tips on how to machine a large arc

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dansawyer

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The project is to add a balancing mechanism to a telescope. The telescope is about 24 inches long and about 10 inches in diameter. My plan is to make 4 aluminum pads about 2 inches long with one side of each pad machined to match the diameter of the scope. The pads will be made from 1/2 x 1 inch aluminum bar stock. They will be mounted by 2 x 5/16 bolts on each pad into the telescope.
I plan to mount two at each end separated by a an inch. A 1/2 inch hole will be drilled in each pad parallel to the telescope. All together these will support two 1/2 inch rods, about 3 inches apart.
I can then mount counter weights to the rods and slide them along the rods to balance the scope.
My lathe is a 9 inch South Bend 9a. Is there any way to machine a 10 inch arc in aluminum?
 
I think you would need a larger lathe or even have the pieces cut by a CNC machine
Is there a way to rethink the design so that the pieces could be bent to shape rather than machined? Just a thought
Perhaps have rubber strips in between to compensate for any gaps if the bend was not perfect?
Does the telescope already have threaded holes?
Mark
ps a drawing would be helpful
 
Last edited:
This came up somewhere before so you might want to search the archives. There were some interesting solutions like putting an endmill in the chuck and then rig an arm holding the work to swing off the carriage and pivot at the radius you want.
 
For your purpose, the arc doesn't need to be an air tight fit. I would lay it out and bandsaw the arc and then finish it up with a drum sander.
 
Send me a plate large enough to contain the 4 pads. I can bore to 10" diameter and send it back for you to cut your parts from the plate. My 16" lathe should handle it.
 
The arc you need is neither precision nor necessary.
Cut the blocks and then either:
a) machine some depth into the center of each block
or
b) use a (brass) rod to provide support at the edges of the block.
 
Illinoyance said:
Send me a plate large enough to contain the 4 pads. I can bore to 10" diameter and send it back for you to cut your parts from the plate. My 16" lathe should handle it.
Click to expand...
Thank you for the offer. I am calculating the depth to see of my design will work. I have 3/4 by 1 inch bar stock. I was going to cut that into 2 inch lengths and machine the 3/4 inch side to fit the telescope.
 
Mitch Alsup said:
The arc you need is neither precision nor necessary.
Cut the blocks and then either:
a) machine some depth into the center of each block
or
b) use a (brass) rod to provide support at the edges of the block.
Click to expand...
Are you saying that effectively creating an edge on each side is sufficient to hold the blocks in place? That seems like a reasonable assumption.
 
dansawyer said:
The project is to add a balancing mechanism to a telescope. The telescope is about 24 inches long and about 10 inches in diameter. My plan is to make 4 aluminum pads about 2 inches long with one side of each pad machined to match the diameter of the scope. The pads will be made from 1/2 x 1 inch aluminum bar stock. They will be mounted by 2 x 5/16 bolts on each pad into the telescope.
I plan to mount two at each end separated by a an inch. A 1/2 inch hole will be drilled in each pad parallel to the telescope. All together these will support two 1/2 inch rods, about 3 inches apart.
I can then mount counter weights to the rods and slide them along the rods to balance the scope.
My lathe is a 9 inch South Bend 9a. Is there any way to machine a 10 inch arc in aluminum?
Click to expand...


I suggest you have a chat with Savarin he has made some pretty large stuff on his 9 x 20 lathe He comes up with some ideas from out left field somewhere, but they seem to work.
 
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