Koen Notes:

Koentopp Guitars
Hey Murray! Thanks! It works like a dream. Here’s a video from a few years back, I’ve updated it since then but you’ll get the idea. The beauty is that every bend is fully supported. The key to its success is close tolerances and the weight on the slats.

TreeHouse Guitars ·
Yep. Brilliant. So you have the heating blanket on one side and a slat on the other?

Author
Koentopp Guitars
TreeHouse Guitars, yessir, I place it on the side where the tightest bend is, with everything so supported and tight, it’s plenty.

Koentopp Guitars
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Some heavy nerdom here: I love working with inspiring people! Last year I made a gravity bender for Will Whedbee @whedbee.cello, one of the most inspiring instrument makers I have the pleasure of knowing. I helped design a bender that could easily bend the tight and wide bends of the C bouts of a cello in similar fashion as my rotating gravity bender. The beauty in all of it was not that it worked so well, but for me to see the updates he made that made it work better for him. He permanently mounted his bender to a post, hung old cast iron window counterweights, and installed permanent thermocouplers, and a few others as well. I’ve always wanted to hang mine on the wall but never wanted to give up the valuable wall space. Well, I finally figured that was dumb as it takes up even more space on a shelf and is kind of annoying to setup and take down. Hanging it on the wall makes it work SO much better with more weight and rotation clearance and everything is right in front of you. The cast iron window weights are another game changer. I can know put 42lbs of continuous tension on the steel as it wraps around the forms and they easily come on and off and store beneath the bender. I’m so giddy right now, I can’t wait to hear this sucker up!!! Thanks Will for always inspiring! 🙌🏻🤓💪🏻🔥

 

 

Super soft Stuff

What veneer softeners do is plasticize cell membranes AND increase permeability of cell walls so as to allow surface cells to fill with a bulking agent (for SSII, glycol) to prevent collapse of the cells under the highest load due to buckling or shear during bending. Much like what filling a pipe with sand does for bending pipe, those glycol-filled surface cells prevent both tension-related failures on the outside of a bend and buckling failures on the inside.

 

 

What we found over 15 years of SSII use and when we bent up all of those scrap sides we had around prior to the Big Clean:

– Most common luthiery woods (plain-figured mahogany, vertical grain maple, cherry, walnut, etc) do not need to be treated if bent using the techniques I have already posted (control the amount of water used, bend as soon as the phase change from liquid to vapor begins in the areas of the bends)

– Rosewoods and other timbers high in resin content don’t benefit at all from veneer softeners. Cocobolo in particular can be bent with heat alone at temperatures under 260 deg F, reducing or eliminating the color changes seen with oxidation of the resins in the bent sides.

– Highly figured wood – especially those that are high in silica content (curly anigre) or have relatively low resistance to water-related buckling (curly mahogany, koa, and other acacias) will benefit from SSII or other veneer softener…the greater the degree of figure present and the tighter the bend required, the more likely a successful bend will be when SSII or other veneer softener is used.

– After bending up most of our orphaned side collection using three different veneer softeners (SSII, Pro-Glue, and Veneer Tamer) and Windex with Ammonia D, we found the following:

– – Veneer Tamer and Pro-Glue Veneer Softener were about as effective as wetting the wood for bending…in other words, they were ineffective when bending our 0000 cutaway (1.6″ radius) in any wood tested.

– – Windex was effective on mild-figured mahogany, and reduced buckling damage on mild figured anigre, but less effective on highly figure mahogany and curly anigre on that cutaway shape (the mild figure anigre was likely repairable or could be sanded out; the high figure mahogany failed on the outside edge of the side in the cutaway but not the waist, and the curly anigre failed almost completely across the cutaway).

— Due to our bending history with SSII, we tested just the sides thought most difficult to bend – a rift-sawn highly figured mahogany side, a flat-sawn highly figured ash side, and a VG highly figured anigre side from a veneer back board known to be difficult to bend without flaws. No bending artifacts were noted.

– Woods known to produce cross-grain ripples in bending (flat-sawn ash, some sapele, etc.) see significant reduction in cross-grain ripples when bent with SSII (and I assume, Windex), but the most dramatic reduction in ripples was due to using solid or near-solid bending forms AND SSII.

So to summarize:

– For builders making Golden Era Martin or Gibson reproductions in the woods used during those periods (e.g., no cuts; few tight waists, mahogany & rosewood) , there is little need for SSII or other veneer softener in bending

– For builders working in figured woods and bend tight cutaway sections, veneer softeners reduce the chance of losing a side to cracks, fiber collapse, or fiber delamination

– The replacement cost of one failed premium side more than pays for a gallon or two of SSII (or Windex at about 1/3 – 1/2 that cost)…cost-effective insurance

– Where bending is delayed due to what the boss used to call ‘head-up-assedness’, SSII reduces the chance of a broken side (although it is likely the side will need to be straightened out and re-bent …which SSII does a nice job of assisting)

– We use SSII because it is the best product for the job, but Windex with Ammonia D will be good enough in many cases and less expensive. We use Waverly tuners in lieu of Grover open backs due to the same philosophy…buy the best product available for the very few situations where that extra performance makes a difference. For some builders, there will be no meaningful difference between a premium product and good enough – economy trumps utility in that case just about every time,