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Author Topic: Correct thread sized tap?  (Read 190 times)

Nvreloader

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Correct thread sized tap?
« on: December 25, 2017, 01:21:11 PM »
Bob

What would be the correct size of tap/die for the ASA threads of a standard air tank?

I have been told several sizes, like 7/8"x14 tpi, 13/16" x 14 ttpi etc,
the thread measurements of the type of threads I have are, .623 to .628 dia x 14 tpi.

Thank you,
Don


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rsterne

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Re: Correct thread sized tap?
« Reply #1 on: December 25, 2017, 07:09:52 PM »
ASA threads are 1/2" - 14  NPS (straight pipe threads).... They are sometimes called 0.820"-14 TPI.... I assume you are talking about the threads on a CO2 valve, or the end of a regulator output.... I have done lots of these using a 1/2" - 14 NPS tap.... most recently on my 6 mm tank block.... The recommended tap drill size is 47/64" but if your tap has lots of taper and you are careful (back it out often) you can use a 3/4" tap drill....

Bob
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Nvreloader

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Re: Correct thread sized tap?
« Reply #2 on: December 27, 2017, 06:52:25 PM »
Thanks Bob

That helps a lot,
Have some adapters to make.... ;)

Tia,
Don

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Bob La Londe

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Re: Correct thread sized tap?
« Reply #3 on: December 28, 2017, 08:05:01 AM »
"Tap Drill"  ?? 

I have a few tap drills, but with the drill tip and then the taper of the tap they are extremely long for their size.  I would think they would not work out well for adapters.  If you meant a tapered hand tap (not bottom or plug) then sure probably.  You can also start it with a tapered hand tap, and finish it with a bottoming hand tap. 

By the way a tap drill is considered a machine tap, not a hand tap, and inspite of the fact that the tap portion is spiral flute its still rarely (maybe never) used for applications where you are not drilling and tapping through. It has to be spiral flute to help clear the chips from the drill point.  They work well in a tapping head (within its speed range) where the material is thinner than the drill portion of the drill tap and the clutch of the tapping head can save you from expensive mistakes... Sometimes.  In a production environment you can have them custom made to your application. 

I happen to like machine taps even for hand tapping, but the average home shop is not likely to have more than a selection of hand taps.  I keep a small selection of spiral point, spiral flute, and forming taps in all my most commonly used sizes. 

If I was making adapter(S) I'd probably thread mill them with spiral interpolation and a single point multi flute thread mill before I took them off the mill, but that's really outside the scope of the average home shop (not all home shops of course). 

If I was doing them on the lathe I'd probably single point them, but that's a pain and just as time consuming as hand tapping unless you are really good.  (Yes I could thread an offset adapter block on the lathe.)  However, you will likely not have to worry so much about the one big issue with hand taps.  Making sure you get it started perfectly straight. 

I use my drill press, a vise, and a center in place of the drill chuck for a tapping guide if it has to be really good and I have to use a hand tap... or I can hand tap on the lathe too... or die thread.  Or machine tap at low speed. 

Anyway, getting it started straight is the big deal for any kind of tapping. 

Sorry.  Went off on a tangent there.  I was just curious if you really meant tap drill. 
« Last Edit: December 28, 2017, 08:07:47 AM by Bob La Londe »
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rsterne

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Re: Correct thread sized tap?
« Reply #4 on: December 28, 2017, 08:19:55 AM »
By "tap drill", I simply meant the size of the pilot hole that you drill before using a tap.... Perhaps I used the wrong term?.... If so, I'm in good company, because is you Google "tap drill size" you get chart after chart of tap sizes, listed with the appropriate drill to use before you use the tap.... and that column is frequently marked "tap drill"....

I have seen taps that have the pilot drill built in, but have never used one.... and didn't even know they were called "tap drills".... When I Google trying to find them I get "drill taps" aka "draps"....  ???

