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| Question about hand taps |
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| Bert:
Hi All I have a question about taps. I am going to order a better quality ¼-20, 3 tap set to augment my utility taps. I have a choice of “Ground tread limits” of 1,2,3,5 and as well a choice of 2, 3, 4 flutes. My question is. For general day to day use in common hobby workshop materials what is the most appropriate tap? . Thanks in advance……Bert |
| Tony Wells:
Two flute taps are stronger. The limit numbers signify the amount over basic pitch diameter they cut, in 0.0001 increments. Usually, a 3 is considered normal. If you are going to plate the part, including the thread, you go higher in the limit number to allow for plating buildup to bring it back to nominal. If you wish a tighter thread fit, you can go lower, and get closer to basic PD. |
| Bert:
Hi Tony Thanks for the reply. That helps a lot. Regards Bert |
| Lew_Merrick_PE:
Bert -- The more cogent question is what you intend to do with these taps? If you are freehand tapping, then an H3 or H5 (.0003 or .0005 inch over pitch diameter) are going to create holes closer than you can drive them. If you are hand tapping with a good tap guide, then they (H3 or H4) are as good as you are going to get. H1 or H2 only make sense if you are machine tapping. As Tony said, the main use for the larger clearance sizes are post-tapping surface finish allowance. I would look into (in order) (1) a good spring-loaded center guide for tapping in a mill or drill press; and (2) making a tap-guide system (there are several posted here in the forum). Cheap taps are no savings. They will cost you more in re-work and damaged holes than they are worth! Stone your taps regularly to keep them sharp! If you are afraid of stoning them, running them in tapped holes in aluminum plate using buffing compound as the abrasive. A dull tap is a major source of frustration! |
| Bert:
Hi Lew_Merrick_PE Thanks for the reply. I am attempting to upgrade my selection of most used taps to 3 tap, higher quality tap sets. When I tap holes I almost always tap in the drill press or mill. I try to avoid free hand taping if at all possible. If I drill a hole on the mill that is to be taped, I try to do that operation at the time the hole is drilled. I do use a shop made spring loaded tap guide as you have suggested. It is a most handy tool. Thanks Bert |
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