Tapping a nylon hole.

[andrew lynerParticipant @andrewlyner71257]

Posted by Nigel Graham 2 on 30/11/2019 22:33:28:

I find the greater problem with Nylon is not cutting the thread , as long as that is fairly coarse, but drilling the tapping (or any-purpose) hole in it.

The steel drill-bit become hot and expands, so binds. The only solution really, is peck-drilling with a short time for the tool and plastic to cool between pecks (I leave the lathe running).

Twist-drills can also dig into the plastic if you are not careful, adding to the risk of binding.

It's amazing that such a soft substance could be so problematical. I have found that drilling a, say, 7mm hole direct, I suddenly get resistance against the cut as if the drill is pushing against something hard. Not at high speed and no 'hot smell'. A small pilot hole seems to help avoid the problem.

[Sam StonesParticipant @samstones42903]

I forgot to mention that swarf can be rubbing too.

It is likely to melt as it tries to stick with the parent material.

This is what happens inside the barrel and screw of injection moulding machines and plastics extruders.

Don't ask me how I know. It's a long story.

Sam

[Robin GrahamParticipant @robingraham42208]

Well, I found a bit of nylon bar drilled nominally 8mm I guess – ID is 8.108 (+/- something), OD is 26.160 (+/- 0.015). It has been in a pan of boiling water for an hour. I'll let it cool in the water overnight, remeasure tomorrow and report later, if still capable of speech after interrogation about the reason for a lump of plastic in the porridge pan.

Robin.

[not done it yetParticipant @notdoneityet]

Posted by andrew lyner on 30/11/2019 21:19:34

…

(I didn't get the balloon bit. Sorry)

That must be the subtle bit.

Let me explain a bit more for you. Blow up a long sausage balloon. Now bend it into a circle and note the hole size. Now blow it up further but keeping the centre line the same. The hole will shrink. Alternatively blow it up just more than originally and bend it into a circle. The hole will be smaller if you use the same ‘centre line’ as previously.

Now blow up the other balloon inside the circle of the first until it almost touches the outer. Now blow it up some more.

[Sam StonesParticipant @samstones42903]

My apologies for high-jacking this thread Andrew.

Don't try this at home. I did many years ago, but I think I got away with it … (Shades of John Cleese).

However, to determine if Nylon was micro-wave 'transparent', I placed a short length of 1/2" dia. rod in the microwave. To my surprise a locallised section (but not all) melted.

I have a theory that the small percentage of moisture (hydroxyl groups?) within the structure turned instantly into super-heated steam sufficient to melt the Nylon. Anyone here who understands polymer chemistry (cos I'm more of an engineer) might like to comment.

This thinking also aligned with the possibility that talc-filled polypropylene (PP) mouldings distorted after being 'microwaved' whereas natural PP didn't.

My theory in this instance was similar to the above speculation that talc-filled polypropylene containing hygroscopic filler (and therefore hydroxyl groups) was also becoming (over) heated by moisture 'attached' to the talc.

Have I gone too far this time?

Sam

 

Edited By Sam Stones on 01/12/2019 00:50:28

[Sam StonesParticipant @samstones42903]

Sorry Andrew!

Having found myself holding the tiger by the tail so to speak, and taking the chance of being viewed as a nerd, (at my age I ain't too worried), dare I mention thermal conductivity?

It was a surprise to me to discover that polypropylene has about the same thermal conductivity as cheese

The relevance being that I was involved in the design of a cheese box to be used for cheese maturing during the manufacturing process.

If you want to know more in this context, then send me a PM.

Sam

[andrew lynerParticipant @andrewlyner71257]

Posted by not done it yet on 01/12/2019 00:13:25:

Posted by andrew lyner on 30/11/2019 21:19:34

…

(I didn't get the balloon bit. Sorry)

That must be the subtle bit.

Let me explain a bit more for you. Blow up a long sausage balloon. Now bend it into a circle and note the hole size. Now blow it up further but keeping the centre line the same. The hole will shrink. Alternatively blow it up just more than originally and bend it into a circle. The hole will be smaller if you use the same ‘centre line’ as previously.

Now blow up the other balloon inside the circle of the first until it almost touches the outer. Now blow it up some more.

@not done it yet: I get the picture now. Balloons are definitely not isotropic solids. They are kept inflated by the tension in the envelope balancing the internal pressure and Rubber definitely doesn't follow Hooke's law; it is very non linear when near its yield point so I reckon all bets are off when trying to analyse what would happen with your two balloons.

