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Sand / epoxy molds

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Old 01-25-2005, 11:55 AM
  #101  
TGoodwin
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Default RE: Sand / epoxy molds

We're using the Fred McClung method of creating a resin-collecting trench at the trailing edge of the wing, which also serves to trim the trailing edge straight later, using a chisel. (See image.)
Hey Mike,

I am not clear on the purpose of the 1"x1/2" wood? I see the image with it along the trailing edge of the wing but what exactly is it for?

Thanks Ted
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Old 01-25-2005, 02:57 PM
  #102  
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Default RE: Sand / epoxy molds

Hi Ted,

I clipped this little image from the Soaring Stuff site, from the ad for Fred McClung's video, to help illustrate.

The wood, acting as a "plug", creates a trench at the trailing edge of the mold. That's a place for the vacuum fitting to go, and a place for excess resin to go, and it also provides a straight line at the trailing edge, so I can trim it with a sharp chisel. I think normally, you'd only do this with a straight-edged surface like a wing, but it may have other uses as well.

And... To be clear about what you may have seen in my photos:
The first piece of 1/2" X !" balsa was glued to the parting board. After the first mold half was made, that balsa "plug" remains stuck in the mold, as expected. (no need to take it out until after the second mold half is done) Another piece of 1/2" X 1" balsa was glued directly to it, and will form a similar trench in the second half of the mold. It's a simple matter to get the balsa out of the cured molds. It will either pop free, or can easily be chiseled out. Then, you have a nice square channel in each mold, right at the trailing edge.

One of the reasons I'm employing that idea is that in this case, I wanted sharp trailing edges. Using this "stick" up against the trailing edge, makes a very clear trim line, where two mold halves joined (with the flashing still on) is not always so obvious. So, they can be trimmed right in the mold, after vacuum bagging, and after joining the mold halves. Since you have a channel in both mold halves, it doesn't matter which mold half the part sticks too when you intitally separate them. Either way, you have the same trim line channel.

Hope all of that makes it clearer.
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Old 02-08-2005, 08:49 PM
  #103  
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Default RE: Sand / epoxy molds

Hi everybody,

Just an additional update and a vote of confidence on the idea of sand/epoxy molds...

I've now made two wing molds (4 halves) and a new vertical fin mold (2 halves) using the sand/epoxy technique, and I have to say I'm hooked. It's MUCH faster, uses less cloth, and results in molds that are as sturdy as you would need in normal use. (wing mold and vertical fin mold photos attached) I've used 3 different kinds of epoxy (doing some testing on alternate brands, and we are back with West Systems) and they all came out fine. We've been using "blasting sand", which is relatively fine, and it's been really easy and intuitive to figure out the mix ratio. Give it a try on one of your next molds... You'll like it!
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Old 02-09-2005, 12:33 PM
  #104  
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Default RE: Sand / epoxy molds

how many layers of cloth are u using? prior or after sand
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Old 02-09-2005, 12:53 PM
  #105  
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Default RE: Sand / epoxy molds

I'm sure Mike will reply, but based on what I've read you use 2 layers of 6oz cloth over the tooling resin, then build up your mold with sand/epoxy and then add 2 layers of 6oz cloth.

JR Gautreaux
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Old 02-09-2005, 01:53 PM
  #106  
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Default RE: Sand / epoxy molds

That's exactly what I've done, JR.

I've changed one minor thing in the process, compared to regular cloth-type molds. That is, I used to start adding the cloth (2 oz., to prevent "print through" ) while the tooling resin was still pretty soft. Now, I wait an extra hour or so, for the tooling resin to become a little more firm, (but not cured) and just use 6 oz. cloth.

I add the 6 oz. cloth, and immediately start mixing the sand and epoxy. Then as soon as I've applied the sand/epoxy mix, I add a bonding layer of epoxy, followed by the final cloth. The whole process goes very fast, once the tooling resin part is done, and no quality is sacrificed. That's why I like it so much.
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Old 02-09-2005, 11:59 PM
  #107  
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Default RE: Sand / epoxy molds

Although not specically related to sand/epoxy molds, check out this F5D mold construction using similar concepts on ezone.

http://www.rcgroups.com/forums/showt...&page=19&pp=15
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Old 02-10-2005, 02:14 AM
  #108  
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Default RE: Sand / epoxy molds

Ooooh... That's a nice one!
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Old 02-10-2005, 12:58 PM
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Default RE: Sand / epoxy molds

OMG, it's happened again, now I want to throw rocks at everything I own.

Mike, you mentioned the System 2000 resins from Fibre Glast. I just got some of that myself, to replace the 88/87 formula I had before, which is now discontinued. I'm also quite happy with it. Can you recommend a good tooling/surfacing resin to use with it? Is the white stuff in the pictures also a Fibre Glast product?

Thx

Duane Gall
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Old 02-10-2005, 01:11 PM
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Default RE: Sand / epoxy molds

Ooops, that one needs a followup.

The "white stuff" I referred to is actually in a photo at post #18, by Mr. Goodwin. Mike, your photos of the trial using the paint can cap show what you call a "tooling resin, painted black" ... would that be the #1099 with black pigment added?

I, too, prefer a black surface for molds. It never occurred to me to try and change white to black by dyeing the resin.

D.
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Old 02-10-2005, 01:20 PM
  #111  
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Default RE: Sand / epoxy molds

The tooling resin we use is the #1099 (white stuff) from Fibreglast, pigmented black with pigment also from Fibreglast.

