Tapping Heads Tapmatic A5 and ?

[GlennW]

I'd say that the PeeDee wires are the best way to go for inexpensive wires. I've seen posts on how some of the other cheaper sets were not anywhere near the diameter that they were claimed to be.

[ctwo]

Harold, I understand your point on cutting to depth, but there was some context there, such as if I did not have a "gauge", and I have neither wires nor a thread mic. Is there a better option without those, and considering what we are most likely making, even considering this particular application? Although, I do cherish doing things right(er).

About the tolerance concerns of thread wires, couldn't there be some mitigation of that using comprehensive charts or a fancy Excel spreadsheet to figure things out?

I'm afraid my old mind is not getting the picture here. Would you please elaborate, so I might better understand your point?
H

In the below post, you will see two square jaws (nuts) on the tool post. One has a combination left-/right-hand threaded stud. That assembly goes into the square slot in the spindle to grip the flats on the end of the tap, when you rotate that stud. You'll probably notice where taps have spun and chewed up the jaw's contact area.

https://www.chaski.org/homemachinist/vi ... 39#p421539

I'd say that the PeeDee wires are the best way to go for inexpensive wires. I've seen posts on how some of the other cheaper sets were not anywhere near the diameter that they were claimed to be.

Thanks Glenn. Those are the only name brand I've really read about.

[Harold_V]

I understand your point on cutting to depth, but there was some context there, such as if I did not have a "gauge", and I have neither wires nor a thread mic. Is there a better option without those, and considering what we are most likely making, even considering this particular application? Although, I do cherish doing things right(er).

Hmmm. Not sure how to respond to this. I'm inclined to say that if you hope to make an omelet, you must crack a few eggs.
From a realistic standpoint, what you have been doing works---it's just that you have no idea where you are, although you most likely would be close. For me to think that's acceptable when I know that in the real world you'd be risking rejection, I find it hard to say just keep doing what you've been doing. The harsh reality is, especially if you're making complementing components and they must fit one another, no big deal. Standards were created so parts could be made anywhere, and still fit. When you use any procedure that leaves you in the dark, you risk not being in compliance with a given standard---even if the part is functional.

The truth is, if you have no means to measure a thread, you most likely have just as good a chance of hitting a functional size by visual inspection as you do by trusting thread depth. I'm not suggesting that you should use that procedure, for it, too, is less than precise.

Bottom line here is unless one is flat broke, the cost of a cheap set of wires isn't beyond reach. What wires will do for you is worth far more than their cost, as a set of PeeDee wires will allow you to measure a wide variety of pitches, assuming you have micrometers for the ranges in question. Remember, shops that work to standards often pay for the real thing---and they're far more expensive, plus a set of those wires is good for just one pitch. Well equipped shops have a huge number of wire sets. For people like Glenn, they are a necessity.

If one must fit a thread, and the part need not be interchangeable with another similar product, it isn't unreasonable to simply make the part in question to fit the mating part. It may or may not comply with a standard, but it will fit. That's not necessarily true of cutting a thread by the thread depth, as the two chief variations that one faces are way too broad to allow a reliable result. That has been my point, and it makes a lot of sense when you consider that the flat of a threading tool has a broad tolerance, and it's highly unlikely that one would have the optimum width so the pitch diameter works out as hoped.

One thing that hasn't been mentioned. The double depth of a thread, as listed on a Starrett fishtail, is measured from a sharp V. We do NOT use sharp V threading tools, and for obvious reasons. So then, when you use the depth chart, how are you determining the proper surface pickup? Where do you start counting? Common sense tells me that you are generating undersized threads unless you have a correction for the lost tip length. See what I mean? Way too many variables for thread depth to be used as a reference to pitch diameter (which is generally the closest tolerance of a thread).

About the tolerance concerns of thread wires, couldn't there be some mitigation of that using comprehensive charts or a fancy Excel spreadsheet to figure things out?

Am I to assume that you are making reference to the tolerance of the wires in use as opposed to the tolerance of the pitch diameter? If so, while one can "do the math" and use a closely related size for measuring, sure, that can be done, but how much time do you think the average guy is going to spend on something like this? It's far easier to just use the prescribed size, for which there are known constants that are applied to the pitch diameters (max and min) for fast and easy measurements. Again, because modern production requires such things in order for projects to be successful, standards have been established. One need not adhere to them, but they sure make life easier.

I'm not well versed on threads, although I have always had to deal with them at a level acceptable by defense. If you'd like to bone up on them, perhaps learn the formulas that apply to thread calculations, you might explore obtaining copies of the H28 Handbooks. A lot more information in them than you can digest, including pitch diameters of threads and thread gauges in all classes. They won't lead you astray, while some of my comments risk doing so.

I'm afraid my old mind is not getting the picture here. Would you please elaborate, so I might better understand your point?
H

two square jaws (nuts) on the tool post. One has a combination left-/right-hand threaded stud. That assembly goes into the square slot in the spindle to grip the flats on the end of the tap, when you rotate that stud. You'll probably notice where taps have spun and chewed up the jaw's contact area.[/quote]

Because there has been failures of parts, I'd be inclined to make the entire assembly, and, yes, I'd single point the threads, assuming it was possible. The internal thread may be difficult, depending on the size. In this case, I'd make the male component first, then use it as a gauge for the internal threads.

Failure of the parts could be controlled by choosing the proper material. In this case, assuming one had a controlled atmosphere furnace (not likely), I'd probably choose 4140 material and heat treat to 50 Rc. You can achieve similar results by choosing, instead, 17-4 PH stainless, which is a precipitation hardening steel. It doesn't corrode, so a controlled atmosphere isn't a requirement, and it is quite stable in heat treat, as, in this case, you'd heat treat to an H900 condition (parts heated and held @ 900°F for a couple hours). No quench. This material is known to shrink about .0006"/inch upon heat treatment, so size isn't a real concern. If you were near I'd even donate the material, as I have it on hand.

H