Well the best way is to CNC or 3D print. If you make by hand, MDF or low-High density foam works well. Are you using a computer to design? Or original part? Ultimately depends on the resources you have available to you.
We generally use MDF. CNC comes at a cost that obviously passes on to the customer but unless the quantities are there the customer will probably run. Part tooling cost can be spread out over the cost of each moulding to make the tender more attractive.
I have yet to find a way to build a plug that doesn’t take work to get to a high gloss finish. MDF, plywood, high density foams, plaster, all have positives and negatives. Sometimes, it’s a combination of materials that works best.
One thing I’ve been looking at recently is direct-to-tooling materials. Axson (and probably others) make urethane and epoxy boards for this purpose. If your mold can be made with a CNC mill or router, this might be something to look into. I have a 5 axis router that makes this process feasible. I haven’t made the jump yet but I may on the next project.
I don’t have access to CNC routers or mills and the volume doesn’t warrant the expense.
I am currently limited to plugs I carve myself. I haven’t tried MDF. If it came in the thickness I need (3" slabs), I could see it having the advantage to me of already having flat sides so it would save me time trying to get the edge true and parallel etc.
What do you coat the MDF with to achieve a smooth glossy finish?
I have some urethane foam here. I used it for plugs a few times. Coating it seems to eat up all the time it saved for carving. I tried coating it with Bondo but I have to believe there is a better way?
Btw I have no issues making a plug from an existing part. I am talking here specifically about original parts that need to be carved.
It’s not cheap but a proper tooling board is worth the money in my mind. I use Sika block 600kg/m3 though mostly on my small CNC machine. The 600kg would be a bit tough (though doable) for hand shaping but the lower densities would be easy for hand shaping. I also do a fair bit of MDF but ultimately it’s a pain to finish nice. Comes down to where you want to spend your money, on materials or labor. A 50mm thick 1m2 chuck of tooling foam is about $200. The same in MDF if you glue a 25mm sheet into a 50mm sheet is about $40-50.
That said the difference in labor to get to a reasonable finish is huge. The tooling board can be sanded straight to 600 grit or higher,put some release on it and laminate. For a better finish you can paint it with something that buffs out nice if you want to make a glossy mold from it. One down side is that uncoated the urethane tooling boards aren’t compatible with prepreg.
MDF you’ll need to sand it, seal it sand it again then think about a coating to get a good finish. After all that even with a good release there is a high chance of the coatings you put on it coming off when you release.
Also on the CNC machine the difference between the two is massive. The tooling board cuts like butter, is easy on tools and comes out with a great finish. MDF is hard to cut, destroys tools and often times the pre sanding finish is terrible.
Also don’t write off a CNC machine. You can build a decent machine for around $1000 that will be able to machine materials up to 50mm thick. If you need thicker parts just make slices and glue it together. I guarantee if you get one you’ll never be happier. I use mine almost every day
I don’t think you’ll be able to “carve” MDF if you are talking about using knives. Perhaps if, by carve, you mean using whatever needed to alter the shape, there are possibilities for you. Power tools - routers, saws, die grinders, small disc sanders, etc can help you with the shaping of the plug but it definitely won’t be as easy as a product like urethane foam.
Nc42 mentioned 600kg/m3 (37lb/ft3) foam. I think that is a bit dense for hand work. I use 12-15 lb/ft3 urethane and it works pretty easy by hand but is still dense enough to hold shape. The big difference in the finished product is cell size. The higher the density, the smaller the cells and therefore smaller porosity in the surface. This translates into less finish work.
When working with both MDF and lower density urethane, I’ve found it better to paint the surface with resin after shaping but before applying fillers and primers. It seals and stabilizes the surface and also fills in a lot of the pin holes from the porous surface. I use polyester resin for this.
After sealing with resin, I usually lightly sand to remove any nibs and bits sticking out. If any filling needs to be done, now is the time to do that. I use a tack free polyester body filler for this. Then I follow with Duratec sanding primer sprayed fairly heavy. After spraying, I fill any remaining pin holes with polyester spot putty and then sand to 150.
Spray Duratec surfacing primer and sand to desired level then polish.
I ordered some of the Duratec surface primer to try.
The tools I have available for shaping are: a router, Dremel, Jigsaw, drill press, hand drill, metal files, finishing sander, wood carving knives and sand paper (with various sanding blocks).
I have mainly been using hand tools for things like shaping / finishing the deep internal areas that I can’t reach with my power tools.
I have been using 3lb foam as I thought it would speed things up but I guess it’s had the opposite effect. I’m going to try a denser one.
What type of resin do you coat the foam with? I have a wide selection on my shelf. Are they pretty much all the same for this purpose?
Chisels and wooden planes work great to shape MDF. Ive made many plugs this way, all by hand back in the day. MDF is actually great to work with other than it sucks up moisture like a bastard
I just use polyester infusion resin. I figure that it will soak in a little deeper since it’s thinner than laminating resin. I’m sure any resin would probably work.
On the foam, I think you’d be happy with 12 lb density. It carves and sands fairly easy but it doesn’t crumble if you look at it wrong.
You are right about the chisels and planes. I was thinking more about knives like you would use when you are whittling. Now that I think about it, carving knives could probably work as well, albeit with some effort. I still think I’d stick to urethane - much easier to work.
I’ve been doing some experimenting and they both seem to have advantages and disadvantages for what I am making.
MDF is cutting easily with a jigsaw. It’s easy to coat and shape fine (ish) detail using metal files for the last mm. It seems to warp and bow fairly easily though when making long thin parts.
Foam is definitely quicker to shape and while it is more delicate it actually seems to hold long straight sides better.
They both have the disadvantage compared to epoxy putty when it comes to hand shaping and surface finish. You can shape epoxy putty by hand and then finish with tools. It can be sanded glossy smooth without additional products too.
It seems like which is best depends on what you are making…
It is not cheap, but it is hard, can be worked easily by both hand tools and CNC, and most of all, if you make a mistake you just melt it down and start over.
I’ve never heard of tooling wax. I’ll do some research.
I did use regular candle wax to make a plug once. I cast it in a silicone mold and then used the wax cast to make a rigid mold for carbon fiber parts like a lost wax process they use in metal casting.
My idea was to melt the plug out when I was done to save time with all the mold releases etc. The only problem was that cleaning the excess wax off later took more work than using mold release
I have been trying to figure out how to make a cf stock with a glossy smooth finish from an original with a texture that can not be sanded off. It has been driving me crazy. I tried casting it in another material that could be sanded but it’s too complex for me to keep the right shape when I’m done.
It seems like it would have many advantages. Cost for one thing. I love the idea of being able to reuse it over and over.
I’ve been doing a little research and it seems that some people are even using it as a mold making material. It kinda has built in mold release properties so for one off projects it could make sense.
Can you sand it smooth? I would expect any type of wax to clog up sand paper immediately but I am thinking about it like candle wax. Is this stuff different in this respect?
I have not used it myself, but I would assume you could polish it to smooth it - anything that would give it a little heat should smooth the wax. Maybe using a flame from a small torch at a distance (it might take a few tries and some experience to not melt the part) would heat it enough to remove any left over milling marks.
I would call their tech support and see what they have to say.
I haven’t used the Freeman product but I have made my own machinable wax, quite easy to do. Just melt paraffin wax and add some LDPE most easily found as plastic painting drop cloth. I can’t remember the exact ratios I used but recipes can be found online. It doesn’t polish up very easily as it clogs sand paper. Itty odd also quite hard and not really suitable for hand working. That said it does release epoxy easy.
