Bending 2mm Stringer

[David Jenkins]

I'd like to put about a 45 deg. bend in a short section of stringer, but I'd like to do it around about a 1" radius. I've tried using an alcohol burner to heat the glass, but the heat is so localized that the minute it's soft enough to bend the glass, it gets a bend radius of something approaching zero. Is there any way to get a gentle, large radius bend into the stringer?

Thanks.

[Monika]

Use a tea light, less heat, better control

[Brad Walker]

Slump it.

[Morganica]

Tea light works. Other thing with an alcohol burner is to hold it away from the flame a bit and keep it moving steadily. Let the weight of the stringer make the curve for you.

[David Jenkins]

Thanks, all.

I think I'll try the slump idea first. Once I've found the right combination of heat, time, and distance between the supports to yield what I want, I should be able to turn out a lot of these in a very short time. Plus, that approach won't require as much manual dexterity as the others.

I'll have to put up with a catenary instead of a circular arc, but ... any port in a storm - right?

[Brad Walker]

I'll have to put up with a catenary instead of a circular arc, but ... any port in a storm - right?

You can get a circular arc if you slump into the right shape, instead of just hanging from supports. Try carving a kiln brick to get the shape you want.

[David Jenkins]

Thanks, Brad.

I was just kidding - the catenary shape will work just fine. I'm really after a semi-uniform gentle curve, and once I get the slump parameters set, as well as the distance between the supports, I'll be able to turn them out in the volume that I need.

[Brad Walker]

the catenary shape will work just fine.

"Catenary" -- which for some reason my spell checker says is not a word -- is one of my favorite words. According to Henry Halem's Glass Notes, it's the perfect curve for the arch of a home made glass furnace.

Now where did I leave that rope?

[lorimendenhall]

oooh I like that word. never heard it before.

[David Jenkins]

The catenary is an Interesting function that describes the shape defined by a wire, chain, or rope, etc. suspended between two supports. It is given by:

y = a cosh (x/a)

where a is the distance between the two supports, and 'cosh' represents the hyperbolic cosine function.

(I just knew a math major would become useful sooner or later. )

I'm not really sure that a piece of slumping glass in free space falls into a catenary or not - seems to me there would be some other variables at play: viscosity, COE, heat transfer velocity, etc. I was just trying to be a vocabulary show-off, I guess.

[Brad Walker]

and 'cosh' represents the hyperbolic cosine function.

Now there's a phrase I never thought I'd see on this board.

I found a web page that discussed the difference between a parabola and a catenary: http://mathforum.org/library/drmath/view/65729.html The target audience was math students, but to me the most interesting part of the page was where the expert (Dr. Math, of course) says: "Once you have learned calculus, you will be able to see that the catenary is the solution to a differential equation that describes a shape that directs the force of its own weight along its own curve, so that, if hanging, it is pulled into that shape, and, if standing upright, it can support itself."

So of course slumped glass would fall into a catenary -- just don't get it too hot.

[DonMcClennen]

for larger radii I drape rather than slump. A piece of pipe or any such shape... place (balance) stringer over.... add heat to stringer with blow torch.

[Mark Kemp]

I've draped over pipe -- guess it was around 1.5" diameter, but in the kiln, not with a torch. I cut the stringer a little longer than I wanted, then trimmed the ends after firing.