Fiberglass mold making help

[pastafett]

Hello,

I have been fooling around with fiberglass on and off for a few years now. I have finally dedided to make a project which I want to make a mold then cast some copies. this happens to be some saddle bags for a sport bike.

I have used advice from some of the forum members on making the plug (model), using cardboard and bondo, and have the shape almost perfect.

I have two questions.

1. what to cover the bondo plug with so that I can get a smooth surface for the mold?

2. what is a simple fool proof method to make sure the mold does not stick to the plug ( a few weeks a go I did a fiberglass over foam plug, put on 6 layers of mold release wax, and then the fiberglass mold stuck and would not release)?

any help would be appreciated. some members like Morrow Sun or bigkidbiggertoys seem to be very expert in these matters hopefully they would have some great advice for me .

any help would be appreciated.

 

[tubachris85x]

Gimmie a second, and I'll take a look and my book on mold making and casting..

 

[tubachris85x]

What I think you should do to help improve your mold releases, is to try to make a plaster mold from your styrafoam plug. I cannot find anything suggesting styrafoam as a mold material, and that is probably why the fiberglass is sticking to your plug.

Also, according to the book, using bondo, in this case, it is closer to alginate, its not recommended for fiberglassing. I suggest to make a plaster mold, it is definatly the cheaper route, and I think you can get better results.

Im just using the book as a source of reference, and he gets very detailed with mold releases.

As for making the bondo smoother, just an idea, you should just sand it, paint a primer grey over it so it reveals the un-even, or rough areas, and sand over it with a high number grit sandpaper.

-tubachris

 

[pastafett]

What I think you should do to help improve your mold releases, is to try to make a plaster mold from your styrafoam plug. I cannot find anything suggesting styrafoam as a mold material, and that is probably why the fiberglass is sticking to your plug.

-tubachris

sorry I was not clearer, I sculpted the basic shape from foam, then covered it in fiberglass and put a final layer of resin, without glass over it then sanded it very smooth (1500 grit paper). Then applied 6 layers of wax mold release. THen when I started to do the process of making the mold, by then fiberglassing over it the new fiberglass (whcih was supposed to be the mold stuck).

I had thought of using plaster as the mold, but had seen where others had used fiberglass as a strong durable mold, and was trying to do that.

I just don't know what they do do coat the cardboard, or bondo so it releases nicely

 

[tubachris85x]

sorry I was not clearer, I sculpted the basic shape from foam, then covered it in fiberglass and put a final layer of resin, without glass over it then sanded it very smooth (1500 grit paper). Then applied 6 layers of wax mold release. THen when I started to do the process of making the mold, by then fiberglassing over it the new fiberglass (whcih was supposed to be the mold stuck).

I had thought of using plaster as the mold, but had seen where others had used fiberglass as a strong durable mold, and was trying to do that.

I just don't know what they do do coat the cardboard, or bondo so it releases nicely

Hmm..I havent heard of that before. You can make a plaster mold from a a fiberglass mold. Can you post some pics of the said mold?

 

[General Grievous]

www.fibreglast.com
To get it Smooth for casting, Wet sand it with 600-800 grit sandpaper.
if you primer it, go to a local auto parts store(oreilly, advanced auto etc) and get a can(spray) of Primer sealer. Made by Duplicolor I believe. it Gives a Nice Smooth finish and seals the Primer. you could even buff it with an auto buffer.
It is pretty easy to make the Mold out of Fiberglass. The Video they sell is pretty helpful.
typically, you use a parting wax 2 coats buff, let dry. Then 2 final coats.
Then apply the PVA Release Film.
To make a Fiberglass mold, it will have to be at least 3 times the Thickness of your Final product. So if you are going to make your parts 1/4" thick, your mold will have to be at least 3/4" thick.
After you get the part prepped waxed and release film applied, the first thing to apply is Epoxy Surface Coat. it is like a Gel Coat that you apply with a brush. it gives you a Nice Smooth and Durable surface.
Then lay your Fiberglass and Resin on top of that.
That is just a Quick description. Feel free to ask Questions and I will help you anyway I can.
Hope this Helps.
Thanks,
Wayne

 

[bigkidbiggertoys]

My preference is to use a silicone jacket, & then a fiberglass mother mold over that. You don't need a release agent to pull your fiberglass copy from the silicone mold jacket & because of the flexibility of the product, some undercuts are OK.
Whenever I make a cheap fiberglass mold without silicone, I use a P.V.A. mold release. This is a self levelling product that you brush a couple of layers on, letting dry between coats, & dries to a plastic film. It disolves with water afterwards to release the copy. You must make sure your plug will release smoothly & not have undercuts or the copy will lock in.
My preference is the silicone jacket for ease of layup but boat hulls & fiberglass shower inserts will use a sturdier fiberglass mold & release agent.

