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Some things about taps, in general:
There are 3 types of taps. Taper, plug and bottoming. A taper tap has either a 6 or 8 thread lead (can't remember, I don't use them much), a plug tap has a 3 thread lead and a bottoming has 1 1/2. The lead I'm talking about, is the number of threads that are tapered to start the tap.
I always use a bottom tap for 6x48 and 8x40, just because I don't like to retap each hole, from plug to bottom. You need to put a little pressure on the tap, when starting it. Taps create their own feed (they're self propelled) and need help starting. You'll both dull them and chip them if you don't feed them into the work.
Finer pitch taps are easier to use. They use a larger hole and the teeth don't remove as much material. I always found that the 6x32 was the worst and have broke more of them, that any other. I did almost exclusively 304SS for over 2 years and broke more of that size.
I once had to make 12 pallets, out of 304SS, 3/16 thick, that had 24 openings each with a average of three, 0x80 taped holes for each opening. That's 864 tapped 0x80 holes (all by hand). I only broke 3 taps, using 18 taps. But, I had to resharped 4 or 5 of them.
You can tell, when a tap dulls, it's subjective though and you need a lot of experience, but, if you here one squeak, STOP!! Get it out and don't use it again. If they get hard or harder to back out, they are dull.
I wouldn't use a spiral pointed tap. You have to grind the tip, to begin with and back it out for chip removal, more than once. They don't make a spiral fluted tap, that I know of, for 6x48 or 8x40 but, they are the best and are bottoming taps.
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What tap type? (Read 1231 times)
