Hi new to forum and new to woodworking so go easy on me. I come to woodworking as an art teacher who, along with my students, has created a bunch of functional cardboard chairs. I’d like to try to make a few out of actual wood. The designs have acute angles involved in them. I’d like to use some type of joinery and glue to build them entirely. My thought is to run a tenon all the way across the 18” boards at an angle and then slip those right into a mortise that also runs across the board at an angle. I have a table saw and tenoning jig to work with but I don’t think it’s possible without some other type of jig. To be clear I’ll just use a part. Picture the top of an acute triangle that has 18” depth looking from the side of the chair. I want the back angled board to butt up flush to what will be the back rest angled board connected with a mortise and tenon that runs all the way across. Any ideas on how to cut it?
edit I attached a picture. I want it like that but longer and at an acute angle. It’s under 45 that’s an issue.
Replies
A picture of the chair design might be helpful. I'm having a difficult time visualizing the joint you need.
In Woodworking there are usually multiple ways of tackling problems based on tools available, skills, personal preferences etc.. Sometimes you need to cut your joinery while your stock is square before cutting the final profile.
Thanks for your reply. Here’s a ideation profile sketch of the top part of the chair. I want the tenons to run all the way through the 18” board. Easy to do on the table saw until angles become less than 45 degrees.
Wow! You picked a tough one to start out with. I still have questions about your vision for the joint. Do you envision the joint being visible? How thick is the material? What is the material? Solid wood or plywood?
Regardless I think barring access to an 18"+ bandsaw and some meticulous chisel work to clean up the joint(assuming you intend the joint to be visible), I don't think the joint as you envision it can be cut in wood.
When faced with an impossible situation we as woodworkers can either throw in the towel or figure out what is possible. Given your drawing I would focus on dowels, or some type of loose tenon. These would be easy enough to cut into leg piece before cutting the final angle on the end. That leaves cutting the mortise into the back as the challenge. Since there is no tool(I know of) that can cut an angled slot with the bottom parallel to the face, I am concerned that a stopped mortise in ¾" stock simply won't have enough depth to make a strong enough joint to deal with the stress of a usable chair. This leaves me thinking a through mortise might be the best choice. It can even become a design element of the chair by using a contrasting wood. You would need to drill out the bulk of the waste with a forstner or good Brad point bit then clean it up with a sharp chisel but it should be doable with the help of a jig or 2. If you want any more help along these lines let me know.
You have definitely skipped wood working 101(most of us start off making square boxes) and went straight to a post graduate course in wood working, but it should be doable.
A Festool Domino could cut the angled slots for its loose tenon dominos, to that basic design. The catch then would be the OP's requirement that, "I want the back angled board to butt up flush to what will be the back rest angled board connected with a mortise and tenon that runs all the way across".
With dominoes, the backboard would still be flush to the backrest all the way across but connected only via intermittent (invisible) dominoes rather than a continuous tongue & groove joint. But, as both types of joint would be invisible, does that matter as long as the joint mechanism employed is strong enough?
Of course, Festool Domino machines are not inexpensive. No. But they make stuff like this so much easier to achieve without the extensive skill to free-cut with a less sophisticated tool set.
Lataxe
That drawing was done by M.C. Escher! Re-do your sketch with the parts all drawn in 3D so we can understand it please.
I see a 18´´ long tongue and grove more than a mortise and tenon here. To accomplish this on the tablesaw one would need to tilt the blade 50 degrees so you would need a 5 degree platform or a elevated rest along your guide that elevates the part at 5 degrees and the blade at max angle of 45 to make a 50 degrees groove. there would be no way to make the bottom of the groove as designed so I would modify the shape as shown below to have a square tongue profile and a square groove bottom. If you elect to raise the plank along the guide, assuming the plank is 30 inches long and the groove is 10 inches from the end, you will need A 2,6 inch block along the guide to lay the plank on, if the groove is at 10 inches from the other end, the blade will need to rise 7/8’’ before starting to cut wood.
