Spars, Mast Hinge, Part 4: Construction of G-10 Step

The G-10 step, ready for drilling
Having constructed a detailed mock-up step out of wood, it was now time for me to construct the real step out of G-10. This material - G-10 - is an industrial grade epoxy-cloth laminate. To put it in more basic terms, it's a solid piece of fiberglass. I had ordered from McMaster-Carr in Atlanta, Georiga a 12 inch x 12 inch piece that was 3/4 inches thick. Officially, on the McMaster-Carr website this G-10 was classified as Flame-Retardant Garolite (G-10/FR4). This Garolite, or G-10, I would cut to form two 3/4 inch pieces that together would be 1.5 inches thick. This was a much more cost-effective approach to this project than ordering a 1.5 inch piece. Now that the G-10 had arrived, I could get to work.

To cut the G-10 into the appropriately sized pieces, I used my Makita brand miter saw. This would ensure a nice, straight cut.
I used a 60 tooth carbide blade.
The G-10 gave this saw and this blade no problems. It was not unlike sawing sapele mahogany, which if you've read some of my other articles, is a dense tropical wood.

With this saw I was able to create two identically sized pieces that matched the dimensions of the mock-up.
Now it was time for me to make some marks. I started by marking the holes where I would mount the halyard plate organizer and the mast hinge itself to the G-10.
I used the reference marks to help me establish where I would drill the holes for screwing the two pieces of 3/4 inch G-10 together. These four holes could not, of course, interfere with the other four holes for the halyard plate organizer and the hinge. Therefore, I placed the marks for these four holes well out of the way.
I marked the center of these pencil mark references with a center-hole punch.
Then I walked outside with my sander and roughed-up the two faces of the G-10 that I would join together with epoxy. I used 40 grit paper for this, just as I did whenever I sanded cured epoxy or sapele mahogany.
It's difficult to tell from this picture, but the 40 grit paper created many small swirls in the G-10. It went from being green and shiny to being greenish-white and hazy.
I decided to use #10 wood screws to join the two pieces together. Accordingly, I used a 5/32 inch bit (two sizes smaller that the #10 screw at 3/16 inch) to establish a hole.
I then used a countersink bit to chamfer the hole. This would allow the flat head of the wood screw to sit flush with the surface of the G-10, or in this case, as I preferred it, slightly below the surface.
The G-10 proved to be incredibly resistant to accepting the threads of the wood screw.
Therefore, I re-drilled the hole one size larger at 11/64 inches.

After repeatedly screwing and unscrewing the first screw into the 11/64 inch hole, I was able to get it to accept the screw.
I then went around and did the same thing with each of the other holes.

Things were still a little tight, so I widened each of the holes on the top piece of G-10 slightly by routing them out with circular motions of the drill bit.
This enabled me to join both piece tightly together with the four screws.
In preparation for epoxying the two pieces together I sanded the top side of the top piece. This would be the side where the screw heads would sit. Since I planned for the screw heads to be slightly below the surface, and since I planned to fill the screw head holes with thickened epoxy, I needed the surface of the G-10 to be rough. This would help with the adhesion of the epoxy.
Prior to my mixing of the epoxy, I cleaned all of the relative surfaces with acetone.
I began by applying neat, i.e., unthickened epoxy, to both of the inner surfaces.
Then I thickened the epoxy with colloidal silica until it reached a peanut butter like consistency. I then spread it on the top of the surface of the bottom piece. In the picture below it appears that there is plastic on the top surface. What you're seeing are in fact the ripples of thickened epoxy.
I then set the top piece on the bottom one, screwed it into place, and applied clamps all around the perimeter. I made sure that the clamps were tight, but not too tight. I didn't want to starve the joint of epoxy. With the small bit of thickened epoxy that remained in the pot, I applied dabs to the screw holes to fill them up.
Concurrently, I began working on the anti-compression block that would go between the bottom part and top part of the hinge. You'll recall that I had determined that the anti-compression nuts available from Dwyer Aluminum Mast Company were not compatible with the original aluminum mast step of the Ericson 25.
I decided that I would use a piece of oak for the anti-compression block. This required me to plane down a piece of oak to the appropriate thickness - somewhere in the neighborhood of 7/8 inch.
I then used the table saw to get the material to the proper width.
One more cut - this one on the miter saw - got the piece to the proper length.
Then it was time for me to drill the four, 5/16 inch holes.
Also at this time I disassembled the block and thoroughly cleaned the original aluminum step.
It had been some 40 years since it had been installed on the mast.
There were pock marks here and there. It appeared that over the years small filings from the stainless steel hardware on the mast had fallen into this reservoir of sorts and created some corrosion from the interaction of the dissimilar metals.
By this point some days had passed and the epoxy on the G-10 had fully cured. With a quarter-sheet sander loaded with 40 grit paper, I sanded away all of the excess epoxy.
Yes, this was a time consuming process. Sanding epoxy, as I have said many times before, is like sanding concrete.

After I had finished the sanding, I did some work with the jig saw. Just as I had done with the mock-up, I rounded the edges of the G-10 step so as to make it less intimidating to lines and more pleasing to the eye.
I used Bosch T118B blades, which are designed for cutting metal.
Despite the quality of the blades, I did not get quality cuts with my Makita jig saw. Ideally, I would have used a band saw.
To make the cuts appear more uniform and professional, I rounded each of the four corners with the sander.
By the time I was finished, all four rounded corners looked symmetrical.
This G-10 mast step was now ready for drilling. For this I would need to call upon a friend with a drill press.
This ends this posting on how I constructed the G-10 mast step for Oystercatcher, my Ericson 25.

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