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Quick Question About Thread Plugs.

JoshJay

Plastic
Joined
Apr 20, 2018
Why do thread plugs have the notch in the go plug? (I can make some obvious guesses but I'd like to hear from you)
 
Why do thread plugs have the notch in the go plug? (I can make some obvious guesses but I'd like to hear from you)

Do they? I don't recall seeing one. Personally I prefer my threaded components without burrs.

Is this common in the USA or do other countries have this too?
 
I can't imagine a precision gage being used to de-burr anything. I know the notch you are talking about but have no idea what it's purpose is. I'll try to post a picture later, I have often wondered myself
 
thread notch doesnt make it a tap. it is so you do not get a bad reading. the no go can not go in and you think its ok but its really a burr you cannot see. once burr gone if no go goes in you can get different reading
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or it is rusted chips still in hole. hole can be blown out 3 times and still have chips in it and after a week it can make a screw or thread gage hard to screw in. you want to check a $10,000 part with thread gage. you dont want a bad reading cause it has a few rusted chips in the hole.
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no gage lasts forever there is a wear element. like gage blocks used to check slot width it wears the gage blocks over time. all gages checked every year for excess wear. those that do not pass inspection are removed from use. i have used thread gages 1000's of times. never had one wear out. not saying after decades it wont wear out. yearly inspection i believe is mostly to catch damaged thread gages that got dropped or damaged some how.
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parts unclamped often have holes go out of round. obviously thread notch in thread gage not going to cut the threaded hole round again like a tap would. 99% of time thread gage is to catch a hole like a pipe thread thats not deep enough. big pipe thread trying to hand tap can easily move a 200lb part thats sitting on a pallet. a lot easier to do part still clamped in fixture. even screw threads the bigger ones often check out as needing to be tapped deeper after checking with thread gage. again easier to hand tap deeper still clamped in fixture. tap handle might be 30" or 40" long. obviously hand held thread gage you not going to tap a big hole deeper
 
I've just thought of a plausible reason for a notch. A blind threaded hole with a tightish thread (especially long) might give a problem with "compressed" air.
 
I think it's just to help get crud out of the thread before the gage goes thru so the gage lasts longer. Also, why you don't need one on the no-go end. It doesn't, or shouldn't, get threaded into anything.
 
I think it's just to help get crud out of the thread before the gage goes thru so the gage lasts longer. Also, why you don't need one on the no-go end. It doesn't, or shouldn't, get threaded into anything.

So it's OK if "crud" stops the NoGo gauge? Who doesn't "clean" the thread (normally a quick blow with compressed air) before gauging?
 
Gordon - I've had operators come get me because of machine alarm, and they can't even hand jog it. Go over to the machine, quick look, "Hey, you have so many chips piled behind the table that the machine can't physically move any more".

I'm glad you work with good machinists, but "who wouldn't clean the thread first?"

Lots of operators. Lol. But hey, at least they are gauging the parts.

Plus clean is a relative term. The 1st shop I worked ran a lot of cast iron housings. There was a deburr/gage bench. The deburring was done with abrasive tools. So of course there was abrasive particles and cast iron dust everywhere. They blew off the parts, but it would never be what you and I would consider clean. Compared to where I work now I would say "oh my goodness, what a dungeon".

But at the time I worked it seemed fairly clean. I worked my way thru community college classes for machining at a large grey iron foundry, so that shop seemed clean comparitvly at the time.

And even with blowing out the holes at that 1st shop, the thread gages still had to be replaced every couple months. The amount of use they got combined with the environment wore them down pretty quick.

I think most lost cost production environments are going to be fairly similar to that.
 
Gordon - I've had operators come get me because of machine alarm, and they can't even hand jog it. Go over to the machine, quick look, "Hey, you have so many chips piled behind the table that the machine can't physically move any more".

I'm glad you work with good machinists, but "who wouldn't clean the thread first?"

Lots of operators. Lol. But hey, at least they are gauging the parts.

Plus clean is a relative term. The 1st shop I worked ran a lot of cast iron housings. There was a deburr/gage bench. The deburring was done with abrasive tools. So of course there was abrasive particles and cast iron dust everywhere. They blew off the parts, but it would never be what you and I would consider clean. Compared to where I work now I would say "oh my goodness, what a dungeon".

But at the time I worked it seemed fairly clean. I worked my way thru community college classes for machining at a large grey iron foundry, so that shop seemed clean comparitvly at the time.

And even with blowing out the holes at that 1st shop, the thread gages still had to be replaced every couple months. The amount of use they got combined with the environment wore them down pretty quick.

I think most lost cost production environments are going to be fairly similar to that.

Brian, a quick blast of air just to clear the thread as much as possible is usually all it takes.

I think the "distance" between or good and bad machinists here is much less than it is in the USA. Part of the reason (and invaluable) is that all machinists here have gone through technical school/college plus as good as all have gone through an apprenticeship. "Slobs" either just don't get hired or last long. Add to that then I doubt if any many machinists will start with less than $30 an hour plus of course all get the 5 week paid vacation, "free" healthcare etc.

Also relevant. As good as all measuring equipment is company supplied and handled with care.

As to how fast your thread gauges wear out then I'm as good as certain it's because operators try and put them in/on too tight threads. Measure the pitch diameter and you'll know where you are in the tolerance. It's much bigger than most realize.

http://f-m-s.dk/2.03.pdf

http://f-m-s.dk/2.03 - inch version.pdf
 
I agree with you Gordon. All things I would expect of a "machinist".

Any quantity of parts the goal is usually set up the job so to use the minimal skill possible. Probably largely due to the lack of actual machinists(which I would define as someone who can take a print and material and fill in all the other blanks themselves).

