Author Topic: Domino Chair Build with Angles (Read 3344 times)

Tukston · « **on:** June 16, 2022, 08:19 AM »

Hi everyone,
I recently purchased a domino 500 in the hope it would help me with a chair build I am working on. I am busy making a test chair out of scrap wood to help me iron out the kinks.

If you see the attachment you will see there are 6 connection points that I was hoping to use the festool for. The front legs I think are manageable using the seat and leg edges as reference to make the tenons. The problem I am having is connecting the back leg to the seat and the back rest to the top of back leg.

My first question would be if it is possible to make these joins accurately with the domino and if so how would I go about this?

If anyone can help me with the challenge it would be greatly appreciated.

Many thanks,
Tukston.

tsmi243 · « **Reply #1 on:** June 16, 2022, 09:38 AM »

Definitely doable. Look for center-referencing strategies for the domino- Chuck has posted his several times, and it's gonna be perfect for this.

Another question, that I don't know the answer to, is how to orient the domino for best strength. The best way might not be the most obvious.

Vtshopdog · « **Reply #2 on:** June 16, 2022, 09:42 AM »

This thread has relevant discussion for seat to back leg joints

https://www.festoolownersgroup.com/festool-jigs-tool-enhancements/shop-made-domino-joiner-jig-for-the-intersecting-lines-mortising-technique/msg670909/?topicseen#msg670909

For seat back to top of leg joint likely you can reference off front of legs and front edge of the seat back piece.

Vtshopdog · « **Reply #3 on:** June 16, 2022, 09:47 AM »

BTW

One really cool thing with the Domino is you can dry assemble everything to test fit your assemblies before gluing.

Tukston · « **Reply #4 on:** June 16, 2022, 10:03 AM »

Thanks Vtshopdog & tsmi243!
I was hoping there was a way - Festool love.

Michael Kellough · « **Reply #5 on:** June 16, 2022, 10:05 AM »

The Domino can be used to make mortises where needed for this design but wood is almost certainly not strong enough to survive someone of adult size actually sitting in a such a chair. Metal would be more appropriate.

The Domino natively aligns with surfaces that are parallel to the mortise and marks that are centered on the mortise so the front leg/seat mortises will be easy to locate.

The mortises for the top of the back legs won’t be much more difficult.

Since the back is curved you’ll need to make a shim to support the fence of the Domino so that the tool/mortise is parallel to the outer face of the leg. If you made this design in cad you should be able to work out the exact dimensions of the perfect shim. Use double stick tape to adhere the shim to the curved back. Depending on how picky you are you might need to compensate for the thickness of the adhesive tape, the closer the shim is to the mortise there more influence the adhesive thickness will have on whether the mortises in the back and legs are coplanar.

For the mortises in the sides of the back legs you’ll again use the fence and marking techniques used on the previous joints but for the mortises in the side of the seat you’ll probably want to make a jig (for each side) that registers with the seat top and provides a stop to position the bottom of the Domino against. And you have to be more elaborate with the positioning marks, making them longer and showing the center of the mortise in both axis and wrapping around the jig.

jeffinsgf · « **Reply #6 on:** June 16, 2022, 10:47 AM »

I agree with Michael. That back leg joint is relying 100% on the strength of the glued in Domino. I would do a half-lap plus a Domino at the least.

jeffinsgf · « **Reply #7 on:** June 16, 2022, 10:49 AM »

Are your backs steam bent or bent lamination?

Tukston · « **Reply #8 on:** June 16, 2022, 02:57 PM »

The back rest is steam bent 45mm thick and 75mm high - the wood is ash.

Tukston · « **Reply #9 on:** June 16, 2022, 02:59 PM »

Great suggestion Micheal. The strength has been a concern, hence first building test version.

Quote from: Michael Kellough on June 16, 2022, 10:05 AM

The Domino can be used to make mortises where needed for this design but wood is almost certainly not strong enough to survive someone of adult size actually sitting in a such a chair. Metal would be more appropriate.

The Domino natively aligns with surfaces that are parallel to the mortise and marks that are centered on the mortise so the front leg/seat mortises will be easy to locate.

The mortises for the top of the back legs won’t be much more difficult.

