[HELP] Cutting a flute on a tap

[ieezitin]

I have made my own tap now i want to cut flutes in it for chip relief, whats better a ball end mill or regular end mill.

it is .636 dia 26TPI i was thinking three flutes, 

All advice is welcome.

Thank you.

Anthony.

[Hopefuldave]

Hi Anthony,
I think the majority of commercial taps have ground flutes, for production it saves a step.

If you're milling the flute, I'd probably use the ball-end mill, the flutes would then have larger radii in the gulley, so less stress concentration (always a good thing!) where a regular endmill would put a corner / very small radius.

Thinking about the stresses applied to the tap, the bottom of the flute is where a stress fracture is likely to start before propagating helically along the tap, or at least that's how it's always looked to me, except when I've bust 'em by bending 'em...

After milling, you'll need to heat-treat the tap, I guess, that will probably leave the cutting edges in need of sharpening, a dremelloid with an abrasive stone or disc is a good low-budget way :)

[DaveH]

I've made the odd tap - only when I really had to. They are a little more tricky than it seems the flutes are straight forward. I used an ordinary end mill and went straight in from the side so it doesn't look like a flute in a tap sense. The tricky bit is the clearance from the cutting edge again I just milled it. Not perfect by any means.
 
DaveH

[TomG]

Using a ball end mill will result in a much stronger tap. Sharp, inside corners create stress concentrations (stress risers) when the hardened tap flexes and if it's going to fail, that will be the spot. This applies to any hardened part, not just taps. Inside corners should always have as large a radii as possible.

Tom

[ieezitin]

Makes perfect sense to me Tom & Dave, I will use a ball end mill..... Now i am going to figure the math to get the cutting edge dead on center, I am going to go with three flutes, Actually I have threaded the bore out but its a little too tight so this tap is just a chaser..

Great thanks for the help... ill post the machining and hardening process.

Anthony.

[trevatxtal]

Hello
I seem to recall that a offset to centre ball mill cut will give a cutting edge on one side.
An end on view of a large tap will indicate which way.
Trev

[ieezitin]

Well I made the tap.



I have used hand soap to stop the sparking that happens when you heat to a cherry red state, the threads are 26TPI which are pretty delicate .





Now I am covering the whole end with wire, again to aid the halting of the sparking problem.




Fully covered now ready for heating.





All finished. I now cleaned it and honed the cutting edge.





Tried it out on my project and it worked fine, I am very happy with it.





Anthony.

[DaveH]

Job well done Anthony,   excellent work  
 
DaveH

[Highpower]

[RobWilson]

  nicely done Anthony. 


Rob