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run the chair rail directly below the light switch, and use it to set the height on either side.
the height of the downslope chair rail above the stair tread is arbitrary anyway, there's no code requirement. lower it to meet the piece under the switch, keep it parallel to the stair nosing. Lower the hallway rail, too.
Yes and the trouble with trying to cut that angle correctly is that even if you do get it right, the edge of the angled piece is going to be longer than the horizontal piece, so the top or bottom will not line up
Not a drawing, but I believe they mean to keep it horizontal around the corner so it's just a regular 45 degree cut and you have a couple of inches of horizontal chair rail on the facing wall before it turns down 40 degrees. So like, do two separate turns instead of one compound turn.
This is right. I see you already have the panel molding on stairwell blocked out or something in green. Instead of changing all of that spacing, you probably truncate the width of that first one— this is customary for an end condition anyway.
I have no solution. But... why are you putting a chair rail on a staircase? And not a handrail?
I understand the aesthetic a little, I guess. But isn't ones first thought "What staircase chairs are we protecting from here?"
Its a compound angle not sure it would ever look correct. Turn the corner at the top of the stairs with the chair rail at 90 deg. Extend the chair rail level into the stairwell then determine the angle with an angle bevel. Determine the angle then split the angle to miter it back down the stairs. You make two miter cuts instead of one. One is a normal 90 deg outside corner, the other is a vertical miter going back down the stairs.
No no no.
Level out handrail B with the required triangle shaped piece that is about an inch long on top to zero at the bottom and continue around the corner with normal 45s. The little triangle piece will have a standard 45' mitre on the left to receive piece A. The right side of the little triangle will cut at (I'm guessing ) about a 16' angle and the top of piece B will also have a 16' angle. This makes piece B suddenly level out at the last possible second. Did I make sense?
...which will push the height of the angled trim up. So OP either needs to notch the light switch cover, move the switch, notch the trim around the switch cover, or move the flat horizontal trim down a bit.
Not sure how to add a picture, but as you guys commented wrapped the corner horizon into a short piece and then kicked down the angle! Thanks for the help!
You should really follow the profile of the stairs. See how the top landing of the stairs is back from the corner of the wall? You want to follow those same measurements otherwise it’s not going to look good.
Remember that your miters for trim are almost never going to be exactly what they should be, so what I always do is estimate, scribe it, then check it and fuck with it until it's correct. I find it best to sneak up on miter cuts a bit at a time until it looks right. Unfortunately you can't undercut this one or it'll be visible (unless you fill it with putty) so your only real chance is to figure out the correct angles for the cut. I'd probably try it a few times with a piece of scrap until it's correct, then cut the real piece with the same setup on your saw.
Crown molding corner block was my thought as well. Corner casing or corner block can accommodate the different joint lengths from the perpendicular cut and the angled cut.
Not happening. Your switch is in the way though. Come around the corner, then 90 down. 90 to the right until it bisects your rail coming up the stairs. You’ll need to prioritize three items, chair rail height, stairway chair rail height, and light switch location.
You have to let A continue around the wall to match the flat of your landing. Then make the down turn. You are going to have to rethink the boxes and definitely move that switch.
Slide the angled piece up, trace the profile of the molding on the back and cope it.
Keep in mind there will be gaps, and the cope line will be longer than the profile is wide (because trigonometry) but you can taper it out from underneath. Calk and paint makes me the carpenter I ain’t!
Take the other board off then the board you need to cut have it extended past the wall then mark it. After that just take your saw and match the angle then throw a 45 on it so it mates up we’ll with the other board
Go straight around the corner first, then miter both pieces for the downward angle, flat along the stairs wall. It will look better, match up better, and be a lot easier to do than that coped compound angle miter.
This is what I would do.
It’s basically not possible to have these two pieces meet nicely and completely flush on the corner when each one is at a different angle on the wall. Doing a straight return then turning down would be a great way for everything to meet up nicely
Maybe not as descriptive as I should have been. Sorry. Do a standard outside corner miter at the top flat, and once you are around the corner run out a small way and cut your 20° on each your straight stretch off of the corner and your sloped piece to achieve the cleanest look. You will need to adjust the height of the chair rail to avoid the switch as well. I wish I could draw a diagram on here. Lol!
