tips on how to machine a large arc

If I understand you correctly, you want to machine an arc in the 1.00 x .750 x 2,00 pad so that it matches the cylinder of the telescope body? I would do this on the bandsaw as suggested previously. A 5" radius arc should be very easy to cut. Clean it up with a drum sander, or sanding drum mounted in the drill press.
Illinoyance idea would work but would require a large expensive plate with a lot of waste. I assume you already have the stock? A similar idea on a larger lathe would be to fix each 2" piece onto the perimeter of a face plate and make the inside cut that way. Given the dimensions of the part you would need a lathe with a swing of about 12+".

Robert
 
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?
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I do custom metal press forming and had to come up with an adjustable radii cutter to cut concave and convex shapes. Most of what I use is UHMW, but I've also cut aluminum with this as it has a carbide router bit and does a really nice job. You obviously don't want to go through all thisand I don't use it everyday, but when I do it does radii faster and easier than my 9x20 or my RF30 and 10" RT. It can do up to 22" radii.
 

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Think how well a v-block holds round parts with 2 points of contact, There you go.

If you cut a radius to fit the telescope, if your radii are just a few thou undersized you will still only have 2 lines of contact, if your radii are a few thou oversize you will have a single line of contact and the part will always be rocking and moving around. I'll bet that telescope is not perfectly round which will make it near impossible to match exactly.
 
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dansawyer said:
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.
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Then I would do it on the Bridgeport. Rotary table, boring head, and Volstro rotary milling attachment are my options.
 
Use aluminium channel, the two open sides bolt to telescope tubes with no problems.
You can also use two bits of channel to make a dovetail by using two different sizes that fit inside each other.
Bend the sides of the inside length out and the sides of the outer length inwards so they fit .
 
Joe Pie on You Tube showed how to set a boring head to cut a desired diameter without having to bore a hole. Using his method to set the dividing head I could set it for 5" radius and cut one edge of a block held in the mill vise. I do have a dividing head large enough. The alternative is to use my Volstro rotary milling attachment. My offer is still open.

Your only cost is postage both ways.
 
If you are going to make it as V-Blocks, then for a 2 inch long part, I would use a 160° included angle. This will sit nice on the Ø10" tube.
 
Decades ago, Fred taught be how to closely approximate a large radius using a flycutter on a vertical mill by tilting the head of the mill.

Divide the diameter of the cutter by the diameter to be cut = sine of the angle to tilt the head.
 
MrWhoopee said:
Decades ago, Fred taught be how to closely approximate a large radius using a flycutter on a vertical mill by tilting the head of the mill.

Divide the diameter of the cutter by the diameter to be cut = sine of the angle to tilt the head.
Click to expand...
Mr. Whoopee, you introduced an idea that sounds revolutionary.
Could you please explain it a bit more for us hobby guys?
I appreciate it.
Thank you.
 
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