centering tenons on an angled cut

[tperson]

Needing some help gents, I think I know how to do what I need to do…just need confirmation. Here’s the skinny: we need new bar stools in the kitchen (we bought some second-hand cheap ones when we moved and they’re not designed to handle the abuse of 5 children). Since I’m a chair-building novice, I scoured the interweb until I found a set of chair plans for a design that were scalable for stools and that matched our décor (link below). I finished the pine prototype last night, a few mistakes made and a few tweaks needed, but otherwise it turned out okay. Man, I can tell you that the pantorouter was made for this kind of construction, all of M/T fit perfectly and they were a breeze to make. My problem is that the two upper side pieces (stretchers?) are assembled at an angle (7.5deg) and when I cut my tenons, they didn’t end up centered. I think where I goofed up, is when I centered the bit at the end of the part and not at the root of the tenon. Make sense? My question is this: anyone got any good/fast/easy/repeatable ways to accomplish this? If I can get this figured out, I can start on the 5 bar stools and 7 dining chairs. Actually, the answer can come right before the tenons are cut…it shouldn’t change anything up until then.

Visualizing the centerpoint is a little tricky to draw since you have to think three-dimensionally. Hopefully the drawing below helps a little. 

chair plans: https://woodarchivist.com/3524-dining-room-chair-plans/

[Chestnut]

Don't. Build the sides of the chair and back of the chair. Then pull the measurement for the front apron off the dry assembled chair.

Also I'd set the side rails so they aren't flush with the outside of the leg it kinda looks odd esp when you have a reveal on the front.

[Coop]

Drew, either I didn’t understand the question or I don’t understand the first part of your answer. Care to elaborate a bit? Thanks

[tperson]

 

On 10/16/2023 at 7:10 PM, Chestnut said:

Also I'd set the side rails so they aren't flush with the outside of the leg it kinda looks odd esp when you have a reveal on the front.

this is the problem I ran into since my tenons aren't centered in the rails

On 10/16/2023 at 7:52 PM, Coop said:

Drew, either I didn’t understand the question or I don’t understand the first part of your answer. Care to elaborate a bit? Thanks

yeah, thanks Coop...I was going to ask for clarification on the first part too.

[Chestnut]

Don't worry about centering the tenon just hit the reveal you want. Adjust the tenon location or mortise or both to achieve that.

Its going to impact the other chair parts so eventually you work off the chair with relative measurements.

[tperson]

Trig to the rescue! I had a stroke of clarity this morning and thought “hey, draw it out completely and use some math to figure it out”…so I did. Looks like the center offset for the angled tenon is 0.082”, which will resolve the reveal issue Chestnut pointed out and make everything look correct. I attached my drawing, it’s a little messy  (it’s been a long time since drafting class) but it gets the job done. Shifting the center by 82 thousandths shouldn’t be a big deal…get the first one laid out correctly and index all the others based on that.

A few missing details from the drawing: 

- NTS means Not to Scale (nothing I draw is, very important to remember)

- tenon length is 5/8"

[B1rdhunter]

I think you just made my head hurt.

[tperson]

been pondering this most of the afternoon and I think I made a mistake...the length of the tenon is 0.625 and should be the hypotenuse of the triangle. The equation should be:

sin(7.5) = x/0.625

sin(7.5)*0.625 = x

0.081 = x

Doesn't change the offset by much (0.001), but that's because the tenon is short and the angle is minor.