BSPP really hard to tap!

rabtrfld · Jan 16, 2019

I needed a peak-reading pressure gage, so I bought an electronic one from Hong Kong, and it's really nice but has 1/4 BSPP thread!
After looking at prices on BSPP-to-NPT adapters (rated 6000PSI), I decided it would be more "elegant" to just get the BSPP tap.
Trouble is, all available taps are plug-chamfered, and the one I got is impossible to turn!
Supposed to be brand new, but looks suspicious under a microscope (see attached).
I'm only tapping 12L14, and a 1/8NPT went through like butter,

Should I order another tap (from a reputable dealer), or enlarge the hole to 1/4NPT and find an adapter?

The tap has to go dead perpendicular to the face, because the fitting is sealed by a copper washer or steel-bonded-o-ring.
So no horsing it in with a wrench. Already snapped a regular tap handle!
I think what I'll do is (if I can tap the hole at all), fully insert the tap in the part, hold the shank in the mill collet,
use that to align the part for clamping, then re-mill the mating face.

Brand new HSS, you think?

gustafson · Jan 16, 2019

get a new tap bsp is not hard to tap

DMF_TomB · Jan 16, 2019

bspp not hard to tap if you got correct size tap drill and turning correct rotation direction and if material is not hardened or heat treated

MattiJ · Jan 16, 2019

Lemme guess, the tap was also cheaply from hongkong/china? :rolleyes5:

Buy a quality tap and it shoudn't be any harder to make than other similar sized thread.

DMF_TomB · Jan 16, 2019

camscan said:
They don't do a lot of hardening or heat treating with 12L14.

.
i work with a lot of case hardened parts. often over 50% of smaller parts are case hardened for various reasons

andrewmawson · Jan 16, 2019

They might CLAIM it's a 1/4" BSPP tap, but if it is why are the crests and troughs not rounded as they should be ?

Limy Sami · Jan 16, 2019

Crap tap syndrome.

FWIW 1/4 BSP is pretty close in dia and pitch to 1/2'' UNF, which SHOULDN'T be hard to tap!

My Clarkson - Osborn book shows a tapping drill of 11.8mm / 0.4646''

rabtrfld · Jan 16, 2019

OK, with your encouragement, I made it work. I just resharpened the tap & it went much better.
Good thing I spotfaced it again after tapping! It was straight enough for a screw but not for the sealing washer.
Looks like with straight threads you either need to power tap, or spotface after (or turn it on a lathe).
Nary a drop at 3000PSI.

The funniest thing is, our friends in HK cut the fitting with a 60-degree profile instead of 55-deg !!
(And very pointy threads, too, for the enjoyment of your O-ring.)
So it is loose as heck! But such a long engaged length it sealed anyway. Too bad, they got the rest of the gage right, nice electronics, fit & finish.

They might CLAIM it's a 1/4" BSPP tap, but if it is why are the crests and troughs not rounded as they should be ?

Failed to notice that - never looked at a Whitworth before. I will be checking that tomorrow on the comparator! Maybe that's normal in HK,
cut "Hui te wo" threads with their everyday metric tool & nobody the wiser because they do both sides the same?

garyhlucas · Jan 16, 2019

So is the gauge accurate? We just found out our HDPE welding issues are because the nice looking chinese temperature controller is off by a mile and not at all linear so you can’t just apply an offset!

john.k · Jan 16, 2019

For some reason,the Chinese sharpen pipe thread taps freehand.......doesnt always end well.........neverthe less,the other day I was forced to buy some high quality HSS taps ,which they were ,made in China,and rather expensive......Depends on the supplier ....quality /usable stuff is made in China......just profit driven importers wont pay the extra dollars.

DMF_TomB · Jan 17, 2019

camscan said:
That may well be so but are they 12L14?

.
there are many alloys case hardened. i believe if they want a free machining grade its a similar alloy but .4% carbon. its hardens slightly but the case hardening gives it extra carbon for the outer skin.
.
and i wouldnt assume any part was made of the proper alloy and ideally heat treated for that alloy. it is very easy to misidentify a steel alloy where even a vendor sends the wrong alloy type. only way to be sure is to test every piece of metal. its rare for steel to be printed on the bar with the alloy identification number like pipe is often made too. obviously with steel pipe you cannot tell low strength steel from higher strength steel by looking at it unless it is printed with identifying markings
.
4140 prehardened and other steel alloys unless labeled hard to tell from other steels
.
and even when proper alloy some steels vary along length of bar in properties. not suppose too but not every bar and every inch is tested
.
i work with alot of harden parts and even case hardened parts. very hard to tap. if heat treated and if a oversize tap was not used the holes often get smaller from heat treatment. very hard to tap after heat treated. they do sell carbide taps for tapping after heat treatment but they are expensive often over $100 even for smaller sizes

steve-l · Jan 17, 2019

I hate BSPP threads. They are designed to seal on a perfectly flat bottom with a copper, fiber or plastic washer, which makes that bottom surface critical. Here is a tip. You can seal at the top much easier like when using NPS fittings. This assumes you have a face there of course. Hydraulic sealing washers really work well in that case. The steel ones with an inner rubber ring.

gustafson · Jan 17, 2019

The ones I use seal at the top

Gordon B. Clarke · Jan 18, 2019

rabtrfld said:
Failed to notice that - never looked at a Whitworth before. I will be checking that tomorrow on the comparator!