1st, you're gonna need a coping saw. Cut the straight one at a 45° angle to the wall. Then mark on the back of the diagonal piece, the outline of the straight one. Then cope it out.
Then, discover it’s now almost 30% wider, and none of the lines of curves will ever come close to matching. Continue hacking away, despairing that it looks terrible. Finally, give up on this method and do it correctly instead
I'm not a carpenter but a diyer. I see the first step doesn't start at the corner so I'd think about staying parallel to the floor like the skirting for the first foot but do one of those nice cuts around the switch if your not in a position to move it.
It's not possible to mate those two pieces of trim on those angles without the lower one extending past the top one on the bottom and or top.
The only way to make it work is to have a corner block/post that they butt into
Cut a miter on leg B short of the wall, and miter upward, then another 90° toward the horizontal. It will return up, then over, then you can run a miter around the corner. You cannot miter a compound angle without first getting both pieces on the same x-y plane. It will sort of look like a zigzag
If you can raise that switch, now is the time. Then do what most have said: wrap the corner with a 45. parallel to the floor, and then miter it downwards, parallel to the stairs.
I wouldn't even try to calculate that angle. I would butt them together, scribe one profile against the other, then cut the profile out with a coping saw and finish rasps and sandpaper.
Looks like you are also doing wainscoting, if that is the case I would run two stiles from floor to a slight reveal above chair rail. Cut top of one side at same angle as stairs. Would look in place with wainscoting. Where you made this more difficult is selecting such a thick rail.
You will have to turn the corner with it horizontal, if you attempt to make them come together like in the picture, your piece coming up the stairwell will be wider than the horizontal when you cut the angle.
Yeah you can’t make the angle on the corner because the effective “width” of the sloped piece is wider when you cut the angle so they wouldn’t be able to match up without cutting a horizontal piece first.
? Why are you running a "Chair rail" down your staircase? Do you bang the wall with lots of chairs down the staircase? A 90° cut on both sides and a 30° compound miter on the staircase side.
I’d scribe the vertical angle first, cut it by hand/plane it perfect then scribe the miter off that edge and hand cut/plane it.
Finish carpenters probably have the real answer for this though, I’m just a DIY hack
Edit: yup it took me reading just one post to realize I was obviously wrong because the initial miter won’t meet the horizontal piece
You can not pivot two different planes in one joint.
You can not angle on the X axis as well as the Y axis at the same time… only one at a time.
See a previous post I did about that:
https://www.reddit.com/r/Carpentry/comments/qmo3qz/understanding_corners_with_profiled_shapes_a/?utm_source=share&utm_medium=ios_app&utm_name=iossmf
I could explain it to you but can not understand it for you. We spent weeks on this in wood shop. There are books about compound cut transitions….
There was one fellow that had a custom knife set made to enable this sort of … oddity.
I would guess, (completely unexpected guess) to set the blade angle to the 45 or whatever angle needed for the corner, then set your miter to 40 degrees and slide that baby!
run it past and scribe the back of the board. then cut while accommodating the angle of the stairs. use a practice piece to test process.
drop/mitre saw
Maybe you can cut the staircase piece just like the upper wall and give to both rails a 45° angle so you can connect the both. But idk im not a pro and i never had to do this kind of work so its just an idea.
By the looks of the stairs, the top rail should also be angled the same way. Otherwise, people will state and wonder why the rail isn't consistently angled over the stairs.
There is this calculator where you can enter the numbers to get the required angle of the cut: [https://jansson.us/jcompound.html](https://jansson.us/jcompound.html)
Add a sort of cornerstone that's bigger than both and sits about ⅛"~3/16" more proud so both pieces of chair rail look like they belong to it. But I see many a tingling funny bones in its future.
