How can I calculate the cornice mitre and bevel angle?

[1SJC]

We're currently coming to the end of our DIY kitchen install - we're nearly complete but currently struggling with our wall unit cornice.

We cannot get the right angle on our chop saw to give us perfect 90° joints.

Online seems to suggest that we need to find the spring angle, which according to our digital angle measure (if we've measured correctly) is 20.5 degrees. However, when we cut with a mitre of 19.3 and bevel of 41.48, the two corners don’t join up.

What’s the easiest way to work it all out?

 

[RandomGrinch]

Personally, I would keep it simple for my poor brain!
Cut a wedge to support it in the chop saw, in the orientation it will be installed, then cut at 45°!

 

[1SJC]

Personally, I would keep it simple for my poor brain!
Cut a wedge to support it in the chop saw, in the orientation it will be installed, then cut at 45°!

Haha, that's so simple... There's me trying to overcomplicate things!

Thank you for your suggestion - I will give that a go in the morning.

 

[big-all]

cut 2 pair wedges rather than one you then have extra plus 2 sets off folding wedges all be it a bit too steep for fine adjustment

 

[^woody^]

Screw it down at the angle it will be fixed to a scrap piece of wood.

 

[lostinthelight]

I find making a mitre box representing how far the cove/cornice sticks out vertical and horizontal so your cutting at the correct angle to how it will be fixed

 

[chirpychippy]

Screw it down at the angle it will be fixed to a scrap piece of wood.

That is a Brilliant idea

 

[Old Salt]

Corners may not be 90 degrees

 

[lostinthelight]

Corners may not be 90 degrees

That affects the angle of cut not the orientation of the piece being cut on kitchen cabinets.
If one wanted to use a chopsaw to allow for +or- 90⁰ out of square then just one side of the box in my pic or any of the other suitable methods mentioned to hold the cornice in the right orientation in the saw and the cutting angle set accordingly