Coligny

Could anybody tell me, with a epoxy mold, would a mix of cabosil, and cotonflox make a good edge (parting lines) for a mold?

regards

C.mrloth

Coligny

Maybe I should rephrase:

When making the mold of the plug, I have found problems with the corners being to brittle, I would like tougher edges.
Will cotton floks, and cabosil be of any help here?

Ed Smith

This would be outside edges/corners on the mold, inside corners on the plug, correct?

When I make my molds, after the gelcoat has set and before I start to build up mold thickness with glass I reinforce all inside corners with chopped glass and resin. This creates a fillet in the corner and allows the following layers to follow the plug contour. I have found that if this is not done there is a danger that the layers may not be pushed right into the corner. This creates a cavity in the corner which will eventually break out.

Ed S

Coligny

Thanks Ed,

but what if I do not use a gelcoat, just epoxy from the word go, what can I ad for a tougher more durable edges?

CM

Ed Smith

Hmm.. cabosil/resin cures very hard and can be brittle. Some reinforcement as you suggest would be desirable. However you do not realy want any glass fibres or other fibrous material actualy on the mold surface. Meybe a thin layer of filler first then backed up with a mix of fibres. In some cases micro balloons can be quite durable.

I always use gelcoat, I do not have chipping problems. For my gelcoat I mix carbon powder with the epoxy resin. It gives a hard durable surface.

Ed S

Mike James

Comparing notes with Ed...

I've been an "epoxy only" person myself for about 15 years. The way I do the molds is to first apply a pretty thick (up to 1/8") layer of tooling resin, then use the method Ed described for reinforcing behind that. (I use #1099 "surfacing coat", from http://www.fibreglast.com )

Another thing...
Often, it's not the surface material itself that makes the edges less than perfect. Instead, it's the precision of the parting board/plug seam. If you're using clay as a sealer, the clay can be pushed around and distorted if you're not careful, and this can make your mold edges rough, giving them a "pitted" or "chipped" look.

Recently, I've adopted the method of using a hard filler instead of clay. I wax and PVA the plug, put it in the parting board, then apply a tough filler, such as epoxy/Cabosil, and let it cure. Then I remove the plug, sand the filler flush with the parting board, and re-insert the plug. This gives a very sharp, precise edge to the mold, and only adds one step to the normal process. Note that, after the hard filler is applied, the plug is generally removed from the "bottom" of the parting board, rather than the "top".

Coligny

Thanks mike,

Now tooling resin, I suppose that is a different resin to your resin used to make parts?

Thanks

Coligny

Mike James

Yes, the tooling resin is quite a bit harder than laminating epoxy.

Coligny

Mike, tooling resin are VERY expensive here by us, would it work if I use tooling resin only in critical areas, like on these edges, and use normal resin for the rest?

Regards

Coligny

Ed Smith

I understand your predicament with regards to availability and expense of materials. With some inventiveness it is sometimes possible to "Make do. However I have learned over many years that for quality and satisfactory results in fibreglass work there is no cheap and easy way.


Ed s

Mike James

I agree with Ed. (again)

I've tried (this year, in fact) several experiments with surface coats, including mixing graphite powder with laminating epoxy, mixing Cabosil with epoxy, etc., just to make sure that these chemicals still do what they used to do. As Ed said, I got "passable" or "good enough for a few parts" type quality, but it's worth the extra money to get the right materials. (or use polyester, which is less expensive. but has it's own quirks)

Sometimes, the materials only seem more expensive. If you use good materials, you'll probably get good results, costing you less "do over" or replacement cost, over time.

Coligny

Thanks,

You guys are confirming my worst "gut feel" suspicions. I have had success with Polyester, but it is just not the same. The point is, we are not making molds for canopies or boats. We are making delicate carefully designed and finished products, and detail is everything to us.

That is why I am back at epoxy. The surface coat is the most expensive, might cost more than the rest of the mold, and that is why we all look for alternatives, but I think one has to look at the time, and labor (Mike loves sanding it seems) that goes into the plug, maybe the surface coat is a small price to pay.
I also think Mike's extra step in making the parting board is worth it for sure, I have done this, and it works.
I used a automotive bodyfiller, but one has to work very carefull to keep it in tact. I prefer Mike's idea with a epoxy resin based filler.

Mike, what is your opinion on the guys that makes a ofset flange on the mold, to create a lip for joining the halves??

Regards

Coligny

mr_matt

My Feedback: (10)

Yeah I would love to hear how this is done as well, I cannot visualize it at all!!

Mike James

Here's the article by Chris Adams, at http://www.scrollsander.com/Soaring-Fuselayup.htm

The #1099 surfacing resin from http://www.fibreglast.com is not that expensive. You can get 6 quarts for about $150, and that will go a looooong way. Check it out. It's white, and so I use black pigment ( also from Fibrglast.com ) to get a black mold surface.

Coligny

I have seen some interesting photo's on the rcgroups forum regarding the method of greating a offset flange. If I find the link I will post it. It was those guys from Germany building the "racketwurm"

It seems rather interesting, but I have not heard how the final results was.

I realise the wet strip joining method adds strength, but in some fuselages, it is really impossible. Especialli since I am planning to use some of the hatch methods suggested by Darrinc (I wonder where he disappeard to anyway)
This will leave almost no openings to work through, but I think his ideas is brilliant, yet simple. I just know from gut feel it is going to make excelent hatches.

Regards

Coligny

sayno2glo

My Feedback: (2)

This is electric pylon model's fuse mold with flanges attached.
Oh, and for strong mold edges I would try aluminum powder filled epoxy. Gelcoats are too brittle.
/Antti

Coligny

Thanks for the picture,

Tell me, how does it work out in the end? I understand the method , but nobody has told me about actual results, was the final join succesfull?

I have heard about the aluminium powder, I will have to check local suppliers though.

Thanks

Coligny

sayno2glo

My Feedback: (2)

cando,
The result is lighter and stronger compared to glass fiber strip. This method needs to be vacuum bagged as you might think.
Best way to make a fuse is to use a bladder and about 2bar pressure which is more than double to vacuum. Then you get it jointed in the same time and you save time also. I have not tried this myself yet so I can't advise further.

Coligny

Thanks,

So many ideas, so little time, how can I choose!

Regards

Coligny