Bending Going Sideways

[cactus bum]

PICTURES BELOW
Hi Folks, I did so well with my rosettes I thought I was on a roll and decided to take on side bending. I began using a lightbulb bending form made with an open top and 3/4" pipes. The scrap hardwood I used was easy to bend and I got good results except for some flats on the outsides of the lower and upper bouts. I borrowed a heating blanket from a friend and made a solid form. On the new form I also took a graduated 3/8" off the surface of the end of each bout and took a graduated 1/8" off the waist to help with springback. The form looks good to me.
I then bent saveral pieces of the scrap hardwood (I would give the species, but I don't know the name. It looks like rubber wood with red streaks going through it, has bad splintering, and is blond like rubber wood.) The bending of the scrap went very well.
I then bent some of my mahogany. There were flats on the outside of the bouts, plus the waist was cracked. The mahogany is of an uncertain species. It comes from the book shelves my wife grew up with in her childhood home. There were two shelves that were nicely quartered, so I resawed one into sides and a back. They were sanded to between .085" and .090". They looked very nice, a bit boring as mahogany is, but nice.
I tweaked the form a bit and it looked plausable to me that it would bend some nice sides. I put in another scrap piece and got good results. Bent another mahogany and it was just as bad as the first.
My ritual for bending is to spritz the wood with distilled water, wrap in foil, make the bending sandwich, then place carefully in the bender. Then I heat the sandwich for 3 minutes, lower the waist press slowly and get it to about 1/8"to 1/4" from the mold at the waist. (EDIT - Actually the space is 1/8", not 1/4") I then do the lower bout and bend it by hand until I feel it is flexible, then move the spring loaded caul over the mold to cinch up the sandwich. I bend the other bout next, add the spring caul, and then screw the sandwich down all the way at the waist. I then carefully add some clamps with cauls that are radiused to the area they are to be clamped. I am not, I think, adding too much pressure to the clamps. I add clamps with cauls because the sandwich wasn't snugging up perfectly to the bouts, and I thought the clamps/cauls would help. It appears clamping nor not clamping has no effect on the flats and cracks in the wood.
I am wondering if any of you builders can spot my mistakes. Could it be the mahogany? I am simultaneously building another guitar with pao Ferro sides and have no extra of that wood for sides. You know I am reluctant to go to another wood to bend when I have not perfected the bending on mahogany. Could it be the form? Is my procedure bad? The photos below will show you where I am at, and how I got there. I am temporarily over my head. Help anyone? Thanks, Cactus


This is the form I am no longer using.
Below is my bending procedure








Below are the ##!*+XZ#! cracks and flats I mentioned. Hope you can make them out.

[kiwigeo]

Michael, two things I'd check first...thickness of side and bending temperature. I havent used mahogany so cant advise on same but others in here will be able to do so.

Your bending procedure is much same as mine so I dont think technique is the problem.

Cheers Martin

[Kim]

Hi Cactus,

I cannot speak from personal experience but believe the formula for bending mahogany is DRY to prevent grain collapse (A bit of damp craft paper against the wood is all that is needed before wrapping in foil) HOT (about 310 to 350 F) and fast. Your blanket should be at least 5 watts per inch and needs to run flat out so it gets the wood very hot quickly. At .085" you should be fine. I suspect you bent too wet and not hot enough.

Cheers

Kim

[matthew]

Or, not wet enough, because after 3 minutes in the cooker your steam will probably have evaporated. dip the rib in the bath for 5 minutes. Wprk quicker. with a heat blanket I am ready to go after about 15-30 seconds. And not HOT enough, i'd say. Listen to the rib sandwich heating up. When it sizzles, steam coming out the sides, its about ready to go.

I don't know about bending mahogany dry. Steam is not essential, but it helps me as an indicator of temp.

You dont want any "pull" on the outside of the curves. Not sure why you are stopping the waist bend 1/4" from the mold, I'd go all the way down and clamp tight. (Others may disagree)

I prefer to bend the tightest curves first.

[Bob Connor]

Not hot enough I reckon.

Get a thermometer (the type that you'd use to roast a turkey)

Start the bend at 100C and turn the blanket off when it gets to 150C.


Bend slowly but it still shouldn't take any more than 5 minutes from turning on the blanket to complete the job.

Mahogany doesn't like a lot of water. A quick spritz with a spray bottle will be sufficient otherwise you'll get rippling in the sides.