 

[bigkidbiggertoys]

Greivous beat me to it

 

[General Grievous]

I Agree with BKBT!
Silicone is Easier.
And what he said about the Undercuts!
I guess it depends on the Shape of the Item.
Show us a picture, that would probably help.
I hate to tell you to do it one way, when there is a better way.
Hope that makes since.
Wayne

 

[pastafett]

Thank you all for your help. I have not used silicone molds before, due to the cost, but will consider it. I have used urethane and it has worked well for some other projects.

I have attached some pictures of the saddle bags, the first one is the concept drawing I started with. The next in order are a side view of the plug done in cardboard covered with bondo, and then in an oblique shot then from the front.

The bottom ridge I put in for some datail. and the upper line in pencil is where the bottom of the cover/lid would come to (I have not done that yet). Before I cast I need to do something with the bottom ridge to make it more flowing/smooth as it transitions from the side to the front.

 

[evan4218]

Brushable silicone with a fiberglass or gypsum shell is the way to go... its fast, easy, and lasts a long time.

Smoothon.com makes allot of great stuff and has dealers all over the US. Theres where I get my gear and they have never done me wrong. Some of the more advanced silicones will require vacuum degassing but that is easy to do.

 

[Forcebewitya]

Ok I have a question about this method. I'm ready to give it a go my question is what type of plaster works best to create the negative mold? If someone knows of one that I can pick up at like Home Depot or Menards that would be great thanks...or is it something that needs to be ordered online?

Forcebewitya.

 

[Qthooga]

This might help -- it's one of the best tutorials that I've read. Has a decent amount of pictures, too. I'd suggest using a silicone sleeve. I've tried other materials just to keep my cost down, but silicone's the only material that I've found that really works. I haven't tried flexible urethane, though -- once I saw how well silicone works when it's lubed up with mold release, I didn't try anything else.

Venkman71's Casting Tutorial: http://www.gbproject.com/plans/mctut/index.html

Just keep in mind that it's going to be a lot of work. Wear your safety gear, too.

 

[Forcebewitya]

Thanks a lot for the link this should be very helpful. Now I just need to figure out which method to use there are so many ways to cast it it seems.

Forcebewitya.

 

[GrottyFurball]

I saw some videos on you tube where a guy was making things the way you described but he used 25 layers of mold release.

 

[pastafett]

I have used urethane before, it seem to work good, it picks up good detail. I used a brushable kind, did a few layers then used a plaster mother mold.

OK got the plug filled, primed and wet sanded down to 600, now some techincal questions for the experts.

notice that the top is open (hand goint into hole, and I have almost finished the top lid not shown) and back side is flat (rt side of smaller picture), and will be attached to the bike on that side, so I wanted to cast it in all one piece. I was thinking of laying the flat side on melamine board, then making a mold urethane/silicon then a afiberglass mother mold.

then for the back side, can I just use a flat piece of metal or melamine, bolt it up to the mother mold from the front and make the cast through the hole in the top.

Does that sound like a plan which would work, or am I way off?:confused

 

[General Grievous]

It might work.
as long as there is enough room to get your hand in through the opening.
wouldn't want to get the FG on my skin since it would burn as it cures.

What type of FG are you going to use?

GG

 

[General Grievous]

The more I think about it, if you are going to make a silicone w/fiberglass mothermold, why not make it a 2 piece mold?
instead of taking the chance of something going wrong. If you bolt or screw the melamine or metal on you take the chance of altering the Shape of the mold. Flexing it or warping it.
If you are just using a Brush on resin with fibers then it should work fine.
If you were laying glass cloth then it might be a problem.
Is the back side Perfectly flat?
I don't think your way off. Your on the right track.
Best thing to do is ask Q's.
When I first attempted FG I had no one to ask.
I had a Corvette that I bought that was a repo. Patched a hole in the front clip.
It came in handy since by the time I sold it, it had been hit 5 times. 4 of them in parking lots while the car was parked.
Then I started doing Hobby stuff. R/C Airplane parts. stuff that was more durable than the plastic parts the planes come with.
So It wouldn't break on the FIRST crash landing
Wayne

 

[pastafett]

1. What type of FG are you going to use?

2. is the back perferctly flat?

GG

1. I was going to do a gel coat (2-3 layers), then back with glass mat, with regular resin.

2. yes it does not show, and it the side I am going to attach to the bike, though flat would be easier.

 

[General Grievous]

So are you going to trim the back to attach it or leave it solid?
Wayne