Sunday, June 2, 2013

Big Bertha In Daylight

Big Bertha in previous incarnations has never worked out terribly well in daylight because of the open tube structure; stray light is always going to be a problem.  I was therefore at first unsurprised when I used it to look at the television towers on top of Big Basin (which is a number of miles away) this afternoon.  But even at 222x, I was quite pleased with the optical quality.  Now, if only it gets dark to see something before I have to go to bed!

During church this morning, I suddenly realized a solution to a problem that has been bothering me about making hexagonal telescope rings to hold Big Bertha to the mount.  It would be impossible to use this metal brake that I have to bend 1/4" aluminum -- but 1/8" thick aluminum is probably too flexible.  But what I bent 1/8" aluminum into the inner part of the lower half of the hexagon, and another 1/8" thick piece to be effectively the outer layer of the hexagon?  Then bolt them together at the vertices of the hexagon, so that I get most of the stiffness of a 1/4" thick ring, with the ease of construction of the thinner pieces?  Even better, I have a large sheet of 1/8" thick aluminum that I could use for this purpose.

I have therefore been experimenting with making a small set of hexagonal telescope rings (like about 2" across) just to get some practice at making them on a small scale first.  And yes, 1/8" thick rings feel stiff enough, but because of the square/cube law, they almost certainly would not be stiff enough for the size that I need for Big Bertha.

I feel the need for a metal shear, but by the time I see the cost and size, I will probably just go to my friendly metal store and pay them to use their shear instead.  The bandsaw that I have just doesn't do that good a job on metal (it is really a woodworking tool), and cutting small slices with the chopsaw is impractical.

2 comments:

Sigivald said...

It would be impossible to use this metal brake that I have to bend 1/4" aluminum -- but 1/8" thick aluminum is probably too flexible.

Your idea (below that quote) will probably work just fine.

But for bending too-thick stock, I've found that if you score it good and deep it should bend just fine, without being weaker than the 1/8" stock in the first place.

(I bet a router with a fence and a 90 degree bit will work on aluminum well enough... carbide is a LOT harder than aluminum, after all, even if the tool was meant for woodworking...

Clayton Cramer said...

Or perhaps use a 1/8" end mill to cut a 1/8" deep channel where I am going to bend it?