Since the back is curved you’ll need to make a shim to support the fence of the Domino so that the tool/mortise is parallel to the outer face of the leg. If you made this design in cad you should be able to work out the exact dimensions of the perfect shim. Use double stick tape to adhere the shim to the curved back. Depending on how picky you are you might need to compensate for the thickness of the adhesive tape, the closer the shim is to the mortise there more influence the adhesive thickness will have on whether the mortises in the back and legs are coplanar.

For the mortises in the sides of the back legs you’ll again use the fence and marking techniques used on the previous joints but for the mortises in the side of the seat you’ll probably want to make a jig (for each side) that registers with the seat top and provides a stop to position the bottom of the Domino against. And you have to be more elaborate with the positioning marks, making them longer and showing the center of the mortise in both axis and wrapping around the jig.

Tukston · « **Reply #10 on:** June 16, 2022, 03:52 PM »

Hi Michael,

Having read your reply in detail I have 2 questions. You mention metal - could you elaborate what you had in mind. Regarding the strength point, i have increased the service area of the top of leg that meets the back rest - leg top is 45mmx75mm - back rest is also 45mm wide. Will help but not sure that it will resolve it.

My second question regards to your last idea of making a jig to connect seat to leg. I am not following you 100%?
What i have done is referenced the top of the seat to make a tenon into the side of the seat . Where I am stuck now is making a corresponding tenon in the leg. Could you please fill me in on exactly what you had in mind?

Thank you for your time. Much appreciated!

Quote from: Michael Kellough on June 16, 2022, 10:05 AM

The Domino can be used to make mortises where needed for this design but wood is almost certainly not strong enough to survive someone of adult size actually sitting in a such a chair. Metal would be more appropriate.

The Domino natively aligns with surfaces that are parallel to the mortise and marks that are centered on the mortise so the front leg/seat mortises will be easy to locate.

The mortises for the top of the back legs won’t be much more difficult.

Since the back is curved you’ll need to make a shim to support the fence of the Domino so that the tool/mortise is parallel to the outer face of the leg. If you made this design in cad you should be able to work out the exact dimensions of the perfect shim. Use double stick tape to adhere the shim to the curved back. Depending on how picky you are you might need to compensate for the thickness of the adhesive tape, the closer the shim is to the mortise there more influence the adhesive thickness will have on whether the mortises in the back and legs are coplanar.

For the mortises in the sides of the back legs you’ll again use the fence and marking techniques used on the previous joints but for the mortises in the side of the seat you’ll probably want to make a jig (for each side) that registers with the seat top and provides a stop to position the bottom of the Domino against. And you have to be more elaborate with the positioning marks, making them longer and showing the center of the mortise in both axis and wrapping around the jig.

Michael Kellough · « **Reply #11 on:** June 16, 2022, 04:25 PM »

Welded aluminum or steel tube would be appropriate materials to execute this nicely minimal design.

You can certainly make the chair with wood in full scale to judge proportions etc. but unless the legs are at least 2-1/2” square I think the stress on the joints would be too high for wood. And you’d need to make custom tenons to get them long enough.

Jeff’s suggestion to use a half lap joint for the back legs might add enough strength…

The jig for the side joints would be simple. A piece of plywood about 4” square with a fence planted on one face at the approximate 15 degree angle of the leg. Make a jig for each side and carefully layout the line representing the center of the mortise or mortises (you need at least two for the joint). A paper template printed from the cad design (with 10mm offset from base of machine to center of mortise) might make it easy to get the marks right. The template should include a reference mark to help position the jig relative to the front of the seat.

ChuckS · « **Reply #12 on:** June 16, 2022, 05:49 PM »

Quote from: Tukston on June 16, 2022, 08:19 AM

Snip.

My first question would be if it is possible to make these joins accurately with the domino and if so how would I go about this?

If anyone can help me with the challenge it would be greatly appreciated.

Many thanks,
Tukston. (Attachment Link)

Your design is fine, and wood alone is enough for strength. Also no other joinery is needed as the loose tenon joinery is robust for chairs and tables. The key rather is the wood species and thickness, which you didn't provide. Twin/double tenons are super strong if you stock is thick enough.

If you Google, you should see that many have used the dominoes alone to build seats and chairs, a few similar to yours in style.

If you plan to make just one chair, the intersecting line method is good enough. If a batch of 4 or 6, I'd make a simple guide jig to do the angled mortising.

