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Author Topic: Getting started with composite parts in Indoor.  (Read 628 times)
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mkirda
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« on: September 29, 2019, 09:09:27 PM »

As I get asked this quite a bit, I thought I should just write up what it takes to get started making composites for indoor models.

Here is a list of supplies needed.
Vacuum pump – Gast pumps are often found on ebay rather cheaply. You can likely find one at Harbor Freight as well. I used a FoodSaver in the beginning. It works.
Acid brushes – Harbor Freight
Nitrile gloves – Harbor Freight
3.5-4 mil plastic sheet – Harbor Freight
Caulk gun – Home Depot/Lowes/Harbor Freight
Inexpensive caulk – Any local hardware store
Wax – Recommend Part-all #2. Any composites store.
Laminating Resin – I highly recommend MGS resin. Nothing wets out carbon as well as MGS. I would recommend getting both the 285 and 287 hardeners so you can vary the amount of time before the resin gels. Wicks carries this. Other composite stores do too.
Fiberglass – You can get away with just two sizes of fiberglass. You want 0.5oz cloth as it is just about exactly 0.001” thick when wetted out. 3.6 oz cloth is just about 0.006” wetted out.
https://www.thayercraft.com/0.56-oz-104-volan.html
https://www.thayercraft.com/3.63-oz-1522.html
Sharp scissors can cut up to roughly 7 layers of 3.5oz cloth. Offset tin snips are a better choice on thicker laminates.
Carbon – ACP/CST have lots available. IndoorFFSupply.com carries the hard to find Toray M60J in small spools.
For a hot box, I use a simple temperature controller that turns on a lightbulb inside a plastic cooler.
https://www.amazon.com/Inkbird-Max-1200W-Temperature-Controller-Greenhouse/dp/B01HXM5UAC/
Nice to have: A cutting mat and rotary cutter for cutting fiberglass to size. Makes things a heck of a lot easier.
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mkirda
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« Reply #1 on: September 30, 2019, 06:08:52 PM »

I forgot to add:

Popsicle sticks, available at most dollar stores or craft stores.
1 oz medicine cups used to mix up small amounts of epoxy. Available at CST/ACP and similar locations.
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USch
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« Reply #2 on: October 01, 2019, 05:33:58 AM »

To me another important tool for working with composites is a weight scale with a resolution of 0,01g. Moulding small pieces you will often need not more than 2-3g of resin plus 0,8-1,2g of hardener, so a precise tool to measure these small quantities is important.

A word about precision of the mixing ratio. Most producers recommend an error of +/- 2% on hardener weight. But that does not mean that up to 2% error the resin-hardener mix will get hard, over that error the mix will not harden at all. The technical quality's of the composite will slowly decrease with the increase of error in mixing and with our kitchen table technologies we are not able to detect the differences.

So a good advice, keep the weight proportion of resin-hardener as precise as possible, mix VERY well and long and keep the moulding at e temperature of at least 25° for 24 hours.

Urs
« Last Edit: October 01, 2019, 05:59:20 AM by USch » Logged

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OZPAF
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« Reply #3 on: October 02, 2019, 11:28:36 PM »

 That is great advice Mike and Urs. My composite work has been on a larger scale generally and thus i was able to get by using syringes as anything less than 10ml of epoxy was not attempted. I will definitely be using a digital scale for small quantities - particularly as these are so readily available

The comment re the amount of mixing I think is also very important, and seems to be often overlooked. Mixing of the resin and hardener should be thorough-preferably using a paddle or popsicle stick and at least for a minute of continuous stirring. A  Engineer friend of mine stated that you should turn the mix almost white with entrapped air and then let it stand for the air bubbles to dissipate.

I tend to always work with warmed Resin and Hardener and also warm the mix - both by sitting the containers in hot water, this helps the reaction and improves the wetting out.

I would always prefer to warm the epoxy rather than thin with alcohol to improve wetting out.

John
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jakepF1D
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« Reply #4 on: October 24, 2019, 01:02:41 PM »

I posted this on INAV, but wanted to copy it here regarding vacuum pumps.

"The Harbor Freight and similar vacuum pumps that are designed for working on A/C systems have one major drawback. They use oil for lubrication, and they end up emitting oil vapor when running. This isn’t a major problem if you have a perfect seal and the pump only runs for a minute or two. If you have any leak at all and the pump is cycling on, it can fill a room with oil vapor in a hurry. I learned this after borrowing a pump from a friend. I’ve since purchased a Gast pump off of eBay for less than $75, and it uses an oilless diaphragm design which completely eliminates this problem. Go with a Gast if at all possible."

I purchased the pump at the link below.  It's a brand new Gast pump that can pull 29inHg, and it doesn't use oil.  It is mounted to an oddly shaped piece of sheet metal, but I plan to mount some simple feet to the bottom and use it as is.

https://www.ebay.com/itm/Gast-Two-Stage-Rocking-Piston-Air-Compressor-Pump-LAA-V118-NQ-100V-2-5A-New/323948272934?hash=item4b6cd25d26:g:82AAAOSwAy5awvY2
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USch
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« Reply #5 on: October 24, 2019, 02:02:06 PM »

An easy way to avoid filling up your working place with oil vapor is to slip a 4-5m length of PVC tube over the exhaust pipe of the pump and coil the tube into 4-5 windings. The oil vapor will condense inside the tube and only air escapes through end of the tube. The exhausted oil quantity is minimal and accumulates in the lowest part of the windings.

Urs

PS: still using a fridge pump found in the '70 on the street and still pulls up to 940mBar!!!
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« Reply #6 on: October 28, 2019, 11:33:42 PM »

That's neat solution Urs. I have also seen the discharge run into a closed bottle with a discharge vent to the air - a basic oil trap.

John
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lincoln
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« Reply #7 on: October 29, 2019, 08:31:43 PM »

If you don't need much of a vacuum, you can put an aquarium pump in a sealed container with the output line vented to the outside. Attach the vacuum line to a tube going into the container. The pump I tried pulled 3 or 4 inches of mercury. I tried putting 2 pumps in series, but that didn't help. Maybe if there was a lot of volume in between the two pumps or there was a way to de-synch the AC going to each pump.

For mixing epoxy by weight, I sometimes use a very simple balance I made. Glue,a 1 oz cup to each end of a light stick. Glue something rounded or with v shape on the bottom to the bottom of the stick to act as a pivot. . It should positioned proportionally tbe,desired mix. For instance, if you wanted 60-40 by weight, you could put the pivot 4 inches from the center of 1 cup and 6 inches,from the other.  The pivot should be low enough that the stick can only move a coupe of degrees if placed on a flat surface. Place an empty cup in each glued cup and add weights to make the stick balances at the pivot. In use, put some of the lesser part of the mix (for example, the 40 of 60/40) in one empty cup and put the cup on the short side of the stick, in the glued on cup. Now put the other cup on the other side and slowly fill it with the greater part until the stick pivots over to that side. That gives you an accurate mix. Pour one into the other and mix, carefully scraping the sides of the cup. Now pour that mix back into the other side to mix and scrape. Repeat a couple of times. No calculations are required.

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lincoln
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« Reply #8 on: October 29, 2019, 08:33:06 PM »

OOPS! The lesser part should be on the longer side.
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