Member postings for Sam Stones

Many containers are vacuum-formed (moulded) from acrylonitrile butadiene styrene (ABS) sheet, while high impact polystyrene (HIPS) can be found in the form of injection moulded yoghurt tubs. Most plastic bottles requiring high burst strength are made from a material called polyethylene terephthalate (PET). Some containers are made by injection moulding plastic around waxed-paper inlays, so be aware of this as a possibility.

Take-away containers are usually injection moulded in polypropylene homopolymer (PPHP), and unless they have been heavily coloured, they will display either good see-through clarity or what is termed contact clarity.

For your convenience, I have extracted the following Resin identification codes from Wikipedia. The number is usually inserted in the centre of a triangle of arrows indicating their re-cycling use. :-

If you are unsure, especially if the sample does not carry an identification code, an easy method for determining if the materials is styrene-based or is a polyolefin such as PP or polyethylene (PE), is as follows :-

Snip a small piece off your sample, and slide it into very slightly soapy (wetted) water. Make sure there are no bubbles stuck to the surface. If it floats, it is most likely to be one of the polyolefins such as PPHP or PPCP, or it could be either HDPE or LDPE. If it sinks then it could be one of the styrenics, OR a polyolefin filled with one or other of a finely powdered mineral.

From the buoyancy test (ie. indicating a density less than water), if it flexes easily and springs back, it is probably PP, but if it lacks this elasticity it is more likely to be HDPE. If it is really soft, then this usually indicates LDPE.

Either of the two polypropylenes are handy materials if you want to produce a light-duty hinge. (Ask me how to do this if you need more information.) Polypropylene copolymer can be identified by carefully folding or indenting a thin (or thinned) sample, and noting if the stressed area becomes lighter (blushes) in colour.

If you plan on using any of the above materials as a source of sheet for model making, you will find that the styrenics (ABS and HIPS) and vinyls (PVC), are readily glued or solvent welded. But test the results on a piece of scrap material first.

Conversely, the polyolefins are quite difficult to glue, without the use of some oxidising primer, or a very briefly applied but very low intensity oxidising flame.

PLEASE TAKE CARE WITH ANY OF THESE METHODS & MATERIALS!

Adam’s posting is to be commended, so "Well done, Adam!"

The fact is, unless we can demonstrate our competence as a genius, or have become a professional student, there probably isn’t enough time in our lives to qualify in `Everything’.

Before clockin-off, one of my favourites stems from when, as a fairly recently promoted technical service officer smartly dressed for the occasion, I was `advised’ by the works manager of a plastics factory as he dashed past me that :-

"All your theory goes down the drain in this factory, you know!?"

With his overcoat flapping in his slip-stream, this manager had blustered past me about half a dozen times on his way to and from his office. Presumably that was necessary to keep the wheels turning? But, how did he know that I was an academic, or anything else about me for that matter?

Soon after his startling revelation, the moulding machine `jammed’.

Then, as if it were standard practice, four or five of his operators took hold and began swinging on a long length of 6x4 timber, trying to free the machine. That was the moment when it was pertinent for me to leave discretely, wondering if a drain had blocked.

Now, at least, I know what DOC means! Thanks again Nick.

Ian (S C),

So would OD = OFF DIAMETER? Or am I entitled to accept that it’s still short for OUTSIDE DIAMETER?

By the way, watch out for those big coils of blue steel. They have been known to find their way inside trousers.

How obvious!  Mutter mumble.

Clearly, only an ignoramus would ask such a question. Especially one who’s been applying DOC’s for about 65 years without knowing it. AND worst still, one who has been surrounded by plastics acronyms since 1950.

Perhaps for us oldies (who, like me, are too lazy to work them out), ME could collect and build a useful acronym glossary?

Thanks for coming to my rescue Nick!

Regards,

Sam

I’m addressing John Coates' second question from the start of his thread dated 14/11/2010 - Turning - how to return a RH cut

As a Myford advocate, I bought my ML7 second hand in the early 60's. As I recall (from the widow who was selling up), the lathe was brand new in c1946. In other words, this was a machine which had been used for about 60 years when I sold up. It served me extremely well in all the time I used it, although I would have preferred a Super 7 based upon my toolroom experiences.

However, I have to say that, because the design of the ML7 saddle did not fully address the Narrow Guide Principle and issues Kinematic, the inevitable off-set forces, particularly those in opposition from the lead-screw and the tool post, eventually caused wear which allowed the saddle to rotate very slightly in the horizontal plane.

This produced two adverse effects. Firstly, it allowed the cross-slide to twitch out of square, and secondly, upon completing an internal pass, it would cause a tool to remove a little more metal if the saddle feed was reversed without first moving the cross-slide forward and cutter (ie. away from the operator and the work piece). The converse was such that the cutter would lift off an external diameter of the work piece rather than leave a spiral as per the experiences of other members.

Hi E,

From my experience of almost 65 years, it seems to boil down to :-

"Where should your patience be applied?"

Will it go into the models you make, or into the machinery you choose? I know what put mine to the test.

Anyway, good luck with your choices. I hope you get as much out of your hobbies as I.

Sam

In my case, there are no straight answers to Eddie’’s questions.

When there's an email address and a quality guarantee printed on the packet, why waste time with the retailer and their rehearsed excuses?

Hi Boldminer,

Thanks Michael.

Thanks to everyone who contributed to this significant though tiny piece of my clock, I had a successful afternoon testing what I considered to be the best combination of ME ideas provided by various Forum members.

Without your help, I think I would now be ankle deep in twisted guitar strings.

With reference to my latest photograph in my John Stevens Skeleton Clock album, and a section of Machinery’s Handbook about mandrel (arbor) sizes , here are some of the facts built into my first respectable attempt.

The mandrel was machined down to size and cross drilled 1.0mm diameter next to the root radius. The free end of the guitar string was threaded through this hole, and the unsupported (cantilevered) mandrel given a couple of turns to `catch’ the wire.

The guitar string was then passed over a plastic (polypropylene) idle pulley of about 19.5mm diameter. I figured that this pulley should be quite large relative to the mandrel.

I positioned the pulley about 250mm from the lathe centre line so that the wire had more freedom to twist on its axis during the winding stage. I elected to leave the pulley with a plain diameter (rather than cut a groove), so that the wire had greater freedom to `roll’ sideways on its own diameter, and because the lathe did not captivate my interest in trying to match the wire pitch to the feed. In other words, I would close-coil the wire, and then `pull’ the spring length into position later. A weight was hung onto the end of the guitar string, and the lathe chuck turned backwards by hand.

IMPORTANT NOTE - TURN OFF THE POWER SUPPLY TO THE LATHE.

With a sufficient number of turns on the mandrel to test the theories, I brought another piece of plastic hard up against the coils. The handle of a toothbrush gripped tightly in the tool post was very convenient for this purpose. I angled the contact face of the toothbrush handle so that the coil at the right hand end of the spring/mandrel would be the first to rotate. I intend to machine a proper face on the toothbrush handle to better suit the geometry.

At this point, the feed-end of the wire was cut, and the cross slide of the lathe very slowly and carefully withdrawn. It was necessary to trim a short tail off the wire so that the spring could readily unwind. The results can best be seen in the photograph.

Here are some details :-