Turning Perspex rod

[sparky mikeParticipant @sparkymike]

Hi .
I need to turn some perspex rod to a smaller diameter. Am I likely to hit any problems? Are there different grades of Perspex/Acrylic on the market and is there anywhere I can purchase short lengths such as 100mm. X 15mm ?

[sparky mikeParticipant @sparkymike]

[JasonBModerator @jasonb]

Sharp tool fairly high feed rate so you don't overheat and melt things.

College do 6" lengths

**LINK**

J

[Phil H 1Participant @philh1]

Mike,

I recently machined some 2" diameter thin walled pipe fittings for a guy who wanted to view the operation of an experimental component and I can honestly say I have had better jobs to do.

The parts had to be machined with a fine feed to ensure a nice clear component and as Jason suggests – it is quite difficult to avoid overheating. I would also suggest plenty of coolant and be careful with the cutting speed. One hazard is that the parts can look ok but if you have tried to machine them too quickly they will crack. I had one example (my first attempt) that looked great but when I held it up to the light it was full of 'silver ribbons' i.e., cracks.

Phil H

[NJHParticipant @njh]

Gray

I did some work with perspex in the past – but mostly milling thick blocks to make gas tight boxes. I seem to remember that the cutting fluid used was parafin? I certainly used chloroform for joining – a very nasty substance but very effective on perspex! We had too some special graded finishing polishes for perspex and, with care (and time and effort!), it was possible to restore a superb original material finish to the work. I found it a very rewarding material to work with but hugely – expensive especially in the larger sizes.

Yes your "ramblings" ( huh! – some ramblings!) are always of interest..

Regards

Norman

Edited By NJH on 25/09/2012 23:09:27

[Steve WithnellParticipant @stevewithnell34426]

Type "perspex rod" into fleabay –

[Roderick JenkinsParticipant @roderickjenkins93242]

Perspex assemblies are often flame polished using a gas torch. It's particularly useful on sawn edges.

Rod

[DismalduncParticipant @dismaldunc]

Many thanks to Rod for the flame idea. I have been faffing about for ages trying to polish the ends of a perpex rod for my optical centre punch (the one that wuz in MEW) half a second in the blow lamp flame and it's as clear as glass .

[merlinParticipant @merlin98989]

A slower setting Perspex adhesive can be made by putting small clean chips of Perspex into chloroform and leaving it for a day or two, shaking occasionally. It has filling properties which help.

[julian atkinsParticipant @julianatkins58923]

i found graham meek's replies fascinating and very informative. thank you, graham!

i have wanted to make some bulls eye perspex lenses for 5"g loco lamps, but have put this off due to lack of info how to turn and polish the lenses from clear perspex bar.

any cheap sources of small dia clear perspex rod please?!

cheers,

julian

[JasonBModerator @jasonb]

I use Micro-Mesh to polish the perspex, this little oiler glass was polished inside and out with it and it comes up crystal clear, better than the photo shows

[NilochParticipant @niloch]

For reasons that escape me we weren't allowed to use chloroform in schools when wishing to bond acrylic. Tensol 12 works equally well but it is best to leave the workshop door open!! Tensol 12 seems to be available on eBay.

[NJHParticipant @njh]

Hi Niloch

I have a suspicion that chloroform may be carcinogenic and, even if it isn't, you don't want to breathe the fumes! See here in the safety section. Better to use the correct perspex adhesive. Note also its gradual conversion to phosgene when stored in the presence of oxygen.

On second thoughts – get someone else to stick your perspex bits together!

Norman

Edited By NJH on 28/09/2012 12:25:07

[Chris CourtneyParticipant @chriscourtney72250]

I do a fair bit of Acrylic fabrication, in particular glueing acrylic sheet. I would be very careful about using Chloroform in a small home workshop… there is a very real danger of anaesthetising yourself!

I normally use Tesnol 12, it works very well as a solvent glue, but it is nasty stuff and you need to have good ventilation, and use gloves to avoid skin contact. If you look at the product data safety sheet **LINK** you will see that the main two ingredients are Dichloromethane (often used as paint stripper) and Methyl Methacrylate which is the monomer of the acrylic.

Please be careful with any of these acrylic solvent glues, they are all fairly harmful.

