Making Bending Molds

[Stray Feathers]

This thread is timely for me. I have just started using a side bender I built. I made a new solid mould for the OM style guitar plan I have been using, and was careful to have an early bending form mate well to it. Also built a new solid mould and solid form for my first tenor ukuleles. No matter how carefully I mated the forms to the moulds, and made spreaders for them, allowing shirt cardboard layers to match the thickness of sides in between, they still do not fit as well as I hoped - that perfection that Bob envisioned. I wonder how much error there is in the bending when the sides are not really clamped tightly to the forms all the way. Maybe this is where John's theory about springback steps in - I need to think that through before I make my next forms. I have wondered whether (contrary to John's video) it might help to take the sides out of the bender sooner, and let them cool clamped in the mould with the spreaders. But they are not supported all the way across the sides, which concerns me. Bruce W.

[Bob Gleason]

I often take the sides out of the bender early, wet them again and clamp them tightly in the holding mold. It works very well for softer, easy to bend wood like mango, light weight koa, some mahogany, but does not work well with the harder woods like rosewood, hard maple, etc.. It is interesting to note that John said Martin takes the temp WAY up and shortens the bend cycle. I've never really let one of my blankets run wild to see how hot it will get. I'll have to investigate that. No doubt it will shorten the life of the blanket, but might be worth it if I can get a better bend. It is really baffling that so many things in lutherie that have been done millions of time by builders, like finishing and bending, still remain somewhat elusive to most of us, It must be a factory conspiracy! They just don't want us to know the REAL way!--Bob

[tippie53]

You can try taking them out warm and clamping but I can tell you that you will have a good bit of spring back

I do take my heat up to 375 and let them in there till cool I get a pretty good copy and fit in the mold
Windex has been a big help.

[tippie53]

today I had to bend 3 sets of uke sides

Here is my bend process
they fit the mold perfectly

Wet paper wood between
started to bend at 275 lower bout upper then waist
heat up to 375F
held at 275 for 10 min
heated to 375 let cool
I did use windex this was hon hog .065 in this
2 tenors 1 baritone
I also let it cool about 45 min
bend both side at the same time

[Morecowbell]

John - thanks for all the details. I seem to recall ammonia being beneficial in wood bending, wonder if that's what the Windex brings to the party...

FWIW with my vast experience of having made and bent one set of molds and sides, mine fit together pretty well. I allowed about 3/32" between the inner and outer and made a solid inner form because I have bent wood before and didn't want the wood to get any ideas about where to go. My previous experience taught me to support the shape wherever you cared about it - when you loosen the fibers all the variations in grain and density can get out, and they often will.

[Bob Gleason]

In my experience, Windex. or ammonia, is bad news on koa. Inside of the side gets stains that can't be sanded out. Some builders don't seem to care about that, but does not work for me. This has been a great thread. Thanks for all the posts.-Bob

[Stray Feathers]

Great thread indeed. Re: ammonia, I bent two sets of uke sides in western (bitter) cherry, and they stained some. I wasn't sure if it was staining, or resin being released, or something left behinf previously, but I used clean parchment. I've managed to clean the sides up okay.

John, in your how-to note, I assume you are also bending with the tighter radii you speak of? Does that mean, e.g., bending the waist curve a little tighter, knowing it will spring back some later? That's beginning to make sense to me. Bruce W.

Edit to add: re: using Windex for bending, I went to buy some yesterday, and could find none with ammonia. I later found some hidden at home (we've turned to using vinegar and water for windows) so am okay for a while, but I wonder if Windex is phasing out ammonia?

[tippie53]

yes just a tad tighter and I rely on the spreader to hold the shape
Bob I agree with Koa you have to be fussy I stopped using Kraft paper because that can stain it Green
I am lucky in that my well is good water straight from Mother Nature.
I used to use distilled water when I lived in town.

[tippie53]

here is a pic of a set of sides in a mold and how they fit

I have a few set of ukes and will get pics later

[Stray Feathers]

Wow - I'd sure be happy with that!