I just received approximately 1 cubic yard of 3/4x7"x8" finished balsa. I would like to incorporate these into a current project I am working on, a chambered balsa surfboard. I would like to join these blocks to create 3/4" x7"x 8’ planks. I am thinking of using my table saw and cutting tenons and mortises. The only problem I have with the that method is the open ends on the mortise will give a weaker joint. I am thinking quite possibly create the tenons on the table saw and then set up a jig with stops on the router table for a mortise to solve the open end issue. Any thoughts on a faster and or stronger method?
Several thoughts here. I’m assuming I understand you correctly that your boards are each 7" wide and 8" long x 3/4" thick, and that you plan on layering and edge gluing the whole batch into an 8’ long x apx. 23" wide x 5"+ thick (for rocker) blank? Based on that, I would not worry about the open ends of your mortise. Why?: Once you have glued up your 8’ x 7" x 3/4" planks you will joint one edge of the long 8’ side, then carefully rip to whatever max. rip width you can achieve (you’ll of course end up with a tad little less than the 7" width once glued up and milled). The reason your open end tenons are ok is because you will want to stager these joints as you edge glue one plank to the other so that you’ll end up having a blank that looks like a brick wall. Each mortise and tenon joint will glue up laying next to the center of the board you glue its edge to (clean facing edge of adjoining board next to the joint). Use gorilla glue or “Titebond II” (though it leaves a slight yellowish line) and your joint will actually be far stronger than the wood itself. Since balsa is soft the walls of your mortise will over flex if your tenons are too tight, so don’t try to get as snug a fit as you would with hardwoods. If they are too tight and flex, you’ll get a bump at each joint. Best to lightly clamp small plywood scraps over and under the the joint to keep it flat with the boards you are end gluing (put waxpaper over the glue line). Be careful pulling the two boards together end to end cuz it’s easy to over tighten and cause the two boards to cock or pivot a bit. Consider a glue jig. Just a flat piece of ply a 30" long x 10" wide or so with a 3"w x 3/4" ply strip glued/screwed along the edge of the length. Line 2 or maybe 3 (no more) boards on the ply jig end to end and lined up along the edge piece. Pull up the length of the 3 boards (24"?) with a clamp at the same time you also lightly clamp the sides into the edge strip (keeps it all straight and in line). I assume you have a experience / knowledge of woodworking since you are attempting this, so you know the drill. I would glue up each plank into 8’ x 7" wide x 5"+ thick “beams”. That will require stacking your 3/4" pieces, staggering the joints as you stack glue (7 or so layers x 3/4" thick each). Make four such beams then edge joint and carefully rip to exact width on the band saw. Cut your rocker profile the length of each beam with band saw, then chamber out the boards carefully. Now joint the sidess of the hollowed beams, then edge glue all four beams together in staggered fashion again. True up the deck and bottom of your new blank, and presto … it’s done (presto is a very relative term eh?). We both know that to get it dead right, you’re talking many hours here! Some like to just barely spot glue up the blank, rough shape the board, then split the boards apart, hollow/chamber, re-glue, final shape. You can get closer safer tollerances and result in a little less overall weight this way, but you will likely have gallons of glue in this blank due to all the joints, this way, so a few more ounces won’t hurt in my opinion. A few of the pros might give their wisdom here, especially Jim Phillips, the master balsa shaper. But as a furniture maker, I know the above method would be sound from the tech aspect. This is probably a lot more info than you need or asked for (got carried away), but I always get frustrated when I get a quick assumptive answer to a question and end up not quite understanding it all. Of course everyone else is no doubt smarter than I. Anyway, I hope this offers a tad help. Enjoy the ride, Richard Mc
I appreciate your input Rich. That’s exactly what I intended on doing, but I thought id throw it out here with the hopes of getting an aha, like I usually get from reading here. I tell you what i did “learn” here(thanks P.Jensen) that will lessen the work and time,laminate the planks using contact cement in lieu of glue and clamps since the strength is in the glass.
