Re: Scarf joint epoxy filler and keel nose question
Posted: Mon Apr 07, 2014 3:17 pmThank you all for your comments. Here's how it turned out:
My first attempt was an abject failure (see the first picture): it was very uneven, with many gaps in the plywood that I tried to fill with epoxy. I decided that "good enough" wasn't a good way to start this project and cut the wood right down the middle of the joint. I then made jig for my router. That thing is a beast - sawdust everywhere very difficult to get "right". You can see some rough edges in my second picture, but I finally got into the groove by picture #3. The scarf for the keelson turned out beautifully. I can write up a longer post about it if anybody wants, but this is definitely better than using a block plane (for me at least). Scarfing the plywood sheet only took 10 minutes or so.
My glue-up didn't work out as well. I think my problem was over-saturation with epoxy. Afraid of epoxy starving the joint, I liberally applied epoxy to both sides of the plywood and then added carbosil-thickened epoxy in the middle in a thin film. Lead weights then pressed the two sides together. In retrospect I should have used more thickened epoxy, but I had plenty of run-out so it wasn't TOO bad. Anyway, I think the epoxy actually oozed out completely in the lower side of my joint. The top part was glued tight, but the bottom had nothing in it at all. It's almost like I didn't put any glue there (but I did - I promise!). I could actually break the joint in scrap pieces with my hands after cutting out the hull sides - terrifying! I ended up injecting thickened epoxy with a syringe to hopefully get it into the deepest part of the joint.
My other problem was that the two sides didn't perfectly align. The top of one plywood sheet was maybe 1mm on top of the other piece of wood. Instead of sanding through the face veneer and weakening the wood, I just used wood-flour thickened epoxy to make the surface smooth. One side is still higher than the other, but there is a gradual gradient from one thickness to the other, so I hope it won't be noticeable from the cabin.
Finally, when fiberglassing the topsides and middle panels, I placed an extra strip of fiberglass at the joint for strength.
My first attempt was an abject failure (see the first picture): it was very uneven, with many gaps in the plywood that I tried to fill with epoxy. I decided that "good enough" wasn't a good way to start this project and cut the wood right down the middle of the joint. I then made jig for my router. That thing is a beast - sawdust everywhere very difficult to get "right". You can see some rough edges in my second picture, but I finally got into the groove by picture #3. The scarf for the keelson turned out beautifully. I can write up a longer post about it if anybody wants, but this is definitely better than using a block plane (for me at least). Scarfing the plywood sheet only took 10 minutes or so.
- First attempt - so bad I cut it in half and started over
- 20140322_205248858_iOS.jpg (44.65 KiB) Viewed 2255 times
- A little rough in the middle
- 20140323_212408621_iOS.jpg (107.65 KiB) Viewed 2246 times
- My cleanest attempt
- 20140323_222906035_iOS.jpg (118.43 KiB) Viewed 2220 times
My glue-up didn't work out as well. I think my problem was over-saturation with epoxy. Afraid of epoxy starving the joint, I liberally applied epoxy to both sides of the plywood and then added carbosil-thickened epoxy in the middle in a thin film. Lead weights then pressed the two sides together. In retrospect I should have used more thickened epoxy, but I had plenty of run-out so it wasn't TOO bad. Anyway, I think the epoxy actually oozed out completely in the lower side of my joint. The top part was glued tight, but the bottom had nothing in it at all. It's almost like I didn't put any glue there (but I did - I promise!). I could actually break the joint in scrap pieces with my hands after cutting out the hull sides - terrifying! I ended up injecting thickened epoxy with a syringe to hopefully get it into the deepest part of the joint.
My other problem was that the two sides didn't perfectly align. The top of one plywood sheet was maybe 1mm on top of the other piece of wood. Instead of sanding through the face veneer and weakening the wood, I just used wood-flour thickened epoxy to make the surface smooth. One side is still higher than the other, but there is a gradual gradient from one thickness to the other, so I hope it won't be noticeable from the cabin.
Finally, when fiberglassing the topsides and middle panels, I placed an extra strip of fiberglass at the joint for strength.