Making a male & female thread in Aluminium. - Page 2

1. You can live peacefully with aluminum/aluminum threads if you're willing to use and maintain anti-seize compound.

edit: somehow I missed Forestgnome's second sentence. Just repeating, then, suggesting anti-seize as 'lube'.

2. Plastic
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Thanks for everyone's feedback. I worked out that the cutting depths I was using were for flat or rounded cutters, not a pointed triangle.

Using the above as reference I was able to cut perfectly.

If anyone is interested my calcs were as follows:

H = COS(30) x PITCH
= .866 x 1.5
= 1.229mm

===============

The aluminium pipe I have was OD:50mmx4mm.

I chose an internal Dmin (Minor Diameter) of 43mm.
The "normal" depth of cut with a curved cutting tip would be 5H / 8. But I only have pointed so I am taking the cut to 5H / 8 + H/8.

INTERNAL Depth of Cut
= 5H/8 + h/8
= (5 x 1.299 / 8) + (1.299/8)
= 0.812 + 0.16
= 0.972mm

===============

The Dmaj (Major Diameter) is equal to:
= Dmin + ((5H / 8) * 2) *multiple by 2 as we need the diameter
= 43 + ((5 x 1.299 / 8)*2)
= 43 + (0.812 * 2)
= 43 + 1.624
= 44.624mm

EXTERNAL Depth of Cut
= H - (H/4)
= 1.299 - 0.325
= 0.974mm

I cut to these values and the thread fit first go with very little slop.

When I have cut to the full depth I run the cutter over again at the same depth another 3 times and it still takes material off. Why is this? heat? give?

Anyway hope this helps someone.

3. Stainless
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Originally Posted by rons
It would be better to have a drawing with all dimensions.

Then look at the Machinery Handbook for things like class-of-fit.

For me, I always make the female side first. Then I use the female part as a gauge when making the male thread. You could go either way but I find it easier
to examine the exposed male threads.

With aluminium I use some anti-seize compound.
I always go male threads first because you can actually inspect them. Then make the female to fit. How are you validating the female thread pitch diameter if you're cutting those first?

4. Diamond
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QT OP: [I run the cutter over again at the same depth another 3 times and it still takes material off. Why is this? heat? give?] heat? If getting hot then your bit is likely the wrong geometry/shape or sharpness.

Tubing can push away from the cut because of the poor rigidity of the tube and the forces made by the cutter/bit/insert.

Plugging the tube ID can make it seem solid to the cut, and the insert/bit geometry can also help reduce cutting forces. Aluminum likes to crush or bunch up ahead of an insert/bit the has little/no positive rake angle or is not sharp enough. I like a positive rale angle for threading aluminum and steel, and an edge that shaves a fingernail. Rake attitude can be a side-cutting edge rake or a top back rake. Think about rubbing a knife-edge on a piece of hardwood..and then turning the edge into the wood so it might penetrate/cut.

*The back-rake for going straight in and the side cutting edge rake for going in at 30* (I avoid going straight in.)

Going straight in causes more cutting forces because you are cutting on both sides of the insert/bit. So on a thread of about 2" x 6tpi that is about .166" on each side of the insert/bit trying to cut all at the same time//like a .333" depth of cut. Wow, that is a lot.

Your bit insert should have about .025/.030 flat. A little too big doesn't hurt, a small flat/radius causes interference.

The OD of the male should be - .010 (about), a sharp fine file might be used on the OD and then the last two passes might help.

The ID/bore of the female should be about .020 bigger than the root/small diameter of the male.

A blue-up might tell where the thread interference is happening and with that, you might adjust your thinking/numbers.

If a repeat job, you might make a male and female thread gauge of steel to save measuring time.

* South Bend "How to Run a Lathe" or another thread cutting book should be bought (your own hard copy). You can Not learn machining by bits and pieces found on PM or any one problem at a time education.

Oh, and the bit/insert has to be near dead square to the part, a thread fish might help insure that .

5. Hot Rolled
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Steel or aluminum is a wet noodle, everything bends and deforms. the last 3 cuts are like a spring pass, less tool pressure.
also the lathe could be worn and loose and deflecting. id guess the latter. most small lathes suck for rigidity

6. Plastic
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I haven't been measuring the pitch diameter; I will get some thread measuring wire so I can do this.
I was thinking of cutting the tightened bolt and nut down the middle and checking it out... haha

The lathe is new; it's a 1236 Taiwanese made, pretty solid machine.

Thank you all for taking the time to reply. It is greatly appreciated.

7. Diamond
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A 60* 1 to 2 thread micrometer can be handy .. First you 3-wire the thread and then check with the micrometer and write down that number for the micrometer check of future parts.. but just for the male thread.
homemade steel gauge for the female

SCHERR TUMICO 1"- 2" THREAD MICROMETER | eBay

8. Diamond
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Originally Posted by AARONT
I always go male threads first because you can actually inspect them. Then make the female to fit. How are you validating the female thread pitch diameter if you're cutting those first?
I see your point. I might try your method. But typically I make the hardest to make part first and then work on the second mating part.
If it was a large size like this here I would probably do it you way. And it appears that the end cap would be harder to make.

For small stuff when I want the tightest fit possible
:
Mill or cut from hex rod to make a nut.
Drill/tap nut.
Use nut to size thread on lathe.
Last edited by rons; 04-13-2021 at 12:13 AM.