How do I......

[finsruskw]

Need to figure out where to drill the clearance holes to mill a hex recess to hold a 1" threading die?
I know to use the bolt circle calculator but where should the center of the holes be located?
Should the center of the holes be the exact corners of the hex I guess is what I'm asking here.

 

[T Bredehoft]

That would suffice. Alternately (and it means a lot more work) have the outside of the corner holes at the point of intersection of the sides.

 

[Cadillac]

If I were doing it I would lay the holes out where the hex lines intersect. The hole size wouldn’t be 1/8 or under.

 

[Flyinfool]

The size and location of the corner holes depends on the size of the hex hole and the size of your end mill that you are cutting the flats with. It also depends on if it is a blind hole or a thru hole. We need more info.

 

[rabler]

A hex has a ratio of 2/sqrt(3) between the distance between flats and the distance between opposing corners. So a 1” hex will have 1.154” diameter for drilling the corners.

Set up a hole pattern with a small drill. I’ll leave it to someone else to give you a perfect answer on the drill size vs endmill size. But roughly your drill bit is going to be slightly smaller than your endmill.

I’m doing this in my head while soaking in the hot tub, but your caliper should give a reality check.

 

[RJSakowski]

I use @T Bredehoft 's method for corner clearance on hex pockets. It removes less material.

The easiest way to clear the corners pf a hex pocket which also involves a minimum removal of excess material is to pre-drill holes with a diameter at least 58% of the end mill diameter and spaced half that distance from the vertex of the hex sides. If using an end mill to plunge cut the relief, it can be done after the sides of the pocket are milled.

If the work is laid out in CAD, it is fairly easy to determine the coordinates of the hole locations. Otherwise, a little math is required. Here is a drawing depicting the situation. The dimensions can be scaled to give appropriate values.