G'day.
I am wanting to make a largish D Bit- .567"- but am baffled by the geometry. There are many versions:
1. some versions- looking from the top- have the cutting edge cut as a single angle cut across the nose and then relieved underneath to allow it cut.
2. some versions are shaped as a hemisphere at the nose and then relieved underneath and the trailing edge relieved a bit so as to not drag and prevent the bit from advancing.
3. Some versions have multiple angles on the nose and usually have two different angles across the cutting edge. Usually the apex is not at the centre line of the bit. It is usually off set so the shorter and steeper angle is on the cutting edge and the the shallower but longer edge is on trailing position.
I hope that makes sense.
This last one would seem to me to leave portion of the metal not being cut very well. It would seem to have the apex of the two angles cutting a "valley" off centre when looking from the top. Why would one want to have a bit cut this way? What function would be served by this design. It appears that the big bucks gun drills are made this way. It would seem to me to put weird stresses on the bit that would make it tend to wander. ButwaddoIknow?
I have only made one a few years ago to use in wood (with a single angle across the cutting face) and it wandered something terrible. I would like to NOT repeat that in metal.
I am wanting to make a largish D Bit- .567"- but am baffled by the geometry. There are many versions:
1. some versions- looking from the top- have the cutting edge cut as a single angle cut across the nose and then relieved underneath to allow it cut.
2. some versions are shaped as a hemisphere at the nose and then relieved underneath and the trailing edge relieved a bit so as to not drag and prevent the bit from advancing.
3. Some versions have multiple angles on the nose and usually have two different angles across the cutting edge. Usually the apex is not at the centre line of the bit. It is usually off set so the shorter and steeper angle is on the cutting edge and the the shallower but longer edge is on trailing position.
I hope that makes sense.
This last one would seem to me to leave portion of the metal not being cut very well. It would seem to have the apex of the two angles cutting a "valley" off centre when looking from the top. Why would one want to have a bit cut this way? What function would be served by this design. It appears that the big bucks gun drills are made this way. It would seem to me to put weird stresses on the bit that would make it tend to wander. ButwaddoIknow?
I have only made one a few years ago to use in wood (with a single angle across the cutting face) and it wandered something terrible. I would like to NOT repeat that in metal.