Chris

[Chris CourtneyParticipant @chriscourtney72250]

One more point I meant to make: The Dichloromethane in the Tensol 12 evaporates very quickly, and seems to diffuse though some plastics. I use a metal container and keep the lid closed all the time except when removing some with a syringe. Some people recommend keeping it in a fridge and using it whilst cold to reduce evaporation. If you are not careful about evaporation then your expensive bottle of Tensol 12 will quickly become too viscous to use easily, and eventually will turn into a solid block…. don't ask me how I know!

Chris

 

Edited By Chris Courtney on 28/09/2012 12:51:05

[David Clark 13Participant @davidclark13]

Wet and dry used wet followed by Brasso.

regards David

[AndyfParticipant @andyf]

Posted by David Clark 1 on 28/09/2012 15:12:49:

Wet and dry used wet followed by Brasso.

regards David

…and if that isn't shiny enough, finish off with toothpaste.

As to solvent welding, a pal of mine stuck some Perspex together for me, and said he'd used ether. if my memory served me right. Or maybe I'm getting my anaesthetics confused.

Andy

[Sub MandrelParticipant @submandrel]

What was the chemical in Airfix glue before they changed to the modern sweet-smelling (ester based?) alternative?

Neil

[Phil CommonParticipant @philcommon62846]

Just a few observations to add the excellent info above. I CNC-route sheets of Perspex for a Chandelier-maker. We rapidly discovered the difference between Cast and Extruded grades. I machine using large dia cove cutters at 18000rpm to sculpt the surface of 15mm and 20mm thick sheets. The cast grade is decidedly easier as it doesn't weld to the cutter, but comes off in large curled snowflakes. The sheet, which has had one entire face removed in the process, stays flat, which is not true for the Extruded. I imagine that the extruded has stresses built-in which become unbalanced once cut.

I also machine one side off of 30mm rods from time to time and these machine beautifully using the same settings.

If these experiences have any relevance here then it might be to suggest that very high speeds in the lathe would be worth trying, along with a range of feeds and DoCs.

[HomeUseParticipant @homeuse]

Hi Andyf – Ether is comercial cloriform – I used to buy it from the highstreet chemest for use in small areo engines ( Ether/CasterOil/Parafin) combination – It also glued together the perspex canopies on the models – Disolve slithers of perspex in ether to make sticky goo and then use in well vented (outside) area. – Dont know if Ether as still available (may be not due to some Health and Safety reg.!!!

[AndyfParticipant @andyf]

I'm not sure that's quite right; chloroform is CHCl₃ (carbon, hydrogen and chlorine). "Ethers" are a class of straightforward hydrocarbons (just carbon, hydrogen and oxygen). The one which was once used as an anaesthetic is diethyl ether, CH₃CH₂-O-CH₂CH₃ , but I don't know if this is the particular ether my pal used to weld Perspex for me. I doubt if you can buy it at the local chemist now; long gone are the days when you could buy the ingredients for gunpowder at the local Boots.

Andy

[Ed DuffnerParticipant @edduffner79357]

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

[Billy MillsParticipant @billymills]

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

[Billy MillsParticipant @billymills]

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.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

For many purposes it is easier and sometimes better to cast Acrylic components in moulds . Material is readilly available and comes as gel and hardener . Moulds can be made from many materials including metals , plaster and rubber .

A Bulls Eye lens for example could be made in a plaster mould using a light bulb as a pattern or a better one in a machined block of Aluminium .

A parting agent is available to prevent Acrylic sticking to mould . When using porous mould material it can be useful to seal the pores with varnish .

Various grades of gel and hardener are available but a simple combination is sold as Embedding Resin packs in craft shops .

Acrylic doesn't like being cast in very big solid lumps and best to make large castings hollow . There is some heat generated when making large castings and this can degrade the material also variable seting times across large sections can cause cracking . In model engineering sizes no problems of this sort are likely .

Perspex polishing compounds are available . Perspex will also successfully burnish using a well smoothed tool .

Cast Acrylic can be astonishingly strong when component is designed properly . Best demonstration of this strength is in small deep going submarines where cast Acrylic is used for the bug eye type observation windows .

Regards ,

Michael Williams .

Edited By MICHAEL WILLIAMS on 29/12/2012 09:43:19

[Author]

Posts