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Thread: Need Some Help With a Scarf Jig

  1. #1
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    Default Need Some Help With a Scarf Jig

    Hello everyone,

    I'm in the process of building a Penobscot 14 and have reached the stage in the build where I have to scarf together two 3/4" planks (1" nominal) to get a length that is 16' long. I tried to get the job done with a plane and found I wasn't exactly skilled enough for them to match up perfectly; after doing some searching on the internet (and here) I found that it's possible to do the job with a router in a jig. Searching around I've turned up two questions that I can't find an answer to and was hoping someone here might be able to explain them to me. The first question relates to getting the angle cut for the jig; I've seen most people saying they made their jigs to fit a 12:1 or a 8:1 scarf and it's been peachy. For mine I know I need a 8:1 scarf (6" for 3/4" planks) but I don't know/understand how to cut an angle for my jig that reflects that; would someone be able to tell me how to figure out the angle that corresponds? My second question deals with determining how high to make the angle cut in the jig; how do you guys figure out how high above the wood the router should be when making the cuts? I've attached a pictuer below to illustrate the type of jig I'm looking to build. Thank you for your help!


    router_2D00_scarfing_2D00_jig1.jpg

  2. #2
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    Default Re: Need Some Help With a Scarf Jig

    I've not actually done it so I could be wrong but logic and reason tells me that:

    If you draw out the 8:1 scarf in profile on a piece of paper - an "L" shape with the long line 6" long and the short line " - that will give you the angle of the slope of the sides by connecting the ends of both line (the hypotenuse of the resulting right triangle)

    Another way to figure it is to understand what 8:1 means - 8 units of length ("run") for every 1 unit of rise. So if you make the rails 24" long, they will be 3" taller at one end than the other
    Last edited by BrianY; 01-06-2019 at 10:58 AM.
    I rather be an American than a Republican.

  3. #3
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by BrianY View Post
    I've not actually done it so I could be wrong but logic and reason tells me that:

    If you draw out the 8:1 scarf in profile on a piece of paper - an "L" shape with the long line 6" long and the short line " - that will give you the angle of the slope of the sides by connecting the ends of both line (the hypotenuse of the resulting right triangle)

    Another way to figure it is to understand what 8:1 means - 8 units of length ("run") for every 1 unit of rise. So if you make the rails 24" long, they will be 3" taller at one end than the other
    http://www.jimsboats.com/webarchives/2001/1oct01.htm

    The correct way is to recess the ends in and hollow the centres slightly to ensure a water tight fit especially shell planking.
    Last edited by Chippie; 01-06-2019 at 11:37 AM.

  4. #4
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    Default Re: Need Some Help With a Scarf Jig

    I ve made possibly thousands of scarphs in wood... never used a jig or a router.
    The key of course is epoxy. If you are using epoxy, a junky fit is crucial... a good fit is a recipe for failure.
    This is a difficult thing for actual woodworkers to get their head around ..
    Side note... it is no more work to make a looooong scarph than a short one .
    Mic you need it to look nice, hollow out the insides, let the edges look cute , but have the epoxy in the center gap.
    If yer not using epoxy... well then you are beyond (my) help.
    bruce

  5. #5
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    Default Re: Need Some Help With a Scarf Jig

    In the last three plus decades dealing with elderly boat, I've done plenty of scarfs putting in dutchmen, planks, replacement frames, cabin sides . . . I always went for best fit I could do. I know many who believe in slightly hollow or rough surfaces for scarfing but I disagree. The thinner the glue line, the stronger the joint and with all that exposed end grain there's no possible need to roughen.

    Epoxy is so forgiving that where the piece does not flex both ways work just fine in many instances. But where an even bend is necessary, a spar or for light dimensional or plywood planks, a clunk of epoxy will make a hard spot. If there is to be failure when the piece is bent into place or in use, it will not be the joint. The failure will be just a little away from the joint do the the translation of the stresses, just as a knotted rope won't fail at the knot but breaks just a bit away.

    Since I only know hand tools, I'd mark a line where the scarf was to end and then I'd saw a bunch of kerfs maybe 1/2" apart full depth at the end of the plank or whatever and just scratching the surface at my end line. Then I'd use a nice big and sharp slick to rough it down. Finish with a long-bed low angle plane.

