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Hi all,

My first time bending mahogany rather than EIR, and my first time bending with my new bending jig, rather than by hand. My process was spritz both sides of the side with water, wrap in parchment paper, then foil. Then, from the bottom of the sandwich, .008 spring steel, heat blanket, wrapped side, .008 spring steel. I placed the sandwich on the bender, let the blanket slowly get to 300 degrees, bent waist, then the bouts. Let cook at 300f for 15 min, then cooled to room temp in the form. I got a little bit of scorching, and a lot of warping in the side. Sides were thicknessed to .085"

I feel like I may have spritzed too much water on the side, but looking for thoughts from the community. I bent the second side the same way, but with less water. I'll take it out of the bender tomorrow and see if it fared any better.

On a related note, any retailers that sell side sets only, genuine mahogany?

Thanks!

Unfortunately, some sets are very prone to that, especially ribbon figure. IMO, the foil is not necessary and maybe even detrimental. You want the steam to be able to get out. And it does look like you used too much water.

That looks like a pretty bad case, but, you can sometimes salvage sides like that by adding stout internal braces going across the grain every 3-4 inches, maybe 1/4 wide by 3/8 high, clamped hard with flat cauls and strong high pressure clamps like a C or F clamp. Sand the water marks and such out of the inside as is, then add your side braces. You’ll be able to tell if it’ll work with a dry fit. If it’ll cooperate, make the frame and then add the braces and put lining between the braces.

Good luck!

Now that it is bent, you could try soaking it and then clamping it to your bending form (no heat blanket )and allowing it to dry slowly under pressure in much the same fashion as you would flatten a piece of veneer. That may take much of the ripple out of it.
I like to bend sides with quick hot heat and little or no added water.
As Ed mentioned, it looks like the ribbon figure was part of the problem, and side braces may help hold things flat.

As a last resort you could try laminating it to another piece of wood.

The failure to properly retain the bent shape and scorching both indicate that any moisture in the bending stack was cooked off well before you accomplished the bend. This was likely due to your over-long cooking of the side prior to bending. Mahogany - particularly figured mahogany - hates excess water, but really needs a strong blast of steam to bend properly (minimal cross-grain ripple and retention) of mold shape after bending.

Other issues:

- A light spritz of the side is a hit-or miss method to calibrate the amount of water available. Using wetted kraft or butcher paper allows surprisingly accurate calibration (brown kraft gives a matte appearance at minimum water for figured maple, a silky/satin appearance at the correct amount of water for figured mahogany, figured anigre, and figured ash, and a glossy appearance for rosewoods where the dang, steam-saturated paper does a nice job of capturing heat-mobile resins from the wood.

- The only reason to use foil in the stack is to isolate spring steel slats from the water in the kraft paper or on the wood. It may be safely left out of the stack when bending with stainless steel slats on all but rosewoods, where the foil barrier seems to eliminate resins from collecting on the slats.

- Envelopes around the wood may produce a number of problems, to include puckering and printing, re-condensing of water vapor and relaxation of the bend, and watermarking. Separate sheets of kraft paper and foil work as well, and avoid these issues. Ideally, all free water in the stack is exhausted by the time the post-bend cook is accomplished, and - indeed - that is the reason for the practice.

- Figure mahogany and other figured woods may need some help with uniform plasticizing of wood fibers. SuperSoft 2 works well here if used according to instructions (apply generously to all sides of ready-to-bend side, allow to fully dry, then bend within 24-36 hours of application). Ammonia works as well, but in the experience of the build/repair shop where I worked, was less effective for highly figured, difficult-to bend woods like curly anigre, plum pudding/fiddleback mahogany, and highly figured fiddleback ash). A gallon is effectively a few year's supply for a prolific small shop builder, and is far cheaper than the cost of one replacement side for a premium set of back and side wood.

- Rosewoods are like honeybadgers; they just don't care. Even without water, most rosewoods are happy to bend with heat only, but will likely scorch a bit and still require some serious resin cleanup.

- Acacias such as Tasmanian blackwood, bay laurel, and koa hate aluminum, picking up a blue undertone where waterborne aluminum ions react with the wood. This is the one time we replaced aluminum foil in the bend stack with non-silicone parchment paper.

- Brown kraft paper works well for everything except holly or the whitest of white timbers. White kraft is a decent substitute, but needs to be wetted out well to hold the same amount of water as brown kraft.