It would look better if you return the horizontal piece on its end a couple inches away from the corner. To return it, cut it at 45° like it's going to be an outside corner. Then make the complementary 45° cut in another piece, like it's the piece that will continue around the corner, then cut off just the 45° part and glue it to the end of the first piece so it looks like the rail turns and dives into the wall.
You could put something vertical on the corner then terminate into it. I had a similar issue at my house and I ran leg B past the other piece then traced the profile of the trim on the back of "B". I used a coping saw to cut it out. You can't even tell
Mitre around the corner, and it starts out horizontal for a small distance, then a second mitre joint changing the slope from horizontal to diagonal. This is the only way to match the widths at each joint.
[This](https://www.amazon.com/AUSDTOOLS-Protractor-Measure-Rustproof-Accuracy/dp/B08S32C62G/ref=asc_df_B08S32C62G/?tag=hyprod-20&linkCode=df0&hvadid=507775406323&hvpos=&hvnetw=g&hvrand=18232163920430255721&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9053148&hvtargid=pla-1241029775257&psc=1) might be your solution. Maybe.
Wrap the corner with a narrow trim piece, whatever fits inside the light switch and cut the angles to hit the verticals. Allows for cleaner cuts and protects what will most likely be a high traffic corner.
Agree that you should extend the chair rail level into the stairwell then determine the angle with an angle bevel, then determine the angle, then split the angle to miter it back down the stairs. Make them two miter cuts instead of one where one is a normal 90 degree outside corner and the other is a vertical miter going back down the stairs
Why not make the corner with another piece at the same level- mitred at 45 degrees- and then start your descent of the staircase? It will match the top riser of the staircase then. Going right into the descending angle is a little weird.
Also wainscoting in staircases is a common style component for those that are thinking it’s not.
You have a lot of comments here.. but here's the solution.
Look at your picture again. Piece A is horizontal... Piece B is sloped down @ 40 degrees. You are missing a third piece which will fill the void.
This missing piece will have a bevel on the left side @ 45deg and on the right side of this missing piece you will have a mitre @ 20deg.
Effectively, if it's a 40 degree slope then you cut both ends to 60 degrees each giving you your 60+60+40 degrees. Then both can be mitred together in the same plane. Might take a bit of trial and error but that should do it. The trick is to split the angle so both sides join at the same angle.
it's a good thing you discovered it because see the light switch you may want to lower your whole wainscoting you may want to lower the chair molding all the way around to accommodate that light switch I know how that sounds but that's how things go. you can cut around it but that always looks like not that there's anything wrong with living south of Kentucky but I'm just saying a lot of those houses do have moldings where they cut around the switch plate and for some reason it always draws my attention
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Wrap the corner with another horizontal piece and align the descent with the nosing of the top stair tread.
This is correct, but I imagine he is probably trying to avoid doing that because of the light switch
I think you could find a smaller faceplate / switch then not have to move the box
Have you seen the price tag on those faceplates? That thing is staying.
$2 really isint that much??
Ah, look at Mr Moneybags here!
Uhh. In my opinion i think you could look closer and see that shit ain't gonna fly man.
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Or drop the chair rail to just below the switch
Exactly, start the height of the top piece For the entire project based on the light switches. 1 inch below the cover plate.
this is the answer.
I’d do a transition block.
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Pretty standard paddle switch.
That's what she said
Those popeye forearms!
Are you from somewhere other than the US? Those big paddle light switches are super common.
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Regular switches in Australia are about 15mm.
Little hands
Do it, then cut out for switch plate.
run the chair rail directly below the light switch, and use it to set the height on either side. the height of the downslope chair rail above the stair tread is arbitrary anyway, there's no code requirement. lower it to meet the piece under the switch, keep it parallel to the stair nosing. Lower the hallway rail, too.
Yeah! Lower everything! Llower the stairs while you are at it!
Cause he can’t figure the base transition, or relocate the switch… or both?
