Sanding, Scraping, and Fisheyes

Being reluctant to tear into the first coat of epoxy that I had applied to the hull panels with 60 grit sandpaper I tried using 100 grit sandpaper instead. Within 18'' the sandpaper was clogged with epoxy. I used several pieces of sandpaper on that first panel. Then I decided to try the 60 grit. That was a huge improvement and I didn't need to wory about taking off too much material. I did two panels with the 60 grit and followed up with 100 grit. That worked quite well and I pretty much thought I had settled on the procedure I needed to follow. But even then I was using up sandpaper fairly quickly even when I tried to vacuum up the epoxy dust frequently to prevent it from glogging the sandpaper.

Then I remembered I had purchased some cabinet scrapers from CLC and decided to give them a serious try. I had given the scrapers a quick try previously but I didn’t quite get the hang of it. As I understand it you are supposed to file the edge of the scraper flat along the length of the scraper and square with the sides of the scraper, burnish the edge so a fine lip forms on one of the edges, and then draw the edge over the work piece while holding the scraper in a curved shape. Well, I seem to be having pretty good success just filing the edge and using it flat on the workpiece with the scraper tilted in the direction I’m scraping. The process of filing the scrapers seems to produce an adequate lip on the scraper without burnishing the edge. And, I have two edges to use instead of the one formed by burnishing. For the initial scraping where the epoxy surface is very rough I used my thickest scrapers (.032” and 0.042” )

The pictures below show some stages in the process:

Low angle view – low spots show up as slightly darker.

High angle view – Gloss from low spots clearly visible.

One thing I like about the cabinet scrapers is that the scraped surface is much flatter than when I use sandpaper. It seems like any padding on a sander allows the sandpaper to yield a bit to high spots and places where the grain of the wood is harder while removing the softer grain. The result is an undulating surface which, I suppose, has a certain amount of character but can also begin to look like you had problems applying the finish uniformly when reflections off the surface show irregularities.

The other thing I like is that scrapers produce much less of the very fine dust inherent in sanding. With scrapers most of the epoxy comes off in fine shavings. In the picture below you can see the white shavings from the epoxy and just a trace of brown shavings from the wood.

I monitor the condition of the surface until only a very few, small, glossy low spots remain. Then I use 120 grit sandpaper to achieve a completely gloss free finish necessary for follow-up coats of epoxy, paint, or varnish.

I am using far less sand paper.

One caution relates to the corners at the ends of the scraper. Sometimes my filing technique results in a very small barb at the ends of the scraper. I haven’t determined whether the barb is formed at the beginning of my file stroke or at the end. The picture below shows the line produced in the epoxy surface by such a barb.

It is important to watch very carefully during the first few strokes when changing to a fresh scraper edge and to stop immediately if the scraper is leaving these scratches and redress the edge of the scraper.

A similar situation can occur if you file too much when creating a fresh edge. It seems like if you go at the edge for too long the continuous lip created by filing sticks out a bit more some places along the edge than others. My best results have occurred when I only file until I can feel a nice continuous pull on the file which means I am getting a clean bite along the entire length of the scraper edge. I also try to place the long dimension of the file as parallel as I can to the edge of the scraper so that the edge produced on the scraper is as straight as possible. You get the hang of it after a while.

I can attest to the fact that when the scraper gets a good bite it can get pretty darned hot. Fortunately it cools off quickly.

As I was doing my research before getting my kit I kept running across the term “fisheyes” as a reference to blemishes that can occur in the surface of the epoxy. I wasn’t sure what they were. They become obvious once you get to the second coat of epoxy. The fisheyes below are about ¼'' across.

With the hull panels precoated it’s stitchin’ time.

I made two little drilling guides – one for the set of holes to be drilled adjacent to the rabbet in the hull panels and another for drilling the holes about ½'' down from the top of the panels. The first picture shows a profile view of the guide used to place holes 1/16'' from the rabbet. The second picture shows both guides.

The point of the finishing nail can just barely be seen near the right end of each guide in the second picture. That nail pokes into the previous hole to guarantee uniform spacing to the next hole. If you work from the back of the boat to the front you need to put the nail in the opposite end when you switch from port to starboard.

There is no problem using the 1/16'' guide (left above) to drill the initial holes in rabbeted edge of the panels (clamped together back-to-back as indicated in the instructions). However, when drilling the second set of holes in the top of the adjacent panel to match the first you need to check about every 5 holes to see if you need to adjust the spacing a little bit. The first set of drilling guides I made had just a little variation in the 4'' spacing of the holes and by the time you drilled 20 holes you could see the misalignment. On this second set of guides I drilled both sets of holes in the guides at the same time with the guides back to back. Even then I needed to adjust just a little every 5 to 10 holes. The picture below shows one guide “in action”.

There always seems to be something you can do on this project. If you’re watching TV you can use a 4” scrap of wood as a guide to cut lots of copper wire stitches. And I discovered the holes in adjacent hull panels were the same distance apart as the diameter of one of my sockets. So, while still watching TV I would take 3 to 6 pieces of wire in my hand and bend them together around the socket.

Made ‘em real nice to insert in the holes. They also looked kinda cool hanging over the edge of a clear plastic cup!

I mentioned last time that the operation had moved to the garage. Wow! Does a day in the high 80’s ever change the viscosity of the epoxy. My basement had been in the high 60’s. Makes you change your application technique quickly.

The worksurface I made is working out great for doing the stitching.

I am finding that if I block up the hull to produce some rocker and then use my clamping arrangement as a second set of hands to keep the portion of the panel I am working on “tangent” to the panel below it, then the stitching process and the resulting fit of the seams woks out great.

I’m leaving all of the stitches a few turns loose so the panels can shift into a comfortable position without stressing individual stitches or the adjacent wood portions of the panels too much.

The masthead is a whole other issue. The portion of the masthead that goes into the mast has a diameter that is too small. So, an “adapter” is sent along with the kit. The adapter is just a piece of aluminum tubing with a diameter a little smaller than the tubing used for the mast. The adapter also has a slit cut down the side so it can be compressed enough to slip into the mast. However, the masthead is too large to fit in this adapter. So something has to be customized. I was successful in gluing the masthead squarely on the end of a dowel that I had sanded a taper on to fit the taper in the end of the masthead. I looked for someone with a metal lathe so I could trim the masthead. No luck. Then I had a brainstorm of how I could use my router to trim the masthead. The setup is pictured here.



The adjustments on this setup were a little crude and I trimmed way too much off the first masthead. I ordered another and tried to be more careful the second time around. Let’s just say the setup was a good idea but I hope the colloidal silica does its job of filling in gaps. I got a slip fit instead of the friction fit I was hoping for.

This is still great fun!