Molding new clear plastic parts

Is the windshield single curvature or double curvature?  That is, can you bend a piece of paper to lie along the windshield?  If so, thin acetate or mylar can be glued in place.  If it has two radii of curvature in different planes (double curved) it will have to be molded.  A picture of the kit piece may help us.

That's a cool bike!  The windscreen looks like the back of a P-47 Thunderbolt bubble top canopy turned backwards.  My guess is that it would have to be vacuum formed.

Tom, is the piece distorted or just melted in spots?

I don't know how to upload a pic to this forum but I can certainly describe it. It is a concave shape curving in every direction. This is from a very low racing motorcycle/sidecar so it has extreme sweep-back, being about two inches wide, and one inch tall but sweeping back from nose to top/rear edge about four inches. The shape is somewhat similar to the canopy of a P51D. The outside is smooth but the inside has deep gouges with maybe 1/32" ridges where the tubing displaced the plastic.

It's not distorted. It just has bad spots on the inside like it's been touched with a hot iron. The spots don't penetrate to the outside.

Years ago, Squadron used to carry sheets of clear PETG plastic which they advertised as "Thermoform" plastic. The instructions which came with the sheets detailed the 'plunge form' technique. In essence, the master part (your windshield, for example) was glued to a dowel and then clamped into a vise. The plastic could be heated over a candle or a burner on the stove until the plastic began to sag, then 'plunged' over the master part and pulled down until the plastic cooled. It worked pretty well for very simple parts (no undercuts or details such as framing, single radii), but it pretty much required a vacuum assist for more complicated shapes or detailed parts. I'm not sure if Squadron still carries these sheets, but I know that PETG is available through Amazon.

Micro Mark now sells a vacu-forming machine.  You need to come up with a pattern.  Maybe you could set up the existing piece to mold a "pattern" from the inside, then work out the bad spots on the pattern piece, and vacu-form a substitute.  Vacu- forming is a popular way to make canopies and windshields.  You could look for an old Mattel Vacu-form, but you'd likely pay as much as for the Micro Mark machine.

Hello!

If the outside is OK, and it's double curvature, like Don wrote, first thing is to create a mold of it, for example of plaster of Paris. If you have a positive copy of the shape, then you can vacuform a new clear part. Hope it helps and have a nice day

Paweł

There are vacuform machines on EBay. They are the same machine that Micromark sells, except they are about $50 cheaper. I bought one and it works very well. I get the plastic in sheets from McMaster-Carr industrial supply. It is a special type of plastic and comes in different thicknesses. Stay away from the very thin stuff as it is tricky, usually .015 to .020 is best. Take the part you have an mount it to a base. Make sure that it has a small gap around the bottom edge (not resing flat on the vacuform table). This lets the vacuform pull the new plastic around the bottom edge to give you a well defined bottom edge on your new part. I usually create vacuforms for scale canopies for kits that I am making to get a scale thinness. I make a resin mold so I can remake one later and because sometime the vacuforming process can crack the original part if you are not careful. One last note: Don't use modeling clay to mount the original piece for vacuforming. Use silly putty or something else. modeling clay seems to have a reaction to the clear plastic and makes it very brittle!

Hi ;

    Here's a silly , but , possible fix .You said it looked like a P-51 canopy . Why not go to an R.C. plane store and see if they have a canopy that size , already Vacuum-Formed ? That is if you have such a store near you , and purchase one the right size or very near it ? .

Here is a video if you decide to go with the Micro-Mark type machine...

Paul