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Machine Shop and Tool Talk Shop Equipment, fabrication, repairs, how to fix it, which tool to use for the job. Machinist shop talk, straight to the point.

Machine Shop and Tool Talk

Taps and Dies Purpose?

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Old 09-20-2017, 06:06:32 PM
tdmidget tdmidget is offline
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Default Re: Taps and Dies Purpose?

Any tap or die should cut the thread to spec. There is a lot of junk out there. Run from "sets" as fast as you can unless just using them to clean rust and goo out of threads. You can get what you pay for but no more. A decent 1/4-20 spiral point tap will set you back close to $15. You can see that buying a set of stuff you may never need and may never work right anyway is false economy. Buy quality tools as you need them. You will save in the long run. After using junk straight flute taps from the cheapo sets you will think you have died and gone to heaven .
As for "chasers" , pure hokum. A tap acts as it's own lead screw. Anything it removes was in the wrong place and should have been removed. Using damaged or malformed threads is a quick path to galling and further damage. Always clean threads before reuse. In the power generation industry we have fasteners quite commonly to 6 inches holding steam at 3500 psi. At every disassembly they are cleaned and inspected, replaced as needed. When in doubt we run a tap or die as the case may be to insure proper thread form.
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Old 09-26-2017, 04:00:41 PM
BillWojo BillWojo is offline
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Default Re: Taps and Dies Purpose?

^^^^ What tdmidget said. Did you used to hang out at Practical Machinist? I am MrBridgeport over there. Haven't stopped by there in ages.
Anyway, only buy quality taps, the stuff a real machine shop uses. Yes, they are expensive but cheap in the long run. Look at flea markets for stuff and stay away from the old stuff. The newer generation of cutting tools is a vast improvement over what came before. Look for spiral point and spiral plug taps.
By the way, on the side of a tap you will see a GH number. Number 3 will cut a standard size thread, Number 4 or larger is used if the part is going to be plated and each increase in number size cuts the thread oversized by 0.0005. That's why if you tap a part with a GH7 tap, the fastener will seem loose.

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