REALLY Interesting Treatise On Thread Restoration

Look around here for some great advice on getting the most out of your tools! Tips and tricks!
Post Reply
User avatar
ARCHINSTL
Highest Ranking Member
Posts: 6216
Joined: Sat Apr 30, 2005 1:52 pm
My tercel:: Goldie is a 1986 SR5 attualmente con Weber/also owned the first T4WD in STL in late '82
Location: Kirkwood, a 'burb of St. Louis

REALLY Interesting Treatise On Thread Restoration

Post by ARCHINSTL » Sat Jun 21, 2014 1:19 am

From Hemmings:
http://blog.hemmings.com/index.php/2014 ... /#comments

I heartily endorse the thread file; it saved my bacon on a control arm bolt. See http://www.tercel4wd.com/viewtopic.php?f=10&t=3267
I think this is a must-have tool!
Tom M.
T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"
"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

keith
Highest Ranking Member
Posts: 1235
Joined: Sat Sep 30, 2006 1:04 pm
Location: Tennessee

Re: REALLY Interesting Treatise On Thread Restoration

Post by keith » Mon Jun 23, 2014 10:45 am

Unfortunately that article is missing all information concerning thread forming dies, also known as restoring dies. Most tap and die sets used in the US are cutting taps and dies, that is they work by removing metal. These work on all types of metals.

In Europe, thread forming dies are often used on softer metals such as aluminum and mild steel. they do not work on harder grades of metal. Let me explain the difference in the taps, the dies work the same way except for the gender switch. In any thread, you have the minor diameter and the major or nominal diameter. The minor diameter is the size of the largest roll pin that you can drop into the hole after the thread is cut. The major diameter is the diameter of the outsides of the thread, which you cannot effectively measure in the hole, you can measure it on the bolt though.

Typically you drill a hole about the size of the minor diameter, the tap then cuts away the material to form the threads. In a thread forming die, the hole is much larger, about half way between the minor and major diameters. The tap is made from a very hard material and it pushes the metal around to form the threads. This makes a thread that is quite a bit stronger than a cut thread. This can be critical in aluminum.

If you cross thread a hole, or strip it, sometimes a roll forming die will restore the threads enough to be useable. Another benefit is that the roll forming dies don't create many chips as it isn't cutting the metal. You can rent roll forming dies at O'Rielly's auto parts, actually borrow them with a big deposit which is 100% refunded on return. i would do this before using any of the other techniques in that article.

For mild steel and aluminum, sometimes a high grade (grade 8 sae or 12.2 metric) will work like a roll forming die, but they work best if the bolt has a "nose" on it, that is a non threaded starter or centering portion on the tip.

User avatar
dlb
Highest Ranking Member
Posts: 6355
Joined: Mon Jul 06, 2009 9:03 pm
My tercel:: none currently, 7 previous
Location: shawnigan lake, bc, canada

Re: REALLY Interesting Treatise On Thread Restoration

Post by dlb » Mon Jun 23, 2014 10:49 am

i've never heard of thread forming/restoring dies, keith. that's really interesting. the technique makes a lot of sense.

User avatar
ARCHINSTL
Highest Ranking Member
Posts: 6216
Joined: Sat Apr 30, 2005 1:52 pm
My tercel:: Goldie is a 1986 SR5 attualmente con Weber/also owned the first T4WD in STL in late '82
Location: Kirkwood, a 'burb of St. Louis

Re: REALLY Interesting Treatise On Thread Restoration

Post by ARCHINSTL » Mon Jun 23, 2014 11:03 am

Thanks, keith; I echo david's remark.
Tom M.
T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"
"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

Post Reply