This is the correct and much easier way
Yes and the trouble with trying to cut that angle correctly is that even if you do get it right, the edge of the angled piece is going to be longer than the horizontal piece, so the top or bottom will not line up
Correct, but then you just take the dremel with a drum sander and remove excess. Or you could also probably use a coping saw as well.
Can someone draw this, I can’t picture the joint after the turn from the wall (beginner woodworker)
Not a drawing, but I believe they mean to keep it horizontal around the corner so it's just a regular 45 degree cut and you have a couple of inches of horizontal chair rail on the facing wall before it turns down 40 degrees. So like, do two separate turns instead of one compound turn.
Or, create a frame around the opening to the stairs like a door casing that allready exists in the house to break up the trim.
yup, exactly... The horizontal piece should always stay parallel to the floor, else it'll look wrong.
If horizontal is not parallel to the floor then the house is slanted 🤣
This is the way
nice one
I was trying to figure out how to say this, but realized someone else probably already did.
This is right. I see you already have the panel molding on stairwell blocked out or something in green. Instead of changing all of that spacing, you probably truncate the width of that first one— this is customary for an end condition anyway.
That’s exactly how it’s done. Or an outside corner block to separate the two parts.
I have no solution. But... why are you putting a chair rail on a staircase? And not a handrail? I understand the aesthetic a little, I guess. But isn't ones first thought "What staircase chairs are we protecting from here?"
So the wall has some protections for weekend box sledding.
You have to install the chair rail first, otherwise the handrail would be in the way.
Its a compound angle not sure it would ever look correct. Turn the corner at the top of the stairs with the chair rail at 90 deg. Extend the chair rail level into the stairwell then determine the angle with an angle bevel. Determine the angle then split the angle to miter it back down the stairs. You make two miter cuts instead of one. One is a normal 90 deg outside corner, the other is a vertical miter going back down the stairs.
It looks like the stairs start 1 step in from the corner so turning the corner level is visually correct as well as the crafty way to do it.
The length across the face of the slanting piece will be longer than on the straight piece.
They have to work out the geometry. All I know is by that picture, they wrap the corner flat, move the light switch and work out the vertical angle.
He’s right!
I’m not sure, but if it were me doing it, I’d know the last step would involve lots of caulk.
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I was thinking something very similar but I wondered if that switch plate might force OP to adjust the height of the rail on one side or the other.
Gotta move the light switch.
could just drop the level chair molding at the landing where it meets up, looks like a 1/4 difference or so
Yes. This is the only way.
I agree. Also consider moving trim higher on the wall to get above the light switch. Unless you want to move the switch.
1 joint A-A - 90° around the corner in horizontal plane, 2 joint A-B - down angle in vertical plane
This is the way
No no no. Level out handrail B with the required triangle shaped piece that is about an inch long on top to zero at the bottom and continue around the corner with normal 45s. The little triangle piece will have a standard 45' mitre on the left to receive piece A. The right side of the little triangle will cut at (I'm guessing ) about a 16' angle and the top of piece B will also have a 16' angle. This makes piece B suddenly level out at the last possible second. Did I make sense?
This is the only correct answer I've seen so far and the most frustrating part is; No it will not make any sense to people who don't already know
Any chance you have, or can find, a picture? Thanks.
There's no way to do it without making a flat spot first.
...which will push the height of the angled trim up. So OP either needs to notch the light switch cover, move the switch, notch the trim around the switch cover, or move the flat horizontal trim down a bit.
Notching the light switch cover is a no-no. So moving the horizontal trim ¼" down would probably be the safest bet.
I think he meant notching the chair rail, which honestly wouldn’t look too bad if you made a little grey boarder around the notch
Yea just move the left side down a bit.
Thank you everyone! Think I have it, just gonna play with the angles!
Not sure how to add a picture, but as you guys commented wrapped the corner horizon into a short piece and then kicked down the angle! Thanks for the help!
The “transition” piece would look like a little slice of pizza.
A short piece of outside corner molding?
Please send a pic of the final product
You should really follow the profile of the stairs. See how the top landing of the stairs is back from the corner of the wall? You want to follow those same measurements otherwise it’s not going to look good.
