angled 1/2" NPT

will gilmore · Nov 6, 2017

I need to put a 1/2" npt thread in some 1" plate at a 30 degree angle (from vertical). The plan is to fixture the plate at the angle, make the hole with a 23/32" annular cutter, then threadmill. I can fit 3 at a time on the table. No tool changer.

Sound reasonable?

Annular cutter: https://empirerigging.com/hougen-23-32-x-2-12-000-series-annular-cutter-12223/

I'm planning on gripping the shank in a ER32 collet. I'll program a stop between each hole to make sure the slug is out.

Finegrain · Nov 6, 2017

And then what? Will you threadmill the threads? If not, then it's going to be quite the fun to make valid threads and/or not break taps.

Mitigation would be to mill out a counterbore a bit bigger than the NTP thread big-end major diameter.

Regards.

Mike

Oldwrench · Nov 6, 2017

Relieve the hole so the thread starts square, otherwise its taper will wedge it sideways in the plate and it will leak.

On edit: Finegrain types faster

HuFlungDung · Nov 6, 2017

I think I'd counterbore the top of the hole with enough clearance to clear the thread and to make a complete circle where the thread will start. Then you'll also know where the gage line is. I'm not a fan of annular cutters either (too delicate) so a flat counterbore is nicer to start any sort of drilling operation on.

will gilmore · Nov 6, 2017

Client did not want a counter bore. Client was not forthcoming about the fitting going in to the part and I'm concerned that there might be a hex or handle that wouldn't fit the cbore. I made a few as tests making a small flat (maybe .635") then drilling up to 23/32 then hand tapping with a center held in the spindle. I need to make 50. Lack of rpm and tool changer made me want to knock it out with the annular cutter then threadmill.

Anthony · Nov 6, 2017

How about a scrap plate clamped to the work with the clearance in it. Threads would start in clamped plate and continue into work. Remove tap, discard plate, finish tapping into work... I would think hole would keep tap somewhat straight.

Modelman · Nov 6, 2017

HuFlungDung said:
I think I'd counterbore the top of the hole with enough clearance to clear the thread and to make a complete circle where the thread will start. Then you'll also know where the gage line is. I'm not a fan of annular cutters either (too delicate) so a flat counterbore is nicer to start any sort of drilling operation on.

I agree will all above. In addition, the annular cutter will leave a standing post, and putting an accurately located hole in at a 30deg. angle is problematic. I'd be more inclined to spotface with a stout 3/4" end mill, then circle mill to .850" dia. or so, giving me a flat surface to start drilling from.

Dennis

will gilmore · Nov 6, 2017

I was planning on threadmilling although Oldwrench's comment has be a bit concerned. Assuming I can make the hole and threadmill on the angle I'd like to hear more opinions on leaking NPT fittings on an angle.

will gilmore · Nov 6, 2017

Modelman said:
I agree will all above. In addition, the annular cutter will leave a standing post, and putting an accurately located hole in at a 30deg. angle is problematic. I'd be more inclined to spotface with a stout 3/4" end mill, then circle mill to .850" dia. or so, giving me a flat surface to start drilling from.

Dennis

No callouts for accuracy. I think this part gets buried in concrete. My concern with the cbore is that it brings the gauge line down into the part. They didn't want it and have accepted the other parts without it.

I've designed the angle fixture to let the slug drop out the bottom.

Bondo · Nov 6, 2017

If this gets buried in concrete, on a 30* angle, and can't extend past the base material... Sounds like it should be redesigned with a welded fitting

Sent from my 2PS64 using Tapatalk

will gilmore · Nov 6, 2017

Bondo said:
If this gets buried in concrete, on a 30* angle, and can't extend past the base material... Sounds like it should be redesigned with a welded fitting

Sent from my 2PS64 using Tapatalk

Above my paygrade.

yardbird · Nov 6, 2017

will gilmore said:
I'd like to hear more opinions on leaking NPT fittings on an angle.

I could see this being a real problem. Might see if the customer would be OK going a turn or two deeper then normal to get more taper contact on the short side to help this issue

I believe this is the reason to spotface a flat surface before NPT tapping at an angle?

Brent

will gilmore · Nov 6, 2017

yardbird said:
I could see this being a real problem. Might see if the customer would OK going a turn or two deeper then normal to get more taper contact on the short side to help this issue

I believe this is the reason to spotface a flat surface before NPT tapping at an angle?

Brent

When I hand tapped I went as deep as the tap would allow. There is no callout for gauge depth. I can only assume that the test parts have been tested and are working.

HuFlungDung · Nov 6, 2017

Why the hell post the question, then? Just go ahead and do it. It doesn't make any difference whether you start the threads above the counterbore or not, the effective thread length is from a flat counterbore that just grazes the surface. and not above that point. So if the client thinks they are getting something better without the counterbore, then they have deceived themselves.

Gordon Heaton · Nov 6, 2017

Theory not withstanding, tapered pipe threads in real life tend to seal at some point along the taper on a line parallel with the threads, NOT throughout the entire length of the taper. Therefore, if you mesh the two threads on an angle, you will quite possibly never get a seal around the entire circumference. Sealing compounds may take care of the problem depending on the properties and pressures of the material to be contained.

As others have said, milling a flat for a 'square' start to the female thread is the safer way to go.

will gilmore · Nov 6, 2017

HuFlungDung said:
Why the hell post the question, then? Just go ahead and do it. It doesn't make any difference whether you start the threads above the counterbore or not, the effective thread length is from a flat counterbore that just grazes the surface. and not above that point. So if the client thinks they are getting something better without the counterbore, then they have deceived themselves.

I was actually most interested hearing comments on the annular cutter / threadmill approach on an angled surface.

Gordon Heaton said:
Theory not withstanding, tapered pipe threads in real life tend to seal at some point along the taper on a line parallel with the threads, NOT throughout the entire length of the taper. Therefore, if you mesh the two threads on an angle, you will quite possibly never get a seal around the entire circumference. Sealing compounds may take care of the problem depending on the properties and pressures of the material to be contained.

As others have said, milling a flat for a 'square' start to the female thread is the safer way to go.

That makes a lot of sense. I'll take one more pass at the client for a counterbore.

Thanks to everyone who replied.

Halcohead · Nov 6, 2017

One add’l issue I’ve had with angled NPT: the incomplete starting threads tend to shear off the thread sealant ahead of the hole, further encouraging leaks.

Oldwrench · Nov 6, 2017

Burying that design in concrete gets my vote...

R. Dan · Nov 6, 2017

I designed thousands of nptf ports that hit a round piece of steel at an angle. ALWAYS put a spot on there first. Drilling and npt(f) porting just doesn't work too hot at an angle without a flat spotface to work off of. BTDT

CatMan · Nov 7, 2017

Bondo said:
If this gets buried in concrete, on a 30* angle, and can't extend past the base material... Sounds like it should be redesigned with a welded fitting

Sent from my 2PS64 using Tapatalk

Exactly what I was thinking. Give me some 1/2" couplers and cut them at an angle. Weld to plate. Done.

angled 1/2" NPT

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