Mitering advice needed.....

Ok it's been at least 20 years since i had to do this last and frankly i have forgotten how to compensate for the differences so i need your advice.
I am putting up trim along the base of the staircase along a sheetrock wall with a 3.5" wide baseboard with a trim cap on top. (i'm using flat wood, what you see is scrap used to get my angles correct.)

It is a 40 degree angle where the two meet but by butting them up together you see the height difference? My vague recollection was somehow you split the difference and cut both at an angle and the joint is not a 90 degree straight up and down joint. how do i do this?

Continue the angled trim line down to where it meets the top of the bottom trim. Red line.
Your angle is the green line.



https://i.imgur.com/m04huv6.jpg

This was my basic reccollection like you illustrate, so if the right piece angle is 40 degrees, if i cut both pieces at corresponding 20 degree angles would that work? i'll try that and let you know.

The most useful tool in my shop for doing miters is the 12" disk sander...

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Originally Posted by myxpykalix

Ok it's been at least 20 years since i had to do this last and frankly i have forgotten how to compensate for the differences so i need your advice.
I am putting up trim along the base of the staircase along a sheetrock wall with a 3.5" wide baseboard with a trim cap on top. (i'm using flat wood, what you see is scrap used to get my angles correct.)

It is a 40 degree angle where the two meet but by butting them up together you see the height difference? My vague recollection was somehow you split the difference and cut both at an angle and the joint is not a 90 degree straight up and down joint. how do i do this?

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I'll either help or look like a fool for not explaining this well. ;)

First you need to figure out the angle. For discussions sake that looks like a 45* angle. So you need a 22.5*, or half, angle to properly mate your joint. Get that protractor out. Or a great shortcut, should you find yourself sans protractor, put a piece of wide tape or paper on the proposed angle. Mark the angle by creasing the paper or marking the tape. Then lay the paper or tape on your miter saw and read the angle off the bed. Once you know the angle divide by two and viola. Works for me when I am trimming boat interiors.

google "how to bisect an angle".
A protractor is your friend.
There are also charts available on line for how to set up your chop saw for compound angles.

"8Ball's" illustration confirmed my original contention (whoever said "a picture is worth a thousand words" was right!). I took my digital angle finder and found that the angle was 40 degrees, so i divided that in half, set the saw to 20 degrees, cut both ends to the corresponding left/right angle and it fit perfectly. This house was built in 1892 but every joint on the staircase was still a perfect angle. Thanks for all the advice

I did a lot of work (especially trim) on my mother-in-law's house that was built in 1810. I was amazed at how straight and level everything was. The beams in the walls were all oak and the house was built directly on a granite slab miles thick. The foundation was made of stacked slate with no mortar. The house was originally an inn.