Scarf joint epoxy filler and keel nose question

[craig]

Hi all, just started my build a week or so ago. First, many thanks go to you all for writing blogs and forum posts about your experiences. I've really enjoyed reading about your progress and these tips make it possible for myself (with very little experience) to build a boat. So thanks!

I have two current issues I thought I would throw out there. First: my scarf joints (working not from a kit) are not perfect, they have some low areas where I need to fill to get a good bond. Is it OK to add wood filler to the epoxy when gluing a scarf joint, in addition to cabosil? Maybe 50-50 mix. Or I could fill the divots first with wood flour epoxy. I just worried that cabosil filler alone wouldn't have enough bulk to it.

Second question: when shaping the keel nose block I accidentally removed too much material from the 'top' (the pointy end). So now it is .5 inches shorter, meaning it has a broader, flatter curve than in the plans. Still shaped like a curve though. Should I remake it or does it matter not that much?

[truenorth]

Craig, welcome to the club.

I didn't do scarf joints so will leave that one for someone else.

On the nose, I poured my lead in my backyard and had to drag the whole thing back to the garage. The centerboard trunk and keel is unwieldy by itself. With lead, it's almost impossible. So, naturally, I swung the nose around and hit a tree, knocking off the tip. It was already attached and could not be redone, so I molded a bit of thickened epoxy around the point and sanded it down. It came out pretty good, considering. Whether or not you want to redo yours is up to you, but from one short nose to another, you should be able to fix it.

Here's the post (about 1/3 down)

http://sunmonkeypocketship.blogspot.com ... iling.html

[craig]

Yikes, hope you had Nose Insurance, else the doctor's visit must have cost a fortune... haha

I think if I use some epoxy (the cure-all???) and jigger things around just right, I can lengthen it by enough so that the difference is trivial (less than 1/4 inch). I'll try it when I get to that part of the keel assembly.

About the scarf joints: cutting these things by hand is a beast. I don't know how everybody else is doing it. I read on people's blogs about how simple a block plane makes them, but let me tell you, my block plane did NOT cut it (literally). I stacked up the wood and planed away for hours without a lot of success. I finally had to resort to a router jig I made up. The first couple of passes were REALLY messy and I eventually had to cut off the last inch/inch and a half of the plywood sheet and redo the scarf taper. I finally got it roughly smooth and said "good enough". It's gluing together now. I used 100% carbosil filler for the scarf itself, and after it dries will make up wood filler mix and slather it on across the outside of the scarf to fill the low points, then scrape and sand off the excess. That should get it smooth.

I believe I slightly increased the plywood thickness at the scarf by overlapping the two sheets too far. I guess I can sand down the top sheet until they are flat.

[chaertl]

Hi Craig,

Block planes never worked for me while cutting scarf joints either. What did was a belt sander loaded with 40 grit sandpaper. As for the filler, go with straight cabo-sil. Wood flour is weaker and some of these joints are going to under a lot of stress. The secret to a good joint is make sure there's enough glue to fill any potential voids and have a clean, flat area to clamp them down while drying.

Chris

[DanaDCole]

I would add that the cab-o-sil should probably be mixed quite a bit thicker for the void-filling areas.

I have read that some people have used power planes successfully for making scarf joints. As with any power tool though, you can easily cut off (or sand off) too much material, and I have found that you can't put it back. If you do try the power plane or belt sander method, practice on scrap wood first. With the power plane, after you get it roughed out, turn down the amount it cuts with each pass. Mine's lowest setting is 1/128". That or 1/64" ought to be safe. Here's a site that sells scarf joint jigs for kayak building: http://www.oneoceankayaks.com/stitchglu ... rfjig2.htm . Don't know if they are any good.

A question to the previous poster: Wouldn't you do the equivalent with a belt sander, i.e., rough it down with 40 grit, then go to finer and finer grits as you get closer to the finished product?

One other point to keep in mind: I have never cut a scarf joint in my life, so why am I even writing this post? But since I have started I might as well forge ahead. Earlier I posted about a finger joint jig I saw advertised in Small Craft Advisor. However, I just checked the website (www.fishbonesupply.com) and am still getting a "site not available" message, so I guess that's out. But surely someone somewhere makes a finger or puzzle joint jig. It would be similar to a dovetail jig but much larger and would include the mirror image.

[chaertl]

Hi Dana,

You could go slightly finer, maybe 60 grit, but trying for a finish quality to the surface will actually close up the pores in the wood and can actually weaken the joint by preventing glue penetration. My schooling was in aviation mechanics and the in the FAA's acceptable practices they state all surfaces for scarf joints are to be cut and not sanded. Personally I can't plane a long plywood joint straight enough to match and the ill fitting joint would be far weaker then any sanding would be.

Chris

[DanaDCole]

Thanks, that's very interesting--and who knew they used scarf joints in airframes? I had suspected that rougher wood made for a stronger glue joint--now I know. My reasoning for going to finer and finer grits was to avoid cutting away too much wood, not an attempt to make it smoother. Anyway, thanks for straightening me out on it (no pun intended).

BTW, did you check that site that shows a scarfing jig? I'd like to get an opinion on whether it might work. Here's the URL again: http://www.oneoceankayaks.com/stitchglu ... rfjig2.htm

[Shudoman]

I purchased the PocketShip kit so I didn't do scarfs for my build. However, I've done them for one of the other boats I built. I also had problems doing them with a hand plane but when I switched to a hand held power planer it was MUCH easier. I've seen photos where people do several layers in a stack but for an amateur like me doing two sheets at a time did the trick.

Bill

[JonLee]

My experience was that cutting them with a hand plane worked really, really well. Just take the time to sharpen on your plane properly before you get started. A sharp plane will make all the difference.

I did finish things off with a belt sander, just to get the last smidge of smoothness.

[herbt]

I have tried a lot of different ways to make a scarf joint including a jig for a circular saw but have found that nothing works better than a sharp hand plane. RAZOR sharp and a little elbow grease. and sharpen the plane frequently, (only takes a couple of strokes on a wet stone) during the process. If you use the method described in the manual you can get a perfect scarf every time, just takes a little patience. Power planes can get away from you and butcher the joint in a hurry. Cabosil should be used as the thickener for scarfs. First coat both pieces with unthickened epoxy to ensure a wet joint and then brush on plenty of thickened epoxy.

Herb