Mold making on the cheap

General Composites Discussions Equipment Talk
#1

So I have done some basic CF projects that have all been just flat projects that get cut out when done (bottle opener, coasters, etc), but now I am wanting to step up a little bit and start making some more complex parts, starting with some shaped part for my bicycle.

I want to make arm rests that are curved to my arms on top and then sleek on the bottom with a bottle attachment in the middle. (I ride a time trial bike, where you rest on your arms and I have a bottle the mounts in the middle of my arms). I am trying to blend all I can together to make it as smooth as possible, also hoping to create a compartment to hold my flat kit.

The final part will end up being two parts, a top and a bottom, both with flanges on the inside and velcro holding them together, this would give me easy install options and easy access to my flat kit.

I will be modeling the part out of sculpey clay and baking it, then i will smooth it like I want, confirm the plug is perfect, cut it where I want the separation to be. I will then place the cut sides down onto a flat surface and apply mold release so I can make 2 female molds out of fiberglass. Where I am lost at now is what I have to do with that female mold, I have read a lot about needing to put in a gel coat, but the cost seems kinda high for such a small part that I am experimenting with. This part would only be 1-2 parts made from the mold. I am also stuck on whether I should use epoxy with the mold or what chemical I should use. I currently mold CF with West 105 system to get the UV protection, especially since this part will spend a lot of time out doors.

Any suggestions would be greatly appreciated.

#2

I would not cut the plug in half, just form a flange and lay up the first half against the flange, then remove the flange and lay up the other half. You don’t need gel coat for the part, or the mold really, but it makes the mold surface smoother and therefore the part nicer.

#3

I see what your saying and its probably a better idea, glad I dont need gelcoat as that was a considerable expense for small experiments.

Since I use west 105, that should hold up well outside without yellowing? What material would you recommend for the female mold and what type of resin would you recommend?

Thank you again for your feedback.

#4

West System epoxy isn’t UV stable, no epoxy really is. Some are much better than others, but West System is pretty average. It will yellow over time.

#5

Using a 2k clear coat or a dedicated composite product like Duratec Sunshield will give you UV protection. If you are used to the West system no reason not to use it.

#6

Is the Duratec Sunshield a spray on thing or brush on after the part is made?

#7

You can absolutely brush it on if you are prepared to do some sanding work. Otherwise it can also be sprayed.

Also, I think you will waste more money trying to take shortcuts on things. Ditching a gelcoat for example, I think your surface finish will suffer as unless you are quite experienced with hand laminating then you will likely end up with voids all over the surface that need to be fixed before you can continue. You don’t need to use tooling gelcoat (expensive) you can use any ordinary gelcoat (quite cheap and can usually be found in small quantities) for low volume production.

#8

Any recommendations for a supplier for cheap gelcoat that would work with my situation?

do I need to worry about using epoxy or polyester with fiberglass as the mold and then using epoxy with the carbon part?

#9

I agree 100% with Hanaldo.

I understand the desire to do it on the cheap because it’s for a single part or a small number but if you want to end up with something you would actually want to use and be proud of, then you should do it right the first time.

Doing it right means buying the right materials and mold release products. It’s also the cheapest way because I guarantee that you will end up buying them eventually anyway, once you realize that, if there was a cheap way of making cf parts, we would all be using it…

If the part is not going to be a cosmetic piece (with exposed glossy cf) and you are prepared to do some filling, sanding and painting, you can probably take some shortcuts but… if that is the case, I wouldn’t bother with carbon fiber.

This has been my experience anyway. I can’t tell you how many cf pieces I have thrown away because they were almost ok… but not quite because I tried to cheap out. It’s so frustrating knowing you have to start again because you didn’t spend $30 on a small pot of gel coat off eBay.

If economy is the number one priority, fiberglass strand is a better choice for you. Whatever you think your budget is for a cf project, you’ll spend at least triple in wasted cf as you go through the trial and error learning curve that everyone goes through.