    I almost always had to make bevels on good wood ends on the hull after removing bad wood. Once I had the bad out, I'd regularize the hole with perpendicular sides and roughed out scarf bevels at each end. Then I'd make the replacement piece on a bench but same basic method of kerf, slick, and plane. With that long bed plane, getting the slope dead flat was easy. Once the replacement part was in, I'd tap it in place with something to leave a mark - chalk line chalk was best - on any high spots on the roughed bevels on the hull. That made it easy to slick my way into having those bevels fit perfectly.

    Really soaking the end grain with unthickened epoxy and then using lightly thickened epoxy for the real gluing made for a perfect, tight, and trouble free scarf. And a clean joint is not much more work than a clunky joint.

    Professionals who do the same job over and over really benefit from a good router and jig. I remember Brad Pease making a jig that he could use in place on the hull and on the bench. Perfecting it took about as long as making four bevels (fitting in one replacement length of planking) took me. But then he had something that ripped through every similar job light lightening. For him, it was well worth it. For me, distinctly recreational, the perhaps a thousand scarfs I've made over the years was not time that cost me anything. Also, I don't own a router and often work off the grid anyway.

    G'luck

  6. #6
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    Default Re: Need Some Help With a Scarf Jig

    Just finished making a couple of scarf joints in the toenail. I set up a similar jig, albeit much narrower. Might note that I used a planer bit in the router--something I hadn't seen before. It make a very fine, finished joint surface.

  7. #7
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    Default Re: Need Some Help With a Scarf Jig

    Draw the taper out on the 2 rails.

    Lower the router a bit at a time until it cuts a feather edge at the end of the plank.

  8. #8
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    Default Re: Need Some Help With a Scarf Jig

    why not make a sled or jig for your table saw ?

    one w/ a fence that you can clamp the work piece to, on edge

    and simply saw them

    th.jpeg

    th-1.jpeg

    or you might get some ideas here

    taper jig for table saw

    as mentioned above i think epoxy would be happier w/ a saw cut edge to glue to instead of a router cut edge

    sw
    "we are the people, our parents warned us about" (jb)

    steve

  9. #9
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    Default Re: Need Some Help With a Scarf Jig

    My jig is for ply, so due to the width, I made it in steel tube, with a ply sledge. I just set the frame with wedges to get the 8:1 then welded the verticals that fit it to the table.
    As for the depth of the router, I set it to the height of the base, which has a bit of sacrificial ply, then put the ply stock in and set to. Jig is 3ft wide.

  10. #10
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    Default Re: Need Some Help With a Scarf Jig

    We used a sled with a hand planer.


  11. #11
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by Chippie View Post
    http://www.jimsboats.com/webarchives/2001/1oct01.htm

    The correct way is to recess the ends in and hollow the centres slightly to ensure a water tight fit especially shell planking.
    In the case of solid timber planking and the absence of good glue,maybe.For ply you risk snapping the plank at the lip as you have created a stress raiser.

  12. #12
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by swoody126 View Post
    why not make a sled or jig for your table saw ?

    one w/ a fence that you can clamp the work piece to, on edge

    and simply saw them

    th.jpeg

    th-1.jpeg

    sw
    Well, basically, because that approach using a plank-length workpiece would be extremely dangerous on a table saw, even if you had a blade large enough to cut through the width of a plank.

  13. #13
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by Saagr View Post
    Hello everyone,

    I'm in the process of building a Penobscot 14 and have reached the stage in the build where I have to scarf together two 3/4" planks (1" nominal) to get a length that is 16' long. I tried to get the job done with a plane and found I wasn't exactly skilled enough for them to match up perfectly; after doing some searching on the internet (and here) I found that it's possible to do the job with a router in a jig. Searching around I've turned up two questions that I can't find an answer to and was hoping someone here might be able to explain them to me. The first question relates to getting the angle cut for the jig; I've seen most people saying they made their jigs to fit a 12:1 or a 8:1 scarf and it's been peachy. For mine I know I need a 8:1 scarf (6" for 3/4" planks) but I don't know/understand how to cut an angle for my jig that reflects that; would someone be able to tell me how to figure out the angle that corresponds? My second question deals with determining how high to make the angle cut in the jig; how do you guys figure out how high above the wood the router should be when making the cuts? I've attached a pictuer below to illustrate the type of jig I'm looking to build. Thank you for your help!


    router_2D00_scarfing_2D00_jig1.jpg
    I ran into the same issue. However, I found it more challenging to make two side pieces for the jig than to make the scarf by hand so I marked the line on both sides of the stock, took off the bulk of it with a hand-held power plane then finished with a hand plane. I think I finished with a block plane set to a thin cut. The first one was the only hard one - don't rush, sneak up on the finished article.

