Holding pipe thread depth on castings that vary

[BobM3]

The castings I have vary a bit in height and I will be tapping a 3/8 pipe thread through the top wall of the casting (with a vertical CNC mill). Are there any tricks to control the depth of the tap? I have 300 pieces to do. I could use a probe and change the vertical offset but I was wondering if there is a quicker way.

 

[Kyle Smith]

A picture would help your case. Pipe threads are pretty forgiving on depth, are you sure you care? Maybe take a skinny cut on the surface prior to tapping?

 

[litlerob1]

A picture would help your case. Pipe threads are pretty forgiving on depth, are you sure you care? Maybe take a skinny cut on the surface prior to tapping?

Agree 100% If you are afraid of going too deep out of tolerance, skim it off.

R

 

[snowman]

Porting cutter.

 

[Bobw]

Its a pipe thread, it'll work even its 4 miles out of tolerance.

But already been said, skim the surface. I know it supposed to be a cast surface,
but who gives a shit as long as it stays in tolerance. I take skim cuts on "cast surfaces"
all the time to make the machining go easier.

When they cut off the runners and risers and sprues and all that, they just belt sand that
"cast surface" down.. All you would be doing is "sanding" the surface with a facemill/endmill..
No harm, no foul, and QC is happy.. If it makes you feel better, you can sand blast the surface
so it looks like shit again.

 

[ewlsey]

Its a pipe thread, it'll work even its 4 miles out of tolerance.

Do pipe threads ever work?

I always spot face them. Gives the QC guy a place to measure his step on his thread gage.

 

[BobM3]

The reason depth is a problem is that the square head pipe plug that screws into the hole looks terrible when the threads are too deep and the plug goes in too far.

It would be tough to make spot facing look good - the casting has a nice raised bit of material for the threads. Cutting into it would partially remove the cast radii blends.

 

[DDoug]

What does the drawing say ? if anything.

I agree with everyone here that says, skim off the top surface to a known height, but if the drawing is dimensioned differently, that takes precedence.

 

[Booze Daily]

You could qualify the other side of the casting off the boss where the pipe tap goes.

You could measure and group them in .010 increments and adjust for each size.

I think I'd just probe them like you mentioned.

 

[BROTHERFRANK]

The reason depth is a problem is that the square head pipe plug that screws into the hole looks terrible when the threads are too deep and the plug goes in too far.

It would be tough to make spot facing look good - the casting has a nice raised bit of material for the threads. Cutting into it would partially remove the cast radii blends.

Can you make your fixture or a stop that registers off the boss (nice raised bit)?

 

[metalmagpie]

Related but not directly: how exactly do you fit a pipe between two fittings? Say for example there are two 90 degree fittings plumbed so that there is 20" between them, bottom of thread on the upper one to top of the thread on the lower. How long do you cut the pipe? In other words, how deep does a threaded-in pipe go in the ideal world? I've been figuring half the depth of the female threads to add on to each end, but I don't know if that's "correct" or not. Seems so simple but ..

Ignore the problem threading both ends in at once ..

metalmagpie

 

[DMF_TomB]

they sell pipe thread plug gages. screw in hole and top of threads should be where the flat is which is the tolerance zone

 

[Scottl]

Related but not directly: how exactly do you fit a pipe between two fittings? Say for example there are two 90 degree fittings plumbed so that there is 20" between them, bottom of thread on the upper one to top of the thread on the lower. How long do you cut the pipe? In other words, how deep does a threaded-in pipe go in the ideal world? I've been figuring half the depth of the female threads to add on to each end, but I don't know if that's "correct" or not. Seems so simple but ..

Ignore the problem threading both ends in at once ..

metalmagpie

Over a 20" distance one or two threads is not a significant amount. When pipes are assembled in complex configurations the pipes are not necessarily perfectly straight and parallel. Pipe compound allows some slack and fittings can be turned a bit tighter if needed.

And both ends are never threaded in at once unless you mean tightening the whole loosely assembled stack at once, which allows for better length adjustment than tightening each joint as you go.

If you are not sure on cutting and threading pipe to a specific length, use a commercially threaded nipple as a gauge to determine how much internal length each fitting takes and then thread your pipe to match the commercially cut threads on the nipple.

 

[Booze Daily]

Related but not directly: how exactly do you fit a pipe between two fittings? Say for example there are two 90 degree fittings plumbed so that there is 20" between them, bottom of thread on the upper one to top of the thread on the lower. How long do you cut the pipe? In other words, how deep does a threaded-in pipe go in the ideal world? I've been figuring half the depth of the female threads to add on to each end, but I don't know if that's "correct" or not. Seems so simple but ..

Ignore the problem threading both ends in at once ..

metalmagpie

Threaded union.

 

[Larry Dickman]

what, does it take more than a few seconds to probe it? Then every part is perfect.

 

[James H Clark]

A little trick that some use, is to wrap a thin wire around the tap at the top of the desired depth. Some like it, some don't.

JH

 

[Illinoyance]

Spotface the casting so you get consistent height for the tapped surface. Then drill and tap.