Mahogany is notoriously cantankerous. Some pieces will behave themselves whilst other can be recalcitrant.

[graham mcdonald]

I'll throw my two bob's worth in as well, having recently bent mahogany sides for a 00. I used a solid mould and a heating blanket. The sides were sprayed with water, wrapped in paper towel (one layer per side) sprayed again and then sealed in aluminium foil. I think is is important to seal the foil wrapping as effectively as possible to contain the steam. Heat the whole thing up with the blanket for a couple of minutes and then clamp the waist all the way down. Pushing the waist into shape can take a minute or two, gradually clamping it down. Make sure the blanket keeps in close contact with the wood/paper/foil sandwich and it should easily be able to be bent around the upper and lower bouts. That can usually be done in one pull against the springs. Cook for 5-7 minutes and turn off. I don't have any timers or thermometers on my blankets, just cook for a few minutes and turn 'em off (and don't leave the workshop while its on!).

A thickness of .080-.090" should bend fine. I can only think that the wood wasn't
a. hot enough or
b. the moisture had been boiled off before bending.

There might also have been a problem with trying to pull in the last 1/4" of the waist after the ends had been clamped around the bouts.

I figure the sides can be bent once steam starts escaping from the foil sandwich and you can hear it hissing a bit. I use the same technique for eight or nine years (since whenever I got my first heating blanket) with mahogany, rosewood, blackwood, tas myrtle and tulip satinwood without worrying too much about temperature or the amount of moisture with few problems.

cheers

graham

[Paul B]

What everyone else said.

I agree with Graham, you need some foil to hold in the steam, otherwise you've lost all the mosture before you even start bending. I even fold over the ends of the foil to keep it in there. I've got a bunch of holes in the slats so I can use a scriber to scratch out the foil and let the moisture out once I'm done bending. That's the benefit of using an aluminium slat instead of spring steel - easier to drill holes in and cheaper.

Your sides look a bit thick, how thick are they? And that clamp at the waist caul looks a bit severe.

Also, if it's Philipine mahogany, aka luan (and it looks like it might be) your results are about what I'd expect - don't ask me how I know. If scrap works and this stuff doesn't it's probably luan.

[Allen]

Well, I'm late to this one Micheal, but I've bent a bit of Mahogany, and never had a problem. Looks just like everyone else has said. Cold and perhaps too thick, but it's impossible to tell from the photo's.

When I bend any wood. I just wet the sides under the shower for a few seconds. Then use my fingers on either side of the wood and wipe them down like a squeegee. They end up just damp, and no more. Then wrap in kitchen paper, and tight wrap in Al-Foil. Heat for 2 minutes with blanket on full until temp is 100 C. Bend and then turn off blanket at 150 C.

I'd recommend the thermometer as Bob suggested. If you aren't sure of the temperature, this could be part of the problem.

[cactus bum]

Wow, the cavalry did come to the rescue. Thank you who responded.

My plan today is go out to the shop and bend a couple of more pieces of scrap, just to make me feel good again. While doing that I will use the thermometer, which only goes up to 100 degrees C, and ascertain if enough heat is there. If it gets to 100 fast I will assume it is continuing to heat up and the rig will go up to the required 150 degrees C. I will also seal the foil to hold in the steam. These procedures should satisfy Martin, Kim, Matthew, Graham, and Allen.

When I borrowed the heating blanket, the owner of the blanket outlined to me his procedure for bending. This includes the idea of leaving the waist bend slightly loose, say 1/8" or less, and cinching up on the waist after the bouts are bent in order to draw the excess space out from under the bouts, sort of to snug it up. I can't see this has much to do with my problem mahogany. BTW, I really leave only about 1/8" of space above the mold waist to allow me to cinch it up after the bouts are bent.

Paul, the clamp above the waist caul is to even out the pressure the caul exerts on the waist. The caul press above the waist presses the caul down slightly unevenly, thats all. The clamps aren't SO tight really. My sides measure between .085" and .090".

After my bending today I hope I can tell if it's the wood or some other problem. I do hope it is the wood, and all I have to do is replace the book shelf mahogany with other material. By using the advice you'all have given maybe I can zero in on the problem. I don't want to cut more mahogany into sides if it isn't going to work. Besides, the book shelves will make excellent three piece laminated necks.

