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Thread: Large mold thickness?

  1. #1

    Large mold thickness?

    We are in the process of laying up some medium-large molds. I want to avoid any warping of the molds.

    How many layers of glass mat and ounce weight do you well versed mold makers use?

    My schedule is usually:

    Tooling Gel coat 20 to 30 mils thick.
    1 layer of 1oz fg mat.
    4 layers of 2oz fg mat.

    I only lay up each layer of glass every 2 to 3 hours apart to prevent overheating of the laminate. I also plan on leaving the curing mold on the plug for 2 days. Think this is long enough?

    I've made many small parts molds before so I don't worry about warpage with those.



  2. #2
    Senior Member EVM_Rob's Avatar
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    Re: Large mold thickness?

    That sounds pretty thick to me. I would work on adding bracing to the mold to reinforce it rather than relying on thickness. I am adding bracing to my 308 hood mold tomorrow. Check my build diary on Sunday night or Monday morning and I will have pics and an overview of the process by then.

  3. #3
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    Re: Large mold thickness?

    i have been taught that you always go twice the thickness of the part you will be making. and i think you could probably lay as much as two layers at a time per day to get more thickness. also i was taught to stay away from bracing where the part will be. in otherwards put the bacing at the flanges. and try to use wood rather than steel. if you brace behind where thier is a part then eventualy it will either print through or warp around the bracing. but heck dont take my word for it ask watson he does not even use bracing, or some of the other guys that been around awhile and do that kind of work

    c

  4. #4
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    Re: Large mold thickness?

    It is according to how many "pulls" you intend to get. Large high production molds are generally about 1/2 inch thick with steel reinforcing. I have some that have pulled a hundred parts or more and still look good. Cheap thin molds will only pull about a dozen or two parts. The other consideration is the resin and gel coat. Tooling gel and tooling resin (preferably a filled system) are an absolute if you intend to pull a lot of parts. The old school method to me is still the best. That is tooling gel, followed by an ISO/DCPD hybrid tooling resin with filler (a ceramic powder). This should be done as a "skin coat" and then, once it comes out of exotherm, build until a little less than a quarter inch. Once that comes out of exotherm, put on two layers of heavy cloth but using vinylester resin and let all of this set up about 24 hours. Then, final 1/4 inch build using the first method of ISO/DCPD filled system. Now when you see people saying it cost 30-40 thousand dollars or more to mold a car. This would be the system. It is bullet-proof and will make superior parts but, you will never sell enough to the kit car industry to come close to breaking even. If you don't do this type your parts will look like cory davis diablo bodies. Now there are many methods and opinions but I know that one works, I use it, D&R uses it, Scout Boats, Pioneer Boats, Key West Boats, Allison Craft. I'm sure most of the boat industry uses it. Mid States Cobra used to but they got bought by Shell Valley, don't know what they use.

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