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NPTF Thread Quality check (Internal Thread)

daniep

Plastic
Joined
Sep 20, 2021
Hi,
We received a print from our customer that has a 1/4 NPTF thread. Now, we are not sure how to use L1, L3, and 6 Step gauges in tandem.
We have seen some online videos and read some articles as well, however, we are not clear on these 2 points.

1) How do we know what is Basic, Minimum, and Maximum from the L1 guage?
2) How do we determine the same with the L3 gauge?
 
If its internal thread use the correct tap or threadmill and check depth with gage.

If its external use the proper insert and check diameter with ring gage.

Dont overthink it.
 
1. The flat on the gauge is Basic. It should be flush with the top of the hole. One turn out is MIN, One turn in is MAX. Some gauges have 3 steps labeled as such. Anything beyond 1 turn is not within tolerance.

2. Once you determine what the L-1 gauge measures, the L-3 gauge has to read the same within 1/2 turn. If the L-1 measures 1 turn out, or MIN, the L-3 should be within 1/2 turn of the MIN. If the L-1 measures MIN, and the L-3 measures MAX, your taper is off.
 
I have a threadmill for 1/4 nptf from lakeshore that cuts internal threads incorrectly, despite being labeled for internal nptf.

I'll get the L1 right at basic, but the 6 step gage will be a tiny bit past the maximum MX depth.

One customer we do work for didn't mind, they dope up the threads and could be NPT for all they cared. But for other work, I can't use those threadmills and I have them labeled as such in the drawer.

So yeah, just making it to basic depth with the L1 might not cut it depending on what you're doing it for. Good on you for actually inspecting it, LOL.
 
I guess that I should re-word that as that there are NPT answers above for a NPTF question.
Obviously many have no clue what "Dryseal" is.

If you are tapping, then your taper is likely fine unless you are off center, but doo you have the 6 step profile gauge?


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Think Snow Eh!
Ox
 
Last edited:
Boy, quite the range of experience in this thread....

Follow post #3 for best results.


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Think Snow Eh!
Ox
I'll admit I glossed over the F in NPTF in my earlier post.

L1 is good for NPT but to truly check an NPTF for proper taper angle you must use the L3 in conjunction with the L1

Post #3 describes this better than me.
 
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Last time I had an PO & drawing that had 1/2" NPTF, I went out and purchased the gages.
Called the customer to ask about something unrelated, and got to talking about 'dryseal' or 'Gas Thread' You know, NPTF threads?
He said "What is a dryseal thread?"
I replied "What your drawing calls for...;)"
Him "Oh, I meant 1/2" NPT Female."
:dopeslap:
 
1. The flat on the gauge is Basic. It should be flush with the top of the hole. One turn out is MIN, One turn in is MAX. Some gauges have 3 steps labeled as such. Anything beyond 1 turn is not within tolerance.

2. Once you determine what the L-1 gauge measures, the L-3 gauge has to read the same within 1/2 turn. If the L-1 measures 1 turn out, or MIN, the L-3 should be within 1/2 turn of the MIN. If the L-1 measures MIN, and the L-3 measures MAX, your taper is off.
Hi,
We have 2 notches on our L1 gauge. Per our conversation with the Baker team, they told us that the 2 notch are minimum and maximum. How do we determine the basic notch here based on the number of turns on the gauge.

Also, we have 3 step L3 gauge. So we don't have one single notch but there are 3 notches on the gauge which makes it difficult for us to assess which is minimum, basic, and maximum.
Do you have any idea how that works?
 
I guess that I should re-word that as that there are NPT answers above for a NPTF question.
Obviously many have no clue what "Dryseal" is.

If you are tapping, then your taper is likely fine unless you are off center, but doo you have the 6 step profile gauge?


View attachment 397625

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Think Snow Eh!
Ox
Hi,
We are using the 6 step gauge as well. Using 6 step gauge is easy since there are clear markings on the gauge.
However, our L1 gauge has 2 notch and L3 gauge has 3 notches. And hence we are facing issues in determining whether the threads are minimum, basic, or maximum.
I am attaching photos here for reference.
There are 4 photos here:
L1 gauge with Notch 1 (Minimum)
L1 gauge with Notch 2 (Max)
L3 gauge with Notch 1&2 (Not sure how this works)
L3 gauge with Notch 2&3. (Not sure how this works)

It is not clear from the photo that you shared. Do your L1 and L3 have multiple notches, or does it have a single notch (for Basic) ?
 

Attachments

  • L1 Gauge Notch 1 .jpeg
    L1 Gauge Notch 1 .jpeg
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  • L1 Gauge Notch 2.jpeg
    L1 Gauge Notch 2.jpeg
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  • L3 Gauge Notch 1 & 2.jpeg
    L3 Gauge Notch 1 & 2.jpeg
    150.8 KB · Views: 14
  • L3 Gauge Notch 2 & 3.jpeg
    L3 Gauge Notch 2 & 3.jpeg
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Last edited:
Call gauge manufacturer tech support.

Yeah, if you don't haver the cert that came with it to tell you what's what, then you may need to call the mfgr and ask what they mean. But IDK who "Blake" is?

I for one don't believe that I have seen that many flats on those before.


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Think Snow Eh!
Ox
 
Hi,
We have 2 notches on our L1 gauge. Per our conversation with the Baker team, they told us that the 2 notch are minimum and maximum. How do we determine the basic notch here based on the number of turns on the gauge.

Also, we have 3 step L3 gauge. So we don't have one single notch but there are 3 notches on the gauge which makes it difficult for us to assess which is minimum, basic, and maximum.
Do you have any idea how that works?
Basic is theoretically perfect. Min and Max are allowable tolerance from Basic (one full turn each way)

For the 2 step gauge, there should be exactly 2 turns between each step. Basic would be right in the middle (one full turn from each)

For the 3 step gauge, Min is closest to the end of the gauge, Basic is in the middle, and Max would be closest to the handle.
 
I have never seen 2 step gauges either. I assumed from the previous post that the Blake Team is referencing the manufacturer, who confirmed these reference Min and Max.

3 step gauges are a little more common. I have a few myself from Emuge.
 
Basic is theoretically perfect. Min and Max are allowable tolerance from Basic (one full turn each way)

For the 2 step gauge, there should be exactly 2 turns between each step. Basic would be right in the middle (one full turn from each)

For the 3 step gauge, Min is closest to the end of the gauge, Basic is in the middle, and Max would be closest to the handle.
What range will be for Basic?
Between Min and a Basic notch or between Basic and Maximum notch
 
What range will be for Basic?
Between Min and a Basic notch or between Basic and Maximum notch

If you keep that up, we all may end up cornfused.


Personally I am not overly used to the term "Basic", but Shirley that is just the means, or zero point. Not a range.
Meaning that the middle is the middle, and your range is above and below rthat X amount.

The key here is that you want your L1 and your L3 to match per depth - related to the means point.

If both gauges are a little deep - that is fine, but if one is deep and the other is shallow, then you have a problem.


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Think Snow Eh!
Ox
 








 
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