I had some twill weave 6oz f/g i have been using for mold making.
I tried 10oz twill weave f/g for mold making and it doesn’t work so great because it doesn’t like to conform to sharp radii. The only nice thing about the 10oz was it builds up mold thickness more quickly.
What f/g cloth, style, weave and weight would you guys recomend for epoxy mold making? There are ots of short and sometimes sharp curves to these molds.
when I make molds I tend to have a bunch of pre cut random and specific shapes cut out, some to fit the curvatures and others just to make up as I go along. I also use chopped fibers mixed with resin in the really wacky contoured edges. I’m using a ~5-6 oz boat cloth, pw.
You must have been spying on my work shop 20_rc51 :D… i do the same with adding chopped fine glass to the epoxy with some calcium co3. I’m also using 6oz woven f/g cloth. It does seem to work well for me…it’s not perfect but i suspect no cloth is “perfect” for mold making.
I also posed the same question to Thayercraft in an email. I hope to hear back from them tomorrow. Those guys are fiberglass cloth experts so hopefully they will have a really good cloth for me.
All my molds are epoxy, (hi-temp and low-temp) I use 6oz plane weave f/g cloth on most of my molds, on complex molds I pre cut the cloth into 4"x4" or 6"x6" squares and overlap each by about an inch or so. I also chop some fiber and mix it up with some resin and fare it into tight corners and radii. For a super tight mold with no voids, after a few plays I lay down some pealply, bag it and let it cure. Do this a few times and you’ll have a super tight strong mold. For a fast and light mold I use some tooling dough between a few plies.
EXCELLENT information guys. I’m feeling like i’m on the right track with the 6oz fiberglass now that i read your posts… also with mixing up some chopped glass like you both say you do, i started doing that little trick this morning when i noticed some voids in the cloth where it didn’t want to stick down around a few sharp corners.
I’m gonna have to start vacuum bagging these epoxy molds like CJ and Hojo have said. The glass gets major major air bubbles when using epoxy and no vacuum:(
I have been laying it down just like you guys said… small square patches of fiberglass, overlapping each other by 1/2 to 3/4 inch. I was doing only one layer to try and eliminate any air pockets and bubbles but darned if they didn’t pop up anyways. lesson learned.
Question: Is there any problem with “oven” curing an epoxy mold at 120F?
Once i get the tooling dough i’ll post up some pics and what i think of the stuff. I’m not even thinking of trying to oven cure those dough molds. You guys can call me the dough-boy lol.
CarbonJoe, for knowledge sake how many parts can you pull with an epoxy dough mold before it is no longer usable?
a good way to not get bubbles in the laminates when open molding is to make sure that the reisn is on the plug before you lay the dry fiber down. This way it wets out instantly without trapping bubbles as you carefully lay down the glass pieces. I ususally add a little bit of excess resin and then lay the sheets of glass worry free and then after compact, then lay a few more ontop to take care of the excess resin and then compact some more.
strips of 4 oz glass as an initial layer- so it’s really easy to get all of the air out, then hit it with a chopper gun until it’s at optimal thickness. Fast and way easy. ;o)
[QUOTE=Fastrr;17426].
Question: Is there any problem with “oven” curing an epoxy mold at 120F? QUOTE]
it really depends on the epoxy system, but I think any epoxy system should have no problems with such a low temp. If you want to cook higher you would want to do a intial post cure on the mold first following the proper cook cycle. often the post cure of a mold is: ramp to 150, dwell at 150 for 2 hours, ramp to 200, dwell at 200 for 2 hours, ramp to 250, dwell at 250 for 2 hours, then ramp to 3oo and dwell for 2 hours. but it really depends on the resin system, some tooling epoxies will require a post cure
shoot, I wish I had a chopper gun set up 
I’ll add 4oz glass to my list of supplies. And thanks for that bit of advice RC51:cool: You guessed it, i was wetting the cloth after i laid it on the mold.
I released the plugs from the two molds today… came out so nice i was lovin’ it. The epoxy surface coat was good, shinny and just about no flaws. One flaw i found is an easy fix. I’m going to add 2 - 3 more layers of 6oz glass on the bigger mold now that i know it’s all good from the inside.
The BEST fiberglass for molds and parts…
…freebies or donated FG!