Okey, what I have envisioned, based on several readings of the description of the challenge is that you have occasion for a long joint between 2 surfaces and the angle is less than 90 deg's. Stepping through several solutions that came into mind was, 1.) a long joint e.g.( sliding dovetail, mortise and tenon, splined(fixed or floating tenon)) and etc... 2.) A joint less than 90 deg. Requires methods to hold materials at complimentary angles for layout, cutting, and for actual joining (glue-up). So, there are several requirements for each phase of development, and they must compliment one another to adequately work to deliver the desirable results ( a viable joint in a chair).
I would begin with a reasonable angled tenon and mortise. Think of a coopered bucket-barrel; maybe add a stop to the joint. Good luck, good fun!
Look at the video series by Christopher Gochnour for the Enfield Shaker Cabinet. https://www.finewoodworking.com/videoworkshop/2018/10/enfield-cupboard-hand-tools-featuring-chris-gochnour. He puts a shelf into place using a tapered, sliding, half-dovetail. It can be done using a hand plane or by just using a ramp cut at the right angle and a chisel. For joints that are shorter the chisel and ramp would be best. There are also full sliding dovetails for a more decorative effect. These are cut on square stock and the further acute angle would have to be cut later.
Hmmm. I made a reply but I don’t see it. Again new to forum. When I try to post it again it says I already posted the same thing. What am I missing? I can’t even figure out this forum let alone how to make this cut!
It got gobbled up by a touchy spam filter. Sorry about that.
esch5995, Haha yes it's a tough one I guess. It just dawned on me after making cardboard chairs for so long how few of the types of designs we were coming up with in my classes you actually see out there. So once I finalized a few of the designs it's just a matter of making them work and be well crafted. I think Lataxe might be on to something that would work.
Lataxe, I did some google research on the Festool Domino and I thought it might work perfectly, though way out of my price range, but then I think I found a problem. In my drawing above that is zoomed in, the piece on the left is the support board for the backrest on the right. The horizontal line is the seat. I could put the dominoes on the end of the support board but how would I put them on an angle into the backrest? Seems the Festool needs to lay flat against the surface it is cutting into.
MJ, Haha I was just trying to illustrate my problem. I don't want anyone stealing my genius designs!
Gulfstar, My concern is that I have to do a variety of angles when all is said and done and I'm trying to find a process to streamline that. I appreciate your detailed description and drawing but I'm not sure I completely understand. Would the edge of the tongue match up flush with the other board?
Gulfstar, I tried what I think you’ve outlined. I just threw a wedge on my mitre gauge under the board. The problem is like you mentioned the groove is at that different angle. While it may function well I’m not sure I like the look.
A spline ?
AnklePicker
You have two potential stumbling blocks to your joint that must be accounted for: the obvious one how do I cut it and the less obvious will it be strong enough to do the job. Some of the suggestions have left me concerned about the latter. If as you drawing implies, you are working with ¾" stock I have serious doubts that any groove you can cut with a tablesaw or router will leave enough material to provide a strong enough joint to withstand the stress that I see being put on a joint that I believe forms the back leg of your chair.
Hence my suggestion to use a loose through tenon which will maximize the strength available, I'm thinking 4 3" tendons across 18" should do the trick. The domino is simply a loose(or floating) tenon cut by a specific Festool machine which most of us can't afford, but you can easily cut a loose tenon with a good set of Brad point bits and some sharp chisels. A few simple jigs and guides should make the job relatively painless and repeatable and I could help you in their design if you like. Do you have a drill press and sharp chisels?
Dominoes: the machine can be operated lodged over the corner of a workpiece (typically to cut into the ends or edges of a workpiece; but also face-on to the larger surface of a workpiece, anywhere in it's area - usually positioned with the aid of a temporary bar or batten clamped across the workpiece. This is easily done if the workpiece is flat on whatever face is being pierced by the Domino cutter.
But is your chair back also curved, in the normal fashion of some chair backs, left-to-right? If so, that will make the joinery (whatever joint type is used) more complex.
However, a Domino becomes even more likely to be the easiest solution, as curved surfaces can be dominoed with the aid of two temporary small spacer blocks on either end of the Domino machine's face, so that they and the Domino machine's face where the cutter emerges stabilise the machine on a convex curved workpiece face.
