Trig formula for splayed box

[user 43606]

Hello can you help me out, I’m looking for a trig formula, it’s for a Compound angle with a butt joint, for a box with sides splaying out at 50 degrees, not the saw set angle, the angle for the edge bevel when marking out on sides with square edges.

 

[Yojevol]

Use an online calculator such as
Compound Miter Saw Calculator

 

[user 43606]

not the saw set angle, the angle for the edge bevel when marking out on sides with square edges, it’s all part of my interest in calculating angles

 

[Spectric]

Think back to your school days, old Harry and his old aunt = Sin = opp/hyp Cos = adjacent/hyp Tan = opp/ adjacent

The other way is to draw the problem in a CAD program.

 

[Yojevol]

A sketch would be helpful

 

[user 43606]

not the saw set angle, the angle for the edge bevel when marking out on sides with square edges, it’s all part of my interest in calculating angle

Think back to your school days, old Harry and his old aunt = Sin = opp/hyp Cos = adjacent/hyp Tan = opp/ adjacent

The other way is to draw the problem in a CAD program.

Yes I use trig a fair bit, I’m more interested in the math, this is more of an advanced short cut formula and it could also be applied to something like a roof Purlin with a compound angle cut and with a splayed Butt joint, not mitered!

 

[galleywood]

As previously stated, a sketch would be helpful.
What is it you are after, other than trig equations that you already use/know?

 

[user 43606]

I’m after the trig formula for the top edge butt joint angle when marking out on square edge material and I know that it’s not for everyone but some guys know this stuff

 

[galleywood]

Which angle is the "top edge butt joint angle".
Are the angles of 60, 63.4 and 26.6 given angles.
Such a limited view of the item does not help me much.

Is anyone else clearer about the matter?

 

[user 43606]

Which angle is the "top edge butt joint angle".
Are the angles of 60, 63.4 and 26.6 given angles.
Such a limited view of the item does not help me much.

Is anyone else clearer about the matter?

I’m after the trig formula for the top edge butt joint angle when marking out on square edge material and I know that it’s not for everyone but some guys know this stuff

I’m after the trig formula for the top edge butt joint angle when marking out on square edge material and I know that it’s not for everyone but some guys know this stuff

Or something like this but I'm after the trig formula for the top edge butt joint angle when marking out on square edge material and I know that it's not for everyone but some guys know this stuff

 

[--Tom--]

To try and get my head round it, based on the photo:

So you want to join 4 pieces of wood, pre cut as triangles with internal angles of 90degree 50degree and 40 degree.

The corners will then be butt joined with 2 of the lengths having compound mitres - similar to if you were coping the ends of the piece for an internal corner on moulding?

The resultant box will then have 4 sides, vertical outside edges, and sloped internal edges?

Hard to help until we know the question

 

[Yojevol]

I think I can see what you are getting at but not 100% certain. It is something that can be worked out using basic trig equations. As they say on Dragons Den, I shall not be investing any more time on this, I'm out.
The question that remains in my mind is WHY. Why a butt joint and not a mitre?
Brian

 

[user 43606]

To try and get my head round it, based on the photo:

So you want to join 4 pieces of wood, pre cut as triangles with internal angles of 90degree 50degree and 40 degree.

The corners will then be butt joined with 2 of the lengths having compound mitres - similar to if you were coping the ends of the piece for an internal corner on moulding?

The resultant box will then have 4 sides, vertical outside edges, and sloped internal edges?

Hard to help until we know the question

To try and get my head round it, based on the photo:

So you want to join 4 pieces of wood, pre cut as triangles with internal angles of 90degree 50degree and 40 degree.

The corners will then be butt joined with 2 of the lengths having compound mitres - similar to if you were coping the ends of the piece for an internal corner on moulding?

The resultant box will then have 4 sides, vertical outside edges, and sloped internal edges?

Hard to help until we know the question

It’s basically a simple splayed box and I'm after the trig formula for the top edge butt joint angle when marking out on square edge material. The splay angle won’t matter so much as the trig formula will be easily applied to splayed boxes with various splayed angles

 

[TheUnicorn]

I think if you rely too heavily on maths in practical applications you have two problems firstly there is always a good chance you have forgotten to factor in an element, so you'll cut your piece and the realise it doesn't fit, secondly any minor mismeasurement leads to a compound error and you can be way off very easily. I'd always prefer to offer up, mark, cut (possibly slightly oversize) then finesse with chisel and sandpaper

 

[Spectric]

Rather than try and solve using trig why not make a small mock up using odd pieces of wood and work backwards, I have had situations where I was convinced I had calculated everything bang on but I was not when it came to the actual workpieces. You can even use cardboard as a template to get you in the right ballpark but sometimes just making an initial test piece is the easiest so when that is right you just replicate it and save cutting and wasting the actual timber. Also don't overlook the fact wood is not stable like steel or some manmade boards so as it changes dimensionaly this will throw out your perfectly calculated joint angles.

 

[TheUnicorn]

Rather than try and solve using trig why not make a small mock up using odd pieces of wood and work backwards, I have had situations where I was convinced I had calculated everything bang on but I was not when it came to the actual workpieces. You can even use cardboard as a template to get you in the right ballpark but sometimes just making an initial test piece is the easiest so when that is right you just replicate it and save cutting and wasting the actual timber.

the trouble with a mock up is transfering measurements still allows a lot of room for compound error. It certainly helps you think in 3d, but I would still expect error and so overcut and finesse

 

[user 43606]

Rather than try and solve using trig why not make a small mock up using odd pieces of wood and work backwards, I have had situations where I was convinced I had calculated everything bang on but I was not when it came to the actual workpieces. You can even use cardboard as a template to get you in the right ballpark but sometimes just making an initial test piece is the easiest so when that is right you just replicate it and save cutting and wasting the actual timber. Also don't overlook the fact wood is not stable like steel or some manmade boards so as it changes dimensionaly this will throw out your perfectly calculated joint angles.

Yes that’s all good stuff and I’ve done that for many years and the maths is all part of the learning and it also relates to roof geometry and advanced roof carpentry

 

[user 43606]

the trouble with a mock up is transfering measurements still allows a lot of room for compound error. It certainly helps you think in 3d, but I would still expect error and so overcut and finesse

Yes that's all good stuff and l've done that for many years and the maths is all part of the learning and it also relates to roof geometry and advanced roof carpentry

 

[galleywood]

Woodchippy777

You keep repeating that you want the "the top edge butt joint angle" but you fail to identify which angle this is on your sketches.
If you really do want help with this, then I think that you should be willing to identify the angle when requested to.

 

[Spectric]

Or you could just buy one of these

https://www.essential-carpenter-tools.co.uk/store/p/ultimate-roofing-square-6975m
and then this series of videos shows many aspects of roof construction

https://www.essential-carpenter-tools.co.uk/videos