Just a detail, but...
We use West Systems resin at this time, not the System 2000 from Fibreglast. They used to sell West Systems resin years ago, but now have their own brand. During the transition, I ordered epoxy from them, and got System 2000, and never noticed the difference between it and West Systems, so they must be very similar.
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Old 02-10-2005, 02:11 PM
  #112  
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Default RE: Sand / epoxy molds

I have a white gel coat. Tooling gel coat. how do i turn it black? =\
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Old 02-10-2005, 02:28 PM
  #113  
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Default RE: Sand / epoxy molds

You can turn the tooling resin to another color by adding pigment to it. See picture. Also, I've heard you can add graphite powder to tint it black. The jars of pigment pictured are available from US Composites where the West System products are available anywhere West System products are sold normally.

JR Gautreaux
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Old 02-10-2005, 03:30 PM
  #114  
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Default RE: Sand / epoxy molds

and thats cool with gel coat?
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Old 02-11-2005, 11:27 PM
  #115  
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Default RE: Sand / epoxy molds

Looking good Mike! See why I will never go back to standard FRP molds.

It makes it just too easy.

Ted
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Old 02-11-2005, 11:57 PM
  #116  
Mike James
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Default RE: Sand / epoxy molds

Yeah, Ted!

The "middle step" of building up the mold thickness, now takes 20 minutes, instead of a couple of hours. You gotta love that.
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Old 02-15-2005, 03:58 PM
  #117  
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Default RE: Sand / epoxy molds

Any cheaper place to buy tooling gel coat than fiberglast for $71.95? Also, where are you guys getting the graphite powder for tinting?
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Old 02-15-2005, 04:38 PM
  #118  
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Default RE: Sand / epoxy molds

The stuff you mentioned is the price per gallon, which is cheaper than epoxy... Not bad, really. (and... It's a polyester gel coat.)

The stuff we use is on this page ( http://www.fibreglast.com/showproduc...0Resins-5.html ) and is an epoxy-based tooling resin. ( They call it a "surfacing resin" ) and is about $130 for 6 quarts. ( #1099 Surfacing Resin )

Graphite powder can be gotten from Fibreglast and most other composite suppliers. It's messy to work with, by the way. We use liquid pigment from Fibreglast.

Opinion...
Having recently tested a couple of different brands of resin, and come back to West Systems, I can say this. Be very careful with buying cheap or substitute surfacing resins. After all, the surfacing resin is actually what your parts "see" in the mold. Although not ideal, you could use a cheaper resin to build up the thickness of your molds and get away with it. But if your surface coat is no good, you've just wasted a lot of time and money. All of us would LOVE to find cheap composite materials, but having done it for about 15 years now, it's been my experience so far that you get what you pay for.
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Old 03-03-2005, 01:52 PM
  #119  
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Default RE: Sand / epoxy molds

In my project, I have need to vacuum form or cast female molds suitable for fiberglass lay up (epoxy and polyester) using a male aluminum master. (Of course, the master is created via CAM and CNC.) Perhaps someone can suggest a suitable material having vacuum/thermal workability, form stability, non-reactivity to resins, and even mold release qualities. The current suggestion from my plastic supplier is PETG though it appears to react to polyester resin. Any ideas would be much appreciated.
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Old 03-04-2005, 03:32 AM
  #120  
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Default RE: Sand / epoxy molds

Mike and others:
How easy is it to maintain a consistent thickness of the sand layer over the whole mold, and how do you measure it as you proceed?
How do you apply the sand layer, do you just pile it on and then distribute it (flatten it out) on the plug, or do you roll it out to the correct thickness (e.g. on a piece of plastic sheet) before it is transferred to the plug?
Also, did anybody pursue the idea of using microballoons instead of sand for this application? (And if so, what are the advantages/disadvantages, apart from the obvious weight saving?)

Magne
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Old 03-04-2005, 07:55 AM
  #121  
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Default RE: Sand / epoxy molds

Magne,

I'd suggest looking at my documentation on doing a composite fuel tank as you can see how the sand / epoxy was used.
http://www.houstonhobbies.com/tips/c...fueltank-3.htm
Day 3 and Day 4 show the sand application.

JR Gautreaux
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Old 03-04-2005, 10:49 AM
  #122  
Mike James
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Default RE: Sand / epoxy molds

Hi Magne,

I think you would need a truckload of microballoons to achieve the same mix consistency, and I wouldn't want to be anywhere near your shop when you were mixing it.

It's really intuitive with the sand mix, to achieve a consistency that you like. On my wing molds, which were about 550 sq. inches per panel, I used 1/2 gallon of sand, with about 10 oz. of epoxy, per panel. I mixed it all up with gloved hands, and just pat handfulls of it into place, yielding about 1/2" thickness. (2 layers of 6 oz. cloth on the inside and outside) Using fine sand ("blasting sand" is what I used) gives much better results than coarse, heavy sand, which has a tendency to separate.

Lots of different ways to achieve thickness, including epoxy paste, from http://www.freemansupply.com/ if you want to experiment.
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Old 03-04-2005, 05:08 PM
  #123  
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Default RE: Sand / epoxy molds

In my project, I have need to vacuum form or cast female molds suitable for fiberglass lay up (epoxy and polyester) using a male aluminum master. (Of course, the master is created via CAM and CNC.) Perhaps someone can suggest a suitable material having vacuum/thermal workability, form stability, non-reactivity to resins, and even mold release qualities. The current suggestion from my plastic supplier is PETG though it appears to react to polyester resin. Any ideas would be much appreciated.
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