Manually milling an arc without a rotary table

I guess I don't quite follow along with multiplying the half-degree by X or Y... Any chance you could express it as a formula? The standard formula for a cricle centered about the origin (or arbitrary datum) is r[SUP]2[/SUP] = x[SUP]2[/SUP] + y[SUP]2[/SUP] for which x and y can be solved as x = SQRT(r[SUP]2[/SUP] - y[SUP]2[/SUP]) and y = SQRT(r[SUP]2[/SUP] - x[SUP]2[/SUP]).

Either way, the issue is granularity. Making discrete adjustments of the hand crank will give you a bunch of zig-zag steps.

Also, I'm not sure who your audience is but, someone could come along an nit-pick the daylights out of you over the term "arc" instead of sphere or hemi-sphere in this particual context -unless of course, the metod produces an arc -but I don't think so because at quick glace of the table, the numeric pattern is symmetric.

Ray



After thinking about it for a while, doing some maths, and doing some checks, I think I have a method to manually machine an arc on a mil without using a rotary table. I would appreciate it if someone would look to see if I missed something or not:
http://benchtopmachineshop.blogspot.com/2013/05/arc-interpolation-on-manual-mill.html
 
That is precisely the way a CNC mill works and it will get the job done if the steps are small enough and you have enough patience. I once had to mill a .012" square hole in a piece of brass shim for an optical application. I used a .005" diameter end mill and worked under a microscope to see what was going on. The individual steps were very apparent at that level. Obviously a larger end mill will make the steps less apparent. I think I would get looking for a rotary table though, it's gonna take a lot of time to create an arc with that technique.

Tom
 
I tried a few times and found that its very nerve wracking. . . . just one little "ohs##t" turning the crank the wrong direction and pooof ! "murphy" follows me around most days. . .
 
Zoltan

Assuming a 10.0000 circumference (diameter?) it would seem that I would move 5.000 in the x axis and 5.0000 in the y axis to complete 90 degrees. That would be 180 steps in your spreadsheet. Have I misinterpreted anything?

Gene
 
What type material will the arc be cut into, and how thick will it be? Will the finished arc be on the outside edge of the piece? Or, is it inide of a square piece? As a cabinetmaker, many methods come to mind. Rough out the piece on a band saw. Swing the arc, with a pivot point against an edge sander. I have made very accurate parts that way. A lot depends on the material.
Larry
 
yes that will work, but man, thats alot of work).
 
It is a lot of work. Might not be bad in 1/2" aluminum. But 3/4" steel is another story!
 
Zoltan

Assuming a 10.0000 circumference (diameter?) it would seem that I would move 5.000 in the x axis and 5.0000 in the y axis to complete 90 degrees. That would be 180 steps in your spreadsheet. Have I misinterpreted anything?

Gene
If you're doing 90* of a 10 diameter circle, then yes, you'd move a total of 5 in the X axis and 5 in the Y axis in a total of 180 steps.
 
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