 300 for 10". Cool overnight.
After lots of different techniques the above has been the best by far. Sides come out looking great. I think the two blankets really dry out the wood.
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.

What happened with one blanket? It seems I'm doing the same as you did but with one blanket and no re cooking. Could it be the re cooking that sets the bend?

That's the idea!

Chris buddy everyone has some good points here and we all seem to agree that the bend is not setting correctly.

SuperSoft II won't help you as Michael indicated and I will add that these sides should be able to bend without it. Although it might help many people have bent sides without it for years. It's a great product and I plan on trying it the next time I am bending something expensive but it's a good idea to get your chops down first without it.

The baked straight idea is interesting. With that said if you do try the method that I use and learned from others here perhaps use a fresh side? You might want to ask some of our sponsors if they have any orphan sides, they usually do since we all are such good benders.........

Also it's really important that the stack is clamped firmly and letting the blanket make even and complete contact with either a slat on the wood or the wood directly if you do it that way which I don't. I use the same blanket and controllers that you have and about 2-3 minutes is all it takes for my stack to heat up enough to start bending. Note the spring clamps on both ends of the stack.

BTW you can iron your sides flat if you don't want to wait for new wood and try again with another method. I am just a little concerned that these sides have been through the ringer and may break when what you do next would have indeed worked with a virgin side.