    If you're looking at a number of scarfs, consider the Gougeon Bros. "Scarffer" which attaches to your Skilsaw or similar. The cut is on the end of the stock so it won't go all the way but you can finish with a hand saw. Warning - I haven't done this myself, I'm relying on a friend's experience on his boat.

    As already mentioned, a slight convexity and epoxy will ensure a good joint.

    Jamie

  14. #14
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    Default Re: Need Some Help With a Scarf Jig

    Lay out the distance for the 8:1 inch scarf by drawing a line square to the center line on the planking stock prior to spiling the pattern. Stack both halves of the plank on top of each other so that the scarf half lengths match their lengths equally with the bottom plank on a backing board that will support the shim end of the lower plank. Using a jack or power plane start roughing the scrarf taking care to keep the surface flat from side to side as the wood is hogged out. When close to the finish switch to a fine cutting jack Japanese finishing pull plank and complete the finished taper. Using a chalked straight edge will alow you to see the high spots that can be shaved off with a block plane or finely tuned pull plane. The result should be two matching ramps of plank stock that can be glued up with g/flex epoxy. When dry, lay the spiling pattern on the stock and transfer the plank shape. It may be necessary to give a slight angle to the scarf during glue up to allow for the curve of the plank thereby not using too much stock for the width.
    Jay

  15. #15
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    Default Re: Need Some Help With a Scarf Jig

    What Jay says. You'd have your planks scarfed by the time you build that jig and it's a lot quieter and more enjoyable to use hand planes vs a router. Stack each plank 6" behind the other and go after it. Power plane to start if you wish then hand plane down to close to a feather edge. Finish with a light sanding, glue and clamp.
    This was plywood, but you get the idea:

    Here's one of scarfing a plank in place:
    Steve B
    Sjogin IIIa
    PAYTON 13' Pea Pod

    RIVUS 16' Melonseed


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  16. #16
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by Bob Cleek View Post
    Well, basically, because that approach using a plank-length workpiece would be extremely dangerous on a table saw, even if you had a blade large enough to cut through the width of a plank.
    This would be a method to cut the tapered rails to make the jig only.

  17. #17
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by John Meachen View Post
    In the case of solid timber planking and the absence of good glue,maybe.For ply you risk snapping the plank at the lip as you have created a stress raiser.
    The OP was working with solid timber John.
    Ply is another issue where I would avoid using it in a curved situation.
    In a flat situation I always used the method I described and avoided feathered edges like the plague.

  18. #18
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    Default Re: Need Some Help With a Scarf Jig

    Edit not working

    ^^
    I have reservations on using a router on ply anyway

  19. #19
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    Default Re: Need Some Help With a Scarf Jig

    My scarf jig approach is here...

    http://forum.woodenboat.com/showthre...fing-Jig-Ideas





    For a one off plank, with epoxy, I wouldn't both with a jig, unless you just like making stuff. Just pre coat the ends with neat epoxy, let it soak in then put epoxy with micro fibres added smeared on each end and 'clamp' it together only semi firmly, wipe off excess and leave it to cure with a bit of heat in the room so its comfortable if its winter. Leave it a couple of days then scrape it clean with a scraper and heat gun.
    Last edited by Edward Pearson; 01-07-2019 at 06:50 AM.

  20. #20
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    Default Re: Need Some Help With a Scarf Jig

    Quote Originally Posted by Saagr View Post
    Hello everyone,

    Q: The first question relates to getting the angle cut for the jig; I've seen most people saying they made their jigs to fit a 12:1 or a 8:1 scarf and it's been peachy. For mine I know I need a 8:1 scarf (6" for 3/4" planks) but I don't know/understand how to cut an angle for my jig that reflects that; would someone be able to tell me how to figure out the angle that corresponds?

    A: Draw the 8:1 slope on the side of one rail. If the rail is 1 inch high, put one mark on the top of the rail, move left or right 8 inches and mark the bottom of the rail. Draw a sloping line between the two marks. Cut along the sloped line to get the first rail, check it for fairness. Then use it as a guide to cut the other rail. Put them together and make sure they are the same slope. If you need to figure out the actual angle, draw it out on a piece of paper and measure it with a protractor.

    Q: My second question deals with determining how high to make the angle cut in the jig; how do you guys figure out how high above the wood the router should be when making the cuts? I've attached a pictuer below to illustrate the type of jig I'm looking to build. Thank you for your help!

