Kyosho Twin Broken Cowl - Making a New Cowling w/Plaster of Paris

R/C Building Techniques Hints & Tricks
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Neons
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Kyosho Twin Broken Cowl - Making a New Cowling w/Plaster of Paris

Postby Neons » Mon May 01, 2017 10:25 pm

I have made Plaster of Paris molds for out of new kit plastic canopies and cowlings along with other parts that have been hard to get or get bashed constantly. I remember flying my small GWS Zero over the club airstrip and the canopy blew off out in the cornfield. I thought I would just order another one. To my surprise they were hard to get without buying another kit. I found one but the shipping was more than the part. The next day after spending time in the corn field up and down the rows I found it. I got lucky. Later I found a GWS Zero kit at an auction and I made molds for the original canopy and cowling.

This is not a hard thing to do but it can be frustrating parting the new parts out of the molds. So I show a few ways to help you get it out of the mold with some easier work. The first picture shows The P of P by DAP. A cut milk carton for the mold support. I have most items shown in the picture but there may be a few tools left out that came into the works as I went along, Cut open any large enough plastic bottle to use as a container for molding. The other tools are in the next few pictures as I go along. P of P is inexpensive and mixes easy with water. I mix it almost loose like a pancake batter. It sets up in about 20 minutes and hardens a little more overnight. The good cowling should be waxed with a good boat or car wax. I just tried some cooking vegetable spray this time but I will say the the wax seemed to work better with a few coats. I used more work time releasing the old cowl than I should have.

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In the second picture you will see I mixed the P of P into the old plastic milk container. The cowling pat is forced down as it naturally wants to float. I just quickly grabbed a pair of bench batteries to weight it down to the point of P of P flowing over the edge. Weight can be lead sinkers bolts or whatever is at hand. Just do not let it touch bottom of the container. The plaster has to be deeper than the part. It was late so I left it for the next day.

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In the next photo you see all the Plaster of Paris all set up and ready to get it out of the new mold.

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Now you need to make the magic plastic tools to get it out of the plug. Look for an old bleach bottle or something similar and cut it open with scissors around the bottle to get the straight mid section out. Cut tapered plastic spoons of different widths. I start with the smaller ones that are not to sharp so it will not damage the mold Push it in slowly with some left and right motion and get as deep as you can. Remove it then move it over a little and repeat all the way around. I then used a larger one all around. I carefully used a flat needle nose pliers and pulled on the edge slowly and it popped out. You really can't pull to hard or it will break the original part. If it does not come out go around again with smaller plastic spoons to try to spread the walls deep as you can get them. Then try the needle pliers carefully again and it will eventually come out..

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Now you will see how the mold looks with the part out. The blue was from the plastic spoon material and I cleaned it out. The hole drilled is for another another helpful way to extract the new epoxy glass part in the finish step should I have problems pulling it. It will be for air pressure blow out with an air gun. Fortunately it was not needed.

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Last edited by Neons on Mon May 01, 2017 10:59 pm, edited 1 time in total.
Bob Pacheco

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Neons
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Re: Kyosho Twin Broken Cowl - Making a New Cowling w/Epoxy

Postby Neons » Mon May 01, 2017 10:57 pm

In this part I am readying for the Epoxy glassing the mold. You will see most of the tools used here.This is not a hard thing to do but it can be frustrating parting the new parts out of the molds. So I show a way to help you get it out of the mold with some easier work. The picture shows a few different types of epoxy I use and are readily available in stores around the area. Polyester fiberglass is very good also as it dries nice and hard.

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I am just going to give some notes on these items in the photo with the supplies. You do not need all these epoxy glass mixes shown here. First not shown is you can use automotive or marine polyester resin with drops. That would be a good choice as it will harden up more solid than epoxy. The next choice that is good is West System epoxy. It will cost the most but it is super. Next on the food chain of epoxy is the large bottles shown here which is not practical as the mount to purchase is not going to make sense here. That was bought for making a fuselage out of epoxy. It technically is a counter top clear coat. It takes days to get hard with time. The same goes for Parks epoxy clear coat. It is found in hardware stores and made locally in Somerset,MA. I used it for this mold. The far left is 2 part epoxy also. That would also make sense to use on this project. That is another inexpensive small amount to use on this. That would be a best choice if you can get the 1 hr set up epoxy. Not much waste here.

The first thing to do now is to make sure there are not bad flaws in the P of P mold. Very lightly sand with super fin paper any thing that may be a bump to a level feel. I have a hole in the bottom of my mold. I just covered it with a tiny piece of tape before adding epoxy. . I have mold release in paste wax and PVA release. Do not worry if you do nt have this. Use a car or boat heavy paste wax to release the glass. three coats is good, Let it dry then try to polish it between coats. I used wax and 3 PVA on this one. It all works. I also used a heat gun to speed things up some. I have a small mixing cup and a Popsicle stick to apply the epoxy in small amounts. We do not need a lot f epoxy and cloth due to the weight on the part.

Once the mold is prepped we go to the fiberglass cloth and cut a small block that will reach just above the top to the bottom. Pour an equal measure of 2 parts of epoxy into the plastic cup. Stir the 2 parts for some time and then either a small brush or the sthick start applying a layer through out the inside of the mold to wet the whole inside of the mold. Let it setup for a while to get tacky. Take a break for a while. When you are ready cut the glass cloth into tapers. I used very light 0.7oz cloth. Put a strip of cloth down into the bottom all the way to the top of the mold. Tap it with the Popsicle stick and another small amount of epoxy until the cloth is wetted out. Then repeat to the next strip with overlap. and another small amount of epoxy. Go all around. Do not put more glass than is needed to wet it all out. You can use some of the excess epoxy as it slides down to the bottom. Keep it light if you do not want a heavy plane. You can give it a second row of fiberglass cloth wedges if you want the same way. Cut another strip of cloth that is narrow for the top edge to be stronger. You want it just below the edge where it is useful after the scissor cuts when it is extracted. Let it dry and harden fo a good day. If you are using polyester fiberglass it may be ready sooner than a day.

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Bob Pacheco

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Neons
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Re: Kyosho Twin Broken Cowl - Pulling the New Cowling

Postby Neons » Tue May 02, 2017 12:05 am

In this part I let it cure for a while while I had other things to do. The process of pulling was the same as earlier with making the copy of the older cowl as the mold. You can see that there is excess glass clothe on the top edge. This is trimmed back and I left about 1/4 inch there to be used in pulling the new cowling out. I used a new set of my magic tool plastic spoons made from a Clorox bottle and went around a couple times. I used my small needle nose pliers and pulled on the top edge cloth and it popped out. I did not use the high pressure air gun as it was not needed this time. I trimmed the rest of the top edge(rear of the new cowl) off with scissors. I then sanded both cowls to get it ready to paint after some spackling of defects was done. I Dremel'd out the holes for air and the motor shafts and mounted the cowls. Two coats of water base paint and I am ready to fly again.
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This last picture show the old plane ready to continue flying in the time to come. It is one of my nicest wind twins in my inventory. I believe the name for it is a Kyosho - Etude.

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Bob Pacheco

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Re: Kyosho Twin Broken Cowl - Making a New Cowling w/Plaster of Paris

Postby ccosta » Wed May 03, 2017 7:36 am

Bob,
As usual very good work!
Carlos


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