Bob, I like the word recalcitrant. Most of us don't remember when we heard a word for the first time in our lives. The first time I heard recalcitrant is when my third grade teacher wrote it on my report card. It was a source of pride for me after that knowing I deserved this funny sounding twelve letter word to describe me. She was right too. Thanks Martin, Kim, Matthew, Bob, Graham, Paul, and Allen. Cheers Now, off to the shop. Cactus

[cactus bum]

OK, here's what's up. I just resawed and put more scrap through the planer to get it to .085" with no sanding. I bent the first piece and it went well. I put the thermometer between the heating blanket and the wood. My thermometer only goes to 220 degrees F (little over 100C). The temp reached 220 in less than 2 minutes, and was getting hotter. I assume this means I have gotten sufficient heat to the material.

I tried to hurry up as I went slowly through the process. I lowered the waist caul and left maybe 1/16" of air space under the lowest spring steel. I did the upper bout then the lower bout with the spring cauls. It felt very good, with no bad wood sounds. I used one profiled external caul on the lower bout because of a little rising off the mold. I let it cook for 5 minutes then turned off the power. I waited maybe 30 minutes and pulled it off the mold. It is near enough to perfect that I could use it for a real guitar side if it were the correct material and dimension.

I put it in my external building mold and began the second test piece. It went well also and was almost an exact repeat of the first. It is not off the mold yet, but I am betting it is acceptable also.

This leads me to think either I don't know how to bend mahogany worth a damn (probably the case) and/or the mahogany I have isn't meant to become guitar sides. Either way, I have decided to use some different material for this guitar. Instead of resawing more of this mahogany I will change to some wood more knowable.

This leads me to ask for some advice in bending pao ferro, which is what the back and sides of the other guitar I am building are made from. If any of you have experience with this species of wood please speak up. (Should I begin a new thread to ask about pao ferro?) Does the stuff bend easily? Does it need soaking or will a spritz of distilled water be sufficient? Does it give undue springback or is there any other peculiarity about this wood? My pao ferro sides are nicely quartered and appear to be the kind of material I like to work with. I mean it doesn't look like it will be a problem wood. I confess I have never worked pao ferro, so any advice is appreciated.

It's lunch time here. Cheers, Cactus

[Kim]

When I borrowed the heating blanket, the owner of the blanket outlined to me his procedure for bending. This includes the idea of leaving the waist bend slightly loose, say 1/8" or less, and cinching up on the waist after the bouts are bent in order to draw the excess space out from under the bouts, sort of to snug it up. I can't see this has much to do with my problem mahogany. BTW, I really leave only about 1/8" of space above the mold waist to allow me to cinch it up after the bouts are bent.

This is common practice when using a blanket and form Cactus. As you say leaving a little of the waist above the form until after the upper and lower bouts are pulled down and secured with moderate pressure does ensure that everything snugs up nicely.

As for pao ferro all I can say is be careful. The dust is a well known respiratory sensitiser and has caused serious health issues for some. Wear a mask when working it and keep the dust off your skin.

For bending I would treat pau ferro as you have your scrap. When using a heat blanket and form I cannot think of 'any' wood that benefits from soaking. Just spritz or lightly wet the wood, apply paper towel or craft paper and seal in foil. If you still have issues try treating the wood with a veneer softener such as Super Soft 2.
http://www.veneersupplies.com/product_ ... cts_id=616

This should take care of any problems but avoid soaking as it tends to invite cross grain rippling and potato chipping of high figured woods.

Cheers

Kim

[cactus bum]

Thanks Kim, for the specific pao ferro info, but also the safety heads up. I did notice a slight skin tickle while hand sanding the sides. I will keep contact to a minimum. OY OY OY Cactus

[cactus bum]

Just an update for those of you who generously answered me. I just took the first pao ferro side out of my bender. It is stained, as expected no big deal, but the shape of the side is WONDERFULLY, UNIFORMLY, fitting into the outside mold. I hesitate to use the word "perfect" for anything I do, but I can see almost nothing wrong with it. My conclusion on the pains of bending the "bookshelf mahogany" is either I am too inexperienced to know how to make it submit to my will or it just isn't in it's nature to conform to my mold's contours. Either way, I will exact my revenge on this "bookshelf mahogany" by making some of it live out it's life as guitar necks. That'll show it who's boss. So, it's my shout. Thanks for the help. Cheers, Cactus

[Bob Connor]

I love it when a plan comes together.

Congratulations Michael.

[Kim]

That's great news Michael, well done.

Cheers

Kim