How do you Accurate Mill a Full Circle?

oskar

oskar

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I want to cut 2 circles in 3/8” aluminum one 8” OD and the other 10” OD

Reading on various threads I gather a rotary table will be the only solution but my question is I don’t see how a rotary table will work unless this table is motorized?

Otherwise I will have to manually turn the table against a speeding end mill which I don’t think it’s safe to do

I don’t have a rotary table yet so I wonder how it works

Nicolas
 
Rotary tables can be used to cut manually. That is what they are for. You can cut conventionally if backlash is an issue with the rotary table.

The rotary table will likely have a worm gear which will translate the rotation in the lever to rotation on the table. They are set up to be able to handle cutting forces. They aren't meant only for positioning.

Depending on accuracy required, time you are willing to invest, and travels of the mill, you can create a chart of points around the outside and drill them, then use sandpaper to clean up the edges. If you have a lathe, with sufficient clearance, that is also an option.
 
The turn tables I'm familiar with have a way to very finely adjust the worm to eliminate most, if not all, of the backlash.

Yep, crank it by hand.

Ted
 
Hi Guys,

Yes I would agree ! Trepanning the discs on the lathe would be the way to go. I can just manage 9" inches on my Myford using an 8" inch faceplate.
A well ground tool and plenty of WD40 or Kerosene. Milling would be awkward and time consuming, plus you would have to arrange some method of workholding.

Actually I've just turned a couple of brass discs 2"inches in diameter by 2mm thick, trepanned out of a sheet 10" square using a drill press.
 
Didn't know about Trepanning which may be a solution (after some practice). Also didn't know about the worm gear on the RT, must be expensive
 
Hi Oskar,

Trepanning is a very very old technique for cutting round holes and plates. Dating from around 6000 BC.
 
BaronJ said:
Hi Oskar,

Trepanning is a very very old technique for cutting round holes and plates. Dating from around 6000 BC.
Click to expand...
Used for making holes in skulls for medical treatment.

In the case of the OP's question buying a rough cut blank from a material supplier and finishing it on a lathe or mill is the most cost effective.
This is a 35" diameter aluminum disk cut with a bandsaw from plate by the metal supplier. This is a lathe faceplate fixture, I drill mounting holes for the part and faceplate mounting first.

Mount it to the lathe and turn it in place then clamp the part to it and do the work. None of this is fast, if the major concern is time when using a manual rotary table then Buck up and buy a powered rotary axis or a 2 axis mill that will interpolate the sizes at the accuracy required.
 
Hey Walker, the size of your shop and equipment are amazing!

I’m retired which means I have tons of time and Trepaning looks like it’s for me but not for a 35” piece, my mini lathe is half that size LOL

Anyway a rotary table might be a good tool to have and I found a place close to my home which they have a reasonably priced one with tilt table for CAD$ 189.00 shipping included. It’s the 5th item on this page

https://www.busybeetools.com/search.php?search_query=rotary

Can you give me your opinion?

Perhaps in the States there are better ones but since I’m in Canada it has to be from Canada to avoid shipping cost, duties and taxes.

Nicolas
 
Manual rotary tables should be easy to find used, most job shops stopped using them 30 or more years ago, I suspect that many of them are entirely to large and heavy for hobby machines however.

For general hobby use a vertical/horizontal tool with a tail stock would be far more versatile.
 
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