[Dutkoski]

I’ve been back at it, off and on as they say, busy busy busy. So during the last few days, I’ve prepared the right wing master plug to be moulded ........ finally.

After the master plug is final sanded to the finish you want (400 grit in my case) you need to make the parting boards that will surround the plug and provide a ledge that the moulds flange will be created. This flange is very important, it needs to define the draft center line so the eventual part can be removed from the mould. If you have a negative draft in the mould, you might not get the part out. Also, making a flange that is narrow is counter productive, prepare to make them fairly wide. This is so there is plenty of room to have your reference indents and bolt holes. Also, if you vacuum bag your parts, the larger flange is needed to attach the vacuum sealing tape.

Some guys seem to use thin hardboard, but not me, I prefer using 5/8” thick white melamine painted particle board material. Easy to obtain from Home Depot. I cut it into 3 3/4” wide strips.

Before anything else, apply parting wax around the perimeter of the wing and after buffing, spray PVA parting solution around the edges. This step is very important for later on.

I then block up the master plug, the wing in this case, using foam that is hot glued together to get the height I need. Generally, I start with the wing root and get the physical center line of the airfoil. I then make standoffs to support the wing root parting board, the upper surface is lined up with the root center line. I use hot glue to secure the standoffs to the work table and the parting board to the top of the standoffs. Don’t use a lot of glue as you need to knock everything off afterwards. Also DO NOT APPLY THE HOT GLUE TO THE SEAM WHERE THE PARTING BOARD MEETS THE PLUG.

Once you have the parting board material all the way around, use bondo to fill in the joint seams and mould ramps to match up any steps that were created. In this case, the area of the dog tooth feature created a slight step along the leading edge.

Next step is very important, you must seal the seam between the parting board and the plug. I normally leave a very slight gap between the parting board and plug, less than 1/32” mostly. To seal this gap, I use bondo, I mix it up in small quantities, about a teaspoon amount at a time. I then use a blunted popsicle stick or credit card material to squeeze the bondo into the seam. Once the bondo has cured stiff, I use a safety razor blade to trim away the bondo. Because you had previously applied wax and PVA to the edges of the mould, the bondo easily lifts off the plugs surface.

After the seams are sealed, I use my Dura Grit spherical burr in my Dremel and create divots along the parting board around the perimeter. These will create a dimple that will be replicated as a divot when you mould the opposite side.

Now the fun begins, after a good cleaning, I like to apply at least three coats of parting wax and then spray two coats of PVA release agent. There are several other parting systems on the market now, but, I have been using this system for about 25 years now and I am very comfortable using it.

[Myzee]

Wow, amazing work John. Someday I will learn this! :P

[Dutkoski]

Well, in everyones life, a little rain must fall ...... and today is my turn I guess. On Tuesday, I had prepared the master plug. I applied a good layer of gelcoat and everything seemed perfect, good even coverage. After a couple of hours, I checked on it and discovered the coating had lifted slightly at the edge of the parting board in one section. But everything else seemed good. About 6 hours later I checked again, holy crap, the whole covering of gelcoat had literally lifted off the master plug and cracked everywhere. This has never happened before, I have made literally dozens of moulds, I was stumped ......

I contacted Rayplex in Oshawa ( where I purchased the gelcoat on Monday ) and advised them. The chap told me that I put in too much hardener, it cured too fast.

So, last night, I prepared the master plug for the wheel well doors on the other wing plug. Mixed up two oz’s of gelcoat with the recommended 4 drops of hardener per oz. and applied the gelcoat. All looked perfect. This morning, I checked and guess what, it did the exact same thing, totally lifted off the plug in a single sheet but, it was dry ...... yeah.

So, I contacted my regular supplier, Composites Canada and spoke with them and sent them pictures of the problem. Also, reordered another gallon of gelcoat, etc. Now waiting for their comments on what had wrong.

If anyone has had similar problems, I would be interested in their solution.