Metric series Threads

[Larry1958]

I am having some issues our Quality Control Dept., I have parts that have a M26 X 1 4h/4h 4start external thread callout. I have always machined threads using a partial profile threading insert. I am being told that my Minor Dia. Min. is undersize and they are rejecting my parts. It is specified to be 24.654mm and I am out about .1mm undersize. I have always assumed that major Diamter, pitch diameter, and minor max. was all that was critical and minor min. was simply a reference unless there's a thin wall condition. Am I wrong? Can anyone stear me to a standard. I know that a UN callout minor diameters are a calculated reference but cant find that on Metric series. Thanks in advance for all the help with this.

[Philcott]

Larry, am I missing something?

 

You say your minor diameter max is .1 undersize... is it still bigger than the minor Diameter minimum? If so, is'nt the thread on spec?

 

Also, on an external thread, minor diameter max, is important, so there isn't interference with the internal minor diameter minimum.

[Larry1958]

Phil,

 

Sorry, I was discumboobiated. Just made edit to original post. Does it make more sense now?

[JerryBenoit]

Larry,

 

What are the specs on your customer print? How is it clalled out, do they just call the thread and class or do they provide the pitch, major, and minor diameter also. I have found looking at a thread callout that they made modification that might be out of the norm. So with getting burn once I allways look at the complete form. Case in point, I had one thread that was a special. They called out the pitch daimeter with .01" total tolerance, however, after looking at the minor diameter and the root radius we had .002" to get the pitch and minor to fit within there spec.

 

You might also want to make sure that you are using an insert that will produce a root with of .250mm. which is what they call for in a class 4h, you are using a class 6h, you should be fine.

 

Jerry

[Larry1958]

Larry,

 

What are the specs on your customer print? How is it clalled out, do they just call the thread and class or do they provide the pitch, major, and minor diameter also. I have found looking at a thread callout that they made modification that might be out of the norm. So with getting burn once I allways look at the complete form. Case in point, I had one thread that was a special. They called out the pitch daimeter with .01" total tolerance, however, after looking at the minor diameter and the root radius we had .002" to get the pitch and minor to fit within there spec.

 

You might also want to make sure that you are using an insert that will produce a root with of .250mm. which is what they call for in a class 4h, you are using a class 6h, you should be fine.

 

Jerry

Thay do call out Major Diameter, Pitch Diameter, and Minor Diameter ranges. However I have always thought that when checking the minor you just want to be sure that minot max. does not exceed requirments (Gaging at Maximum Mat. condition), and min. is just a reference.

[JerryBenoit]

Larry,

 

here is the norm on that thread callout I also provided the class 6h. The info is from gage maker.

 

Jerry

Thread Class 4h & 6h.pdf

[Larry1958]

Larry,

 

here is the norm on that thread callout I also provided the class 6h. The info is from gage maker.

 

Jerry

Thanks. I use the same but have always pretty much ignored the Minor Min. in the past. It is not our customer that is rejecting the parts but rather our Q.C. dept.

 

I have always thought that the Depth of thread did not matter, This is why they manufature inserts that can cover a range of pitchs.

[JerryBenoit]

Larry,

 

To an extent, yes you are right. However, looking at Kennametal and Sandvik both make their insert to a class 6h thread but they use different standards. While both may cut the thread. The form may be slightly different then want your engineer wants. There is also the possibility that there could be a mistake on the print. Like I mentioned before, in that case, the engineer did make a mistake and we caught it before it was cut.

 

Jerry

[K2csq7]

have always pretty much ignored the Minor Min.

 

I have always thought that the Depth of thread did not matter,

If it's on the print, you know it has to be in spec.

 

Sounds like you have a good Q.C. dept. You know the course of action that needs to be taken.

 

You simply need to tell the customer what you have. It probably wont affect the function of the part, but you have to follow the rules.

They gave you a tolerance, your parts are not inside that tolerance. Black and white to me.

 

Thay do call out Major Diameter, Pitch Diameter, and Minor Diameter ranges.