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Using brown parcel tape on patterns for GRP moulds?
interestedparty - 14/2/11 at 06:20 PM

I've often heard of people doing this, they make a pattern, then cover it with brown parcel tape which apparently the resin doesn't stick to, and so no release agent is needed.

What I am wondering is, if I was to do this then the edges and creases in the tape would be printed into the gel coat of the mould, is it feasible to flat and polish the mould surface to get rid of them?

smart51 - 14/2/11 at 06:24 PM

It doesn't need to be the brown stuff. The clear works as well and doesn't leave as much residue. I covered a wheel with tape and made my cycle wings on them. (using a wheel bigger than the one for my car!). All the marks, folds, edges and creases are shown in the part you're pulling off them so either put enough gel coat on to sand back or apply filler to build up the surface. On my wings, the tape marks are on the underside so it didn't matter. See here for the results

Fred W B - 14/2/11 at 06:31 PM

Question is, is it more work to wax the pattern 10 times, or flat the marks out of the mould? Assuming you can put enough gel coat on to give you enough depth to flat back?

Depending on the shape of the part, it would seem easier to finish the convex part, rather than a concave mold, in my limited experience.

I do use the tape trick on flanges, but not on the part surfaces.

Cheers

Fred W B


[Edited on 14/2/11 by Fred W B]

Benzine - 14/2/11 at 06:35 PM

That's what I did ^_^:













Then that mould was taken off, filled, smoothed with a lot of elbow grease then a mould taken from that which was grafted onto bonnet:


interestedparty - 14/2/11 at 06:54 PM

quote:
Originally posted by Fred W B
Question is, is it more work to wax the pattern 10 times, or flat the marks out of the mould? Assuming you can put enough gel coat on to give you enough depth to flat back?



Well, it's not just the waxing, I'm assuming that using the tape I could get away without having to seal the porous (wooden) surface of the pattern too.


quote:
Originally posted by Benzine
That's what I did ^_^:


grafted onto bonnet:




Have you got any further than that yet? If so, how did it turn out? Did you combine the nosecone and bonnet, I'm not quite sure what I am seeing there

Benzine - 14/2/11 at 06:59 PM

quote:
Originally posted by interestedparty

Have you got any further than that yet? If so, how did it turn out? Did you combine the nosecone and bonnet, I'm not quite sure what I am seeing there


Turned out pretty good, after releasing from the mould there were raised edges from where the tape was but they were tiny and didn't take much work to flatten. Yes I did combine the nosecone and bonnet (after painting & fitting: ==>piccy<===)

[Edited on 14/2/11 by Benzine]

Fred W B - 14/2/11 at 07:00 PM

quote:

I could get away without having to seal the porous (wooden) surface of the pattern too.


Fair enough, but if it has a significant texture it will print through the tape anyway. Melamine certainly does. My thoughts are that to get the mould to a good enough finish I think you will go through the gell coat, so will have to skim with surfacing filler anyway, so you may as well do that on the pattern.

Although, if you only want to make one part, you could just do a rough pattern, make a rough mould, make a rough part, and then finish the part with filler.

Cheers

Fred W B

Edit - more or less as the poster above did




[Edited on 14/2/11 by Fred W B]

dave - 14/2/11 at 10:28 PM

I would go for mould release or honey wax it costs about £12 a tin.