It's slightly more difficult if you want to domino a concave surface but it can be done if the curve is mild so the cutter can reach and pierce the workpiece despite the Domino machine's face where the cutter emerges being held away from the workpiece area to be cut into. Double-sided sticky tape applied to either the workpiece or the Domino machine face would help to keep the machine in place.
All moot, though, if the machine cannot be acquired for budgetary reasons.
But it might be possible to do something similar with a router and dowels...... You'd need some angled sub-bases to tilt the router to the required angles.
A long tongue and groove or splined joint on a curved surface, though ..... that would be somewhat of a challenge!
Lataxe
PS Just seen E's reply re loose through tenons. That seems the most practical solution if the Domino is not an option. It'll take a bit longer. It's unlikely to be quite as neat unless one of your students is a time-server cabinetmaker. :-)
Possibly a dovetail router bit? You would need to rout a slot with angles on both sides, and then glue an additional piece into the slot to make it a parallelogram instead of trapezoidal. Then you would use the same router bit to cut the tenon on one side, and a router bit with the opposing angle to cut the day shoulder of the tenon. See picture
lets try again:
I don’t think we can find a dovetail router bit with such a large angle but the infill piece got me thinking. Carve a wide recess on the back plank and glue in two infill pieces (green).
Yes, I can only find them for milling machines, not sure if they can be used in a router.
Man what a resource this forum is! You all are great. While I did rack my pea brain around this for a while, I didn't expect it to be this difficult!
esch5995, I completely understand your strength concerns and I too have them. There will be a lot of weight, especially coming down on that bottom back joint when all is said and done. My first prototype is going to be appropriate size for a kindergarten kid so I think I'll know more after that. Hey I make them work in CARDboard for crying out loud! I was hoping to solve this problem using only the table saw and tenon jig if possible. I have some chisels but pathetically I don't have a drill press at the moment.
Lataxe, I'm sold on the Dominoe and if the final mock up even looks remotely interesting I may consider getting a well used one!
Gulfstar, Very interesting, I think I may be able to make that work! I can also use better hard woods for the infills. I need a flat top saw blade to chunk out that recess. I'm gonna give it a try tmrw!
Ben, I think we've come up with an idea for a tool in need! You make it and I get half!
Annoying amount of exclamation points in that post of mine but hey, I appreciate the help!!!
Myself, I likes an excited new woodworker as it rubs off so I rush to the shed to try an impossible thing before breakfast. Of course the smell of fresh-brewed coffee and the impossible thing grinning up at me as it shakes it's wee head side-to-side means I am soon at the dining table eating toast and thinking about a possible-thing, for after the dawg walk and lunch.
Oh I forgot....
!!!!!! :-)
Lataxe
Ben, that is an interesting find, would you know the max rated rpm ?
Ankle picker, I would expect that there is a lower stretcher or a 40 degree wedge in the joint to strengthen the assembly.
AnklePicker
While I have significant doubts that any type of stub tenon that I estimate will be around ⅜" on the short side(assuming ¾" stock) and ⅝" on the long side will have the strength you need, and that includes the domino, I wish you luck on making your vision a reality.
PS. Used drill presses are significantly more available and less costly than Domino Joiners. Just look for one with a minimum 16" swing(that would let you put the through tenons within 2" of the edge of an 18" piece).
Have you considered doing them with hand tools?
A guide block will ensure accurate angles.
AnklePicker
There maybe a low cost solution to your lack of a drill press.
https://www.garrettwade.com/portable-drill-guide-jig.html?SCID=W4011000&gclid=CjwKCAjw88v3BRBFEiwApwLevfnESZqvsHOQBTHqoYz5_bGmkA2_yheWGOcnOoKg4yA46mOgSXHyDhoCRe0QAvD_BwE
Portable drill guides could get the job done. Just clamp a straight board across your workpiece and slide the guide along drilling as needed.
The through tenon IMO is the only chance of having a strong enough joint for what I believe you want to do.
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