Tell me I'm crazy.....

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Batmanacw

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I think 118⁰ drill bits drill a more round hole than 135⁰. Has anyone tested that? Am I crazy?

I like using 135⁰ split points as much as anyone. I often start them gently and don't bother with spot drilling.

The 118⁰ just seem to stay self-centered in the cut because of the chisel point.
 
Batmanacw said:
I think 118⁰ drill bits drill a more round hole than 135⁰. Has anyone tested that? Am I crazy?

I like using 135⁰ split points as much as anyone. I often start them gently and don't bother with spot drilling.

The 118⁰ just seem to stay self-centered in the cut because of the chisel point.
Click to expand...
yep, I posted that about a year ago. NYCNC did a little study. Everyone here disagreed with it. I'll see if I can find the posting.

edit: https://www.hobby-machinist.com/thr...-0-or-140-0-instead-of-90-0.97057/post-910155
 
My understanding is that the purpose of the split point was to reduce the chisel to virtually nothing. The chisel point doesn't have a cutting edge but scrapes away the material to drive the drill deeper. This requires a great deal of force, especially noticeable on larger drills. A pilot hole equal or larger than the width of the chisel tip greatly reduces the force required.

As to what angle is best to use, I have never seen a scholarly study on that subject. I seem to recall that old timers used a sharper angle for drilling brass. Supposedly, the 135º tips are better for drilling stainless but I don't know if that is due to the angle or the fact that they usually come with a split point.

As to wandering of the drill on starting, I would expect that a chisel point could wander unless the center punch was larger than the drill chisel. If the drill started off the spindle axis then conceivably a hole diameter larger than the nominal size could be made, much like what happens when the drill lips aren't equal.
 
RJSakowski said:
My understanding is that the purpose of the split point was to reduce the chisel to virtually nothing. The chisel point doesn't have a cutting edge but scrapes away the material to drive the drill deeper. This requires a great deal of force, especially noticeable on larger drills. A pilot hole equal or larger than the width of the chisel tip greatly reduces the force required.

As to what angle is best to use, I have never seen a scholarly study on that subject. I seem to recall that old timers used a sharper angle for drilling brass. Supposedly, the 135º tips are better for drilling stainless but I don't know if that is due to the angle or the fact that they usually come with a split point.

As to wandering of the drill on starting, I would expect that a chisel point could wander unless the center punch was larger than the drill chisel. If the drill started off the spindle axis then conceivably a hole diameter larger than the nominal size could be made, much like what happens when the drill lips aren't equal.
Click to expand...

I'm not concerned with walking. I'm talking about hole accuracy and roundness.
 
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