Specifications and Sources For 1/2-13 Spiral Flute Taps

I have an upcoming job that will require drilling and tapping a number of 1/2-13 H3 blind holes, 3/4" deep, in 1 1/4" thick, 316 stainless plate. I would prefer to use a name brand spiral flute bottoming tap. Looking at several vendors I see nomenclature I am not familiar with. Some brands list their products as "Bottoming" taps, while others list "Modified Bottoming" and "Semi Bottoming" styles.

I also see prices all over the map. Everything from $27.00 a copy to upwards of $60.00 a copy. Any help would be appreciated wading through the maze as to which brands and style would be best suited for this job.

For taps when it really counts I've always used OSG, but Guhring is certainly a great pick as well.

Is threadmilling an option? That'd be my first choice.

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The terms bottoming, modified bottoming and semi-bottoming just refer to the number of threads chamfered at the end of the tap. Modified bottoming and semi-bottoming have a thread chamfer between bottoming and plug taps. These chamfer's just make it easier to tap difficult materials at the cost of needing a deeper hole to get full thread depth.

Any of the major manufacturers (Balax, OSG, Emuge, etc. will have good taps. Just call up tech support and ask for their recommendations for your specific application. I personally like slow spiral taps. Whether you use coolant or tapping fluid will make a difference.
I called Balax several years ago for advice if I could form tap M2.5 in heat treated 15-5 ss at RC35. I do a about 200 holes a year.

I also tap M12 x 1.75 in the same material with an OSG tap using flood coolant.
Call the pro's, they know more than I do. Call more than one company and compare notes.

projectnut said:

I have an upcoming job that will require drilling and tapping a number of 1/2-13 H3 blind holes, 3/4" deep, in 1 1/4" thick, 316 stainless plate. I would prefer to use a name brand spiral flute bottoming tap. Looking at several vendors I see nomenclature I am not familiar with. Some brands list their products as "Bottoming" taps, while others list "Modified Bottoming" and "Semi Bottoming" styles.

I also see prices all over the map. Everything from $27.00 a copy to upwards of $60.00 a copy. Any help would be appreciated wading through the maze as to which brands and style would be best suited for this job.

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I have next to zero expereince with stainless, but we got something like 6-700 holes with a 3/8-16 guhring tap in 4140ph (28-32Rc). I would say ask Guhring, OSG, and Balax (Balax is my go to for form tapping fyi). Emuge makes good taps, but they are spendy spendy!