Look at "table" no. 3. Top and bottom radii should be the same. r = 0.13733 P

http://f-m-s.dk/1.09.pdf

Whitworth pipe (55º) profile threads are more common in the world than the 60º.

http://f-m-s.dk/3.05.pdf

BSPP has gone international (ISO) and is now a "G" thread. ISO 228-1

BSPT has also gone international (ISO) and is now ISO 7-1

BSPT is now one of three.
Internal parallel Rp (not to be confused with G type)
Internal tapered Rc
External (always tapered) R

Gordon B. Clarke · Jan 18, 2019

steve-l said:
I hate BSPP threads. They are designed to seal on a perfectly flat bottom with a copper, fiber or plastic washer, which makes that bottom surface critical. Here is a tip. You can seal at the top much easier like when using NPS fittings. This assumes you have a face there of course. Hydraulic sealing washers really work well in that case. The steel ones with an inner rubber ring.

I'll stick to your old denominations in this post to avoid even more misunderstandings than you have.

BSPP is designed to "seal" the same way as NPS is just as BSPT is designed to "seal" as NPT.

Now I'm wondering why you "hate" BSPP threads as their function is no different than that of NPS.

BSPT are "pipe threads where pressure-tight joints are made on the threads". (ISO 7-1)

BSPP are "pipe threads where pressure-tight joints are not made on the threads". (ISO 228-1)

If you read carefully it doesn't say HOW you seal, just that it shouldn't be on the thread.

Now try reading Pipe threads, general purpose (inch) ANSI/ASME B1.20.1 and then

Dryseal pipe threads (inch) ANSI B1.20.3

Personally I find the ISO easier to follow and understand than the ANSI. Maybe you were only familiar with the ANSI before moving to Germany?

I might have a slight advantage given that I have well over 100 thread standards in my library and that I read them now an then. When I reference a thread standard then it's usually because I have it.

I also have ThreadPal so more often than not I don't need to read.

rabtrfld · Jan 18, 2019

Wait a minute -- I never suspected that BSPP was supposed to seal at the BOTTOM. If that were the case, one could finish the hole with an endmill and it would be perfectly perpendicular to the hole, no need to spot face. but
1) how could you possibly tap the hole perfectly all the way to the bottom, especially without scratching the seating face? Is that why they only sell plug taps?
(unless the fitting had a nonthreaded boss at the bottom, which mine doesn't)
2) shame on me for not having a 29/64 endmill in my back pocket.

BTW -- the 12L14 bar I used was cutoff scrap from a turret lathe, so not HT yet. But we make millions of parts out of 12L14 and most of them get case hardened.
I cringe when a lot of people say it isn't recommended!

When I use 12L14 scraps on a manual lathe I can see fine dust rising up in my face under the worklight, ugh! But nothing like the screw machine guys using recycled oil that some percentage of it must date back 10 years. :ack2:

dian · Jan 18, 2019

"When I use 12L14 scraps on a manual lathe I can see fine dust rising up in my face under the worklight"

well, now, thats really weird, anybody else seen this? machining dry, right?

Miguels244 · Jan 18, 2019

All the G fittings I have used seal at the top.
Although I can certainly see uses for a seal on the bottom.
But for that I would look at tapered fittings.

Miguels244 · Jan 19, 2019

Gordon B. Clarke said:
I'll stick to your old denominations in this post to avoid even more misunderstandings than you have.

BSPP is designed to "seal" the same way as NPS is just as BSPT is designed to "seal" as NPT.

Now I'm wondering why you "hate" BSPP threads as their function is no different than that of NPS.

BSPT are "pipe threads where pressure-tight joints are made on the threads". (ISO 7-1)

BSPP are "pipe threads where pressure-tight joints are not made on the threads". (ISO 228-1)

If you read carefully it doesn't say HOW you seal, just that it shouldn't be on the thread.

Now try reading Pipe threads, general purpose (inch) ANSI/ASME B1.20.1 and then

Dryseal pipe threads (inch) ANSI B1.20.3

Personally I find the ISO easier to follow and understand than the ANSI. Maybe you were only familiar with the ANSI before moving to Germany?

I might have a slight advantage given that I have well over 100 thread standards in my library and that I read them now an then. When I reference a thread standard then it's usually because I have it.

I also have ThreadPal so more often than not I don't need to read.

Is there a spec for sealing methods on PP fittings that you know of?

Tyrone Shoelaces · Jan 19, 2019

gustafson said:
The ones I use seal at the top

We used " Dowty Washers " in conjunction with BSPP threads wherever possible.

Regards Tyrone.

BSPP really hard to tap!

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