Miter Angle Calculator for Unequal Board Widths

[Bernie Kopfer]

I am making some drawer front frames with unequal widths of trim molding. I know how to and will probably end up simply using the bevel gage method. But there surely is a online calculator somewhere that you simply enter the two widths and desired final angle and out comes the miter angle to set the saw to. Anyone know where to find this calculator? Thanks

[Jerry Miner]

I don't know of an on-line calculator, but if you're making square corners---and you have a scientific calculator---you can use the inv. tan function based on rise/run.

Let's assume you are using 1" trim on one side and 1 1/2" on the other. You then have a 1" "rise" and a 1 1/2" "run". Divide 1 by 1.5, you get .6666...

Take the inv. tan of that result and you get 34.7 degrees. That's your miter angle.

You can substitute any two values for the rise and run. Hope this helps.

Unequal miter 8-27-15.jpg

[Matt Zettl]

Thanks for that succinct solution, Jerry. Just simple high school trigonometry does indeed come in handy from time to time.

Matt

I don't know of an on-line calculator, but if you're making square corners---and you have a scientific calculator---you can use the inv. tan function based on rise/run.

Let's assume you are using 1" trim on one side and 1 1/2" on the other. You then have a 1" "rise" and a 1 1/2" "run". Divide 1 by 1.5, you get .6666...

Take the inv. tan of that result and you get 34.7 degrees. That's your miter angle.

You can substitute any two values for the rise and run. Hope this helps.

Unequal miter 8-27-15.jpg

[lowell holmes]

I would loft it on a scrap of plywood or board. This allows using dividers to mark the cut line on your stock. Chair makers use lofting a lot. I lay out the chair on a piece of plywood and use it for a pattern.

[Roy Harding]

I don't know of an on-line calculator, but if you're making square corners---and you have a scientific calculator---you can use the inv. tan function based on rise/run.

Let's assume you are using 1" trim on one side and 1 1/2" on the other. You then have a 1" "rise" and a 1 1/2" "run". Divide 1 by 1.5, you get .6666...

Take the inv. tan of that result and you get 34.7 degrees. That's your miter angle.

You can substitute any two values for the rise and run. Hope this helps.

Unequal miter 8-27-15.jpg

Perfect - except I get 33.7 as the solution.

Here's a solution you can put into an Excel spreadsheet

In cell A1 - put the dimension of the NARROW board
In cell B1 - put the dimension of the WIDE board
In cell C1 - put this formula (without the quotes)- "=DEGREES(ATAN(A1/B1))"

[Shawn Pixley]

I get 33.7 degrees as well. Triganometry is your friend though I use it 1-2 times per year on average.

The calculations get more complicated if the ultimate corner isn't 90 degrees. I'll have to think a bit to calculate those. Normally, I'd draw or loft it out.

[Bernie Kopfer]

Thanks for the input. I've always wanted to make use of my scientific calculator!! FWW has a cove angle calculator for table saws on its website that is easy and I presumed that someone would have put together a unequal board width miter calculator.

[johnny means]

Any online right angle calculator would do. This is one I use a lot.http://www.csgnetwork.com/righttricalc.html

[Tom Ewell]

Use my cadd to draw out the plan, all dimensions/angles come from there.
Now if I could just be as physically precise in the shop as the cadd is on paper I'd be in great shape, 'close enough' works pretty well though.

[Bernie Kopfer]

Any online right angle calculator would do. This is one I use a lot.http://www.csgnetwork.com/righttricalc.html[/

This is exactly what I was looking for! Thanks

[Peter Quinn]

I've found calculating the angle and finding it exactly on the chop box can be two different things. I prefer to lay it out manually as this creates a set up block I can use in conjunction with the saws laser to set the angle correctly. I cut a piece of plywood with a square corner give or take 8X10. I run the horizontal piece along the 10" length, laying it flush to the edge, trace its inner edge, then run the other piece similarly along the perpendicular edge. Where the two pieces meet forms one point, the corner is the other, I connect them and draw a line some distance out to form a long hypotenuse. To this I can set the chop boxes laser line very accurately, because my chop box doesn't have a big enough miter gauge to shop degrees, minutes and seconds, so accurately dividing an angle by 10ths by eye is not practical. This also eliminates any measuring error that may result in calculation error, as you are not rounding the widths of the two pieces to the closest line on your rule, but simply using actual numbers whose value by this method is irrelevant.

[Tom M King]

Just lay one board over the other one, and mark it. Try with scrap first, and then measure the angles.