Side bending....keeping the ends from cupping

[John Coloccia]

How do you keep the ends of the sides from cupping after bending? I usually just clamp them into a mold and let them dry like that, but I'd like to fool around with free building, especially since the luthier I've started studying with is a proponent of that system. I'd like to maybe get an idea of how that works so I can practice a bit.

It's a no-brainer to do it in a bending machine, and when I do I get perfect results with just a little bit of care, but I'd really like to be able to do this free hand on a pipe and get acceptable results. The machine is sort of cheating because I can "cook" the wood with the heating blanket while it's in the bending form. Bending form = inverted mold, so that's no good for what I'm looking for. Anyhow, I don't want to have to make a new form for everything anymore than I want to make any more mold. I HATE making molds, and more than that I hate storing them.

Maybe someone can show me the light :)

[chiesa dan]

Regarding cupping: keep the las few inches dry; than helps.
Regarding bending sides more generally: even if you use a mold, it is good practice to bend the sides so they rest unaided pretty much exactly on the outline of the instrumet they are intended for.
I have seen and used many different side bending machines and i talked about it extensively with several colleagues: first, you do not get perfect results, nor consistent. It's just the nature of wood. One side can come out of the machine closer to the final shape, the next much less so. So the machine is a tool to get you closer and save time with the hand bending.
For myself i found i can get to that point in the same amount of time or faster by hand, and bending by hand more, i got very good at it so i save time on the inevitable last hand bending part.
I have seen a few apprentices struggle very much with the hot pipe, and to start thinking the solution was using the bending machine; those who stuck with the pipe finally got it. Those who convinced themselves the machine was faster and better, just settled for inferior results.
I don't have picture of the sides resting on the outline, but you can see they 'make sense' without a mold (and most of the time i DO use a mold):

178723 178724

I know it can be intimidating, frustrating, time consuming at first, but hand bending is THE method. There are no tricks, no free lunches, just developing a good technique through time.
To me, to force machine bent sides into a mold in not an acceptable practice.
One last note: the 'bending pipe' cannot be literally a hot pipe; it HAS to be a compound of curves (the egg shape of the commercial bending irons). It's almost impossible to bend sides proficiently on a single radius. The 'universal' benidng irons, then, have a too small of a curve so they make it more difficult... But you can use one of those ok.

[Mike OMelia]

I dunno... I certainly respect all of you for wanting to do that. Building and storing both molds and forms can be an issue. But I do not see it as a huge issue. Once they are done, then its just a storage issue. And I agree that the freedom you have is an attractive thing. But, I like repeatability (without a lot of effort). Robert Taylor uses bending machines. As for the ends, keeping them dry is the key. Brad Way and Mike Doolin have bending designs that clamp the ends and tension the ends. Mabe one day I will build one of those. I did learn a huge thing here. Did not know about the professional bending pipes with compound curves! I certainly get that concept!

Mike

[John Coloccia]

Hmmm....it never occurred to me to just not wet the ends. Simple solution.

Re: forcing into a mold.
Just to be clear, I never force anything into a mold. I just clamp it in the mold to dry so it doesn't deform over night, or alternately leave it in the machine for a bit so it dries essentially clamped into a mold. It's when working without a mold that I have a problem with the ends cupping, but the sides fit the shape properly regardless.

[george wilson]

It sounds like you are bending your sides too wet. By the time the sides have been bent around the bending iron,they should be pretty dry. Are you soaking them a lot? I just ran some hot water over them,repeating as needed,but didn't get the sides soaking wet.

I built a bending machine out of 3/4" aluminum,with 1/4" thick side templates that I now use. It is a souped up,indestructible Fox bending machine with refinements,like a heated waist caul also machined out of aluminum blocks,lined with furnace luting cement,and with a nichrome element inside it. It has 3 300 watt light bulbs inside the main form,and the whole machine gets as hot as a clothes iron. The wod gets trapped between 2 sheets of stainless steel,and I haven't fractured the curliest maple,or 50 year old Brazilian yet with it.

I actually do get perfect results with it. I let the machine get good and hot,wear gloves,put in the wood and let it cook for about 20 minutes,then let it get cold before removing the sides. This machine will take a LOT more heat than those plywood ones,and can't catch fire. Probably why it works better. I regulate the heat with a built in light dimmer switch which I haven't moved since I determined the right amount of heat without scorching the wood.

I made several templates for it,which take a few minutes to change. I need to post pictures,I guess.

[John Coloccia]

Yeah, I normally get them pretty wet unless it's figured wood or something else I think my fall apart on me. I didn't think I was getting them too wet, though. I'm starting to think that what I do is make all of my bends, but never really come back and dry out the end because there's really not much bending to be done there. I think it's a combination of maybe a bit too much water, and just ignoring the ends completely. I'll have to make up some practice sides and experiment a bit. I'll do one like I normally do, and another paying special to the ends, and then I'll know for sure if it's this simple :)

I should also mention I'm a bit rusty on the pipe. I've been using the machine for a while now, so it serves me right that I need to practice!

Thanks for the help, everyone. It's amazing how sometimes you just miss the simple solutions.

[Mike OMelia]

I make a sandwich. 1 slat of stainless, 1 layer of brown paper, spritz the paper, the wood, another brown paper layer and spritz, bending blanket, the other slat of stainless. I use painters tape at the various levels to hold stuff in place. And tape to hold the sandwich together. I mark the waist point on the top slat. Keep the ends dry. Really, only spritz where the wood bends. But if you get cupping, then use a clothes iron to repair.