【转帖】min. full thread

yang686526

min. full thread
what is the textbook definition of "min. full thread"?  
not sure there's a text book that covers it, i don't recall seeing it in 14.5.
however, the definition of min is given in asme y14.5m-1994 at section 2.5, essentially it means minimum and there is no explicit maximum, this is determined by "other elements of the design".
full thread is an abbreviation of 'fully formed thread form' or something like that.  
essentially the thread must be of fully form with not taper or 'run out' etc for the length stated.
i many situations i use the term "min full thread, do not break thru"
i like kenat's explanation of min full thd.
many companies, including where i am now, specify calling out thread depth on blind holes this way in company standards in order to assure the minimum full thread form required for the design without specifying a plus / minus tolerance for the thread depth. it gives manufacturing some dimensional leeway and avoids overly tight tolerances on the tapping process.
  
here is a simple chart that i use.
dale disalvo
sr. mechanical designer
pro-e wf3.0
missourian = shut up and "show me"
i had to look at that a minute as the nomenclature struck me as back to front initially.
i always used the rule of thumb of needing 3 extra thread pitches for the tap hole.
kenat,
cool stuff...good chart
matt lorono
cad engineer/ecn analyst
silicon valley, ca
folks-
"min full thread" is sloppy and unnecessary because the thread depth callout fully defines acceptable limits for the threads.  for example, if i call out a .112-40 unc-2a blind tapped hole that is .20+/-.03 deep then the full thread depth must be more than .17 but less than .23.  technically, if you call out no maximum depth for the thread then the machinist can tap all the way through the part while still meeting the drawing!
   
tunalover
tunalover i disagree.
specifying min full thread simplifies inspection in many situations.
functionally for many threaded holes the important thing is that there is enougth thread that the mating fastener doesn't bottom out.
this allows a simple gauge of the minimum required depth to be used, rather than having to have both go & no go gauges.
if you actually read my post you'd have seen i brought up the addition of "do not break thru" to resolve the situation you mention in your last sentance.
do you seriously double the inspection when there is no functional requirement?
  
kenat,
if  you say "do not break thru" then the very real possibility exists that the pilot hold drill point can go so close to breaking through then a less than paper thin thickness can develope that can eventually break through and expel conductive debris into your assembly.  that's just one bad thing that can happen with inadequate (read: sloppy) control is brought forth.
i honestly don't know why people seem to think that asme y14.5m-1994 is inadequate for dimensional control;  you won't find such notes in there because there is simply no need for them.
  
tunalover
both great arguments. i have experienced myself what tunalover indicates. i needed a very flat external bottom surface. the drill point touched the internal surface and created a slight bulge externally.
the "do not break thru" note did not help us.
the only way we could avoid this was to dim the depth from the thd/drill starting surface with a "max" dim, and "min full thd".
chris
solidworks/pdmworks 08 3.1
autocad 08
i think the control of the tap drill depth is being ignored here.
tap drill depth (1) should be specified, and (2) will limit the thread depth max without imposing a full thread depth tolerance that will need to be inspected and possibly rejected though the fastener design may not be compromised.
the whole reason for min full thd is to avoid this.
at our place, we control this by specifying the tap drill depth as:
"minor ? (depth symbol) .xx ± .03"
and make it the first line of the thread callout.
moreover, min full thd should always be: "min full thd (depth symbol) .xxx" for blind holes.