Lincoln · « **Reply #13 on:** June 16, 2022, 06:43 PM »

How will you join the front legs? As per your drawing, where they join to the underside of the seat?

Tukston · « **Reply #14 on:** June 17, 2022, 02:03 AM »

Hi Chuck,

I am using ash wood with a width of 45mm x 75mm - certainly enough space for 2 10x50 tenons.

I am a newbie and so if you have any info on making jig and line methods please hook me up.

Many thanks!

Quote from: ChuckS on June 16, 2022, 05:49 PM

Quote from: Tukston on June 16, 2022, 08:19 AM
Snip.

My first question would be if it is possible to make these joins accurately with the domino and if so how would I go about this?

If anyone can help me with the challenge it would be greatly appreciated.

Many thanks,
Tukston. (Attachment Link)

Your design is fine, and wood alone is enough for strength. Also no other joinery is needed as the loose tenon joinery is robust for chairs and tables. The key rather is the wood species and thickness, which you didn't provide. Twin/double tenons are super strong if you stock is thick enough.

If you Google, you should see that many have used the dominoes alone to build seats and chairs, a few similar to yours in style.

If you plan to make just one chair, the intersecting line method is good enough. If a batch of 4 or 6, I'd make a simple guide jig to do the angled mortising.

Tukston · « **Reply #15 on:** June 17, 2022, 02:05 AM »

Yeah, I plan to join the leg to the seat with a domino. The leg sits under the seat - 45mmx45mm in dimensions.

Quote from: Lincoln on June 16, 2022, 06:43 PM

How will you join the front legs? As per your drawing, where they join to the underside of the seat?

ChuckS · « **Reply #16 on:** June 17, 2022, 04:46 AM »

[ Specified attachment is not available ]I have had connection issues here, so I need to be brief.

You need to decide on the orientation of the tenons and its pros & cons - see A vs B. For illustration purposes, I picked A for making the guide jig.

Under A, no jig is needed to mortise the seats. Just use two fence settings. First mortise the top tenon on ALL seats, then reset the fence to mortise the second tenon (the bottom one).

Make a jig with two fences (top and underneath - one for mortising the left leg and one for the right) and two index marks to position the DF using the center line on the base of the machine for alignment. Correction: You need only one center index mark on the jig (not two as shown in the hastily drawn sketch).

If joinery B is used, two jigs can be made.

I hope this makes sense to you, but I have no access to my old photo files for a while to share more jig photos. Other members can help you more.

Tukston · « **Reply #17 on:** June 17, 2022, 11:23 AM »

Hi Chuck, your drawings and descriptions have certainly made it much cleaner for me. There is just one detail I am not getting. Looking at the mortises in the seat itself - your drawing A. To achieve this one uses the plate on the domino - the plate enables height placement. What is not clear to me is how do i reference this height on the leg? I cant see away to use the plate on the domino, this has to be folded back to 0 degrees otherwise I dont have access to the leg to make the mortise. I am assuming the jig is gonna replace the plate on the leg mortises. Just not 100% how?
Thanks for helping Chuck!

ChuckS · « **Reply #18 on:** June 17, 2022, 03:10 PM »

First, the "plate" you use is the term for the "fence" in my book, the bottom of the machine is the baseplate.

The following notes assume that you already know that the distance between the center point of the cutter and the baseplate is exactly 10mm.

1) To mill the mortises on the legs, first determine where you want them milled on the legs.
2) Instead of marking the center lines of mortises on the legs, lay out the pencil lines 10mm from those center lines. (Dia. A)

3) Place the jig on the leg blank with the jig's index mark edge aligned with one of the pencil lines (Dia. B). Repeat 3 for the second mortise.

4) Plunge the machine to make the first mortise.

I hope this helps.

Tukston · « **Reply #19 on:** June 18, 2022, 12:17 PM »

Chuck you are an absolute legend! I really appreciate the time you put in this for me I am sure many others. I totally get it now, thank you!

ChuckS · « **Reply #20 on:** June 18, 2022, 03:01 PM »

I've learned my share from others.

Good luck with your project. (Try out the jig on scraps if necessary.)

P.S. For structural strength, use tight to tight width setting for all the joints.

