Manually milling an arc without a rotary table

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.

OK. Where do I find that in your spreadsheet? I must be missing something.

Gene
 
I once manually milled my then house numbers 2158 in a fairly fancy font out of 1/2x5 x14" brass. It was time consuming and wasn't quite prefect, but it was pretty close. I pebbled the background inside the border and darkened it with gun blue and polished the foreground and lacquered the works. It can be done.
Michael
 
OK. Where do I find that in your spreadsheet? I must be missing something.

Gene
If you enter in a circumference of 31.415 (the circumference of a circle with diameter 10) then your X (column A) and Y (column B) movement for 90* sums to 5 and 5.
 
What machine do you have? I have a 6" Phase II Rotab I can make you a deal on!
 
If you enter in a circumference of 31.415 (the circumference of a circle with diameter 10) then your X (column A) and Y (column B) movement for 90* sums to 5 and 5.

Understood, thank you.

Gene
 
There are all sorts of formulas to describe circles. I just have one question:

Is a circle a polygon?
 
I tried something similar on my 7x12 lathe - the method does work, but you have to careful do it in a way that does not allow for cumulative errors. My lathe does not have DROs, so this was a problem for me. On a mill with DROs I think this method would work just fine, but it takes a long time and it's easy to make a mistake. On the other hand, sometimes you just have to work with what you have, and that's part of what makes hobby machining a fun challenge.

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
 
I've made bearing races b4 on the lathe. i turned a piece of stock to the same diameter as my outer race. Then i set up an indicator on my cross slide and had this piece on the ways. Like a tracer.It worked very well, dont see why you couldnt do the same on the mill. These were bearing caps and i was cutting the concave inside of them to fit a radial ball on a shaft. Same as the inside of an outer race on a ball bearing. Never tried it on the mill but im sure it would work. No math involved just hand feeding and keeping your eyes on the indicator
 
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I remember doing a few impromptu jobs, without having access to a rotary table.

Hog/Bandsaw, them out to your line, then use a 2-3 foot cheater bar to (feed/finish), the rest of the cuts...only taking off a few thousandths at a time.


As long as you don't slip.

A slip up could be disastrous. And, a destroyed workpiece.

I know some pieces were at least 3/4" thick steel.
 
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