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Old Aug 07, 2014, 12:53 PM
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Seattle, WA USA
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MDF backing Corian wing mold

I'm close to cutting a set of wing molds for a 60" DLG. I have some of the "Formica" brand counter top material that is similar to Corian I wlll be CNC cutting the surfaces.

The material I have is 1/2" thick and I will be machining out about 3/8", leaving only 1/8". That will need "backing" and I've read that often a second layer of the Formica (Corian) is laminated with epoxy.

My frugal way of thinking has me wondering if other materials might work for the backing. Something like MDF perhaps. If using MDF I know sealing it for moisture would be very important but that's easy to do. My main concern would be different expansion rates from the MDF and Formica perhaps inducing warps when heating for curing.

Anyone have thoughts for / against MDF? Or maybe some other (inexpensive) material that might work?

Thanks, Rick
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Old Aug 07, 2014, 02:58 PM
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Albuq, NMex USA
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I have a piece of MDF that is actually two 1" pieces 12"X32" that I epoxied together for CNC milling a 31" top wing section. Turned out ok but had two deeper full length grooves (1/16") that somehow got into the nc file. Anyway, put it outside about one month ago in the hot NMex sun and through the past several weeks of our monsoon season with several torrential downpours. Just check it and it is still straight and not wrapped at all.

MDF is a lot more stable that I initially thought it would be.
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Old Aug 07, 2014, 04:21 PM
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Mdf

I've been a cabinet maker/furniture maker for a very long time. I like MDF for alot of things but I wouldn't consider it to be similar to Corian in any way. If another sheet of the same plastic is too expensive, maybe you can find some "takeout" pieces from a kitchen remodel. I would also think maybe a left over cutoff of some kind of stone countertop would be more similar to Corian than MDF. Also you could try some of the formulas of the DIY Corian in one of the other threads down the page and pour your own backing sheet. You also might consider doing the first couple molds out of MDF, with MDF buildup, in case things don't work out well on the CNC side.
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Old Aug 07, 2014, 06:20 PM
Blind Hawk
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@ MikeC. This kind of surprises me. If i leave MDF out in the weather it swells almost immediately. Perhaps there are different glues used in MDF....

@RudyF. I'll research the DIY Corian, that is not something I've been aware of. I've done a few molds with both Corian and MDF. For this particular mold I'm about to cut my 5th "test" out of MDF attempting to get it "just right. I've done some research trying to find "takeouts" too but no luck there as of yet.

I'm just a hobby builder and will only be making a few wings, I always am looking for the most cost effective (ok cheap) solution.

RdJay
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Old Aug 07, 2014, 10:18 PM
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Albuq, NMex USA
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Maybe different glues. Had not thought of that.

The 1 " from a lumber yard smells much stronger than the 3/4" from Home Depot.

For the price you can not beat MDF encapsulated with epoxy for proof of concept designs.

Downside is the dust and odor.
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Old Aug 07, 2014, 10:33 PM
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I'm currently working with MDF; hand shaping flying surface plugs.
A composite builder friend of mine told me how to treat the MDF with epoxy and apply heat with the heat gun turned up on high. Three successive applications at least, with no curing time in between.
The MDF soaks up an astonishing amount of the resin and it goes in very deeply.
The result is a very stable product.
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Old Aug 08, 2014, 06:26 AM
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Use the moisture resistant grade of MDF and you'll be fine. We use to back patterns when theyare machined with no issues. However, it MUST be the moisture resistant grade...
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Old Aug 08, 2014, 06:29 AM
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corian expands alot more than MDF

i have a set of wing moulds and i thought it would be a good idea to warm them up for the cure

as i opened the molds they peeled back like a banana .. must have been more than 40-50mm when the molds were unbolted and just lying ontop of each other ...

as they cooled down they went flat again .... next time ill let the moulds cool first
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Old Aug 08, 2014, 03:56 PM
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Sweden, Dalarna County, Sälen
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Backing up corian with mdf is a big BIG no no! It just goes banana!
Not familiar with formica but if it is as strong as corian, 1/8inch might be strong enough. Im down on 1/16inch in the root of my upper wingpanels an that held up fine. Only made one wing so far though...
If you do find something cheap that works. Please let us now.
Good luck with your build.
//Kalle
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Old Aug 08, 2014, 04:57 PM
Blind Hawk
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Thanks for all the input guys.

I'm pretty well convinced now that the MDF is a bad idea. This thread - http://www.rcgroups.com/forums/showthread.php?t=2165394 has me thinking that I could simply pour a 1/2" or so thick layer of DIY Corian after machining and I might be golden. I'll report back any success or failures.

Rj
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Old Aug 09, 2014, 12:30 AM
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There used to be three types of MDF that you could get from cabinet supply houses (at least in Nor Cal.) The plain, regular stuff, pretty heavy and loves to absorb water, there was a waterproof variety made with exterior glue. There was also ultralight MDF that was more like it was made from Balsa dust, it came from Ecuador. I would think reg MDF impregnated with epoxy would be just as good as waterproof and easier on cutting tools. I would think either way you would be coating them with epoxy after rough cutting, then doing a finish cut into the hardened epoxy/MDF composite.
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Old Aug 09, 2014, 05:16 PM
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Quote:
Originally Posted by rdjay View Post
Thanks for all the input guys.
.............................. has me thinking that I could simply pour a 1/2" or so thick layer of DIY Corian after machining and I might be golden. I'll report back any success or failures.

Rj
Not a good idea in my mind at least for a couple of reasons.
The added mix layer will required post curing.
Also, the new layer will shrink very slightly during the cure process and this might also warp your nicely cut Corian mould.
It might be better to make a layer of your DIY Corian on a flat glass sheet and carefully cure it first at room temperature, then post cure it to the optimum temperature for the particular resin you will be using. Then epoxy the new slab onto the back of your mould.
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Old Aug 16, 2014, 08:59 PM
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United States, WA, North Bend
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Rick, just back it with corian. The Bart is worth the investment.

AVB backed his scratcho molds with 3/4" plywood but I would still worry about the thermal expansion issue.

Lee
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Old Aug 16, 2014, 11:03 PM
Blind Hawk
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Seattle, WA USA
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Worth the investment, yes but I pride myself in being "frugal"

I have a "plan" if it works will be cheap. If it fails I'll back with Corian. I'll post the results either way.

Soaking up the sun at Lake Chelan for the next few days so not much work getting done on Bart.

Rj
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Old Sep 01, 2014, 10:40 AM
Blind Hawk
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Seattle, WA USA
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The simplest solution seems the best. I made some MDF backing pieces but just left them loose. No need to attach them to the mold, no worry about expansion differences.

Only one test layup so far but results are promising .

Rj
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