Question about hand taps

[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

[Lew_Merrick_PE]

Bert -- They will pry my TapMatic heads out of my cold, dead fingers...

I served my apprenticeship long enough ago that I was expected to make most of my personal tools.  One of those projects was a set of t-handle type tap wrenches with matching guides.  The bodies of the tap wrenches were sized such that the retaining/clamp nut sat within the diameter of the body.  This allowed a guide to be bored (and bushed) to assure alignment.  As part of the exercise, I measured all the taps to find the correct length that would allow full motion of the wrench within the guide for each range of taps.  (I lost three roll-away cabinets of tools when my shop was torched in 1973.  The fire was fed by 5 tons of Brazilian rosewood and 3 tons of ebony -- not much survived that heat.)

[Dean W]

If you are freehand tapping, then an H3 or H5 (.0003 or .0005 inch over pitch diameter)...

Unless I've forgotten what I used to know, (surly possible), the H3 limit will be .0015" over, and the H5 will be .0025" over basic pitch dia.  Each H limit equals .0005", rather than .0001".  There is a coverage area at the spec too, but no need to muddy the waters further.

Bert, I would go with H3 limits and three flute for general shop use, and if you are talking mostly fractional inch sized taps.

Dean

[Paddy OFernichur]

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!

Lew,

I'm sure you've had good results doing the "stoning" thing, but I can't see the benefit. I'm not seeing how this can keep a tap sharp, especially with the method of buffing compound/abrasive used in tapping or re-tapping a hole. All I can see there is pronounced flank wear, and loss of the coating if there was any. What I do with worn taps is replace them.

Years ago there were tap sharpening methods that involved 12V9 or 15V9 type (shape) wheels on tool & cutter grinders. Those would just take a pass in the flutes, along the face of the "hook" in the teeth. That was in the days before high-performance taps that use very complex geometry and high-tech coatings to assure consistent tap performance.

I also have questions about the source of the data you have for the "H" limits of taps. This website shows something different, and in my experience (like Tony's) the jumps are more than a few "tenths".

http://www.newmantools.com/taps/taptech.htm#cla

[Lew_Merrick_PE]

Paddy & Dean are correct about h-values being .0005/.0003 rather than .0001 deltas.  I have been working these past few weeks with SAE AS5202 o-ring glands where the tool adjustment bands are .0001 increments.  This first thing that goes when you get old is your.... what was I saying?

[Tony Wells]

Yes, my mistake. Thanks for the catch. 0.0005, not 0.0001. A bit of wear and that would be gone anyway.

My apologies.