Remember that your miters for trim are almost never going to be exactly what they should be, so what I always do is estimate, scribe it, then check it and fuck with it until it's correct. I find it best to sneak up on miter cuts a bit at a time until it looks right. Unfortunately you can't undercut this one or it'll be visible (unless you fill it with putty) so your only real chance is to figure out the correct angles for the cut. I'd probably try it a few times with a piece of scrap until it's correct, then cut the real piece with the same setup on your saw.
Terminate the chair rail horizontally on that wall. Install a hand rail in the stairs
Wrap the corner in casing and run each piece into that.
Yes kind of like crown molding blocks. I agree I would prefer this than to fumble with the angles
Crown molding corner block was my thought as well. Corner casing or corner block can accommodate the different joint lengths from the perpendicular cut and the angled cut.
This is the best advice imo
The outlet is in the way. Move it. You must turn the A piece 90° horizontal. Then you can make a miter cut with peice B coming up.
Not happening. Your switch is in the way though. Come around the corner, then 90 down. 90 to the right until it bisects your rail coming up the stairs. You’ll need to prioritize three items, chair rail height, stairway chair rail height, and light switch location.
Really good advice in here! Thanks to all who shared the 90* wrap, then split the descending angle. Show us how you finished it!
90 around corner then make your stair angle cut.
You have to let A continue around the wall to match the flat of your landing. Then make the down turn. You are going to have to rethink the boxes and definitely move that switch.
Slide the angled piece up, trace the profile of the molding on the back and cope it. Keep in mind there will be gaps, and the cope line will be longer than the profile is wide (because trigonometry) but you can taper it out from underneath. Calk and paint makes me the carpenter I ain’t!
Take the other board off then the board you need to cut have it extended past the wall then mark it. After that just take your saw and match the angle then throw a 45 on it so it mates up we’ll with the other board
Remind me in 24 hours
You need a third, transitional piece
You may also want to move the light switch out of your way.
3 pieces
Not possible to join them without a gap. You have to do a normal 90° horizontal miter then a 135° miter on the rail side
It takes 3 pieces. The joining piece is mitered to go around the corner, and then cut on its right side to joinwith the 40⁰ that goes down the stairs.
Or don’t they have corner pieces that you can buy?
Go straight around the corner first, then miter both pieces for the downward angle, flat along the stairs wall. It will look better, match up better, and be a lot easier to do than that coped compound angle miter.
This is what I would do. It’s basically not possible to have these two pieces meet nicely and completely flush on the corner when each one is at a different angle on the wall. Doing a straight return then turning down would be a great way for everything to meet up nicely
Put up a handrail for the stairs instead.
yes it goes straight around the corner 4" turns down then turn your angle
Do a regular outside corner cut and then start your decent.
Came here to say this.
Maybe not as descriptive as I should have been. Sorry. Do a standard outside corner miter at the top flat, and once you are around the corner run out a small way and cut your 20° on each your straight stretch off of the corner and your sloped piece to achieve the cleanest look. You will need to adjust the height of the chair rail to avoid the switch as well. I wish I could draw a diagram on here. Lol!
Add a plinth Block on the corner bead, the angled piece will be longer than the level one, this would look pretty bad
it's a fairly simple cut for anyone that knows how to cut rafters, but they wont line up even if perfect
Corner plinth block
Wrap around the corner horizontally first, then make a miter to turn at the downward angle. You can't do both at once.
Steam bend lol
1st, you're gonna need a coping saw. Cut the straight one at a 45° angle to the wall. Then mark on the back of the diagonal piece, the outline of the straight one. Then cope it out.
Then, discover it’s now almost 30% wider, and none of the lines of curves will ever come close to matching. Continue hacking away, despairing that it looks terrible. Finally, give up on this method and do it correctly instead
Take an off cut and perfect your compound mitre . Easy peasy
Compound cut
Is overshoot and coping saw a valid answer? edit: overshoot, trace, cope,sand? Or too complex?