Crazyraceguy · « **Reply #21 on:** June 18, 2022, 04:20 PM »

My concern is more the structural integrity of the front legs. They are totally unsupported in any way. Building something to look like that drawing is one thing, but actually sitting on it? If you tied the legs together with a stretcher of some kind, it would strengthen to whole assembly a lot. It would drastically change the look though.

ChuckS · « **Reply #22 on:** June 18, 2022, 09:41 PM »

Crazyraceguy's comment drew my attention to the front part of the chair as my focus was on the angled mortises only, with apologies. I now realize that your sketch is a little different from this that I had in mind:

The front legs need to be attached to the seat in such a manner that they can handle the shear force. To do that, stretchers as Crazyraceguy suggested, are one way. Or the legs can be attached to the notched seat, similar to what's shown in the curved chairs above (but a DF700 or a router/jig would be needed for the reach).

ChuckS · « **Reply #23 on:** June 18, 2022, 10:21 PM »

Quote from: Tukston on June 17, 2022, 02:05 AM

Yeah, I plan to join the leg to the seat with a domino. The leg sits under the seat - 45mmx45mm in dimensions.

Quote from: Lincoln on June 16, 2022, 06:43 PM
How will you join the front legs? As per your drawing, where they join to the underside of the seat?

Just saw this reply. On second thought, such a joint using a twin tenon might survive the shear stress in the absence of any stretcher.

I'd build a prototype chair (half side) with 2x4 material to test both the angled jig and joinery strength.

Crazyraceguy · « **Reply #24 on:** June 19, 2022, 10:10 AM »

Quote from: ChuckS on June 18, 2022, 10:21 PM

Quote from: Tukston on June 17, 2022, 02:05 AM
Yeah, I plan to join the leg to the seat with a domino. The leg sits under the seat - 45mmx45mm in dimensions.

Quote from: Lincoln on June 16, 2022, 06:43 PM
How will you join the front legs? As per your drawing, where they join to the underside of the seat?

Just saw this reply. On second thought, such a joint using a twin tenon might survive the shear stress in the absence of any stretcher.

I'd build a prototype chair (half side) with 2x4 material to test both the angled jig and joinery strength.

That was my point about the front legs. I just can't see the seat slab taking the forces chair use. Chairs are quite different for tables. Sure, tables get moved, and that is usually the worst thing to happen to them, but it's not like a chair. The force on a table in generally just gravity, straight down. Chairs take side loads and a lot more movement.
You could glue that up with two tenons, oriented either way and the wood of the slab will most likely be the fail point, splitting along the grain when enough force is applied.
The rear legs are at least tied to each other by the backrest. That adds a ton of strength to them, plus the fact that they are connected to the slab out in the middle, rather than a corner. You could even "let them in" to a dado, even a shallow one would add a lot of strength there. None of that is helping those front legs. They are just "out there" with no support (and no real way to add any without changing the look)

cpw · « **Reply #25 on:** June 19, 2022, 10:19 AM »

I agree that the front legs are the weak point. When designing a chair (or table); you have to think about what is going to happen when someone stands on it as opposed to using it the way you intended.

Tukston · « **Reply #26 on:** June 20, 2022, 05:11 AM »

Thank guys for pointing out the weakness in the design. You bring up a very good a point.

I have included a cross support in the design so that there are 2 points of connection for the front legs. I am hoping the thickness of the wood combined with the support beam should do the trick. Ideally I should also have a cross support beam from front to back but I am hoping the thickness of wood will be enough for general use.

I have looked at domino placing and I see the rule of thumb is to have twice the thickness of the domino space between each domino. Regarding the front leg, I should really be using 6mm domino (according to the rule) but looking at it I kinda feel like the 8mm is the better option as far as strength goes. Does anyone have thoughts on the placement of dominos for strength?

Steve1 · « **Reply #27 on:** June 20, 2022, 10:18 AM »

I like how you added the taper to the rear legs. Looks better (and stronger joint).
You might want to try the same on the front legs.

Tukston · « **Reply #28 on:** June 20, 2022, 01:43 PM »

You right Steve. Thanks!

Crazyraceguy · « **Reply #29 on:** June 20, 2022, 05:38 PM »

There you go. That lower stretcher will help a lot.

Grain direction of the seat slab?