What's the best way to finish the seat corner this bench?

[kidwellj]

I'm finishing a bench for our kitchen, which is intended to add a bit of seating + storage and hide two big radiators. Now that I've finished the carcass and am starting to put in the ply sheets I'm trying to find a good way to adapt the original design away from a straight back to a slightly angled back. The main problem this presents is that I've got to do some angled cutting to ensure the sheets can be fixed in place securely. This isn't too hard for the edges that sit against the frame, as my track saw can adapt to an angle, and I'm proficient enough to use a carpenter's bevel to ensure the angles work. But what the heck should I do with the corner in-between the two bench pieces where the two backs meet?

 

[gcusick]

You’ve got 2 choices: do some trigonometry to calculate the dimensions and angles of the pyramid that defines the intersection of the two backs; or fit one right into the corner and scribe the other one to it.

 

[Jacob]

...... But what the heck should I do with the corner in-between the two bench pieces where the two backs meet?

Find another longer piece and cut an angle to meet the other piece on the long side?

 

[kidwellj]

You’ve got 2 choices: do some trigonometry to calculate the dimensions and angles of the pyramid that defines the intersection of the two backs; or fit one right into the corner and scribe the other one to it.

Yeah, so that's sort of what I'd figured. I can possibly resurrect my knowledge of trigonometry, but what's befuddling me is the necessity of calculating angles on the vertical edges of the three intersecting sheets/pieces. Was hoping there'd be some carpenter's shortcut that simplifies this sort of joinery...

 

[Jacob]

Yeah, so that's sort of what I'd figured. I can possibly resurrect my knowledge of trigonometry, but what's befuddling me is the necessity of calculating angles on the vertical edges of the three intersecting sheets/pieces. Was hoping there'd be some carpenter's shortcut that simplifies this sort of joinery...

It's a good question and there is a carpenter's shortcut that simplifies this sort of joinery!
You "scribe"
Your short back piece is too short and you now need another longer piece to replace it.
You only need to cut one angle on this one piece.
This means offering up the long enough piece up to the other piece and draw a pencil line to match the angle, as best you can.
Cut it and offer up again. If it isn't a good fit draw another pencil line and cut again.
Fine adjust with a block plane if necessary.
When it fits then cut the easier square end to length.

 

[Inspector]

If you don't want to scribe (easy) you can use one of the online calculators. Fill in the boxes and they figure out the angles for you. Magic Trig. Search Compound Angle Cut Calculator if you don't like any of these.

https://jansson.us/jcompound.html
http://www.pdxtex.com/canoe/compound.htm
https://www.blocklayer.com/compoundmitereng.aspx
https://www.wwgofga.com/compound-miter-calculator/
Pete

 

[ajs]

There's doubtless some easy trick with a speed square that roofers use all the time. No, I don't know what it is.

Not too difficult to calculate a mitre mathematically though assuming this is at 90°.

First of all decide whether you are basing your measurements on the front or back faces of the panels and keep this clear in your mind or you  will confuse yourself.

The "key" to the problem is calculating the length of the mitre joint. Fortunately Pythagoras works in three or more dimensions just as easily as it does in two, just add on the extra terms. So assuming a vertical height  h and a (matching) horizontal distance  d between the top and bottom of each panel the length of the mitre  m is simply

m = sqrt(h² + 2d²)

that gives you the length of the side on the flat. You can then use simple 2D trig to calculate the cutting angle. That just leaves the angle of bevel for the cut, where simplifications really pay off - if it's a 90° corner and both sides lean back at the same angle the bevel will always be 45°.

 

[Jacob]

There's doubtless some easy trick with a speed square that roofers use all the time. No, I don't know what it is.

Not too difficult to calculate a mitre mathematically though assuming this is at 90°.

First of all decide whether you are basing your measurements on the front or back faces of the panels and keep this clear in your mind or you  will confuse yourself.

The "key" to the problem is calculating the length of the mitre joint. Fortunately Pythagoras works in three or more dimensions just as easily as it does in two, just add on the extra terms. So assuming a vertical height  h and a (matching) horizontal distance  d between the top and bottom of each panel the length of the mitre  m is simply

m = sqrt(h² + 2d²)

that gives you the length of the side on the flat. You can then use simple 2D trig to calculate the cutting angle. That just leaves the angle of bevel for the cut, where simplifications really pay off - if it's a 90° corner and both sides lean back at the same angle the bevel will always be 45°.

Nope. Any half skilled id iot joiner learns early on how to scribe a simple joint like this one.
45º wouldn't come into it at any point.
It's the hands-on method you'd use if you were totally innumerate/illiterate, never heard of Pythagoras, had no kit, no roofing square, not even a sliding bevel or a protractor. Just a pencil, or if not, just a nail to scratch a line. And a saw of course, and perhaps a block plane for fine adjustments.

 

[thetyreman]

I'd scribe in a new piece on the short side...

obviously it would need to be a new longer piece to that when you cut the waste away it's overhanging the edge, then you can mark the edge and cut to the exact line, should be virtually no gaps if done correctly, all you need is a compass/pencil and and hardpoint saw.

 

[Jacob]

I'd scribe in a new piece on the short side...

obviously it would need to be a new longer piece to that when you cut the waste away it's overhanging the edge, then you can mark the edge and cut to the exact line, should be virtually no gaps if done correctly, all you need is a compass/pencil and and hardpoint saw.