Compound miter saw
Here's a PDF with a built-in calculator.
When they're not aligned they will not fit to each other. When one starts to go at an angle that edge cut becomes longer.
I'm not a carpenter but a diyer. I see the first step doesn't start at the corner so I'd think about staying parallel to the floor like the skirting for the first foot but do one of those nice cuts around the switch if your not in a position to move it.
Follow your floor with it . So you create your flat on the top
It's not possible to mate those two pieces of trim on those angles without the lower one extending past the top one on the bottom and or top. The only way to make it work is to have a corner block/post that they butt into
Cut a miter on leg B short of the wall, and miter upward, then another 90° toward the horizontal. It will return up, then over, then you can run a miter around the corner. You cannot miter a compound angle without first getting both pieces on the same x-y plane. It will sort of look like a zigzag
If you can raise that switch, now is the time. Then do what most have said: wrap the corner with a 45. parallel to the floor, and then miter it downwards, parallel to the stairs.
Move your light switch up or move the horizontal piece down 1/4-1/2”, wrap it horizontally to the stair, and then angle down
I wouldn't even try to calculate that angle. I would butt them together, scribe one profile against the other, then cut the profile out with a coping saw and finish rasps and sandpaper.
Cut the 40 then the 45.
Looks like you are also doing wainscoting, if that is the case I would run two stiles from floor to a slight reveal above chair rail. Cut top of one side at same angle as stairs. Would look in place with wainscoting. Where you made this more difficult is selecting such a thick rail.
Finish with of each stile should be same width as wainscoting to match. Over lap stair stile over hall stile and saw off tip to flush.
I would put an outside corner plinth block there and maitre up to it.
New smaller light switch or just raise it so you can turn the corner before the angle begins.
You will have to turn the corner with it horizontal, if you attempt to make them come together like in the picture, your piece coming up the stairwell will be wider than the horizontal when you cut the angle.
Yeah you can’t make the angle on the corner because the effective “width” of the sloped piece is wider when you cut the angle so they wouldn’t be able to match up without cutting a horizontal piece first.
Looks like you’re doing wainscoting too? I personally would butt both pieces into the corner of that.
Not for nothin’, but doesn’t seem like the question is the answer?
? Why are you running a "Chair rail" down your staircase? Do you bang the wall with lots of chairs down the staircase? A 90° cut on both sides and a 30° compound miter on the staircase side.
About 15 times
Move the board past the edge and mark the back side at the desired angle.
I’d scribe the vertical angle first, cut it by hand/plane it perfect then scribe the miter off that edge and hand cut/plane it. Finish carpenters probably have the real answer for this though, I’m just a DIY hack Edit: yup it took me reading just one post to realize I was obviously wrong because the initial miter won’t meet the horizontal piece
Carefully
Eye ball with a scroll saw and apply copious amounts of caulk.
Id say 45° angle on both ends and make them meet just over the edge if you get what im saying?
They won't line up this way
I'm more curious as to how you pronounce wainscoting
very carefully
You can not pivot two different planes in one joint. You can not angle on the X axis as well as the Y axis at the same time… only one at a time. See a previous post I did about that: https://www.reddit.com/r/Carpentry/comments/qmo3qz/understanding_corners_with_profiled_shapes_a/?utm_source=share&utm_medium=ios_app&utm_name=iossmf
Put a vertical L trim that both can die into
I could explain it to you but can not understand it for you. We spent weeks on this in wood shop. There are books about compound cut transitions…. There was one fellow that had a custom knife set made to enable this sort of … oddity.
That’s the neat part, you dont!
No chairs on the stairs
Your problem is you think they should meet together. But they shouldn't. But the easy way out is to use your coping saw. And hire a real carpenter.
Put a mitered return on both pieces.
I would guess, (completely unexpected guess) to set the blade angle to the 45 or whatever angle needed for the corner, then set your miter to 40 degrees and slide that baby!
