# Radius/Corner bit setup.



## wla421 (Dec 19, 2010)

Hi all,

Can someone instruct on how to properly set up a mill for corner bits? 

I have some parts that I am making for a custom brake application for my WL/KH hybrid, and it is ugly with all the square edges.

I want to pretty it up some, but am not sure how to go about setting up my mill so all edges will have the same radius.

Photos are extremely helpful.

Thanks to all in advance.

George


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## kvom (Dec 19, 2010)

I assume you are talking about a corner rounding bit.

You have to "calibrate" the bit to get an even radius with no "ledges". Take a piece of scrap that's square and align the bit in the z-direction by touching the flutes, and the x direction by touching the barrel. Then move the bit down and in progressively, recording your dial settings or DRO readings until you get a satisfactory form. Then write these down so you can repeat the setup on a good part.

If you have a mini-mill with no DRO on the quill it will be more difficult to get the Z height correct. Sometimes it's wise to leave a bit of extra material in the Z dimension that can be removed conventionally if the bit cuts a ledge.


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## shred (Dec 19, 2010)

I used the 'Ledge' effect a lot on my PD engine-- the steam control block and the valve tops:












I have a few different sizes of corner-rounding bits that I pick up surplus-- they're annoyingly expensive to purchase.

To set them up, all the ones I have the rounding part is set from the OD of the tool-- the OD is on 'center' of the round cut. Subtracting the radius will get you to the edge of the cutting part. This doesn't seem to be true for the length-- on some of them the end is not on center of the round. Presumably all that data is available when purchased new, but I don't have it.

Anyway, although it can be mathematically determined, I usually just fiddle with some scrap until I get the cut I want and go from there. The trick is to set up the cut along the fixed jaw of the mill vise and flip the part around so each edge gets cut appropriately. In the picture below, I've cut one side, then flipped the part around to do the other without changing any settings.






If you have to reset Z to match other parts, the best bet is to zero off the bottom of the tool on the workpiece and write down how deep you have to cut.


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## wla421 (Dec 19, 2010)

Fellas.

That is just what I needed, 

I have played with some scrap, and I think I got it how to set it up.

I will take a picture of what I am working on and post it.

thanks George


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