thread nomenclature 2

[mielke]

for UNC external threads are the root diameter and minor diameter the same thing?

 

[KENAT]

Without taking a look at ASME B1.1 I can't remember for sure but I'm inclined to say NO.

The root radii is, if memory serves, the radii at the root of the thread form.

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[MintJulep]

No.

http://en.wikipedia.org/wiki/Unified_Thread_Standard

 

[mielke]

wiki does not talk about 'root diameters' but from their image is it the same as Dmin?

 

[KENAT]

Let me try again.

Root radii the the radius at the bottom of the 'saw tooth' shape you see if you like at a thread from the side/section it through the middle.

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[MintJulep]

No.

Dmin is (essentially) the MMC of the male thread profile.

 

[CorBlimeyLimey]

mielke,

The wording you've used is a little ambiguous. For the intent of the question you've asked (ie. the diameter measurement across opposite root radii), the answer is yes, they are the same. Root and Crest dia's equate to Minor and Major dia's.

But as KENAT is trying to point out, the use of the term root dia can be somewhat misleading. The root is the curved portion at the bottom of the thread form. That curvature 'could' be expressed as a diameter.

 

[MintJulep]

The minor diameter is a basic dimension necessary for definition of the thread profile.

ASME B1.1 distinguishes between the basic profile and the design profile since the basic profile is difficult to manufacture (essentially impossible for rolled threads).

The design profile allows for rounding of the root of an external (male) thread such that the root diameter will be smaller than the basic diameter.

 

[Cockroach]

Root and minor are the same diameters. "Root diameter" is just the venacular for "minor diameter", but specifically applies to the external pin.

You have a crest diameter in a box, a root diameter on a pin.

That sort of thing....

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[metalonis]

I agree with Cockroach. I've always considered "root" diameter and "minor" diameter of an external thread to mean the same thing.

 

[ione]

Take a look at the link below

http://www.roton.com/glossary.aspx#

 

[KENAT]

I'm not convinced 'root diameter' is good terminology, and certainly don't see it in a quick browse of ASME B1.1. Doesn't mean it's not used in an ISO or something somewhere I know.

Simplistically it might be taken as similar to the minor diameter but I'm not sure it would hold up in court.

I'd also avoid using it because of the potential confusion with root radii.

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[ornerynorsk]

Root and minor are NOT the same thing. In generally accepted practices, Root refers to the actual, whereas minor is a more theoretical dimension. See the diagrams in Machinery's Handbook for clarification.

 

[KENAT]

ornerynorsk, that was kind of my thinking, but the one reference I looked at didn't even appear to have it used that way.

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[CorBlimeyLimey]

From

http://www.roton.com/glossary.aspx

Root Diameter
A term referring to the minor diameter of a screw thread or the major diameter of a nut thread. Root diameter has been replaced by the more accurate terms "major diameter" and "minor diameter". See discussion of major and diameters diameters in the Identifying Screw Threads section.

Minor Diameter
On a nut thread, the minor diameter is the diameter of a cylinder formed by the crests of the nut threads. On a screw thread, the minor diameter is the diameter of a cylinder formed by the roots of the threads. Formerly, the minor diameter was called the "root diameter" and it still commonly referred to as root diameter. See the Minor Diameter entry in the Identifying Screw Threads section for more details.

 

[ione]

CorBlimeyLimey,

There must be an acho somewhere (see my post 28 Jul 10 8:47)

 

[CorBlimeyLimey]

I guess there is. Sorry, I overlooked your post.

 

[ione]

No bother

 

[CoryPad]

ISO 5408 Screw threads - Vocabulary, second edition from 2009 has the following definitions:

root diameter (D, d₁, d₃, D₄): diameter of an imaginary cylindrical or conical surface tangent to the roots of a screw thread

Note 1 - For external thread, the root diameter is the minor diameter. For internal thread, it is the major diameter.

minor diameter (D₁, d₁, d₃): diameter of an imaginary cylindrical or conical surface tangent to the roots of an external thread and/or to the crests of an internal thread