Creating M27x3 Tapered Plug 1

[vagulus]

Creating a tapered thread using a 3D Printer is very much akin to single-point cutting a thread on a Centre Lathe. I trust I am not the only one left with such memories tongue.

Currently I am attempting to create an M27 tapered plug using the standard BSPT format including the standard taper of 1°47' (1.788°). There is something, however, Uncle Google is reluctant to reveal. Wikipedia, that fund of general knowledge, remains silent. I even opened my 22nd Edition of Machinery's Handbook for the first time in years. (Who remembers Machinery's Handbook?) All to no avail! mad

As I understand it a BSPT Male Thread, at the pipe end, is undersized in comparison to the equivalent BSPP Female thread. I cannot find out how much undersized it should be. Such a specification will define the number of turns of thread before the minor diameter of the thread equals the OD of the pipe (ending the thread cut) which in turn defines the number of turns of thread involved.

Would someone please help with a specification of the thread undersize. A reference to appropriate documentation would be appreciated.

If working from the undersize is not the correct way to define the thread, please relieve my ignorance and tells me how the job is done.

Thanks

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Artificial Intelligence is no match for Natural Stupidity

 

[3DDave]

If no one knows about it, where did you get that 27 X 3 BSPT identification from?

 

[vagulus]

Hi Dave

My device has ports to accept standard plastic garden hose fittings. The thread is M27x3. In the development stage, I wish to plug those ports. A Tapered Plug is my solution.

The thread form will be regulation M27x3. The taper will be the BSP Taper (tried and true) of 1°47' (1.788°).

This version was printed with the big end thread one half thread depth oversize and the small end thread one half thread depth undersize. What I want to know is whether or not there is an accepted standard for these over/under size dimensions.

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Artificial Intelligence is no match for Natural Stupidity

 

[3DDave]

Garden hoses use straight threads. See

https://en.wikipedia.org/wiki/Garden_hose#Standards_and_connectors

It's more typical that plugs have an o-ring at the shoulder of a hexagonal flange that fits into a chamfer in the body of the mating part.

Note too that pipe threads can leak unless used with a sealant, such as teflon tape or pipe thread sealant.

As far as I know tapered threads don't have a tolerance on the diameter of the thread - they are given a specific diameter and then a number of threads and tolerance on that number from the end of the part. Since M27 isn't a standard tapered thread there won't be a standard for it.

 

[vagulus]

Thanks Dave for, "Since M27 isn't a standard tapered thread there won't be a standard for it. "
That's what I needed to know.

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Artificial Intelligence is no match for Natural Stupidity

 

[drawoh]

vagulus,

I playing with a 3D printer at home. The process is not accurate, and you need to build clearance into your model. 0.1mm? Start testing, and taking notes.

--
JHG

 

[vagulus]

Of Course!

That's why my plugs came out undersize. Thanks, for reminding me.
Nominal Size ^2 / Actual Size. That's the formula.

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Artificial Intelligence is no match for Natural Stupidity

 

[drawoh]

vagulus,

I draw gear and screw profiles using construction lines. I use my clearance value to space my actual geometry away from the nominal construction line positions.

--
JHG

 

[Rputvin]

You should be able to find a gauge depth for the BSPT threads closest to your M27 (1"?) and extrapolate something workable to your plastic plugs. Distance + taper angle will work out what that diameter would need to be. Or just start with the 1" geometry and use a quick 27/25.4 scale factor.

https://amesweb.info/Screws/Images/British-Pipe-Thread/BSPT-External-Thread.jpg

https://amesweb.info/Screws/bspt-thread-chart-calculator.aspx