2014-02-28

Post IX - Bracing and Scarphing

This week I needed a bit of advice and so posted a thread at the woodenboat forum. I asked about the best way to brace and square the molds to the surface of the strongback. Is it better to add square braces to each mold, or can I rely on the inside keel strip and the well-braced stern and stem molds to keep the whole thing rigid. Bert Langley, a member there, indicated it would be best not to just rely on the inside keel, but to add square braces and perhaps temporary strips at the turn of the bilge to keep things rigid until I have my first few rows of hull strips in place. This advice was echoed in a few other members' answers, so that's what I plan to do. This week I just added the square bracing because I still need to scarph the inside keel piece. 

Figure 20: MDF square braces for each MDF mold not otherwise braced


Making and bracing all those molds took quite a bit of time, and I ended up splitting the MDF on a good number of them because I was screwing into the "end grain" of it. The stuff is kinda pressed in layers, so screwing into the thickness is impossible unless you pre-drill and pre-countersink. The splits were annoying, but I realize it at worst they will still serve to keep things square until I affix the inside keel and temporary bilge strips. At that point a few compromised braces won't matter. 

Next came the fun part - making shavings! I had some lessons on scarphing by hand at Harry Bryan's shop last fall:
http://www.harrybryan.com/

He taught the class techniques for getting decent scarph faces using either a framer's slick or jack plane, instead of a powersaw and jig. This appealed to me because all of my hand tools are of decent quality (antiques, largely) but my power tools are a bit shit. So I traced the requisite 12:1 lines on the ash keel sticks and set to work. You'd think it would be hard to do this with hand tools but it is surprisingly relaxing. Procedure:
  • line up the sticks so that the end of one is offset from the end of the other by the 12:1 ratio. In my case I have 5/8" thick stock, so I offset by 7.5". 
  • Clamp it so that the lower stick's end is at the edge of your workbench. 
  • Set the plane for a nice deep cut (No.4 stanley plane worked well for me). You have to cut on both sticks together - start the stroke on the top stick and follow through onto the lower one, keeping material removal as even as possible between the two sticks. 
  • Start on one corner and whack it down to within a couple millimetres of the line. Follow up on the opposite side, then do the centre, and you should have something approximating the 12:1 slope on both sticks, but offset from the final line by a millimetre or so. 
  • Set the plane blade for a nice thin cut - the thinnest you can manage while still taking a full-width shave of the stock
  • Checking the lines frequently, continue planing until you reach your line
  • Put a straight edge along the scarph surfaces at several points to check flatness, remove material from high spots with short strokes of the planer if necessary. 
And that's it. The whole procedure only took about 15 minutes. 


Figure 21:  Sorry no progress shots, but this is the end result


 Figure 22: Closeup of the "feather edge" that you're supposed to get if you did it right. 


Gotta love the big swirl chip that flies off at the end of each stroke and the nice shearing sound it makes when the blade is good and sharp. The plane has always been my favourite tool for that reason. 

Figure 23: Chips!


I ran out of time, but I'm going to glue this up over the weekend (WEST epoxy and adhesive fillers) so that it's ready to put on the mold for next week's shop night.

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