"Full Thread Depth" blueprint definition

Full thread depth is the minimum distance in which a male thread (bolt) will freely thread into. Normally it is a specified dimension and is shy from the full depth of the drilled hole to allow for tap lead (imperfect threads) and clearance for chips. Typical practice is too leave at least

6 to 8 threads (6 x thread pitch).

1 3/4" deep hole?

Stephen R.

Full thread depth is the depth that a thread gage will screw into a tapped hole. A tap is tapered on the end so there will be partial threads below the full thread depth.

Fred

================ Unfortunately, this is one of those cases that it means what ever the person that did the print says it means.

There is the additional problem that many prints are now being created/updated "off-shore" or by technicians whose native language is *NOT* [shop] English.

There is even a question on how to gage this, as the thread plug gages also have incomplete lead-in threads.

Best advice -- get clarification and GET IT IN WRITING.

By logic, given the apparent length of thread engagement, 100% depth of thread is meaningless as the bolt/screw will fail in tension long before the threads strip. Thus they are apparently referring to the total dept of full thread. BTW - it is always better to increase the length of thread engagement rather than the depth of thread to increase stripping resistance.

Tapping to the bottom of a blind hole is a right bitch, and should be avoided whenever possible. Even a plug tap will leave one or more partial threads at the bottom. It can be done with a specially ground flush end tap. Such an operation requires a large amount of operator finesse [mainly to avoid cross threading at the start], and such a tap is good only for a very few holes. It is also likely that you will need to cut, back-out, remove chips, repeat, several times. This is expensive and requires the best operators. It is also generally pointless as almost all male threads have one or more incomplete lead in threads.

Unless you have exceptionally thick material or need a water/air tight condition, it is always better to drill a through hole. It gives the chips some place to go and you won't break the tap by hitting bottom if you are power tapping. If you can't drill though, drill as deep as you can. Just removing the chips from a blind threaded hole can be a major PITA.

Unka George (George McDuffee) ..................................................................... The arbitrary rule of a just and enlightened prince is always bad. His virtues are the most dangerous and the surest form of seduction: they lull a people imperceptibly into the habit of loving, respecting, and serving his successor, whoever that successor may be, no matter how wicked or stupid.

Denis Diderot (1713-84), French philosopher. Refutation of Helvétius (written 1773-76; first published 1875; repr. in Selected Writings, ed. by Lester G. Crocker, 1966).

No, they do not. Proper thread plug gages have the starting thread ground at a right angle, where there's a thread with full form, so they gage depth properly.

Harold

I don't know if it is a proper definition, but when I draw stuff for someone else to make, I specify the depth of the full thread, ie: Drill and tap 1/4-20 Min .75" full thread, x places. As a machinist/cad designer I get complements on my drawings for their readability and usefullness :-) They may not follow strict iso drawing protocol but they get my parts built. I have spent hours going over 'proper' drawings and wishing to do great bodily harm to the guy who drew them. Pratt & Whitney and Michelin were the worst, everything was there, but god was it hard to find.

James Crombie

The official ANSI version of your hole note would be:

3X 1/4-20 UNC x .75 DP MIN

For sticklers, thread class should be included as well:

3X 1/4-20 UNC-2B x .75 DP MIN

I have my default blind hole note template set up with a MAX tap drill depth as well:

3X 1/4-20 UNC-2B x .75 DP MIN TAP DRILL 1.25 DP MAX

The drill depth is not really necessary unless there's some feature you don't want to break into, but makes it clear that you do want a blind hole, and otherwise doesn't hurt as long as you leave a generous allowance beyond the MIN tap depth.

Ned Simmons

Get a clarification of what he mens. A 1.75" deep hole threaded all the way down to the very end is going to be expensive! The other thing is the tapping drill size. If he's meaning to have the hole drilled so that the full depth of the threads are done on the hole, that is something else. I'd suspect that the guy doesn't know what he's doing with the drawing so explain to him that it costs x to drill and tap a regular hole and it then costs x times more to drill and tap a near bottom hole and x times more for a fully bottomed tapping in the hole. My bet is that he'll quickly realize that all he needs is the hole down for 1" or less even of threads and leave some room for a regular tap to get there. I've seen these kinds of idiots all the time and sometimes I just let it pass and just nail them for their stupidity and sometimes I teach them what they did wrong.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

The thread depth might makes sense if using a standard length bolt to attach an unknown/variable thickness item to the part being made. Especially if working under water, a long way from the bolt rack.

Mark Rand RTFM

Any bolt of decent quality will only have 1" of thread anyway unless the bolt is specifically made for some really special purpose.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

Bit of a broad statement that. 1" wouldn't be enough for a half nut on some of the bolts we use

Mark Rand RTFM

Mark Rand wrote in news: snipped-for-privacy@4ax.com:

IIRC the standard is in the neighborhood of 3 x dia.

I probably should have said the typical small bolt. It would be silly for a

5" bolt to have only 1" of thread!

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!