|
| this is quite simply because a drill bit uses 2 flutes. even in thick metal, if the bit is sharpened even the slightest off center, the bit will always drill a triangle shaped hole. it is because the outside edge of the long cutting edge will grab the metal at the edge of the hole and "walk" the short cutting edge around until it touches the outside edge of the hole, and so on. An uneven bit used like this for any amount of time will eventually break off where the flutes meet the shank from working back and forth.
on sheet metal, as has been said above, the web of the bit has no anchor, and for an amount of time the cutting edge is unsupported except for downward pressure, allowing the corners of the bit to dig in and walk the cutting edges around. | |
|
Why do drills make a triangle hole instead of round in thin sheetmetal
