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nsaint
04-08-2008, 04:12 PM
I am a woodworker using segmented cuts to make bowls. Assume the following;
N = Number of sides
S = Slope
MA = Mitre Angle

In a book I am using the formula to figure out various tool and angle settings is;
Mitre Angle = inverse tan (1 / [ cosS * tan (360 / 2N)])
Blade Angle = inverse tan (cosMA * tanS)

I am trying to put this into a spreadsheet so I can choose various parametrs such as sides and then display the BA and MA values.

The book tells me that a Slope of 15 with 6 sides should result in an MA equal to 60.85 degrees and a BA equal to 7.44 degrees.

How do I get this into excell and do what I am trying to do?

Any help would be greatly appreciated.

mikerickson
04-08-2008, 05:08 PM
If you have the number of sides in A1 and the slope in A2, then

=ATAN(1/(COS(RADIANS(A2))*TAN(PI()/A1))) will return the mitre angle.

If you put that formula in B3 then

The difficulty is that these returns are in radians, so the formulas need to be changed to

and

mdmackillop
04-08-2008, 05:16 PM
As in

nsaint
04-08-2008, 09:24 PM
This was very helpful, but I seemed to run into a snag. If the Slope is set to 90 the blade angle returns 45. In the case where the number of sides = 6, slope = 90, the mitre angle should equal 90 and the blade angle should equal 30, but it doesn't.

The formula appears to work in all other cases except for a slope of 90.

Thoughts?

Also, thanks for the help with this, it seems we are very close and your guidance has been helpful.

mdmackillop
04-09-2008, 12:39 AM
Rounding errors
try 89.99
A bit by bit spreadsheet to show what changes.

nsaint
04-09-2008, 05:04 AM
Thanks mdmacillop and mikerickson for your help. Yes, I had already used 89.999 to get the desired results, just annoying that I have to do that.

mdmackillop
04-09-2008, 05:21 AM
This version contains a little VBA code to change C6 to 89.99 if you enter 90.

nsaint
04-09-2008, 06:10 AM
Thanks again for the help. I found a function called CFEET I used to convert my values to feet and inches. I have attached this here just to show what your help has done for me - thanks again.

This forum has been a great help!!

mdmackillop
04-09-2008, 06:14 AM
Nice to see the practical implication (and the bowl!)

mdmackillop
04-09-2008, 08:53 AM
Because of the code you may get macro security warnings each time you open the workbook. See here (http://vbaexpress.com/forum/showthread.php?t=9545) for how to avoid these.