303 stainless steel threading problem

hello all -

this is my first post and metal working is a hobby. while i take my hobby
efforts seriously and try to solve problems before asking the experts, this
problems' solution is escaping me.

being an active ham radio operator i build everything i can before i buy. this
project is a mobile antenna mount that requires a 3/4" deep blind hole tapped
3/4"-16 tpi in piece of 303 SS. i am using an 11/16" tap drill, a kodiak TiN
coated KCT241528 bottoming tap. i have tried using this configuration with rigid
dark and light cutting oils, and a thread cutting wax from a local hardware supplier.

i use a 15" iron workers wrench to turn the tap and center the tap in the piece
using a dead center held in a 1/2" collet in my (unnamed) mill. one hand rotates
the tap wrench, the other hand keeps pressure on the quill to keep the tap centered.

the threads cut are torn and ragged looking along the entire depth of threading.
i turn the tap one half turn, then reverse the rotation a quarter turn to cut the
chips. every two or three turns i remove the tap to clean the flutes of chips.

smaller taps that i have used on ss, 4140, 12L14, and 1018 always seem to be clean
using the same process.

i have no idea what i am doing wrong so those of you with the patience to deal
with a newbie please chime in.

thanks!

You are starting the threads with the bottom tap?

Bottom tap is only for the last couple threads, tap sets have three taps that are used in order


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thanks to both.

i am using the bottom tap to start and complete the entire thread.

my wrong assumption was that a tap is a tap. while i do deserve it
thank you for not blasting me out of the water for this egregious
mistake!

it will take a few days for msc to get the proper taps out to me
and i'll report back the results.

thank you

Use a starter tap or through hole tap to start the hole and pull it it out just before it bottoms out in the hole so you dont run the risk of breaking it off. The use the bottoming tap for the last couple threads.

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problem solved.

i ground a 3/8" hss blank into a threading boring bar and cut the threads on my lathe.

thanks for the help and your patience!