2 Flute, 3Flute 4 flute taps

[woodchucker]

I could not get a gib screw out of my taper attachment that I bought. It was abused. rusted in. This is the follower on the cross slide.
I drilled it out and tried with an extractor, heat.
Ok, so I drill it to size then start tapping. Rather than go all the way. Let's see if I can lay new threads in.. 10-32 about 3/4 of the way, then that uneasy feeling I'm about to break a tap. I try another , not any better. I noticed I had a 2 flute tap, figured it has to be more stout, so I give it a try, it cuts it like butter. No resistance.

So why do we have 2,3,and 4 flutes, if the 2 are so much more stout. I realize that a spiral tap will be even better and cut across an interrupted slot.. but man 2 flutes really cuts well.
So why do we need 3 and 4?

 

[Ulma Doctor]

simply put for chip removal in different materials and relative strength.
a 2 flute tap will have a lot of surface area in contact with the parent metal, that is not always desirable- but it will have high strength for harder materials
3 and 4 flute tools will have less surface area in contact and will run cooler and can remove more chip volume in comparison, for softer materials
spiral taps have even less cutting edge in contact , but can be very brittle- (don't ask how i know that ) used on both hard and soft materials

 

[Splat]

Which brings to mind a question. I know it depends upon hardness of the metal but is depth of cut what determines using a roughing endmill opposed to a standard, non-roughing endmill?

 

[Ulma Doctor]

Which brings to mind a question. I know it depends upon hardness of the metal but is depth of cut what determines using a roughing endmill opposed to a standard, non-roughing endmill?

it has more to do with surface finish whether you use a roughing endmill or not, as well as speed of travel.

as the name implies, a roughing endmill is for maximum stock removal not much consideration is made for surface finish.