# Inside Radius



## Coomba (Jan 21, 2015)

Will someone direct me to a video, or explain how a large inside radius, or an arc, is cut on a manual mill.


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## Karl_T (Jan 21, 2015)

I can think of three methods

rotary table
boring head
fake it in with small X Y moves and large diameter cutter

which one interests you for this application


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## Holescreek (Jan 21, 2015)

You need to be more specific as to the shape of the part. If need an inside radius vertical cut you use a ball end mill or an end mill with the radius ground on the corner of the flutes.


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## chips&more (Jan 21, 2015)

Use the outside of a shell mill cutter or slitting saw cutter or similar.


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## Holescreek (Jan 21, 2015)

Here is an example of an "arc" cut horizontally using a rotary table:




You could also do it with a boring bar or a hole saw.

This is an "inside radius" cut vertically:


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## Coomba (Jan 23, 2015)

Holescreek said:


> Here is an example of an "arc" cut horizontally using a rotary table:
> 
> 
> 
> ...



Yeah!! The example on the rotary table. Now how do I learn how to do that. Thanks Holescreek.


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## Holescreek (Jan 23, 2015)

Mount a rotary table on your mill and set your X&Y zeros on the center hole of the table.

Locate the center of the arc you want to cut on your workpiece by scribing crossed lines or a center punch mark.

Mount the part on the rotary table (with spacers underneath to raise it off the table) and use a pointed wiggler or other means to position the center of the workpiece under the spindle.

Figure out the diameter of the end mill you will be using and mount it in the mill.

Subtract half the diameter of the end mill from the desired radius size and move either the X or Y of the table that amount and lock the table.

Bring the cutter down to the workpiece while turning the rotary table hand wheel.

Continue until the desired arc is cut.


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## Coomba (Jan 24, 2015)

Holescreek said:


> Mount a rotary table on your mill and set your X&Y zeros on the center hole of the table.
> 
> Locate the center of the arc you want to cut on your workpiece by scribing crossed lines or a center punch mark.
> 
> ...



Is the radius then determined by the location of the part on the rotary table?


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## JimDawson (Jan 24, 2015)

The arc center is the center of the rotary table, thus the further the cutter is away from the center, the larger the radius it will cut.  So you have to position the part to have it's radius on the arc (rotary table) center


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## Frank Ford (Jan 25, 2015)

Here's a piece on setting up and cutting a 5 inch (approx) radius on a rotary table, along with some stuff about making a fixture plate top for it:

http://www.frets.com/HomeShopTech/Projects/RotabFixturePlate/rotabfixtureplate.html


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## Coomba (Jan 27, 2015)

Thanks guys, Got it!


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## Calandrod (Oct 8, 2022)

So I have a similar question. I’m trying to replicate this screwdriver handle. What would be the best way to cut these radii?  I am brand new to machining still. I am using a Bridgeport.


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## Karl_T (Oct 8, 2022)

I assume you do not have a huge rotary table. that would make it easy.

If you have a DRO, you can do what I call manual CNC. Lay out that curve in a drafting program. get an offset curve the size of a large end mill.  find the Y value every say X of 50 thousanths and put it to paper. Now move both the X and Y by hand to each point. With a bit of practice you can do any odd shape this way.


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## jwmelvin (Oct 8, 2022)

If you have a way to spin it and a boring head, you could use those.


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