# Milling a circle



## Peacons (Oct 17, 2019)

If one doesn't have a rotary table, how would you mill the  circumference of a circular piece with a small stem (think banjo shape)?


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## KMoffett (Oct 17, 2019)

Bandsaw!


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## Peacons (Oct 17, 2019)

No metal cutting bandsaw, just one for wood.


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## bill stupak (Oct 17, 2019)

If it's aluminum you can still cut it on a wood bandsaw. I do it all the time


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## catsparadise (Oct 17, 2019)

Manual milling machine (file)?


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## darkzero (Oct 17, 2019)

Does it need to be an accurate size? If no belt sander.

Or if there's a through hole, there's the method of sticking a pin through the bore, rest the ends of the pin on the top of the vise jaws, clamp the part, mill, then rotate & repeat. If you rotate it enough & in small increments you'll minimize the faceting & can clean up the rest with a file.

Or a corner rounding endmill if it's small enough. Some people use radius router bits too.


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## Peacons (Oct 17, 2019)

It is aluminum and I have cut it before with that saw. Just looking for another way.


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## Latinrascalrg1 (Oct 17, 2019)

Does it have a hole in the center of the circular portion?  Can you mount it flat with a tight fitting bolt through the center to act as both a pivot point to make the cut and to help hold the material flat and keep it under control as you manually rotate the work?


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## Janderso (Oct 17, 2019)

plasma cutter.


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## machPete99 (Oct 17, 2019)

Router set up with spiral carbide drip and pivot attachment. (Generally need hole at center).
Or rotary table on a mill.
CNC if you got it.
Or a suitably sized lathe.


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## benmychree (Oct 17, 2019)

Nobody has yet suggested that it would be appropriate to buy the rotary table, so I will ----- !


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## Mitch Alsup (Oct 17, 2019)

benmychree said:


> Nobody has yet suggested that it would be appropriate to buy the rotary table, so I will ----- !



I was going to suggest this!

It is as simple as this:: If you need to mill something round and don't have a rotary table, then buy a rotary table.


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## pontiac428 (Oct 17, 2019)

It's the "stem" on the part that is the deal breaker.  A plain circle can be cut several ways on the mill, but a circle with a stem would mean getting out the rotary table or going with @Latinrascalrg1 's suggestion.


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## Flyinfool (Oct 17, 2019)

How good are you at trig.
Calculate the location of the 2 corners between the dia and the stem, then do the math for each 1° and make a lot of small moves around the perimeter. It will be so close to round that I doubt you will see the facets. If you do some quick work with a file or sandpaper will clean it up.

I did this for a cam that I had to make, It was tedious but it worked great.


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## tjb (Oct 17, 2019)

Much along the lines of Flyinfool's suggestion, you can calculate the coordinates of the perimeter.  Here's a link to Tubalcain's approach to laying out the coordinates for making a spoked flywheel.  He calls it the 'DRO method'.  At about two minutes into the video, he tells you how to calculate or look up the coordinates.

By milling more holes, you can make very nearly a full circle and clean it up with a file/sandpaper/etc.

If the link doesn't work, just go to youtube and do a search on 'how to cut a circle on the milling machine'.  His video is 'Machine Shop Tip #153...'.

Regards,
Terry


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## Peacons (Oct 17, 2019)

This may help. On this site you can see several parts with a feature like I described


			USS Monitor engine


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## francist (Oct 17, 2019)

I think if I needed to make parts like that I would do as much as I could on the mill or shaper, and then freehand cut, file, and sand/grind the rounded lobe ends as required. Curved shapes like that can be pretty forgiving to the eye, and while a round shape may not end up being geometrically perfect it may be quite acceptable visually. Having said that though, if you’re looking to make a stack of them then it may be worth it to find a small rotary table.

That’d be a really cool model to see completed — good luck if you take it on.

-frank


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## brino (Oct 18, 2019)

Here's an interesting method I saw posted here a while ago:
(I believe this is what Will (@darkzero) posted about above......)





-brino


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## Peacons (Oct 18, 2019)

Already into it.  Currently working on some of the.more linear parts.


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## Peacons (Oct 19, 2019)

Finally broke down and ordered a rotary table.
Now just have to figure out how to use it!


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## ttabbal (Oct 19, 2019)

Joe Pieczynski on YouTube has a series of videos about rotary table use. Tubalcain has some as well. Good places to get at least the basics.


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## NortonDommi (Oct 19, 2019)

Joe Pie has a a good video on the Rotab.


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## brino (Oct 19, 2019)

Peacons said:


> Finally broke down and ordered a rotary table.



No one can convince you to buy new tools like this lot can! 

We are a bunch of "enablers".........that way we can say "Honest Honey, I'm not as bad as those guys!"

-brino


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## darkzero (Oct 19, 2019)

brino said:


> No one can convince you to buy new tools like this lot can!
> 
> We are a bunch of "enablers".........that way we can say "Honest Honey, I'm not as bad as those guys!"
> 
> -brino



Someone here once told me their wife hates me. I certainly don't want anybodys' wives hating me. Some women can be crazy. So now I try to just keep my mouth shut.


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## Peacons (Oct 20, 2019)

I sold it by saying it would save my fingers from harm


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## tjb (Oct 20, 2019)

darkzero said:


> So now I try to just keep my mouth shut.


Um, Will, maybe you should have used this smiley?


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## brino (Oct 20, 2019)

Peacons said:


> I sold it by saying it would save my fingers from harm




oooooooowwwwwwwww......I gonna use that one!
-brino


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