Vacuum moulding

I would like to make a replica of some ladies bike dress guards.

I have a pair already which are on a bike from the mid 80’s.

They are clear and perfectly suit bikes of this type.

All modern guards are tinted or made of mesh which is not ideal.

Can you take a vacuum mould of something which is plastic without damaging it?

I ask as I know that there is a fair bit of heat involved in the process.

Would I be better off using the originals to make plaster moulds or something and then vacuum mould that?

You can see the guards in question in this photo on my Wife’s bike.

You can still but those, they’re common here in NL.

I’ll do some googling for you later

How would you vac-form from soft plastic like that?

Sounds like a whole load of ballache but I don’t know why mesh or tint aren’t acceptable.

The things over the back wheel under the rack? Looks like clingfilm and coat hanger to me. I’d make a replacement from that…

In seriousness though are they not pretty much flat looking at that? What needs moulding?

If you tried to vacuum form a hot plastic over another plastic item, the plastic ‘former’ would probably deform.  Vacuum forming only gives you a limited depth – something like 2:1 depth to width maximum, not the 5:1 or more needed for your part. Can’t think of any process where you  could mould this affordably – clear PVC and wire rods probably better

heating plastic and overlaying another layer of plastic is likely to end with both pieces of plastic fused together and then impossible to separate.

In the picture above the material looks like a vinyl film, which would not take to any hot moulding processes.

https://hollandbikeshop.com/en-gb/bicycle-parts-city-bike/dress-guards/dress-guards-28-inch/hesling-dress-guard-28-5-lucra-w-transparent/

Interesting that most of them seem to be Smoke rather than Transparent though

If you vacuum form over something you won’t get a copy, you’ll get something bigger.

You need to take a cast of the inside of it. We used to do this with RC car body shells in school, and it worked. You need to use tape or something to create something that will hold water, then fill it with plaster of Paris. When that dries, you use that as your vacuum form and cut off the pieces you don’t need.

You will probably have to insert some wire into the form to stop it breaking when you handle it.

Thank you all for the comments.

I really like the clear style, the moulding of the plastic adds the rigidity and stops it deforming.

I appreciate the pitfalls of the heat applied during Vacuum moulding, I will have to try the plaster of Paris route.

I don’t get why they are all smoked either.

I didn’t reply to this again as you already have a few options for buying them. Don’t try to mould it, it’s surely a waste of time when you can still buy them.

If you do manage, it will be of interest to anyone who wants to make full guards for their mud chucking fatbike… 🙂

Make a wire frame, tape polythene over it then heat-shrink the polythene with a heat gun?

All modern guards are tinted or made of mesh which is not ideal.

Not so, but if you are just looking at UK shops or using English search terms, I can see why you might think that.

Try ebay.de or ebay.nl and use the search terms Mantelschoner or mantelschutz and rockschoner (coat and skirt saver or protector), they are available in transparent, but if the bike gets used, they scuff up on the inside quickly, messing up the transparent effect.

https://www.ebay.de/itm/Mantelschoner-26-1-Union-Basta-Rockschutz-Hesling/151946913334?hash=item2360bde636:g:-fsAAOSwQctbTyFl