Compasses, or just hand pencil held can do it, or pencil plus bit of scrap cut to length as a spacer.

 

[Sandyn]

What about making a corner post. Draw lines where the backs meet it, then profile to a round taper? I'm trying to visualise if that would work. I have a habit of trying to create impossible solutions.


I would not box in radiators You need really good air flow to maintain their output. They will turn into fluff traps especially if you have pets and full of HUGE spiders, but really cosy to sit on in winter.

 

[hlvd]

Run one into the wall and scribe the other. A mitre will be weak and prone to open up.

 

[hlvd]

There's doubtless some easy trick with a speed square that roofers use all the time. No, I don't know what it is.

Not too difficult to calculate a mitre mathematically though assuming this is at 90°.

First of all decide whether you are basing your measurements on the front or back faces of the panels and keep this clear in your mind or you  will confuse yourself.

The "key" to the problem is calculating the length of the mitre joint. Fortunately Pythagoras works in three or more dimensions just as easily as it does in two, just add on the extra terms. So assuming a vertical height  h and a (matching) horizontal distance  d between the top and bottom of each panel the length of the mitre  m is simply

m = sqrt(h² + 2d²)

that gives you the length of the side on the flat. You can then use simple 2D trig to calculate the cutting angle. That just leaves the angle of bevel for the cut, where simplifications really pay off - if it's a 90° corner and both sides lean back at the same angle the bevel will always be 45°.

This method only applies to a perfect world situation, everything squared up, perfectly level, pencil marks in the correct place, saw set to the exact angle and user’s ability to follow those lines.

In the real world you’d run one into the wall square on and scribe the other with a block of wood and pencil, followed by a fettling with a plane to get the joint nice and tight.

 

[Ollie78]

Just take one past the corner and scribe the other to it. Once scribed run a batten up the longer bit for supporting the scribed bit.
I built a very similar "banquette" as they are apparently called. A bit complicated as it needed removable panels for access to stuff. ( buttonfix to the rescue).

Not sure about your upholstery plan but I had issues with the one I made.
I Took the parts to the upholsterer and he did a separate square cushion in the corner, client was not happy with that so if all had to go back and be re done.
Worth thinking about the cushions.

Ollie

 

[kidwellj]

What about making a corner post. Draw lines where the backs meet it, then profile to a round taper? I'm trying to visualise if that would work. I have a habit of trying to create impossible solutions.


I would not box in radiators You need really good air flow to maintain their output. They will turn into fluff traps especially if you have pets and full of HUGE spiders, but really cosy to sit on in winter.

Given that heat from rads only really moves upwards (as opposed to outwards from front) my plan for radiators is to put covering on the top that allows for maximum airflow. I was looking into stamped aluminum sheets with a pattern that is 60% open, or possibly wicker with an even high rate of surface open. The rads are *very* overspecified for the room, even though it's fed by an ASHP.

 

[kidwellj]

What about making a corner post. Draw lines where the backs meet it, then profile to a round taper? I'm trying to visualise if that would work. I have a habit of trying to create impossible solutions.


I would not box in radiators You need really good air flow to maintain their output. They will turn into fluff traps especially if you have pets and full of HUGE spiders, but really cosy to sit on in winter.

I like the *sound* of integrating some visual structure with a corner post - any images out there on the internet that show what you mean by this? Not quite able to wrap my head around the details on this...

 

[kidwellj]

Just take one past the corner and scribe the other to it. Once scribed run a batten up the longer bit for supporting the scribed bit.
I built a very similar "banquette" as they are apparently called. A bit complicated as it needed removable panels for access to stuff. ( buttonfix to the rescue).

Not sure about your upholstery plan but I had issues with the one I made.
I Took the parts to the upholsterer and he did a separate square cushion in the corner, client was not happy with that so if all had to go back and be re done.
Worth thinking about the cushions.

Ollie

Yep, I'm just going to have simple cushions for the bottom, plywood will serve as the back. @Ollie78 - got a pic of your banquette? Would love to see this in action! I had not run across buttonfix before, was thinking about putting on side panels via magnetic clasps and hidden push hinges for access and maintenance, especially for hoovering out those huge spiders @Sandyn is thinking of.

 

[kidwellj]

Just take one past the corner and scribe the other to it. Once scribed run a batten up the longer bit for supporting the scribed bit.
I built a very similar "banquette" as they are apparently called. A bit complicated as it needed removable panels for access to stuff. ( buttonfix to the rescue).

Not sure about your upholstery plan but I had issues with the one I made.
I Took the parts to the upholsterer and he did a separate square cushion in the corner, client was not happy with that so if all had to go back and be re done.
Worth thinking about the cushions.

Ollie

I hadn't though of structural integrity on the corner, but @hlvd raises a good point. I suppose I could run battens using plugs off the exposed brick wall behind and then fix to this. Will have to have a think about how to integrate stability on that corner overall thought. I get @Ollie78's point here - how did you run the batten specifically for your work?

 

[rogxwhit]

And I always thought that it was normal to work out what I was going to do before I started doing it ... ;-)

 

[Sandyn]

I like the *sound* of integrating some visual structure with a corner post - any images out there on the internet that show what you mean by this? Not quite able to wrap my head around the details on this...

My poor explanation. If I could do a image dump from my brain, it would explain better. Util that is available, I'll do a sketch.

You could put some feature on top at the corner.
I think that can be made. You could put a similar feature on each end.