Thread's chamfer size 2

[elinah34]

Hey everyone,
I wonder if there is a standard or a common rule in which I can find what should be the chamfer size in a male (outer) and a female (inner) thread.
I remember that I heard that what matters is the pitch size, and by knowing it we can determine the chamfer size.

 

[JohnRBaker]

I think the rule-of-thumb was that, in the case of a male thread, that the flat area was equal to the minor thread diameter. For a female thread, it was that the outer diameter of the chamfer would be equal to the major thread diameter.

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
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[BrianE22]

One common rule for tapping is to chamfer to a diameter = screw thread major diameter.

 

[JS_]

On hardened materials you need to counter bore a couple thread leads to prevent thread tear out on the edges...

 

[JohnRBaker]

Counter-bore or counter-sink?

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[mfgenggear]

it is very perplexing that I could not find this in my machinist handbook.

here is a link. this is similar to what I use.

https://www.pmpa.org/knowledge-tool.../table-of-contents/thread-relief-and-chamfers

 

[JohnRBaker]

Bad link...

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[elinah34]

It seems there isn't some definite rules, at least based on the varied answers.
mfgenggear - thanks, I read it carefully but it seems that these chamfers can be afforded when you have a lot of threaded length, but when trying to use these rules when you have a short nut - about third of it is "wasted".

 

[mfgenggear]

elinah34
sorry about the broken link. yes the typical for lead in on holes is 1-1/2 threads, for a nut depending on the width it varies.
most of my customer had their own internal requirements. for tapped holes I would use a counter sink , external threads a chamfer.
generally rule of thumb as well as others said internal thread minor diameter plus .015-.020 per surface. in your case need to evaluate
and leave enough threads for strength. I would suggest a small counter sink to assist with the tapping cycle as a lead in.

 

[drawoh]

elinah34,

What is the context of your question?

Any time I drill and tap a hole, I use a bigger tool, usually a drill, to clean up the edges of the hole. I do this fairly quickly by hand, and I check it for burrs, not dimensions. I don't know what real machinists do. I have never had cause to worry about it.

Your drawings should specify that sharp edges and burrs must be removed. If you want to call up a chamfer, call up something that meets your requirement.

--
JHG

 

[elinah34]

I have a low profile 10-32 manufactured nut, and its height is about 3 mm. If you calculate how long the thread is if we follow the guidelines above we will be left with a short thread - less than 3x lpitch

 

[drawoh]

elinah34,

If this is a nut you are designing, you need to control the number of threads. Perhaps you need a section view specifying the minimum effective thread length. Perhaps you need a thicker nut. Perhaps you need to calculate and specify screw torque. Perhaps you need to specify a high strength material for your nut.

--
JHG

 

[mfgenggear]

I agree with Drawoh left out important information. the reason to chamfer or counter sink
lead in for tapping or threading
if no break a sharp thread will be present, and subject to damage
.118 inch (3 mm) thickness may not be sufficient, depending on the application.
OK if we may ask why is this nut so thin.

 

[elinah34]

mfgenggear and drawoh - thank you for your answers. I have a limited space (I have no access to my CAD, since it's in my work's computer, and that's why I don't add a cross section photo for explaining better) in which I have to adjust a custom nut...that's the reason I need a 3 mm height 10-32 custom nut. I know it's not ideal, and I hardly have 3 threads participating in the tightening - but this is a constraint I have to deal with. So limiting the torque might be the compromise.
Is the only aim of the countersink in a threaded hole is easing the engagement of the threads (male and female)? If the answer is yes, I guess the countersink size isn't that important...

 

[Compositepro]

The countersink is not essential, but it does greatly ease the alignment of parts for engagement of the threads and removes the fragile parts of the thread that get easily damaged.