1/2 x 28 UNF

mofosheee

mofosheee

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Lost in this rabbit hole. Rebuilding a vintage motorcycle engine and task with making various unobtainable threaded fastners.
I've searched the internet and am able to find data on 1/2 x 28 UNEF taps and dies. For reference I have been using;

1/2 - 28 UNEF : Thread Dimensions (Machining Doctor)

1/2 - 28 UNEF : Basic Thread Dimensions (Pitch, minor & major diameters, depth, lead), Tolerance range for all applicable classes and much more
www.machiningdoctor.com www.machiningdoctor.com
& I search for; 1/2 x 28 UNF taps and dies on Ebay or Amazon .................only UNEF flavors display.
I cut 1/2 x 28 threads on my mill........... and my 1/2 x 28 UNEF tap is reluctant to thread into this hole.
No data on 1/2 x 28 UNF or does it exist?

Thank you forum!
 
What class of threads are you trying to duplicate? Class 2A and 3A have United National Extra Fine threads slightly different major and minor diameters.

UNEF - 60 Degree Unified National Extra Fine Thread

torqbolt.com torqbolt.com

I doubt you'll find a UNF 1/2-28 tap or die in that the United National Fine tread designation is currently 1/2-20.

1/2 - 28 28-UN : Thread Dimensions (Machining Doctor)

1/2 - 28 28-UN : Basic Thread Dimensions (Pitch, minor & major diameters, depth, lead), Tolerance range for all applicable classes and much more
www.machiningdoctor.com www.machiningdoctor.com

I'm not sure how old the motorcycle is you're trying to restore. Thread standards changed several times over the years. I believe the most recent SAE standards for imperial threads were introduced in the late 1930s or early 40s. Prior to that many companies made proprietary fasteners to corner the replacement parts market. I have a lathe made in 1916 that has a number of proprietary threaded fasteners. The original owner (my wife's grandfather) had where withal to collect the necessary taps and dies needed for future repairs before they became so obsolete they would have to be specially made.

As an FYI many of the obsolete thread standards can be found in the 10th through 13th editions of the Machinery's Handbook. There are several copies available on eBay with prices starting in the $25.00 range.

ON EDIT: I responded to this thread earlier this morning when the only post was from the OP. There were 4 new responses when I returned, but mine was not one of them. I refreshed the page several times and my response finally appeared. It appears the forum is having several problems with access from different devices and posting responses from members. In addition, the links I posted to information about thread classes and thread types aren't active.
 
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You will not find a 1/2-28 UNF, it doesn’t exist, that thread pitch in 1/2” is UNEF.

How did you determine the thread you need for your application? There is a 1/2-27 UNS, is it possible you were off a bit when determining what threads you need to cut? Dimension data for that thread is in Machinery’s Handbook, or you can find it here too:

 
OTmachine said:
Not understanding how you cut threads on your mill, unless by thread milling. What dimensions do you need? Internal, external, P.D., tap drill size? I may be able to help.
Click to expand...
Using this cutter and program. Yes, I'm getting it. I don't know what I don't know. I should have stated that I wanted a 1/2 x 28 UNF to
check the threads I cut using the machine. 1/2 x 28 UNF only exist when I force it by a program
 

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