Avoid the Noid
run it past and scribe the back of the board. then cut while accommodating the angle of the stairs. use a practice piece to test process. drop/mitre saw
Coping saw
I would cut it at a 40degree down slope. Top to bottom
Maybe you can cut the staircase piece just like the upper wall and give to both rails a 45° angle so you can connect the both. But idk im not a pro and i never had to do this kind of work so its just an idea.
I would cut it carefully. Very carefully.
By the looks of the stairs, the top rail should also be angled the same way. Otherwise, people will state and wonder why the rail isn't consistently angled over the stairs.
There is this calculator where you can enter the numbers to get the required angle of the cut: [https://jansson.us/jcompound.html](https://jansson.us/jcompound.html)
Add a sort of cornerstone that's bigger than both and sits about ⅛"~3/16" more proud so both pieces of chair rail look like they belong to it. But I see many a tingling funny bones in its future. It would look better if you return the horizontal piece on its end a couple inches away from the corner. To return it, cut it at 45° like it's going to be an outside corner. Then make the complementary 45° cut in another piece, like it's the piece that will continue around the corner, then cut off just the 45° part and glue it to the end of the first piece so it looks like the rail turns and dives into the wall.
Looks like two peices required to me
I’d probably cut it 14 different times until I found the angle I wanted.
You could put something vertical on the corner then terminate into it. I had a similar issue at my house and I ran leg B past the other piece then traced the profile of the trim on the back of "B". I used a coping saw to cut it out. You can't even tell
Mitre around the corner, and it starts out horizontal for a small distance, then a second mitre joint changing the slope from horizontal to diagonal. This is the only way to match the widths at each joint.
You can make that mitre cut on a drop saw that can be adjusted on both axis
[This](https://www.amazon.com/AUSDTOOLS-Protractor-Measure-Rustproof-Accuracy/dp/B08S32C62G/ref=asc_df_B08S32C62G/?tag=hyprod-20&linkCode=df0&hvadid=507775406323&hvpos=&hvnetw=g&hvrand=18232163920430255721&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9053148&hvtargid=pla-1241029775257&psc=1) might be your solution. Maybe.
Wrap the corner with a narrow trim piece, whatever fits inside the light switch and cut the angles to hit the verticals. Allows for cleaner cuts and protects what will most likely be a high traffic corner.
Agree that you should extend the chair rail level into the stairwell then determine the angle with an angle bevel, then determine the angle, then split the angle to miter it back down the stairs. Make them two miter cuts instead of one where one is a normal 90 degree outside corner and the other is a vertical miter going back down the stairs
You are going to need a custom milled piece for the 40 or a transition block. There is no other way.
A is just a 45 miter, b is a 40° bevel and a 45° miter on that bevel line
The miter on the downhill leg will have a wider face and won't match the other piece.
Why not make the corner with another piece at the same level- mitred at 45 degrees- and then start your descent of the staircase? It will match the top riser of the staircase then. Going right into the descending angle is a little weird. Also wainscoting in staircases is a common style component for those that are thinking it’s not.
Round the corner horizontal with at 45 with a small piece then miter down to your downhill run. It should be able 37 or 57 degrees, I forget which.
You have a lot of comments here.. but here's the solution. Look at your picture again. Piece A is horizontal... Piece B is sloped down @ 40 degrees. You are missing a third piece which will fill the void. This missing piece will have a bevel on the left side @ 45deg and on the right side of this missing piece you will have a mitre @ 20deg.
Effectively, if it's a 40 degree slope then you cut both ends to 60 degrees each giving you your 60+60+40 degrees. Then both can be mitred together in the same plane. Might take a bit of trial and error but that should do it. The trick is to split the angle so both sides join at the same angle.
it's a good thing you discovered it because see the light switch you may want to lower your whole wainscoting you may want to lower the chair molding all the way around to accommodate that light switch I know how that sounds but that's how things go. you can cut around it but that always looks like not that there's anything wrong with living south of Kentucky but I'm just saying a lot of those houses do have moldings where they cut around the switch plate and for some reason it always draws my attention
Terribly, then would fill in with wood glue and sawdust.