# Bit dimensions



## Al Smith (Jul 9, 2010)

Here's one for those of you who know bits and math.
I purchased a plunge ogee bit for my CNC machine, overall diameter 1 5/16, inches, plunge cut depth 3/4 inch, plunge tip diameter 3/16 inch, shank size 1/4 inch.
My question is what is the diameter of the 2 curves in the cut itself, the *manufacturer has no idea*. 
Here is what I have come up with - - either - 

The diameter is 1/2 of the cutting depth since there is a continuous curve to the cutter which makes the diameter of the curve 3/8 inch - or - take the 1-5/16 diameter, subtract the 3/16 plunge diameter which leaves 1 1/8 diameter divided by 2 which is 9/16 inch with 2 curves which when divided by 2 is 9/32 inches in diameter. 

Or am I making a mountain out of a molehill. I do know that the difference is critical on a CNC machine when cutting external or internal diameters.

Thanks for your help
Allen


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## RJM (Apr 11, 2010)

Al Smith said:


> Here's one for those of you who know bits and math.
> I purchased a plunge ogee bit for my CNC machine, overall diameter 1 5/16, inches, plunge cut depth 3/4 inch, plunge tip diameter 3/16 inch, shank size 1/4 inch.
> My question is what is the diameter of the 2 curves in the cut itself, the *manufacturer has no idea*.
> Here is what I have come up with - - either -
> ...


I think you are asking for the diameters (or radii) of the resulting ogee contour. If so, they could be anything (within limits) since the tangent points can be moved and the straight lengths of the profile can be adjusted. You could find which drill bit shank best matches the concave radius on the bit, then cut the profile on a piece of scrap and use a drill bit to measure the concave radius on the workpiece (which is convex on the bit).


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## Al Smith (Jul 9, 2010)

You are correct and that is what I did, turns out to be 5/16 to 9/32 so 5/16 will do. I just could not imagine the manufacturer not knowing the information on their product but they probably had it made in China, should have gone to Eagle I guess.


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