Garry Posted January 24, 2004 Posted January 24, 2004 The first thing to do on my Spindrift project is to make 12' sheets of plywood out of 8' sheets. I wanted to do it using scarf joints but don't have a precise way to do it. Here is what I came up with. I stacked the four 1/4" sheets that needed beveling, stepping each one back 3". Then marked a line 3" back on the top sheet. I pinned them together to maintain alignment using straight 2x4s for backup. Then I took a belt sander with a coarse grit and started sanding using the stacked angle as a starting guide. The bed of the belt sander spanned two pieces so it started at the right angle. As I removed material, the glue line between each ply was revealed and then it advanced toward the top of the bevel. I paid attention to keeping the glue lines straight and parallel to give me a good approximation for an even cut. I had sanded far enough when the top suface of each piece was sanded back to the tip of the next piece (or to the line on the top piece). It was easy to even up the glue lines by sanding the areas where the glue line was not as far advanced as it should be. The rough surface will make an excellent bonding surface. A little variation in the bevel surface should be made up by the epoxy or a slight thickness of the finished joint. Quote
Tom Lathrop Posted January 24, 2004 Posted January 24, 2004 Gary, As you have discovered, it's no big thing to make scarf joints and your method is a completely acceptable one. I question the need for 12 to 1 bevels though since I have never had or seen a failure on 8 to 1 scarfs which are much easier to do. Some designers set the length of a boat to fit the max length that can be made using a minimum number of 8 to 1 scarfs, so longer scarfs might require an extra one. Quote
Garry Posted January 31, 2004 Author Posted January 31, 2004 Epoxied the scarf joints last night. This is my first bond on the boat and my first work with RAKA epoxies. I haven't taken the "clamps" off yet so I hope it turns out good. I coated each surface twice, then added a layer of epoxy thickened with silica. It was a little awkward handling such large sheets so I pinned the joints in place by driving a few small finish nails though them. Then, to get a light but even joint pressure, I covered the joint with stacks of books. Finally, a practical use for all those sailing books I have accumulated over the years. Garry Quote
Greg Luckett Posted January 31, 2004 Posted January 31, 2004 Hi Garry, I have been reading with interest your sojurn into scarfing. I have yet to walk the path but will when my long delayed Spindrift project gets rolling. When you remove the clamps, check the thickness of the scarfed area and see it it stayed the same as the panel is. I am worried that by scarfing with the belt sander, too much or too little material will be taken away. If this is not the case, I will try your method. It was my intent to getting a scarfing jig for a circ. saw and do it that way. Thanks, Greg. Quote
Tom Lathrop Posted January 31, 2004 Posted January 31, 2004 I hope that your panels came out all right but it is not easy to get much clamping pressure with weights. Figure out the PSI that you obtained and you will find that it is very low. Epoxy does not like a lot of pressure but you need to get the panels to conform to a proper glue line. Unless I am doing panels that are to be finished bright, I clamp the scarf joint with a board on each side screwed together with drywall screws. Drill holes in the top clamp board so that the screws draw the panel tight. The small holes left by the screws are easy to fill later. I also use the finish nail idea to keep the panels in alignment. Quote
Garry Posted January 31, 2004 Author Posted January 31, 2004 Greg, Thanks for your interest and comments. I was a little concerned about thickness variations also and I am curious how it will turn out. But after some consideration, I don't think it will be a problem. The alternative in the plans is for a butt joint with fiberglass patches similar to the seam taping. This would add to the thickness and would have to be faired out. So if the joint is significantly thicker or thinner, I can adapt by adding tape and/or sanding and fairing as needed. If I were trying for a clear finish, I would want to be more precise with the scarf joint for appearance sake. But I plan to paint and I think for structural concerns there will be NO problems. Quote
Garry Posted January 31, 2004 Author Posted January 31, 2004 Tom, Thanks for your comments also. I was writing a response to Greg's message when you posted yours. I thought about screwing through the boards to clamp them together but it seemed to take very little pressure to close up the gaps (using 1/4" okome plywood). So I hope I did get the gaps close enough. I'm at work half a day this morning so I'll see how it came out soon and let you know. I figure I have room to cut it out and try again if necessary. Quote
