# Finding what angle to cut.



## James Wiencek (Jun 7, 2019)

howdy all, been building stuff for myself around the house most of what i worked with just involved 90 degree angles, but recently i wanted to make myself a coffin shaped bookcase. And i have been second guessing myself to much mostly cause i never worked with these kind of angles and i don't wanna be wasting wood.

Now if i'm not wrong i would just divide each degree of the angles by 2 and those would be the angles i need to cut at. for example i would divided the 80 degree angle by 2 making a 40 degree cut for that board, then divide the 76 degree angle by 2 making a 38 degree cut, and then join those two boards? thanks for an help or correcting in this!

here's the blueprint i am going to be working with


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## GeorgeC (Jul 30, 2008)

I do not understand where you are getting the numbers that you are labeling the angles. They all look like they should be 90 degrees to me.


George


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## James Wiencek (Jun 7, 2019)

Where F and E intersect on the blueprint , there's a 80 degree angle and a 76 degree angle


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## woodnthings (Jan 24, 2009)

*It's a plan view ... of the top!*



GeorgeC said:


> I do not understand where you are getting the numbers that you are labeling the angles. They all look like they should be 90 degrees to me.
> George



It's "coffin" shaped in plan view, so none of the angles are 90 degrees.
:|


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## woodnthings (Jan 24, 2009)

*You can't saw at a 80 degree angle*



James Wiencek said:


> Where F and E intersect on the blueprint , there's a 80 degree angle and a 76 degree angle



There's no index for 80 degrees on any saw, so the saw setting will be 90 degrees minus 80 degrees, or 10 degrees for bevels. The same applies to 76 degrees. 90 minus 76 is 14 degrees. You will have a slight offset in width at the intersection because they are not equal angles.


I suppose you could take the entire angle and bisect it to eliminate that issue. So, 156 divided by 2 equals 78 degrees. 90 degrees minus 78 equals 12 degrees. :vs_cool:


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## Terry Q (Jul 28, 2016)

I respect all the work you put into figuring out the exact angles.

I would have laid two boards at the angle that I figured looked best, measure the angle with my bevel gauge and divide the result by two and not worry if the seam was parallel with the ends.
Both boards having the same angle would make it easier join with a spline or other means if desired. You would only require one jig to hold the boards at the desired angle as you machine it.

Owning something like this can be extremely useful once you deviate from 90 degree angles.

https://www.lowes.com/pd/General-Tools-Instruments-Digital-Analog-T-Bevel/50175571


In woodworking there is always more then one way to accomplish something.


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## gmercer_48083 (Apr 9, 2016)

James Wiencek said:


> howdy all, been building stuff for myself around the house most of what i worked with just involved 90 degree angles, but recently i wanted to make myself a coffin shaped bookcase. And i have been second guessing myself to much mostly cause i never worked with these kind of angles and i don't wanna be wasting wood.
> 
> Now if i'm not wrong i would just divide each degree of the angles by 2 and those would be the angles i need to cut at. for example i would divided the 80 degree angle by 2 making a 40 degree cut for that board, then divide the 76 degree angle by 2 making a 38 degree cut, and then join those two boards? thanks for an help or correcting in this!
> 
> here's the blueprint i am going to be working with


Yes Your thinking is right. Use the complimentary angles on your table saw by subtracting The angle you want from 90 degrees when you tilt the blade.


Example: 90* - 80* = 10* tilt angle.
Example: 90* - 53* = 37* tilt angle.
Example: 90* - 49* = 41* tilt angle.
Example: 90* - 76* = 14* tilt angle.


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## DrRobert (Apr 27, 2015)

Normally you divide the total angle by 2, but not in your example. A 40 and a 38° cut will result in a total angle of 78°.


The same with the other two joints: you have one 98° and one 106°.


The total angle is 156° & you have already specified 80 and 76 as the complimentary angles. Common sense also tells us looking at it, a 40° angle would be much, much steeper than the pic shows.



I would point out that unequal angles will result in different miter widths so either the inside or outside surfaces will not line up perfectly. It will probably be a small discrepancy, 80 vs 76, but just something to think about and do some test pieces first.


Hope I'm making myself clear.


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## B Coll (Nov 2, 2019)

*Miter*

The angle where E and F intersect should be bifurcated equally, which would be 78/78 degrees. The miter cut would be 12 degrees (90-78=12).


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## FrankC (Aug 24, 2012)

B Coll said:


> The angle where E and F intersect should be bifurcated equally, which would be 78/78 degrees. The miter cut would be 12 degrees (90-78=12).


This is an old post so hopefully he has figured that out by now. :smile2:


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