Tap drill size for 1/2 -10 Acme

[DavidR8]

Could you just rough-grind an HSS tool for this? You could basically just 'undersize' a cutter and depth and let the ACME tools cut as little as possible.

Using the 60 degree tool you have to make sure you don't cut them 'too wide'.

I can try though I doubt my capabilities to grind an internal threading tool

 

[ErichKeane]

I can try though I doubt my capabilities to grind an internal threading tool

The nice part is it doesn't have to be 'good', since it is just a roughing tool.

 

[devils4ever]

You can buy carbide Acme internal threading tools. I didn't think my mini-lathe was up to the task although I may try it in the future.

Check these out.

 

[MrWhoopee]

not sure I'd be too concerned about 'depth' so much as 'width'. If you cut too deep (in the bottom of the thread) you are just hitting the 'relief' part of the thread. If you cut too wide, you are taking out the force bearing-surfaces.

That is actually what I was thinking of, cutting to correct depth for a 60° thread would be too wide for an Acme.

 

[DavidR8]

That is actually what I was thinking of, cutting to correct depth for a 60° thread would be too wide for an Acme.

I would likely only make a couple of passes to remove a bit of material.

 

[SLK001]

I recommend that you DON'T use a 60 degree threading bit, but instead grind your own ACME profile on a piece of HSS. You'll want to go deep enough to remove most of the material (that you DON'T want) and a 60 degree bit will remove material that you DO want. The ACME bit doesn't have to be perfect, because your tap will clean it up to your final spec.

 

[DavidR8]

The tap arrived today.
I drill a hole in the mild steel stock using a Z letter drill.
The tap wouldn’t even begin to bite no matter how much pressure I put on it.
So either the tap is junk or it needs a bigger clearance hole.

 

[nnam]

How about try a larger hole and put a bevel to it?

 

[DavidR8]

How about try a larger hole and put a bevel to it?

Yeah, I’m going to increment up, bevel the start and see what happens.
Started with .413, I think I’ll try a 27/64 or 7/16 and see how that goes.
I measured the tap and the bottom of the thread is dead on .406.

 

[devils4ever]

The tap arrived today.
I drill a hole in the mild steel stock using a Z letter drill.
The tap wouldn’t even begin to bite no matter how much pressure I put on it.
So either the tap is junk or it needs a bigger clearance hole.

Where did you get the tap? I think I bought mine from McMaster-Carr or MSC.