Perspex and Sheet Metal

Someone can do this, but you don't have the budget/knowledge.

If you have a mechanical drawing of the device, AutoCad would be nice, you could get it produced by stereo lithography.

If you do it by hand, you have to heat the plastic and form it around tools/molds/forms and this isn't something easy to do.

What's a PIV?

A hair blow-dryer would do just fine

Sory but a hair dryer doesn't concentrate the heat enough. It tends to blow it in a wide area.

When I worked in a model shop we used perspex for everything and we used a heat strip to focus the heat along the bend line. The heater is simply a heater element like you have in a stove but in a straight line. The heater is mounted in a U channel for protection. Thin aluminum heat shields are fastened to the box or channel housing the heater rod. The seperation between the two shields defines the heating zone.

If you wan a sharp bend keep the heating area narrow. For a more gradual bend leave the shields wider apart. We typically used 3000 watt heater strips. A hair dryer is only 1100 or 1500 watts.

It does take some practice to judge how long to heat a sheet of perspex for a good bend. Too much heat and it sags. Too little heat and you risk cracking the sheet. Might help to have a little timer handy while experimenting

Also works well for post forming of arborite laminate when making custom furniture. The heater strips are industrial. Not something you would find in a consumer product supply store. Try Chromalox catalog to get an idea of what to ask for. Then go to electrical wholesaler like westburne, Nedco, Etc.

Post script to bending perspex. If the individual sheets are small enough you might get away with cannibalizing a counter top toaster oven. Some of them have a quartz radiant heating tube instead of the conventional resistive heater rods. I have not used the Quartz tubes but it may work just fine.

BTW if you need a precision timer control, try cannibalizing an old microwave oven.

Typically these get junked becaue the magnetron blows or else the door interlocks get out of alignment thus preventing it from turning on.

The timer controls activate the magnetron by operating a relay with contacts that can handle 1500 watts. Jumper out the door interlock and you can program in any time interval you please. Precise and repeatable.

I once had to do a prototype batch of ferrite coils. They had to be baked at a certain temperature for a couple of hours. I installed a thermo couple sensing controller scrounged from an industrial machine. The thermo couple wires got inserted into the toaster oven cavity from the back. The actual over was controlled by the relays in the controller. Since the baking interval was in hours, not seconds or minutes I used an electric clock for timing. Now I have a microwave overn control board.

Its amazing what you can find and improvise with, from the dump.

How does Perspex compare with Plexiglas?

they are both trade names for the same stuff along with about 15 other names. look here

I've done some work like this with Plexiglas. The two problems I ran into was getting it hot enough to form without charing or igniting it. Also, when it gets hot, it tends to hold the heat, and takes a heck of a long time for it to finally cool down.

Use water like a blacksmith to cool it down

No. I'm serious! Even holding it under cold running water, it took a long time to lose its heat.

Yep! which is why its a good idea to limit the area being heated. It tends to lessen the total amount of heat stored in t mass. And if you do not maintain the exact angle or curvature of bend until it cools, you ruin the work.

So what did you do with the tempered perspex? Lots of internal stresses. Looks really neat under polarized light.

Both are trade names for PMMA Poly(methyl methacrylate). Commonly called any of acrylic, Perspex, and Plexiglass. As acrylic can also refer to other polymer types, anglophone Europeans (though not exclusively they) tend to use the shorter of the unambiguous names (perhaps that makes it sound more impressive when they use polysilabic words for other unnecessary situations...)
Like most polymers, the properties will vary according to production details (and possibly additives), so there are those who claim that branded Perspex is less brittle than branded Plexiglass, but I'm in no position to make this comparison.

If you google Plexiglass and open the Wikipedia page, you'll find a refreshing inconsistency of terminology.

I don't know where you are or what our resources are.. but if it is complex, I would recommend modelling it in a 3D cad such as solidworks and then having it 3D printed. Then you can build it to accept transparent materials. there are expenses, but its neat and clean if you can do it.

other than that, I would probably carve it out of laminated wood blocks or something else that can be glued, and sealed, screwed, etc. Another idea as proof of concept is to use PVC pipe from your local hardware store (North America) and you can probably use plexiglas (perspex) sealed with silicone sealant. I'm thinking you only need one to prove concept. or you can use the old sight guage tube to determine fluid level, as it will be much easier to implement.

I used to do plastic fabrication using sheet materials. You can order acrylic with a paper mask and draw your patterns on the paper and cut them out by hand with a scroll saw or band saw fairly easily. I used a CO2 CW laser cutter. Make sure that you round all of your inside corner cuts so that the acrylic will not crack when bending it. If you have access to a 10amp variac 0-120v and a few feet of ni-chrome wire you can set up a simple line bending setup easily or you can purchase a 36 x 1in strip heater from your plastic supply company for about $35.00. Cover a few boards with felt so that you will not mar the surface of the material. Acrylic becomes flexible around 325degrees you can feel the softness of the material by using a few test pieces. To make conical shapes use a stabilo aqua pencil to draw your lines and bend small line segments to form the shape you want. The lines wipe off with a wet paper towel. If you need a truly round shape make a male mold from sheet metal or wood then cover in felt. Using a heat gun and gloves evenly heat the piece then wrap to the shape you want. Use a fan to cool your piece not cold water unless you want to create a lot of surface stress which will cause the material to make tiny fractures called crazing and break down the road. Use a weldon 16 or weldon 4 from IPS to glue pieces permanently together or use acetone on the edges and silicone.

You can also purchase clear PVC pipe and fittings

Good Luck jack@jmsis.com

I just made a case for my rock saw out of clear polycarbonate. Used a propane torch to heat it under a mandrel and used heat shields to limit the heat zone. One trick you can do with some plastics is make a negative form then heat the sheet and lay it in the form to cool. If you want to get real fancy mount it in a frame and vacuum it into your negative.

Surprised you haven't googled heat plastic forming. http://www.google.com/search?hl=en&q=Heat+plastic+forming&aq=f&oq

Brad

Ram44 = Ram x 44 = 44 Times Ram Ram. (Good) ==> In fact I have not tried out of my own but used many times a bends and curve type shapes of perspex sheets. I (it is guess but with my experiences may be in reality also) think bu using hot air or by slightly heating (please check the melting point of perspex before applying heat) it can take required shapes. While giving shapes use support of same type shapes. For that purpose wooden logs are better. Better use 4 to 5 mm thick perspex sheet.

i am going to use an oven to heat up 3mm perspex sheet and create a cylinder (pipe)

i already machined a pvc pressure pipe so that once i soften the perspex and "wrap" it around the pipe i will get the required internal diameter. for the conical sections i have a sheetmetal piece made around which i will form the perspex piece. will report the results soon as i am done.

more on PIV : http://en.wikipedia.org/wiki/Particle_image_velocimetry

Thank you

RAM.

thanks all;

i heated the 3mm perspex sheet for around 10-20 mins at 126 deg Celsius. then rolled it inside a sheetmetal duct which i had previously made. as it sarts to cool, as i pull it out of the oven it starts to loose its flexibility, once inside the sheetmetal piece its outward movement is resisted by the sheet metal. i have not seen it bend inwards in any case. the edges just touch each other and a touch of epoxy at the seams seals it well. i have been able to create clear perspex tubes (with seams), conical ducts, and many curved shapes in very little time with very little equipment or effort.

once again ..thank you all.

Cheers!

RAM.