Spot Drill tip compensation

Mike:

This is an interesting & excellent question. I would assume that most CAM systems have a feature that automatically compensates for this when you enter the flat width (Gibbs does). But let me try to create a manual formula for this:

First; caliper the width of the flat on the tip. Let's call that "F". Now spots drill have various included angles, so let me try to account for the common included angles.

The Dia. is the OD of the chamfer you want. The Z Depth is the amount you'd feed INTO (-Z) the part from Z zero.

Included Angle

60 Degrees (.866 X Dia.)-(F X .866) = Z Depth

82 Degrees (.575 X Dia.)-(F X .575) = Z Depth

90 Degrees (.500 X Dia.)-(F X .500) = Z Depth

118 Degrees (.300 X Dia.)-(F X .300) = Z Depth

120 Degrees (.288 X Dia.)-(F X .288) = Z Depth

135 Degrees (.207 X Dia.)-(F X .207) = Z Depth

Now realize that I haven't actually tried any of these on a machine - so experiment in a piece of scrap first. PLUS there may be some small discrepancies due to measurement error (it can be hard to get an accurate measurement of some of those spot drill ends due to the flats on your caliper tips).

Do you mean a normal 90 degree spot drill, or a 60 centerdrill? That's one thing I like about SURFCAM. Tell it which center drill you have and the diameter you want the top of the chamfer to be, and it figures the depth for you. That's how I do it. What software do you program with?

Later,

Charlie

I program as though the tool has no flat--if it needs to go deeper ( and it always will ) it gets edited or the tool offset gets reset at the machine....reason beings when done this way your first part will NEVER come out oversized on dia.

I would think the opposite to be true. A .100 flat on a 90 degree spotting drill gives you a .200 dia. chamfer with only a .050 depth.

I've been in a couple shops (valve body type work) where we'd program from the "hip" of the drill or spotter. The tool is set to the hip with the presetter so we're all on the same page when it comes to size. Also makes for the most accurate way to set depth of the full diameter regardless of size.

-- Bill

Sounds like a great tip to add to the "I Hated Working For Haas" blog you're putting together. ;>)

Jon Banquer San Diego, CA

Give the man a cigar...

There's an inserted carbide spot drill out there -- can't remember the name now, I'll get it Monday -- anyway is has the property that the chamfer comes out to the theoretic value, that is, if you want a .250 diameter chamfer you go .125 deep.

-plh