Lexan Tubes and Vapor Polishing 2

[Haf]

I am in need of Lexan (or a similar polycarbonate) tubes with an ID of 1/8". Apparently, Lexan tubes are not made with ID's less than 1/4" (I was told this by a plastics supplier). Initial web searches seem to confirm this. Can anyone suggest a supplier?

Another option, of course, is to get Lexan rods and drill an 1/8" hole through its center. The problem with this is that I need good optical clarity on the inside surface. Does anyone know of a good (and relatively inexpensive) way to achieve this through machining and/or polishing? The tubes will be about 0.5" long with an OD of about 3/8".

I have heard of a process called vapor polishing that can be used to polish machined plastic parts, but I don't really know what's involved, how it affects tolerances, or how expensive it is. Anyone have experience with this?

Thanks,

Haf

 

[crun]

Vapour polishing of acrylic plastics involves the use of a chemical called Dichloromethylene (also known as Methylene dichloride) - there is a better than even chance that this stuff will work on polycarbonates too.

I have some notes on the subject somewhere around the place but have not been able to lay my hands on them just now, but the process is fairly simple. A small amount of Dichloromethylene (lets call it DCM from here on, huh?)is put in a pyrex flask with a rubber stopper which has a glass tube through the stopper and a rubber hose attached. Along with the hose connection it is a good idea to push a thermometer through the bung and into the DCM so that you can keep an eye on how hot it is getting. Some sort of non-plastic nozzle at the other end of the hose is handy.

Gently heat the flask to 40 degrees C and direct the vapour down the hole you drilled. The vapour melts the surface on the inside of the hole and surface tension pulls the imperfections left by drilling flat. I've used this process to polish acrylic lenses, but have not tried it on polycarb.

DCM is not good stuff to breathe (it is similar to Methyl Ethyl Ketone - M.E.K. which is the active ingredient in model airplane glue, but DCM is even more agressive, so do this in a well-ventillated area. It is also important to keep any volatile chemicals off your skin so rubber gloves are a must.

Before you go overboard and buy all sorts of kit to do this, it might be a good idea to repeat your query on the chemical engineering forum. Someone there is sure to be able to clue you in on the properties of DCM, Polycarbonate interaction and on the safety precautions for handling potentially hazardous substances.

I hope this helps

Crun

 

[hacksaw]

where can you get small quanties of either methylene or ethylene di-chloride.

most of the suppliers require bulk purchase.

 

[crun]

It is a tad difficult to answer a question about where to get chemicals in any sort of specific way without some idea of where the person asking the question actually lives. (I live in New Zealand - next stop south being Antarctica) Added to that is the fact that most countries have rather idiosynchratic laws about who can sell what chemicals to whom - so, like I said, I cannot be all that specific but I can point you at a few possibilities.

Companies that specialise in fabricating display stands and equipment from clear plastics are likely to use vapour polishing and could possibly be talked into letting you have a small amount of DCM to experiment with.

Your local chemist or pharacist can probably be persuaded to order a small quantity once you satisfy him/her that you are not some closet loonie, or want it for illicit purposes. (Most reputable chemical suppliers will ask what you want chemicals for - quite understandably, they don't want to be involved with a Unibomber or kitchen drug maker)

In my own case I have no trouble getting it in 500ml bottles from a local chemical supply company. (I make up my own firearm bluing solutions that I use when restoring antique guns - most of the ingredients can also be used for making explosive devices and I had to send them a copy of my formula before they would agree to supply me with what I needed. In the current world climate that is quite understandable, huh? Anyway, be prepared to answer their questions because their concerns are legitimate and they are not just being nosy)

Another possibility is anyone in your area who makes paint stripper because DCM and MEK are both ingredients used in such products. (MEK will even chew through powder coatings!

Getting back to my earlier point, if anyone is asking where to get materials it might be a good idea to specify what country they are in or the responses may be less than helpful.

I hope this helps -Good luck

Crun