Model pipe thread question

[AOG]

I need some help. I am working on Elmer's twin vertical wobbler and I have run into a problem. It's time for me to drill and tap the intake for a pipe stub.  Elmer calls out  3/16 MTP  which is a standard I have never heard of much less have. Normally google is you friend but not on this subject. Along the way I have learned of the existence of NPT ( which I know about) but I also learned of the existence of MTP, UST and ME pipe threads on model pipe fittings. This last one really confuses me because I thought ME threads were straight threads. Can some one please give me a quick primer on pipe threads as used in model engineering.

Thanks

Tony

[Brian Rupnow]

Just use the closest straight thread and use a dab of Loctite to keep it from leaking.

[philjoe5]

This might help.  At  a model show one of the sales guys gave me quite a description of the various ones we're likely to encounter.

http://www.pmmodelengines.com/model-pipe-threads/

Cheers,
Phil

[Don1966]

Hi Tony, the MTP pipe tap and die are for model engines and you can get them from PMR or here http://www.britishfasteners.com/index.php/categories/model-engineer-taps
Make sure to look under model engineer taps and die. These are straight taps and die. You may want to use straight taps and dies like 1/4x40 or 3/16 x 40. If your going to run them on steam use the taped ones if air use the straight theads. PMR has the tapered tap and die but are vary expensive.

Don

[b.lindsey]

Phil's link is a good one. I use 3/16-40 straight thread instead of the MTP tapered version, but only because I already have the taps and dies.

Bill

[sshire]

I had the same issue with an early build of one of Elmer's.
I did get the MTP tap and die.
After that, I've standardized on ¼-40. Loctite thread sealer ( not thread locker).  No leaks and easier

[mklotz]

Loctite 565 thread sealer is what PMR recommends for their boiler kits.  I used it and it seems to work well.

[AOG]

Can you have a straight pipe thread? I thought that by definition a pipe thread was tapered. If you use a straight thread on a pipe aren't you are going to have problems with sealing it or is this only applicable in full size practice?

Tony

[AOG]

Sorry it looks like my post crossed with three or four others. I will take a look at doing a straight thread and using a sealer.

Thanks everyone

Tony

[Jasonb]

I just use straight ME threads with no problem, bit of sealer if needed.

BSP (British Standard Pipe) which is a full size thread is commonly used in its straight form and what I use on the larger models where NPT is specified.

[derekwarner]

Guys......pipe or tubing and fittings/thread forms is one of the most mis-understood and mis-quoted engineering concepts in the Fluid Power Industry

1. NPT [taper] an American concept is a 60 degree thread form and was designed to seal in the root of the thread without the aid of sealant. Many references to NPT will include the term 'Dry Seal' which is self explanatory
2. BSP [R Form] a European [British] concept is a 55 degree tapered thread form [Whitworth] however seals against the flank of the corresponding M&F elements. This format requires an additional sealing element....& yes in older years was RED lead & hemp]....in latter years TEFLON sealing paste or tape won over
3. BSP [G Form] a European [British] concept is a 55 degree parallel thread form [Whitworth] however again seals against the flank of the corresponding M&F elements. This format in modern times is the British accepted Standard for soft sealing of hydraulic fittings as the requirement to eliminate external leakage

Derek

[kvom]

Dryseal (NPTF) and NPT threads are not the same.  Dryseal threads use no sealant and are made leakproof by crushing the threads when connected.  These are needed only for high-pressure/high temperature applications.  For small models operating on air a straight thread with sealant is fine.