1000 holes tapped 1/2-13 UNC in 5/8 304SS. Should I use a form-tap or cutting-tap?

I'm bidding a job that calls for 1000 2B 1/2-13 UNC tapped hole through 5/8 flat stainless. Grade of stainless is not specified....was planning on 304 to keep the cost down. Any grade of stainless is acceptable.

What would be the best type of tap to use?

Thanks.
gm

I would normally use a spiral flute at that size and wouldnt worry about tap breakage. Thats in a blind hole though. I am sure any cut tap would be fine. I like to use TiCN or TiN for SS. I use Form taps at smaller diameters.

i got 1000 holes on 1 cut tap before I ran out of parts to make. Tap did not break 3/8 16 threads

I would do my damndest to get 303 plate. Or some other free machining stainless like 416. You may have trouble finding 5/8 in a free machining grade, but try.

304 turns and mills semi-okay, but it sucks to drill.

I'd drill with a YG1 cobalt 11.75 mm stubby drill, 140 point, Tin coated. Chamfer 120 degrees to .520", and tap with a OSG EXO form tap.

I'd plan on using 2-3 drills and 1 or 2 taps for the run.

Double that for 304, and add 50% to the run time. If you're lucky. And probably go to a dream drill ($$) if you have TSC.

Whatever you save on material with 304 you will give back twice on time, and chamfering the backside will be much easier on a free machining stainless.

If you have to use 304, consider thread milling instead of tapping.

Thanks. Sounds like you've been down that road a few times. Appreciate the advice.

From what I've found, 303 is about twice the money. Does that sound right?

gmoushon said:

Thanks. Sounds like you've been down that road a few times. Appreciate the advice.

From what I've found, 303 is about twice the money. Does that sound right?

Click to expand...

I just paid 2.30 for 303 rods. Flats can be more expensive, I don't know what you are actually using.

Flats and plates are more readily available in 304 so usually cheaper, but I can't say by how much is reasonable. I bought some 5/8 x 1-1/2 303 flats that were almost impossible to find, and they were expensive. 3/4 x 1-1/2 was readily available and cheaper per pound, but it would have been break even on real cost per part.

What I do know is this- if the only material spec is "stainless steel", pick something besides 304 if the job is drill and tap 1000 1/2-13 holes!

guest said:

I just paid 2.30 for 303 rods. Flats can be more expensive, I don't know what you are actually using.

Flats and plates are more readily available in 304 so usually cheaper, but I can't say by how much is reasonable. I bought some 5/8 x 1-1/2 303 flats that were almost impossible to find, and they were expensive. 3/4 x 1-1/2 was readily available and cheaper per pound, but it would have been break even on real cost per part.

What I do know is this- if the only material spec is "stainless steel", pick something besides 304 if the job is drill and tap 1000 1/2-13 holes!

Click to expand...

Thanks again for the feedback.

The job is a bar that's 2" x 3.5" x 5/8" with two threaded through-holes in each. I had considered thread milling but have never done it. Machine is a Haas VF2 so it has the capability. Don't know if thread milling would make enough difference to offset the tooling?

I had one job that involved drilling a 1/32 axial hole through 1/4 stainless...2" total depth. Can't tell you how many drill bits I broke! Finally realized they sent 304 instead of the 303 I ordered!

Sounds like one might be better off getting 303 that is thicker and milling it to 5/8 if the money works out...hmmmm...

Is that 1000 holes in one piece of plate ?
As seemed.

What happens if a tap breaks in one hole due to an inclusion or hard spot, or just plain bad luck.
Can you rework the hole that might have edges or internals buggered.

So that even if the tap was removed via edm or acids or whatever, there might likely be a scar on the internal wall, or the entry.
Go/no go gages would gage right but the hole would have an error not in spec to 2B.

In the real world the error is almost certainly immaterial.
But someone at the customers end and or an end user with a very very expensive test jig might complain if You are unlucky.

Do You eat the expensive plate and redo another one with 1000 holes at your cost ?
If the customer is ok with possible scars or barrel inserts shrink-fit, re-tapped, then it´s probably great.
And the customer signs off on them, in advance.

Not trying to be critical of You, at all, or a know-it-all.
You probably have it handled.
Just pointing out something that at least some others may not have considered.

Just that 1000 perfect holes in once big SS piece can turn a 10.000 job into a 50.000$ job.
And the thread-mill solution suggested seems to me to be essential.

Sorry for the confusion. 500 pieces with 2 holes each.
gm