This gets us to method for figured mahogany and other hard benders:

1. SuperSoft 2 the sides and allow to fully dry before bending; add blue tape tabs to index the waist if using a Fox-style bender

2. Build the sandwich with (from top to bottom): slat/blanket/slat/foil sheet/wet craft paper sheet/dry wood/wet kraft paper sheet/foil sheet/slat. DO NOT PRE-WET THE WOOD - the kraft paper is your water reservoir for the bend.

3. Load the stack in the bender without delay, using spring clamps to maintain contact between all elements (this means at least one pair of clamps on the upper bout and two pair on the lower after the bending cauls are mounted)

4. Set the temp for maximum (fastest rise) and turn it on. If using a router speed controller, this is the full-on position on the rocker switch.

5. Watch for the first signs of steam generation in the area near what will be the widest part of the upper and lower bouts. Once those early tendrils of steam are seen, START BENDING...DO NOT DELAY! Bring the waist down to 1/4" to 3/8" off the mold, then lower bout, then upper bout/cutaway area.

6. Upon completion of the bend (this should take no more than 4-5 minutes total even with a cutaway ram), watch for exhaustion of water in the stack (no more steam… yet another good reason to eschew envelopes), then turn the temperature control down such that max temperature in the stack does not exceed ~300 for mahogany and closer to 260-280 for rosewoods. Really, you can leave the router control set to something like the 2/3’s mark just short of the yellow and run that for 30 minutes if you do not have a thermocouple to monitor temp.

7. Turn off and unplug the blanket, then give the stack 12 hours to cool and dump any residual moisture trapped in the waist area.

There are several YouTube videos on bending... look for the one on bending figured mahogany by my old boss for what is a lengthy, but somewhat useful exposition.

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For the times they are a changin'

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Thanks all for the suggestions, and thank you Woodie for the thorough response. Hopefully this other side comes out of the bender better today, and I'll also be using many of the above tips on the next set.

If you want to buy sides only, email RC Tonewoods. They are a sponsor and I bought a couple side sets from them lately. They told me at the time that they had a lot of Genuine Mahogany in stock. Send a picture of yours and they can try to match the color.
Kent

Did I read correctly that you had the heat blanket directly against the wood? That could be an issue.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

The sandwich was in this order:
Spring steel, heat blanket, foil, parchment, side, parchment, foil, spring steel.

Thanks! I have a handful of items in my cart on their site, I'll send an email about the sides.

Dr. Kennedy had a valid concern... blanket next to wood is a recipe for scorching and other issues. best to have the blanket outside the slats, with a third slat to prevent abrasion damage to the blanket if used on the top of the stack.

One other thing to consider is that the energy the blanket is adding to the stack goes toward the the phase change from water to steam, so waiting for the temperature to rise to final bending temp almost guarantees that most of the moisture has already been cooked out of the package, resulting in lots of cross-grain ripple and excessive spring-back.

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For the times they are a changin'

- Bob Dylan

Heat blanket should be out side of spring steel.The wood will pick up the patterns int he rubber. Maybe ask John Hall about bending sides for you. He seems Tonewood and offers kits as well. Plus he is very helpful about info and techniques.

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John also has a good video about side bending with times and temps…

I'll also suggest you consider what slat material you want to use for a given bend. Stainless spring steel is not nearly as springy as the blued spring steel, and aluminum flashing has absolutely no spring effect. In general, the more figured the wood, the less tolerant of excess water, and the tighter the bends, the greater the role slat material plays in success in bending.

As can be seen in pipe bending with a back strap, the slats take excessive tension and compression loads out of the wood and into the slat material, as well as providing quite a bit of cross-grain restraint of wood movement. The springier the slat material and the greater the thickness, the greater the support for both tight bends and resistance to ripples in the flat sections of the side shape. The downside of super-springy slats is that when it comes time to remove the side from something like a cutaway ram, good technique is needed to avoid damage.

For something like a dreadnaught shape in an easy-bending timber like EIR, aluminum flashing can do the job, while for figured mahogany with a tight waist, blue spring steel slats provide an extra level of support.

Slats are usually a lifetime investment if good spring steel, but we still had two sets of spring steel (three slats each), and three sets of spring stainless (three slats each). For a hobby builder, that might be hundreds of dollars best invested in other tooling or materials, so consider your needs and pick a set of slats that will support at least your near-term and mid-term needs.