If you are determined to try it on the cheap with no gel coat, I would advise you to use epoxy putty for the mold instead of fiberglass. Epoxy putty can be more easily repaired and the surface can be sanded relatively smooth. You’ll never repair and sand a plain fiberglass mold smooth. You’ll just make holes in it while filling your room with toxic dust.

Don’t cut your plug in half btw. You will want the two halves of the mold to fit together with no alignment issues and you’ll have zero chance of achieving that unless the mold is made around a single piece plug.

For complex, tight or small curves, you’ll want a method of holding the cf in place against the mold surface too. Most people use vacuum bagging or infusion but if you don’t want to invest in that, you’ll need to make good mold inserts.

This is the other reason I recommend epoxy putty. It’s cheap and you’ll get enough with a one gallon pot to make a good mold and any inserts needed. Most importantly for a beginner project, it’s forgiving, easy to use and easy to correct mistakes as you go.

I can’t tell you how much money and time I have saved by being able to easily salvage a mold I snapped in half or chipped the edges on etc.

#10

I have only seen large quantities of expensive gel coat, but I guess I need to look more extensively.

As far as cutting the plug in half, I need the final part to have a top and a bottom as it will be storing stuff and needs a way to be able to attach and remove it from a bike, and I was going to make the plug as the part I needed, then cut where I needed to make it work like a compartment. I dont want to just leave one end open for aerodynamic reasons, and parts may fall out when I am riding.

I have done some basic small parts and fully understand the experimentation phase of things, currently I already have a Vacuum Bagging set up and have vaccum bagged all my parts.

Another question about vaccuum bagging, when I pull the part, there were small pinholes in the part between the fiber weaves and I ended up coating again with epoxy to get that glossy look, any suggestions, or is there a way to get that look off the mold and out of the bag?

#11

It’s hard to help much more without seeing a pic of what you’re trying to make.

I can’t speak for everyone else but I know that when I am making something in carbon fiber, I choose the method and techniques based on the specific shape I am trying to replicate.

IMO, a lot of problems people have are a result of them trying to use that same vacuum bagging or infusion process for every part, regardless of whether it is right for that project or not.

In general, holes can be caused by a number of things including (but not exclusive to): trapped air in the resin, inconsistent pressure across the part, too much or too little resin, poor lay-up technique, issues with the quality of the mold surface, clumpy application of mold release products etc etc…

If you post a pic of the object you want to make, I can tell you broadly how I would make it if it were my project. I am sure others would be happy to do the same. I doubt we all work the same way…

#12

Hey- another option instead of using gelcoat is to use graphite powder and colloidal silica in your west systems epoxy as a gelcoat-like layer, then back it up with a few layers of glass. The graphite powder can is like $20 and lasts for awhile.

Good luck!

#13

I just saw some tooling gel coat on ebay for like $30… why cheap out?

I understand doing this on the cheap, i’m sure we’ve all been there… but from the past experiences, having the right tool or material will not only save time and money, but make a better part. Surely you must know this already.

Do you have a picture of the part you’re making? I’m curious what it looks like. Sounds like this is very doable. But the work to make 1 or 2 good parts is the same as making 100… Really it’s all about the molds. Tooling is the foundation for all things composites.

#14

Just images in my head for now, been sidetracked getting tiling done in my house and getting the house ready for the baby thats due in a few weeks.

I will get on making a model of what I want to make ASAP though.

#15

Congrats!!!

First baby? I have one as well… he’s almost two years old now… He’s basically become my world. I go to work and then take care of him. Best creation to date. Though I don’t have any time now to work on my personal projects… I’m just starting to come out of my baby cave and thinking about what I want to make next.

Keep at it!

#16

Thank you, yes first baby.

On top of that, I am focused on trying to get into the local Fire Department, so unfortunately any projects are on the back burner for a bit.

#17

For when the project is back on, take a look at plasti-paste 2 from smooth-on.

I have been using it to make hard shells for molds. It can work as both mold and gel coat if applied right (I.e. A very thin first layer to avoid air bubbles before adding the rest).