Saturday, February 6, 2010
Keep your head in the game
Planking continues. Broad strakes are hung. This posting will cover the scarphing process, as well as a couple of other items.
I am a firm believer in scarphing planking stock in place, particularly for lapstrake construction. Scarphing a large panel to length and cutting planks out of it results in much more waste than the method I am using. At $65 per 4x8 sheet, waste adds up. There is also the consideration of edge set. In carvel planking, you can edge set (bend a plank in place after it has been cut to shape) to your heart's content. The frames are generally in place before planking commences, so the fastenings take care of the resulting extra twist. In lapstrake planking one generally fits the frame after planking. This results in the laps getting tweaked out of shape by edge setting them.
Speaking of sheet goods, I have used 2 1/2 sheets of 4x8 to date. I have a sheet of 4x10 for the sheerstrakes. I REALLY hope I can get both sides out of the one sheet, but I anticipate having to buy a partial sheet to wrap it up. I have a significant pile of off-cut 8 foot lengths. There might be enough in the stack to plank the Nutshell Pram I want to build as a tender for Strider.
I talked in the first posting about the "meditative" nature of hand cutting the scarphs with a block plane. What a load of hooey. I confess openly and fully to cheating. I used my 4 1/2" angle grinder to cut the scarph joints. Because the veneers in the plywood serve as a visual guide, careful use of this tool (with an 80 grit disc) gives a perfectly cut 8:1 scarph in about 3 minutes. I do recommend that you cut at least one by hand so that you can appreciate the convenience of the grinder method. I also recommend that you cut a sample scarph with the grinder before diving in to the real deal. I do not, under any circumstance, recommend this method for scarphing solid stock, particularly cedar. Why would one waste the opportunity to make a nice pile of cedar shavings, anyway?
You can see the process in photos. Fit each half of the plank separately. I left a little bit of extra width on each plank section in the area of the scarph joint so that it can be faired through after the glue-up. Mark where the planks intersect. Here is where you need to start paying attention. It doesn't matter whether the scarphs face forward or aft, but do them all the same way so that you don't have to keep track during the process. I am facing all of the scarfs aft, so the end of the forward plank is marked on the aft plank. DO NOT CUT THE AFT PLANK ON THIS LINE!!! Add the length of the scarf (2") to the aft section of plank. Clearly mark which side of the plank is shaved for the scarph before removing them from the boat. This is the most common, and most frustrating, error that is made.
With the plank sections on the bench, stack them so that the scarph lines are butted tight to each other. clamp them firmly in place and make sure that the feather edge of the lower piece is supported. Double check that they are stacked so that the material is removed from the correct side. When you are happy, grind away. wear a respirator and take little bites.
Less than one pop song later (if you want to take it really slow, put on "High-Heeled Boys" just like the classic rock station DJs do when they want to take a lunch break) you will have a nicely cut joint. Use the veneer lines to guide you, and check with a straight edge when you think you are done. A couple of swipes with your block plane will true it up.
Take the sections back to the boat and re-hang them. You'll have to come up with some clamping blocks to put everything where you want it to go. Again, do a dry run to make sure, and don't forget to mask the area around the scarph and your clamping blocks. The final photo in the series shows the scarph joint after sanding the next day. Remove the bulk of the squeeze-out with a scraper and a heat gun. If you try to sand it all off you'll get a wave in the plank from sanding the differing densities of the materials.
The last photo shows the use of a jump stick to pick up the lower edge of the next plank. I used it to determine keel and stem bevels, too.
It appears that I am limited to five photos per post, so I'll end this one here. Next time we meet will be after the planking is complete. I apologize in advance for the delay. I'm sure I'll be nursing a bit of a hangover after the "whiskey plank."
Next post will cover all of the pain-in-the-butt things that have to get done before you can flip the boat and admire your work.