thread questions fron a QA point of view

[cherokeechief79]

i have 2 questions that im curious about that maybe you guys know the answer.

i have a 5/8 round shaft and it has a 1/4-28 tapped hole in it that states .25 min depth.

they want the hole depth minimum as well.

we went to about .350 to the shoulder and if you measure the length of a screw and thread it in and subtract whats sticking out we get more than .25.

the part has failed for being about .02 shy.

thats less than 1 thread.

they claim you cant measure it to the highest point of the 5/8 round.

its no big deal i can fix it but i thought i could measure it this way.

 

the other question is with threads cut on a lathe.

its a j thread and has a large root radius.

it chatters slightly and you cant really see it well untill you look at it with a loupe.

are there any rules for rejection of threads with slight chatter?

does it go back to the title block which states the min (usually) surface finish?

 

 

[Matthew Hajicek - Singularity]

27 minutes ago, cherokeechief79 said:

they claim you cant measure it to the highest point of the 5/8 round.

This is where the error is.  AFAIK depth of a hole is measured to where the center axis meets the surface by default, so it would be to the highest point.  If they want something different they need to say that.

[cherokeechief79]

the hole is also countersunk so i think that screwing a gage in and counting how many threads it takes to come out is inaccurate on a curved surface like this.

 

[AHarrison1]

On 2/27/2021 at 2:12 PM, cherokeechief79 said:

they claim you cant measure it to the highest point of the 5/8 round.

Who is making this claim, your Q.C. dept or engineering?

It is up to your engineering dept to tell you where to measure the depth from.

There is a .026" difference in height from the top of the 5/8 round to the intersection of the 

threaded hole and the bar.

If it were me I would drive both the drill and tap 0.1" deeper.

The 0.25" is a minimum depth requirement so you could go 1/2" deep if you wanted to

[cherokeechief79]

i was told to drill the hole to the min depth as possible.i went about .15 beyond the .250 depth of where i thought the correct depth was.

what i should have done is not important now.

im just trying to find out for my own knowledge if the thread depth should be taken from the highest point on the 5/8 round or should it be taken from how many turns it can be screwed out from the bottom.

the sideview on the print shows a hole woth the shoulder at .25 deep and threaded to the bottom right up to the shoulder.

it seems to me measuring how many turns out would be tread "engagement" not thread depth.

our QA dept is making this claim.

[Matthew Hajicek - Singularity]

1 hour ago, cherokeechief79 said:

im just trying to find out for my own knowledge if the thread depth should be taken from the highest point on the 5/8 round or should it be taken from how many turns it can be screwed out from the bottom.

Since the purpose of a print is to communicate what is desired, it's good form to clarify anything that could be ambiguous or misinterpreted.  That's the responsibility if the engineer drawing the print.  Without such clarification, what you did is accurate to the print.

[htm01]

was taught in trade school that it's from full dia of the thread

[cherokeechief79]

5 minutes ago, htm01 said:

was taught in trade school that it's from full dia of the thread

meaning what its actually measured from the 2 low points of the 5/8 diameter?

this would mean they are measuring it correctly by counting turns out.

 

[htm01]

1 minute ago, cherokeechief79 said:

meaning what its actually measured from the 2 low points of the 5/8 diameter?

 

correct

[JB7280]

I've been multiple places that say multiple different things.  In my opinion, a fastener, with the both ends faced off so they are perpindicular to the axis is the most accurate method.  We had a customer that was VERY specific and particular about their thread depths.  To measure those we used Leitech gages, which use the same principle, albeit, more precisely.

[Vins]

Those Leitech gages look like a game-changer!  I had not heard of them until this thread, thank you.  ( No pun intended...)

[JB7280]

1 hour ago, Vins said:

Those Leitech gages look like a game-changer!  I had not heard of them until this thread, thank you.  ( No pun intended...)

They're not cheap, but they worked well for the jobs we needed them for.

 

Like $300-600 for a 1/4-20, depending on whether you want standard or "hi-resolution"

[Vins]

1 hour ago, JB7280 said:

They're not cheap, but they worked well for the jobs we needed them for.

 

Like $300-600 for a 1/4-20, depending on whether you want standard or "hi-resolution"

I wouldn't want to buy a whole cabinet full of them but fortunately we are limited on the threads we produce.

[JB7280]

2 hours ago, Vins said:

I wouldn't want to buy a whole cabinet full of them but fortunately we are limited on the threads we produce.

That works.  We had them for 3 specific threads that couldn't easily be measured by other methods.