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#1
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Cutting scarfs
Started working on my Tolman Skiff. I began by cutting the bottom
pieces from 1/2 marine ply but these have to be scarfed together to make longer pieces. The specified angle is 8.1 degrees and the directions describe a scarfing jig to be made with a circular saw but they require a larger saw than mine. However, I did buy a "Sawzall" to deal with some rot on my house. I tried various ways to do this with little success. Finally, I simply cut inclined cuts about 2" apart all along the scarf area angled at the 8 degrees. Then I used the Sawzall to cut the scarf cutting each of these out. This gave a reasonable first and second attempt. Then, I used the sander to make it nicer and make sure the layers of ply formed parallel bands. I think my first two scarfs are ok. |
#2
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Cutting scarfs
Just a caution. Having made quite a few successful scarfs of 4' wide sheets
of plywood, I managed to screw up the last set badly. My sin was to mix too much wood flour in the epoxy. The result wasn't fluid enough and I ended up with voids at the edges of the scarf joint. For scarfing, the mix should be a fluid, not a paste since there is limited clamping force available, even with my scheme of driving drywall screws thru the joint into a backup 2x6. You do want lots of epoxy squeezing out all the edges (and a drop cloth to protect the stuff underneath your work area.) (I'm working with 3/8" marine ply sliced into strakes for a lapstrake hull so the voids can't hide easily.) I'm fixing the bad areas by playing dentist; cutting the voided area back to solid wood and epoxy with my 4" grinder and then filling the cavity with epoxy thickened with milled glass fibers. A layer of fiberglass on the outside finishes the job with what I think is "good enough." I can lift a 20' long strake at one end and wave it around without it breaking. When the strake bends, the curve is smooth and uniform thru the scarfed and unscarfed areas. 8.1 degrees is a 7:1 scarf, while 8:1 is the roughest I've seen recommended, 7.125 degrees. On the other hand, some people use butt joints with fiberglass on each side, so ???? Roger http://home.earthlink.net/~derbyrm wrote in message oups.com... Started working on my Tolman Skiff. I began by cutting the bottom pieces from 1/2 marine ply but these have to be scarfed together to make longer pieces. The specified angle is 8.1 degrees and the directions describe a scarfing jig to be made with a circular saw but they require a larger saw than mine. However, I did buy a "Sawzall" to deal with some rot on my house. I tried various ways to do this with little success. Finally, I simply cut inclined cuts about 2" apart all along the scarf area angled at the 8 degrees. Then I used the Sawzall to cut the scarf cutting each of these out. This gave a reasonable first and second attempt. Then, I used the sander to make it nicer and make sure the layers of ply formed parallel bands. I think my first two scarfs are ok. |
#3
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Cutting scarfs
Understand that a plywood scarf should be 12:1. |
#4
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Cutting scarfs
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#5
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Cutting scarfs
OK, I went out and bought a power plane. It is WAAAAAAAY easier with
it and it makes better scarfs. |
#6
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Cutting scarfs
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#7
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Cutting scarfs
Brian Whatcott wrote:
On 15 Oct 2005 16:00:36 -0700, wrote: OK, I went out and bought a power plane. It is WAAAAAAAY easier with it and it makes better scarfs. Now I am getting moody. I looked round town at the last mention of a power planer - and drew a blank (population 20,000) There is not meant to be any power tool that I don't own. That's what my wife says, at least Brian Whatcott Altus OK If you can't find one locally, how about: http://cgi.ebay.com/MAKITA-ELECTRIC-...54745518QQcate goryZ42283QQrdZ1QQcmdZViewItem might have to cut and past that url Jonathan -- I am building my daughter an Argie 10 sailing dinghy, check it out: http://home.comcast.net/~jonsailr |
#8
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Cutting scarfs
Says Who?
Plywood scarfs (9mm panels) on my boat are 8:1 and I have had no problem whatsoever with that. Every scarfed offcut I destruction tested broke elsewhere but the scarf joint. 12:1 scarf is for the strakes to make a hollow mast and other high load spars. Klaus |
#9
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Cutting scarfs
A belt sander will do this job just as well and is much more widely useful
than a power plane. In either case, finish the scarph surfaces with a sharp handplane. Check with a straightedge. "Jonathan W." wrote in message ... Brian Whatcott wrote: On 15 Oct 2005 16:00:36 -0700, wrote: OK, I went out and bought a power plane. It is WAAAAAAAY easier with it and it makes better scarfs. Now I am getting moody. I looked round town at the last mention of a power planer - and drew a blank (population 20,000) There is not meant to be any power tool that I don't own. That's what my wife says, at least Brian Whatcott Altus OK If you can't find one locally, how about: http://cgi.ebay.com/MAKITA-ELECTRIC-...54745518QQcate goryZ42283QQrdZ1QQcmdZViewItem might have to cut and past that url Jonathan -- I am building my daughter an Argie 10 sailing dinghy, check it out: http://home.comcast.net/~jonsailr |
#10
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Cutting scarfs
Jim Conlin wrote:
A belt sander will do this job just as well and is much more widely useful than a power plane. In either case, finish the scarph surfaces with a sharp handplane. Check with a straightedge. The problem with using an edged tool on any surface that's been sanded is that the inevitable grit that's left behind does a number on the cutting edge. That's one major advantage of using a power planer rather than a belt sander. The others are reduced sawdust and greater ease in maintaining a flat surface. Belt sanders are great for rounding things over. ;-) |
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