Turning Perspex rod

As an alternative to buffing there are some interesting videos on youtube regarding flame polishing acrylic. I think I read somewhere that perspex can't be flame polished but you'd need to check on what's possible for the type and grade of material you use.

Examples:

**LINK**

**LINK**

http://www.youtube.com/watch?v=PF8ckO-22fc&NR=1&feature=endscreen

http://www.youtube.com/watch?v=QhAXbA2lmnE&NR=1&feature=endscreen

Edited By Ed Duffner on 27/12/2012 08:12:38

Edited By Ed Duffner on 27/12/2012 08:12:54

Edited By Ed Duffner on 27/12/2012 08:15:39

Have also worked a bit of acrylic . If you are trying any kind of cutting it will only work with razor sharp tools otherwise it tends to weld to the tool edge then shatter. For circular sawing of large sheets triple chip carbide tiped blades work very well, other blades tend to jam and shatter the sheet.

Turning goes well with honed HSS. Have not read that you can't flame polish Perspex, it has worked fine for me and others for years. Laser cut perspex has a polished edge appearance and is easily ( and frequently) mistaken for abrasive polishing or flame polishing.

Had the leaking tank problem with some etching tanks some while back. Solution was to use silicone rubber as a seal and bolt the tank sides together.

Billy

Did a bit more digging about flame polishing Perspex as Ed is normally bang on the money. Came across a site which suggested not to flame polish matt or frosted types - it might look a bit odd for some jobs.

The people who know about Perspex produce a very useful info sheet **LINK** . They make the point that you might induce stresses which is exactly what happens every time you work almost any material. But there is no great no-no on flame polishing perspex.

Billy.

Well, you learn something new every day. Didn't know about flame polishing Perspex.

When I was an apprentice we made marine equipment that had perspex components. Some of these were glued together. The chemi lab made up the 'glue' , this was a colourless liquid Araldite that had a usable life of about 10 minutes. It was a question of paint the sufaces, bond, clamp together then leave for 24 hours. Parts were often stuck the wrong way round etc. Up to the canteen to get 1 pint boiling water into which about 20 catering tea bags was stewed for an hour or so. Overnight this softened the araldite .

MEK ( methyl ethyl ketone, butanone) is a very common industrial solvent widely utilised in cellulose paint thinners. It is much less volatile than acetone. I would not advocate sloshing it around in a small room but opening a bottle is very unlikely to cause any problems. Because it is less volatile than acetone (which is widely sold and used to remove nail varnish) it is safer both from a fire hazard and a toxicity point of view.

MEK is a good solvent for Perspex (plexiglas, polymethyl methacrylate) and can be use for solvent welding it.

Mike

Perhaps there are a couple of important points left.

Cast and Extruded are very important distinctions, the mechanical properties of these two types are quite different. Cast tends to have more internal stresses as supplied which tends to increase as you machine it. It is normal to anneal -around 90C- to remove these stresses. ( this stress from machining is also common to many other plastics). Cast Perspex is in some ways like glass to work.

It might be that the stress cracking that Gray experienced in old Perspex could have been fixed by annealing.

The whole story can be seen here **LINK**. This is the most detailed account of using Perspex that I have seen and also has a section on how the material reacts to many common chemicals.

Billy.

This is all interesting stuff. Was MEK in the old glue or the new?

Neil

Chloroform in air and sunlight oxidizes to Phosgene. Phosgene will kill you and was used as a poisonous gas in The First World War. This is why Chloroform is always kept in a dark coloured glass bottle and is never inhaled directly.

JA

There is a good summary of the toxicology of MEK at this link:

www.ccohs.cas/oshanswers/chemicals/chem_profiles/mek/health_mek.html

All chemicals should be treated with respect not alarm.

Mike

Most of the MEK solvent based glues for polystyrene plastic kits aren't tenacious enough for acrylic. It's also worth mentioning there are two types of Tensol cement. One is air drying and the other has a catalyst to cure it. The latter is what you want for laminating sheets because obviously the airdrying version would stay wet inside once the edges had set. Both are quite syrupy and VERY odourous. I'm tolerant of most thinner/paint/resin/glue aromas but this stuff is pungent. Both can be thinned with Dichloromethane/Trichloromethane but obviously you need to watch evaporation in big sheets. The air drying Tensol, not unsurprisingly tends to shrink down a lot as it dries and although the catalyst type does too, it's does so far less. The airdrying one also tends to stay a little soft even when dry where the catalyst type becomes as hard as the acrylic and may be sanded and polished in the same way.

Superglue takes to acrylic exceptionally well but most of the superglue accelerators you can spray on to speed up the setting tend to embrittle the surface of the acrylic and you get the cobwebbing mentioned previously on the surface.

Edited By Chris Trice on 30/12/2012 02:05:56

Thanks for posting that link, Billy

An excellent reference !

MichaelG.

Edited By Chris Trice on 30/12/2012 11:22:30

That was mostly the model figures and some of the military vehicles which were intended more as toys. The actual construction kits were always styrene. Some of the VERY early and highly collectable kits were moulded in acetate.

I remember the little bulbs, ten the white and blue tubes. Yes, when it went 'off' it left behind a brittle, transparent material. If you made a mistake and went back to repair it and were too greedy with the glue, eventually the plastic would go soft beyond the joint. It wcoudl take weeks to go hard again - how many times did you come back to a model finished teh night before to find it had 'done the splits'.

You could make a sort of plastic putty by dissolvinjg sprue in glue (I now it is technically 'runners' not sprue but everyone called it sprue when I was a kid.

The biggest loss is that of the transparent display stands - apparently the moulds have been lost. Remember how the bit at the top always broke off?

Most of my planes used to hang off nails in the wall. I knew when my mum had dusted them as she would repair them at random trying to huide the damage - I don't know how many times I said leave the repairs to me!

Neil

Au contraire:

**LINK**

Here you go Neil:

Edited By Chris Trice on 30/12/2012 23:35:34

Hi Chris,

You've made a happy man feel very old...

Neil

I've got about 400 kits in the loft acting as insulation, mostly Airfix and all pre mid seventies. I've got about a dozen of the glass bottles of paint which are approaching 45 years old yet with a two minute shake visually look as good as the day they were filled.

Hi Chris,

Unassembled? Must be worth a bomb!

I have about twenty part-used tinlets mostly from the 70s. It takes a LOT of stirring and the addition of a drop of proper thinners (not white spirit) and you can get t to perk right up.

Neil