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Anonymous Poster

Threading Standard

09/15/2007 4:00 AM

Hi

can any arrange the detail of UNC thread?

How can I decide the drill sizes in mm for that type thread ?

Regards,

Ram
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Mr. Truman Brain
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#1

Re: Threading Standard

09/15/2007 6:08 AM

Depends on your tolerances! UNC is like any other thread, a max and min core diameter! look for the drill size that will give you your core diameter? chech this out! To convert drill size to metric, multiply by 25.4 to give you your drill size! the number drills sizes, you will have to do a bit of research on you own but there are many sites that will do that for you!

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ram murti
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#4
In reply to #1

Re: Threading Standard

09/16/2007 7:38 AM

Thank you very much Mr.Truman Brain

Ram Murti Yadav
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sidevalveguru
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#7
In reply to #1

Re: Threading Standard

09/17/2007 4:56 PM

The "old school; shop-rat" rule-of-thumb for tap drilling is:

Diameter - 1/pitch. i.e. 1/4-20 gives .250 minus 1/20 (.050) = .200

If you use the lookup chart it will give a #7 drill (@ .201")

This gives very closely 75% thread depth; a very goodbalance between tapping effort, & thread strength.

(works even easier in the metric system!)

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#2

Re: Threading Standard

09/15/2007 11:18 AM

Since you did not specify which thread. I can't look it up.

The info you would like is available in a shop reference manual for all threads unified and metric. Their is a paper back hand book version for students and apprentices.

cost is about $20.00 US

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#3
In reply to #2

Re: Threading Standard

09/15/2007 11:22 AM

I began to answer him in similar fashion, but I am so longwinded I feared my coffee would turn before I got to my point. That is if kept track of it.

cr3

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PWSlack
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#5

Re: Threading Standard

09/17/2007 6:18 AM

http://homepages.tesco.net/~A10bsa/bswgo.htm

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unclefastguy
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#6

Re: Threading Standard

09/17/2007 10:03 AM

Rule of Thumb I learnt from several machinists is that the pilot drill size should be about 60% of nominal thread size for UNC and 70% for UNF. Thus just do the conversion to metric for mm pilot drills.

Hope this helps.

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ireland tool
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#8

Re: Threading Standard

09/29/2007 9:54 AM

To determine the tap drill size use the following formula:

MAJOR DIAMETER OF THREAD - minus .01299 X amt. of percentage of full thread

divided by number of threads per inch

equals drilled hole size

EXAMPLE: 1/4-20 UNC THREAD USES A TAP DRILL SIZE OF .196 INCH OR IN METRIC 5mm.

OR THE BEST WAY IS TO CALL YOUR LOCAL CUTTING TOOL DISTRIBUTOR FOR HIS ADVICE. I HOPE THIS HELPS YOU.
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mrainey
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#9

Re: Threading Standard

10/06/2007 2:53 PM

If you'd like to see some inexpensive software that displays just about all the thread manufacturing info you'll ever need, here it is:

http://mrainey.freeservers.com/METhreadPal.html

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