Designer Posted January 31, 2004 Posted January 31, 2004 When I need to scarf, I stack up my sheets and use an electric plane to remove the bulk of the wood and then fine tune it with a hand plane. In my boatbuilding class I encourage my students to hand plane the lot. The first lesson is sharpening and tuning the plane. By the time they have planed all their scarfs they have developed proficiency with the plane. If one is going to do much boatbuilding you better know how to use a plane. There is no tool that can handle all the bevels and adjustments and fitting of the various parts on a boat as accurately and quickly as a plane or spokeshave. Like Tom, I have sandwiched the scarfs between 1 x 6's screwed together with very good success. The jig in the picture is the one that we use in the class. It has clamped hundreds of scarfs by now. It consists of a 4 x 6 on the under side, a 2 x 6 on top of the ply, on top of that is a 4 x 6 sitting on 2 x 2 spacers at each end. The whole lot is clamped together with 4 pipe clamps and 3 pairs of wedges are driven in tight from opposite sides. There is construction grade plastic release used between and outside of each scarf. We always use a small brad at each end of each scarf to keep the alignment as the a glue joint becomes very slippery when lubricated with epoxy. All that pressure might seem excessive but you need to overcome resistance to force all of the pieces to be straight and true and get adequate pressure in the middle of the sheet. [attachment over 4 years old deleted by admin] Quote
Garry Posted January 31, 2004 Author Posted January 31, 2004 Well, my scarf joints came out fine.... except for one thing. Somehow, when I was stacking the second joint on top of the first, the plastic that I was using to separate them got "sucked" into part of the first joint. So that part didn't bond at all. This also let some of the epoxy run over the plastic and bond the two sheets together. When separated, the top skin was pulled off one sheet in a few small places. I can't explain how this happened since the first joint was tacked together with three finish nails before the plastic was laid in place. The nails were still in place and I was careful not to move the bottom sheets when stacking the top sheets in place. Fortunately, the worst of it is in the center portion of the sheet and only goes about 1/3 into the lap of the joint. I have thought about cutting the joint out and doing it again but I've decided to just patch it and run one piece of tape over it. I've removed the unbonded plywood. I'll fill with thickened epoxy and lay the tape over that. Most of the worst of it will be cut out and it will be in the low stress portion of the hull. The tape will probably make it stronger than before anyway. Not a great start but it will work out all right. Good thing I wasn't planning on finishing it clear. Quote
Charlie Jones Posted January 31, 2004 Posted January 31, 2004 I also do my scarfs with a hand power plane and finish with a smoothing plane and a block plane. Takes about 20 minutes start to finsih. I think I posted a series of pictures of doing just that sometime early last summer. Quote
Greg Luckett Posted January 31, 2004 Posted January 31, 2004 I also do my scarfs with a hand power plane and finish with a smoothing plane and a block plane. Takes about 20 minutes start to finsih. I think I posted a series of pictures of doing just that sometime early last summer. Is that full 4 foot wide panels? Quote
Greg Luckett Posted January 31, 2004 Posted January 31, 2004 Graham, Is that you in the first picture? Greg. Quote
Designer Posted February 1, 2004 Posted February 1, 2004 Greg, No it is not. Yes they are 4' wide scarfs. Gary, With the loose part of the scarf removed and filled and a layer of tape over the joint it will be just fine. You may have noted that I said to use construction grade plastic, thin plastics like Saran Wrap have an incredible ability to get sucked into the glue joints so should be avoided at all cost. Quote
Greg Luckett Posted February 1, 2004 Posted February 1, 2004 Wow, that is fast. Darn Charlie, another goal for me to attain along with those pretty fillets you do. I have managed to only need butt joints so far, being able to avoid any bending of the panels at that point and also could hide the stringer. Scarfing is definitely in my future. Wish I could visit somebody and watch the process being done. I don't think I have any films of it either. Know any films available? Quote
capt jake Posted February 1, 2004 Posted February 1, 2004 Anybody here tried the John Henry scarfing jig? It is attached to a Makita hand planer.?? It is on my list of tools to buy, I already have the 4" Maktita planer. Quote
Greg Luckett Posted February 1, 2004 Posted February 1, 2004 Anybody here tried the John Henry scarfing jig? It is attached to a Makita hand planer.??It is on my list of tools to buy' date=' I already have the 4" Maktita planer. [/quote'] I have a Makita Power Planer Model #N1900B. Tell me more about this scarfing jig please? Thanks, Greg. Quote
capt jake Posted February 1, 2004 Posted February 1, 2004 Jjohn Henry always has an ad in the back of Wooden Boat. He doesn't have a webpage, but he has e-mail. If I recall, they are about $140 or so. Contact informaiton is; John Henry Inc. PO BOx 7473-WB Spanish Fort AL 36577 251-626-2288 scarffer@bellsouth.net The small picture is on page 129 of #176 (jan/Feb) I think it looks like a slick way of doing this. I have heard positive comments on his jig. Quote
Greg Luckett Posted February 1, 2004 Posted February 1, 2004 I did a Google search and found a link with a small picture and the address. Is this tool worth the cost? Opinions, of course? Thanks, Greg. Quote
capt jake Posted February 1, 2004 Posted February 1, 2004 Greg, you are like me!!! I have been looking for opinions for a while. Seems a bit pricey, but if it works as claimed??? Quote
Greg Luckett Posted February 1, 2004 Posted February 1, 2004 I have a picture with text too, from a book of a scarfing jig that can be made to use with a router. Should I post it here? I do not like it much. I found another one which I like much better at http://www.seqair.com/skunkworks/WoodWkgMethods/GaugerScarfJig/Gauger.html West system for the circ. saw. I have been considering buying it. 875 Scarffer 1 ea. 3.0 $53.95 That John Henry one seems too high priced. I need more details before I drop the hammer on that tool. Quote
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