1/4-40 MTP into aluminium?

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DianneB
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1/4-40 MTP into aluminium?

Post by DianneB »

Has anybody used 1/4-40 into aluminium? Does it work? Will aluminium take the 40 tpi?

I am trying to de-clutter the connections between the tender and my 1-1/2" scale American. The American has a 3/8 aluminium buffer plate and I could save a lot of space if I can get a seal by tapping into the buffer from both sides.
earlgo
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Re: 1/4-40 MTP into aluminium?

Post by earlgo »

Were it my problem, I'd get a piece of similar size and alloy aluminum and try it using WD-40 as a lubricant. If it doesn't work out then you won't have ruined your actual part.
JMHO
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tornitore45
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Re: 1/4-40 MTP into aluminium?

Post by tornitore45 »

Should be no problem. As always for tapping: Good sharp Tap, Lubrication, right size hole, Alignment and patience.

It took me while to accept all of them are required, no broken taps since.
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spro
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Re: 1/4-40 MTP into aluminium?

Post by spro »

FWIW. I would test exactly this proposal and see what I've seen. That's an extremely fine thread into aluminum and it doesn't leave much enduring thread. A part could be cross-threaded and barely realize it. Since it is TP, the fitting is deforming the threaded hole and aluminum galls and seizes. Thread lube can help but with radical changes of temperature, what is thread and what is a wedge with broken strings. ? I would try the test with the type of metal fitting envisioned. The fitting metal makes a huge difference with instant electrolysis.
johnfreese
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Re: 1/4-40 MTP into aluminium?

Post by johnfreese »

A spiral point or spiral flute tap would be best but I suspect they are not available in 1/4-40. Definitely, a sharp tap is necessary to prevent tearing. I generally use wax, similar to DoAll's Tool Saver wax. I think it gives better lubricity than WD40.

To clarify, I am referring to tapping wrought aluminum. Aluminum castings are different. Their tendency to tear is much greater.
spro
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Re: 1/4-40 MTP into aluminium?

Post by spro »

Yes but this is M TP which means the inner diameter is 1/4" . This is a larger fitting, I thought. Anyway 40 TPI in aluminum, is too fine to me.
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DianneB
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Re: 1/4-40 MTP into aluminium?

Post by DianneB »

Good points!

I think I will find a different way and try to avoid problems.
johnfreese
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Re: 1/4-40 MTP into aluminium?

Post by johnfreese »

I learned something today. Model Taper Pipe threads. Never knew they existed. Tried to google it to find the thread spec but came up with nothing useful.
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Re: 1/4-40 MTP into aluminium?

Post by Steggy »

johnfreese wrote:A spiral point or spiral flute tap would be best but I suspect they are not available in 1/4-40.
See this McMaster-Carr item. It's not inexpensive nor is it an MTP form, but it can be made to work.
I generally use wax, similar to DoAll's Tool Saver wax. I think it gives better lubricity than WD40.
The usually-recommended lubricant for tapping aluminum alloys (e.g., 5052-Hxx or 6061-Tx) is a 15/85 mixture of petroleum-based cutting oil and mineral spirits, resulting in a thin and flowing lubricant.
To clarify, I am referring to tapping wrought aluminum. Aluminum castings are different. Their tendency to tear is much greater.
Aluminum extrusions are denser than casting, which is why the different behavior. A sharp, uncoated "gun" tap lubricated with 15/85 has the edge in working aluminum. :D
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DianneB
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Re: 1/4-40 MTP into aluminium?

Post by DianneB »

johnfreese wrote:Model Taper Pipe threads. Never knew they existed.
I like them 'cause they seal up nicely and have LOTS of threads engaged when snug. They are a little tricky to get the threads straight so I do pipes in the late with a tailstock die hold and do internal threads in the drill press using the chuck to keep the tap straight.
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NP317
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Re: 1/4-40 MTP into aluminium?

Post by NP317 »

I built all the fine plumbing on my Allen Ten Wheeler using MTP threads. I did also use steam sealing joint compound. No joint leaks ever.
The deep blue colored stuff. That original container is long gone and I don't remember the name.
I'll use the same for my Mikado, but with a different joint compound sealant that I have. It heat-sets.
The SuperScale fittings I have use compatible threads.
~RN
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Re: 1/4-40 MTP into aluminium?

Post by spro »

I have learned from this discussion. My experiences with that fine thread were limited.
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