Because Greenridge was all about ripping the bandaid off, I got to bend a bunch of scrap curly anigre sides which were composed of the unmatchable third side out of a veneer backer board blank (Greenridge milled quite a bit of their own wood from veneer backers and a local supplier that would ocassionally see some nicely figured stock). On an SJ Venetian cutaway shape, SuperSoft II and blued spring steel slats provided a perfect side. Leaving out the Supersoft step resulted in some impressive cross-grain ripple. Run the bend with stainless slats, and you got cross-grain ripple and blowout in cutaway. My own first project (12 fret O) was in curly anigre and was a painless experience.

Needless to say that my own slats are blued spring steel and I have a quart of SuperSoft 2 that came with me from Greenridge.

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For the times they are a changin'

- Bob Dylan

Interesting observations Woodie.
I've been using 2 blued steel slats under the sandwich, and hold the top one of those in tension with springs, to better support the sides..
Also I use 3 bending forms in the bender instead of 2 with lateral supports.
I've been having better results with this system.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Great info Woodie!
I recall watching Todd's video back when I first started bending with the Fox bender - have been using this technique (along with SS2) successfully ever since...

Rob

For what it’s worth, and it may be overkill, I have been using two blankets on all my bends (top and bottom) ever since I heard John Mayes recommend it back in the ancient times of the forum. I think the sides heat more evenly.

Blue tempered shim stock here too.

Another shout out to John Hall and Todd Stock for some great how-to videos. The moistened brown wrapping paper was a wonderful idea as well as the technique of bending the waist only halfway or so at first and completing the bouts. Then going back and finishing the waist to get better support.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Great advice here. Woodie and others nailed it when they said, with non-oily woods like Mahogany & Sapele and to some extent koa, start bending as soon as you see stream. If those woods after it gets to 300 it becomes brittle. I like to heat and bend before that happens.

I also find it helpful to use two blankets, standard size and a small one that goes in the waist. Then I plug the waist blanket in, bring the waist in, unplug, then plug the big blanket in and do the bouts. Saves scorching in the waist also.

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Joe Beaver
Maker of Sawdust

Excellent point on the bending forms! Adding one additional center ply in the mold reduces deflection in flat areas of the shape by a factor of 8 or more - this is very similar to adding a support to the center of a long beam spanning a room in terms of the bounce seen when walking on the floor above. We had some early solid bending forms, but settled on three or four ply (four ply for super-tight cutaways) as standard practice.

_________________
For the times they are a changin'

- Bob Dylan

Another thing that has helped me is not to completely depend on the spring pressure of the upper and lower bout cauls to stabilize the sides when completing the waist bend. I stick a couple of long clamps on as well. The slats will still slide but the support seems much better.

Three piece molds for me as well or solid if serving double duty as a laminating form for double sides.

It seems like about 260 degrees on my probe corresponds with steam starting to roll out pretty well so that’s when I usually start and am complete when it hits +/- 300-310.

IMG_1673 by Terence Kennedy, on Flickr

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Having had this problem in the early days I have gone to town on my moulds. Any cupping is now pretty small. Cheers Dave

Thanks for that video, it was good, and not too long....

https://youtu.be/Q7vd9wGG4LM?feature=shared

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Measure Twice,

Karl Borum

when you bend you have to control the heat , the time . and moisture.

My rule is.
Thickness .075
this gives you .010 to sand and scrape flat

Slats
.008 is too thin

not all slats are the same

Stack
slat paper wood paper slat blanket

I dampen the wood not wet it too much water will warp

Temp
you can start to bend at 240F
No need to go past 300 and no need to hold it there

I will hold 275F and you don't want to wrap things allow the moisture to escape , water is more for heat transfer effiniciey


I do the waist last this allow you to press the wood. If you do waist first , the wood , slats and blanket fight the bend and your reproducibility
is lowered.
you can find a bending library on you tube Blues creek guitars bending library you will get some good info there.

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John Hall
blues creek guitars
Authorized CF Martin Repair
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You Don't know what you don't know until you know it

Thanks to everyone in this thread, theres so much good information here.

On guitar number 7 I had some "rope figured" some kind of mahogany can't recall exactly what it was. When I bent my sides the same thing happened hills and valleys following the figuring.

In my search for a solution contacting my friend John Hall at BluesCreek afforded me the opportunity to buy two new bending caul springs and he had cauls available off the shelf so I bought one of these too. He, John also advised me to use less water and start using a third caul on my BluesCreek bender.

So in the words of the great Mick Jagger - "so I did..."

Never built with that wood again and never had the problem again but from that point on I used less water and a third caul.

Second call being the cutaway? and 3rd?

Sent from my SM-N960U1 using Tapatalk

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Pat