PS you would perhaps need a tube connecting the two air masses to balance out the pressure, I think.

Andrew

[andrew lynerParticipant @andrewlyner71257]

It just struck me that the thread title must be wrong. The hole itself is, in fact, made of of AIR.

[Mike PooleParticipant @mikepoole82104]

Very true, we always talk of tapping a hole but in fact tap the material surrounding the hole, full marks for pedantry Andrew I do like people to say what they mean

Mike

Unfortunately answering the question my wife actually asks doesn’t win me any brownie points, I must learn to answer what she meant to ask
 

Edited By Mike Poole on 01/12/2019 22:56:37

[andrew lynerParticipant @andrewlyner71257]

[HopperParticipant @hopper]

The hole is not made of air. If you take the air that's in the hole and place it in the middle of the room, it is no longer a hole. The hole is still back in the piece of nylon.

[andrew lynerParticipant @andrewlyner71257]

Posted by Hopper on 02/12/2019 00:49:19:

The hole is not made of air. If you take the air that's in the hole and place it in the middle of the room, it is no longer a hole. The hole is still back in the piece of nylon.

The air that's gone into the room is still a 'potential hole', though and the air in the hole is now a new actual hole.

But this gets a bit tenuous when you put a brass threaded rod in the hole. I don't think you could now call it a brass hole.

Collapse of argument.

[not done it yetParticipant @notdoneityet]

Nevermind, Andrew. If you go back you might notice that the simple analogy (of a fluid changing a volume) is somewhat entirely different to linear, area, or volumetric expansion due to temperature increase of a solid.

Mike,

I, too, have that problem. I always say ‘if you ask the right question, you might get the right answer’. The answer to ‘how do you spell that?’ was always ‘T – H – A – T’. One of the big failures of students, during exams, was of not actually answering the question posed!

Back in 1967 our ‘A’ level Biology exam had a question on cell division. Most of my class answered it as mitosis and only a very few of us answered it as meiosis. I was right, but I remember I kept very quiet, when a group of us were chatting after the exam, until I had carefully checked the exam question paper. I’m sure the exam was marked to take into account the easy mistake that most made.

Another simple error, by many, was the ‘Proficiency in the Use of English’ exam. Summary and précis did not have the same meaning….

[andrew lynerParticipant @andrewlyner71257]

@not done it yet "a fluid changing a volume". A fluid is fluid so the result of expansion will be in the direction that it's 'allowed to flow'- or the detailed pressure conditions around it. It's always in the details of the conditions that the substance is subjected to. Under a powerful Press, a lump of metal will flow outwards when its temperature goes up. Or, more likely, will form a waist or bulge as it cools down (depending on the temperature of the press faces and the relative temperatures through the lump. Some hard sums to do there, I think.

I have to apologise for this excess of Physics and Pedantry but I frequently read and post on Physics Forums, which is wall – to – wall in both respects. I use a pseudonym on that forum to protect the innocent.

"only a very few of us answered it as meiosis". Teenage boys' minds are mostly concentrated on sex. Surprising there were not more right answers. Or was it just down to sloppy spelling?

"‘Proficiency in the Use of English’ exam" I done that won and I weren't bad at English at the time.

[Michael GilliganParticipant @michaelgilligan61133]

My definition [which I believe to be valid in both practical and philosophical terms] …

The hole is an absence of Nylon

MichaelG.

[Martin WParticipant @martinw]

Michael

That is only true, as in this case, when specifically applied to nylon. Might it not be better to say that, "The hole is an absence of parent material"

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Martin,

You will note that I wrote the hole, not a hole

… as such, it was in the context of Andrew’s item.

MichaelG.

Edited By Michael Gilligan on 02/12/2019 13:03:28

[SillyOldDufferModerator @sillyoldduffer]

Posted by not done it yet on 02/12/2019 09:30:15:.

…

Another simple error, by many, was the ‘Proficiency in the Use of English’ exam. Summary and précis did not have the same meaning….

Go on then, I'll bite, what's the difference?

Dave

[Martin WParticipant @martinw]

Michael

I had noticed that and totally agree that the statement was correct in this context. I was just broadening the description to include the lack of matter in virtually any parent material. . That said I am not sure that this definition would apply to a black hole which theorists predict contains a lot of matter

Cheers Martin

[andrew lynerParticipant @andrewlyner71257]

In the Arctic they fish in ice holes but seals come up to breathe in air holes (same holes, sometimes) Riddle me that.

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