The shop I work in now is all machinists. No operators. Floors are painted white and the whole 9. Much more fun and challenging work, and the quality expectations are much higher. I like it a lot, but is certainly different than you might say "commodity" machining. I never even simply drill minor diameters any more. Even those are always interpolated and checked with gage pins. To much time into parts and tolerances too tight to risk it. It is more of what I always think of as a "European(german in particular)" shop. I always wonder if the Germans are good at "marketing" or if the average shop there is much more precise than the average shop here? Any thing I've ever used from Germany is always very nice, I will say that.
 
got news for many if not all the chips are blown out of a hole after a few days the chips will start to rust solid and all the air blowing in the world aint going to get them out.
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many obviously aint had a chip lugger full of chips rusted to a solid mass weighing easily over 1/2 ton requiring a 40" long air hammer chisel to break the mass into smaller chunks. or using 6 foot prybar to breakup mass of rusted chips
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and no hand held anything whether tap or thread gage with small size handle going to allow tapping a hole that might normally require a tap handle 12 to 60" long
torque like 20in/lbs on thread gage and 20,000in/lbs on a big tap
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bit of a difference in torque
 
I'm surprised no one has commented my post #8.

I've just thought of a plausible reason for a notch. A blind threaded hole with a tightish thread (especially long) might give a problem with "compressed" air.

I'm certain a plug thread gauge has never been made to also clean a thread. I have seen and experienced thread plug gauges (and ordinary plug gauges) that required patience because of compressed air in a blind hole.
 
That notch is a cheap easy way to "blunt start" or "block" remove the imperfect thread to the first full profile of the thread on the manufacture of a thread gage. True, it catches crud when entering the thread gage into the thread. And true, it's used for determining if a thread is cut deep enough, length wise to to qualify to the dimension given on the engineering drawing or work instructions for that given part.

Ken
 
That notch is a cheap easy way to "blunt start" or "block" remove the imperfect thread to the first full profile of the thread on the manufacture of a thread gage. True, it catches crud when entering the thread gage into the thread. And true, it's used for determining if a thread is cut deep enough, length wise to to qualify to the dimension given on the engineering drawing or work instructions for that given part.

Ken

It could be used for that purpose but why then the entire length of the Go thread? Has anyone ever seen a similar notch on a Go thread ring?

Is this something you know for a fact or, like me with "avoiding compression in a blind hole", taking a guess?

If threads needed "cleaning" to be inspected what about those that weren't inspected? The Go thread gauge is after all at the bottom of the tolerance and should go in easily. If not then your external thread (screw, bolt etc.) will have a bigger problem.

I'm trying to imagine the reply from a customer who rejects the parts and is asked, "Did you try with a notched thread plug gauge?"
 
It could be used for that purpose but why then the entire length of the Go thread? Has anyone ever seen a similar notch on a Go thread ring?

Is this something you know for a fact or, like me with "avoiding compression in a blind hole", taking a guess?

If threads needed "cleaning" to be inspected what about those that weren't inspected? The Go thread gauge is after all at the bottom of the tolerance and should go in easily. If not then your external thread (screw, bolt etc.) will have a bigger problem.

I'm trying to imagine the reply from a customer who rejects the parts and is asked, "Did you try with a notched thread plug gauge?"

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hole is normally blown out 3 times. holes will look clean. notch is for small particles no average human can see that might give a false ok. that is the no go might not go in cause .001" of a burr or metal dust not seen
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if that little notch helps no go to go in proving threads are too big and out of specs then it is worth having the thread notch.
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when you machine many metals you get a fuzz on surface that many will use nylon abrasive on OD parts to remove the fuzz and then wipe with a rag and it appears as black dust. obviously on internal features it is not as easy to clean. like when boring a hole to +/-.0001" tolerances that fuzz can easily give a false reading. is there a technical term for fuzz ??
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nobody saying to force the thread gage in the hole. if it turns hard obviously use a tap first to clean out the hole. some of us actually worry about .001" or less of stuff that is not easily seen. notch is for rust too not easily seen
 
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hole is normally blown out 3 times. holes will look clean. notch is for small particles no average human can see that might give a false ok. that is the no go might not go in cause .001" of a burr or metal dust not seen
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if that little notch helps no go to go in proving threads are too big and out of specs then it is worth having the thread notch.
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when you machine many metals you get a fuzz on surface that many will use nylon abrasive on OD parts to remove the fuzz and then wipe with a rag and it appears as black dust. obviously on internal features it is not as easy to clean. like when boring a hole to +/-.0001" tolerances that fuzz can easily give a false reading. is there a technical term for fuzz ??
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nobody saying to force the thread gage in the hole. if it turns hard obviously use a tap first to clean out the hole. some of us actually worry about .001" or less of stuff that is not easily seen. notch is for rust too not easily seen

I'm at a loss to understand where you're going with that. I'm guessing what you have in mind is a single threaded item. I'm not.
Either someone in the company is going to have problems assembling or worse yet, the customer.

Clean with a tap? Why even bother with a gauge if a tap can be found?

Rust? How long do you think most wait before inspecting? I don't know how common your thinking is in the USA but if it is then it helps me understand if the USA is sinking in the "battle" for quality. I'm guessing you've never tried delivering anything to Japan.

Personally I don't remember ever seeing a thread plug gauge with a notch. Now you also seem to be suggesting that a NoGo thread also has a notch. How common are they in the USA or anywhere else? How often have you made and inspected threads? I'd put my number at "thousands".

I'll try again. A Go thread plug gauge is at the lowest part of the thread tolerance. If it can't just be screwed in then what about screwing in a bolt?

There you go again with the ±0.0001" tolerance. Remind me again what you work with or have worked with?
 








 
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