mklotz
Well-Known Member
Maybe an example will help...
Suppose your dial is attached to a shaft threaded 10 tpi. That means that one rotation of the dial corresponds to 0.1 inch movement of whatever the shaft drives (e.g., cross slide). The thread on the shaft has to be relatively coarse else you would have to spin the dial an inordinate number of times to move it a significant difference. That gets tiresome quickly.
If I want dial divisions that correspond to 0.001", that means I need 0.1/0.001 = 100 divisions on the dial. Let's say that I think, for easy viewing, the divisions should be 0.125" apart so I can visually interpolate 0.0005". That means the circumference of the dial must be 12.5". Dividing by pi tells us that the dial would need to be ~4" in diameter.
A 4" dial is fairly big for a small lathe. (Many small lathes have 4" *chucks*!)
As you can see dial design becomes an engineering trade-off complicated by several human operator concerns.
Suppose your dial is attached to a shaft threaded 10 tpi. That means that one rotation of the dial corresponds to 0.1 inch movement of whatever the shaft drives (e.g., cross slide). The thread on the shaft has to be relatively coarse else you would have to spin the dial an inordinate number of times to move it a significant difference. That gets tiresome quickly.
If I want dial divisions that correspond to 0.001", that means I need 0.1/0.001 = 100 divisions on the dial. Let's say that I think, for easy viewing, the divisions should be 0.125" apart so I can visually interpolate 0.0005". That means the circumference of the dial must be 12.5". Dividing by pi tells us that the dial would need to be ~4" in diameter.
A 4" dial is fairly big for a small lathe. (Many small lathes have 4" *chucks*!)
As you can see dial design becomes an engineering trade-off complicated by several human operator concerns.