    A: You can make it as high as you want but all that matters is the business end of the jig. We only made ours a few inches high, sloped down to the thickness of the jig base. Then you can adjust your router depth so you start the cut at the measured 6 inch lines on your board(s) and finish up at the feather edge. You can do 2 boards at once if you want, make your sloped jig rails twice as high in that case. You might consider leaving the cut a bit proud and finish it up with a belt sander or hand plane or unicorn gronicle. I'll see if a can find a picture of our sled but here is one I had in the files, not sure who the image credit goes to...

    scarf jig.jpg

    We used 1/4 inch okume ply on our Penobscot 14, tried several methods. Found that the feather edge could tear out and asked Nat B. for a tip, he replied to "clamp the edge of the plywood to a stiff board so the feather edge is backed up by solid wood." Probably not an issue with your 3/4 inch plank but that might help someone else out there in the metaverse. Speaking of 3/4, what type of wood are you using that is going to let you make that twist and turn up by the stem? Steaming something?

    belt sander scarf.jpg
    Our Penobscot 14 build can be found on our Small Boat Restoration blog.

    Tip1: Not sure how you are lining off your planks but remember to make sure the scarf/overlap is accounted for in the total length of each half plank. On one of the first planks I forgot so the aft plank I cut was short at the end, the length of our 12:1 scarf i.e. 3 inches.
    Tip 2: If you plan to finish you boat bright, try to keep the plank material matched up so there is not a big difference in grain/color mid plank or side to side. We got quite a variation from the 4 sheets of ply that we used, so we painted.

  21. #21
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    Default Re: Need Some Help With a Scarf Jig

    Found pictures of my scarf sled. I was not building fine furniture, I was building a boat that I planned to go gunkholing with, run her on and off the beach. The scarfs came out good enough to epoxy them together, sand, fair, prime and paint.

    IMG_8388.jpg

    IMG_8389.jpg

    For those using plywood, you can see where the different sheets of plywood took on different finish lives of their own as the first barrier coat of epoxy was applied. Had I wanted to finish the boat bright, I should have kept better track of which sheet went where, and then try to stain them to a more uniform color before the epoxy. The scarfs did not have perfect feather edges, but very little fairing was required.



    And speaking of feather edges, the planks get handled a lot, be careful to not take a chunk out of the edge. Luckily the chunked portion of this scarf was going to be trimmed off.


  22. #22
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    Default Re: Need Some Help With a Scarf Jig

    Ok - so I have some minor progress, scarfed the keelson and glued it together. Scarf is 12:1 and will be backed up by the centerboard case logs.
    [IMG]33-ScarfingKeelson-1_zpsbfe7e6ea by Tom Fulton, on Flickr[/IMG]
    [IMG]34-ScarfingKeelson-2_zps5b1fa814 by Tom Fulton, on Flickr[/IMG]

    Simple manual scarfing guide. In this case was 12:1 I attached two side rails to the side of a plank used as a base. At the end the rails are flush to the base of the jig and raised the rails to 1" high at 12" from the end. you would do this at 8' from the end. Clamp your stock to be scarfed on the jig and cut witness cuts to near the depth using the rails as a rough guide, rough out with a chisel and use the guide to support your plane to finish. This works for me and I do not have a good eye or steady hand.

    If you want the angle this is the math: The tangent of the angle is 1/8 = 0.125. The arctangent of 0.125 is 7.13 degrees.
    Look up SOHCAHTOA on the web for the trigonometry. It will be harder to measure the angle than to take the simple approach.
    Steamboat

    I get by with the judicious use of serendipity.

  23. #23
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    Default Re: Need Some Help With a Scarf Jig

    Wow! Thank you guys for all the input! I'm simply amazed. I finished making the jig last night so today I'm going to try my luck with cutting the planks. I'll be sure to post here how it goes. Thanks again!

  24. #24
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    Default Re: Need Some Help With a Scarf Jig

    once you get your planks fitting to suit you remember...

    secure(nails screws big clamps...) the opposite ends of both planks to a common work surface and put plenty waxed paper under the scarf for glueing

    once glue is applied to both surfaces the sickery planks will try to escape your intended positioning and get wonky on you

    sw
    "we are the people, our parents warned us about" (jb)

    steve

  25. #25
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    Default Re: Need Some Help With a Scarf Jig

    When I scarfed my keel, once I had the ends lined up with my straight edge or string, I put a couple of dowels in the scarf to keep things lined up. Worked well and no holes to fill.

    DSCN0744.jpg
    Last edited by Mike Seibert; 01-10-2019 at 01:22 PM.

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