Bob
« Last Edit: December 28, 2017, 08:26:37 AM by rsterne »
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Bob La Londe

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Re: Correct thread sized tap?
« Reply #5 on: December 28, 2017, 08:49:42 AM »
That is of course the problem with descriptive nomenclature.  It sees drift over time based on usage.  A tap drill chart shows taps sizes and drill sizes.  I have one in in my quick reference binder I use in the shop.  A tap drill chart does not show "tap drills" as the existence of the chart would be redundant, but it does show "tap" drills.  LOL

You would be amazed how many people only know about hand taps, and think they are called starter tap and finishing tap.  LOL. 

Tap drills are pretty common in hex drive as cordless drill motors and cordless hex drives that seem to be where they are most often used to drill and partially plug a hole when it breaks off.  https://www.toolnut.com/dewalt-dwadt5set-impact-ready-5-piece-drill-tap-bit-set.html?utm_source=google_shopping&gclid=EAIaIQobChMI0-qKiZSt2AIVkYl-Ch01EApXEAYYAiABEgJoafD_BwE  Came up in the ads at the top when I searched for Tap Drill.  Usually they are referred to in some form of "combination" in most consumer ads and catalogs. 
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rsterne

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Re: Correct thread sized tap?
« Reply #6 on: December 28, 2017, 10:19:50 AM »
To be clear, I only use hand taps, mostly plug, followed by a bottoming tap if necessary.... I seldom use a full taper tap, as I find the plug tap starts straight when I use a tap handle with a pilot on the back end, held (loosely) in my lathe chuck as a guide.... I will continue to use the term "tap drill" in my threads when referring to the pilot drill I use before tapping a hole.... as that seems to be common usage now....

with apologies to historical usage....

Bob
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Nvreloader

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Re: Correct thread sized tap?
« Reply #7 on: December 28, 2017, 07:21:32 PM »
Thanks Guys, Great info.

The reason for my question was, I have numerous adapters, from the JT 88g type to Co2/Hpa standard tank/bottles sizes,
they run from .800" (smallest diameter) to the large end at .829" dia, most run .820"/.825" size bracket,diameter across the threads tops.

I have to make a couple Co2 transfer adapters/couplers, 1-1/4" hex alum, going to transfer some of those 88g Co2 cyl into a larger tank, for less messing around etc.

Tia,
Don
  • Western NV
NRA Life member

"We must reject the idea that every time a law's broken, society is guilty rather than the lawbreaker.
It is time to restore the American precept, that each individual is accountable for their actions"
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Bob La Londe

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Re: Correct thread sized tap?
« Reply #8 on: December 29, 2017, 06:48:48 AM »
To be fair most machinists I know would think I was talking about the drill (many object to the term bit) for a hole to be tapped if I said tap drill. 

If I said drill bit they might say, "A bit is either a lathe bit or a brace bit or a piece that goes between the teeth of a horse." 

Now technically a brace bit is a drill, but according to some machinists a drill is just a drill.  Its not a drill bit.  LOL. 

Drill Makes a Hole (Not all things that make holes are drills.  LOL)
Drill Motor Turns a Drill
Drill Press Turns a Drill
Hand Drill Turns a Drill
Brace Turns a Brace Bit

Its really not so much historical usage, but common vs shop usage and sometimes type of shop.  Many a young machinist will have no clue what a brace is because its not typically used in a machine shop.  He might think its the same as a gusset.  He would be wrong of course since a gusset is a piece of fabric that reinforces clothing.  LOL. 

Then there are the other things...  Go into your local box hardware store and ask for a star drill.  (Its not called a bit either LOL.)  Wait for the confused look on the face of the young associate trying to help you.  If he or she is quick they might say, "We don't have that brand, but we have DeWalt and Milwaukee."  LOL.  If you are lucky enough to find an older associate the light may dawn and they may say, "I don't think they make those any more." 

As long as I am off ranting in nowhere land how about a laser drill.  Or a sonic drill.
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rsterne

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Re: Correct thread sized tap?
« Reply #9 on: December 29, 2017, 09:24:23 AM »
I have actually used a star drill.... and a brace and bit.... I still have a few bits, but no brace any more....

Is my age showing?....

Bob
  • Coalmont, BC