Member postings for Sam Stones

ASP

You'll find the whole complex by way of excellent photographs and text in this link.

**LINK**

It provides an amazing and informative step by step coverage from about 2003.

Leave yourself plenty of time.

Sam

Mechanically complete, I would be doing this project and those who designed and built it a disservice by trying to describe it.

Take a look ...

**LINK**

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

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

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

Drilling (and machining) especially thermoplastics can be problematic if the drill/cutter is rubbing.

This heat can be enough to expand the plastic, and even take it above its melting point.

Because the heat is local, it would be (perhaps) the one exception where the hole reduces in diameter (as has been discussed here … "Reamer size Questions"

**LINK**

Taken slowly with very sharp cutters (sharp as for wood), and the appropriate coolant, should be the aim.

Localised heating/melting can be a source of stress and potential failure, as in stress cracking and crazing.

For comparison, the coefficients of thermal expansion of certain thermoplastics (Nylon, polyethylene, polyacetal) can be almost an order of magnitude greater than steel.

See here ...

**LINK**

Did you intend that pun about the drift Dusty?

Hi Panos,

You might like to consider an adjustable reamer (for the 1/4" at least). Not sure how small they go.

Would a tapered reamer (and therefore a tapered hole) work?

Regards,

Sam

**LINK**

Andrew,

I get concerned for those handling polyacetal (POM, Delrin etc.) for the first time.

While I fully agree about how easy it is to machine, do not be tempted to burn the swarf. As with other polymers (e.g. PVC), the fumes are very noxious. You'll know (and remember) if you get a whiff.

Please see also ... **LINK**

Good luck.

Sam

Andrew,

I haven't tried this with nylon, but machining (truing) polyurethane rubber skate wheels came out better after they had been in the freezer for a while.

I could imagine that, as with most materials, nylon will shrink further, will be harder, and may tap to a marginally larger size.

I could also imagine under such cold conditions, a new (very sharp) tap could either shave a whisker off the existing threaded hole, or indeed tap a larger hole from scratch.

Watch out that you don't generate too much heat in the process.

Although I've machined nylon on a number of occasions, I too prefer machining polyacetal (Delrin).

Sam

Neil,

Perhaps the thread pitch will affected, but surely the hole will also increase in diameter at higher temperatures?

In a word David - 'MAGIC'

I didn't have this picture loaded in my albums, hence this delayed follow up.

This device for testing rotary switches features various uses of polyacetal. Black for bearings, and I think there's a slab of white with all those 'spikes' poking through. It may however have been high density polyethylene but I can't remember.

Sam

Nice work Ian, and I trust you didn't mind my interjection re the fumes. I'm no chemist, but I think burning POM liberates formaldehyde.

Compared with nylon and polypropylene, I much preferred machining p.acetal.

Sam

And ... don't sniff the smoke if you happen to overdo the flame treatment of polyacetal. You'll know why (and never forget) if you do.

Other than this (after a bit of practice on something which doesn't matter), I'd go along with Ian's 'flame polishing'.

It's also a useful (actually a commercial) technique for oxydising (oxidizing US) the surface of a crystalline polymer (plastic) prior to painting.

Incidentally, there are many grades of amorphous plastics which are blended or otherwise modified with other materials, rendering them less polish-able (Ugh!)

Sam

Play safe

The two basic families of materials being discussed here are either crystalline or amorphous.

I'd like to suggest (although I haven't tried), that polishing items of crystalline materials, e.g. polyacetal, Nylon, polyethylene, polypropylene, etc. need to be deep frozen, or at least taken below their glass transition temperature.

I have machined (trued up) with some success, polyester (rubber) skate wheels directly from the freezer.

I also question, during the abrasion and polishing, if the surface of crystalline materials is being continually 'pulled apart', thus introducing (let me call it), a broken surface. Someone with good microscopy (and photographic) skills might like to intervene here.

Acrylic, and other amorphous materials on the other hand, are (generally) a breeze to polish.

Good luck,

Sam

Many thanks Michael.

Yes, it was a Google search. I had been thinking that their 'speed-of-light' results was them just showing off.

Not knowing of such a simple device, your explanation shows clearly that I have much to learn. [The more we know, the more we don't know.]

By the way, I had never realised how popular I was with 12.7 mega-hits

Sam

I often wonder about the benefit of a search result that might look like this ...

About 1,940,000,000 results (0.60 seconds)

It's obviously a very impressive result. But who would ever consider wading through 1.9 billion references?

What's your take?

Sam

Thus 'seduced' by the idea that the finest silk resolved the problem attributed to rayon , would anyone in the EFHC care to repeat the test with rayon (filament), thus dispelling my thoughts that some other effect might have fixed the endurance issue?

Just curious, Bob.  

Personally, I would be concerned for the longevity of rayon versus silk in terms of environmental factors, none the least being UV.

Here in Australia we have lots of it scattered around. Don't ask me how I know.

Sam

Edited By Sam Stones on 04/10/2019 00:00:11

I highly recommend the Clickspring video of the player card press mentioned above by not done it yet.

It would have to be one of Chris's best.

http://www.clickspringprojects.com/

Sam

Edited By Sam Stones on 02/10/2019 01:46:16

This was my version of a nutcracker which I designed and prototyped to be injection moulded in polyacetal. Several metal parts formed the mechanism.

I based the action on a typical mastic-gun mechanism. The (fly-back) release was spring-loaded using the same lever seen at the front of this picture.

Please excuse the poor quality images, they are rephotographed (digitised) from paper prints.

Although parts were eventually injection moulded (and could be snapped together with integral 'undercuts' minus those crude 'U' shaped clips), I never got to see the finished article. I was informed by a colleague however, that they were 'perfect' for cracking lobster claws.

The acid test for a nutcracker would surely be opening macadamia nuts?

BTW, there are more even poorer images in my nut-cracker photo album.

Sam