uhm… seems kinda complicated and I dunno what kinda strength you’d wind up with . I’ve never been that crazy about end-grain to end-grain glue joints, y’know? Especially with something as absorbent as balsa, it’s likely to starve the glue joint or suck up a lot of glue and go overweight in a hurry. If it sucked up enough glue, you might have some hard sections that’d make for unpleasantness when you were working it too, going from real soft balsa wood to glue-impregnated hard balsa. What I might do is this - make one helluva big chunk of balsa ‘butcher block’ gluing four sides and not the ends with any decent woodworking glue. This’ll give you an end-grain balsa billet of 8" thickness. Make them of a width you can resaw on a bandsaw for the appropriate thickness for bendable, formable panels ( glue them up to make sheets) , then use them for the skins of the board, form ( they’ll squish some to make that easier) , glass one side, flip and glass the underside - see Paul Jensen’s boards for a similar method.Then, if you want the balsa 7"x8" sections for appearance value, resaw 'em thin and glue them on . As an alternative. cut your blocks to 4" long ( less if you want to get cute with a form for gluing the bottom contour) , make an end-grain ‘butcher block’ of approximately the outline shape you want and glue it up in three ( left, right, center) full-length pieces, separated by wax paper so you can clamp it all at once or in individual sections against something like the back of your workbench. Chamber them as desired, glue up the whole thing and shape it and glass it. Again, something like this would be something you could bandsaw to your rocker and outline shape, before chambering, in fact that’d probably be a Real Good Idea. Your offcuts - well, there’s end-grain balsa sheets again for other projects. From the sounds of it, you have enough balsa there to be damn near a lifetime supply. hope that’s of use doc…
don’t the pine window an door guy’s use a finger joint bit?..ambrose…
That they do, though I don’t know if Herb has a wood shaper or router table that those finger joint cutters run on/require. Though they can look kinda cobby when you work the wood some, not nice, crisp lines in the glue-up lamination. Another alternative is what’s called a glue joint, which you can do with a moulding head for a tablesaw. For cutting end-grain blocks, probably best to do that with a tenoning jig, just so it doesn’t get away from ya while cutting. Delta’s moulding heads and tenoning jig( I can reccommend the Model 34-183 from my own experience ) shown at the link below, a better priced moulding head at http://www.sussexsawandtool.com/specialty/molderheadcutters.html - the cutters may fit the old Craftsman moulding heads which can be picked up cheap at yard sales, etc. hope that’s of use doc… http://www.deltawoodworking.com/index.asp?e=139&p=2397
would a door shop that has a shaper set up be too pricy to farm the job out?.. ambrose…?
You know Doc, this is why I come here, you guys are like one big think tank over here. Let me tell you what Im up to. I had enough Balsa for a 100"x15"x2&5/8" board(15pieces of 1"x4"x100" balsa) with a finger jointed 1/2" eastern cedar stringer. I wanted a 22"-23" deck so I need to come up with filler material. I looked at some balsa a local shaper was selling, but the balsa he had was kept on the ground in a leaky tin shed and showed water damage. I mulled and mulled over laminating eps foam to come up with the shortage, but I wanted an all wood chambered board. I though about using western red cedar, but the weight was a concern, eastern cedar was nice and the weight wasn’t bad either so I was leaning towards that route. Then I remembered I had a 3’x3’ box filled with 8"x7" scraps of balsa. I looked at it and cringed at the thought of tenoning it all, and not to mention the frankenstein look the board would have. But now you gave me a solution. After reading your response I immediately went and layed the pieces flat and staked them up. I saw that not only am I glueing the face(as you know it will have less absorbtion and a stronger joint)but will create an offset grain when I laminate it to the rest of the structure. I did do a profile of the rocker template and will be cutting the rocker on my band saw and chambering using the hole saw method before laminating it together. I will be adding two more stringers for a total of three. Thanks again Doc, and while Im at it, thanks for the tip for reparing my G&S a few weeks ago( network error killed the response)
Good question - the guy I send stuff to gets $50 an hour for shop time, but it’s good value for money for the stuff I don’t want to tool up to do. Which, I’ll admit, is rare, I’m a tool junkie. You can’t touch a shaper setup …well, a decent one that’s not a router with delusions of grandeur…for under $500 or so, new. I’d say it might be worth doing. http://www.deltawoodworking.com/index.asp?e=139&p=2397
De nada, Herb…had a couple thoughts after I wrote that… they may be of use. Make it up in 4 lengthwise sections rather than 3, which’d give you at least one full-length flat side to clamp to/against on each piece. Clamping the curved sides, mebbe several strips of lauan ply, hot glue or brad gun some blocks to 'em to keep the clamps from slipping. Kinda laid up in several layers, like how you’d laminate a curved wooden piece up, but no glue in between these, just temporary. If you have a sizable band clamp, you’re laughing already. If you have a dowelling jig, that’d be real nice, as then you can make some locating pin holes and thus trace your rocker template to make a close rocker cut on the bandsaw for all sections, minimal evening out needed when you assemble the pieces. You could have one set of holes in your rocker/profile template that you make dowel holes from and just use those for laying out the cuts on all the pieces, if I’m explaining that well. Rather than a hole saw ( assuming you’ve got or have access to a drill press ) you might want to use a Forstner bit or bits. Mebbe lay out your chambers on that profile template as well, so you can trace 'em ( again, locating pins would be a beautiful thing) , 'cos with the forstner bits the drawback is they don’t tend to be much more than 3" long, so you’d prolly have to drill from both sides of each piece. You can get import steel Forstner sets pretty cheap at most of the woodworking outlets, they do a very nice, clean, nearly flat-bottomed hole and once started they don’t tend to wander much the way a hole saw can in soft materials. Hope that’s of some use doc…
I would NEVER use endgrain glue ups for general woodworking and furniture aps, but as Paul Jensen mentioned, and I agree, the structure comes from the glass job and since all planks are staggered and glued, the end grain glueup is no issue here. Hope it all works out for you. Richard Mc
what a great sandwich,those 100’’ pieces of bread make those shorties smell like cold cuts…MMMMMMMMMMMMMMMMMMMMMMI just got an order of zap a gap gluethat stuff sets in 20 seconds if you wanted to make em open face sandwiches an then true up the whole lengths… My termites dream of the balsa in my shed but they just dont have the condiments…ambrose… adventures in the shop wheeeee …21 century
Maybe try to stagger the joints as to entrap the end to end connection.