Replies

1. 
   SgianDubh | Jun 06, 2002 06:25am | #1

   The dihedral angle is 96.08°, therefore divide by half to find the bevel (blade tilt) = 48.04° and set the blade to the complimentary angle of 42° which is near enough.

   The mitre setting is found by establishing the angle that the edges of the sloping planes of a polyhedra describes to the base line as viewed from a point perpendicular to the face, which I call the true angle. Your structure is (in effect) for my method of calculating an 'upside down pyramid', better described as a hopper so the base line I'm using is the top edge of your seat back, and your 19° lean back becomes my 71° lean in of a pyramid face. The true angle is 71.97°, so set the mitre gauge to 18°.

   To recap, the saw blade tilt is 42°, and the mitre setting is 18°. I'm treating the seat back that slopes at your stated 19°as a panel that I would cut using these angles on a sliding table saw. If you plan to use a series of horizontal bars that meet as a mitre in the corner some slight rejigging in your thinking in manipulating  the figures I provided will be needed to suit, i.e., each of your horizontal slats is effectively a broken up pyramid side.

   Joe Fusco provided a very useful link here, at  http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=20779.1  in answer to a topic asking about the similar cuts needed for crown mouldings. I think the link earlier is good. Click on it anyway.

   Here's a graphic illustrating the way I visualised your question that might help. Slainte, RJ.

                                     View Image">

   RJFurniture

   
   

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   Edited 6/5/2002 11:42:32 PM ET by Sgian Dubh

1. 
   albee104 | Jun 06, 2002 01:23pm | #2

   Thanks for the help. I,ll give it a whirl later today.

1. 
   SgianDubh | Jun 06, 2002 04:35pm | #3

   My pleasure. I took a closer look at Joe's chart and calculator just a few minutes ago. If you punch in your figures, i.e., 90° corner angle, and a 19° crown 'spring' angle you get the same result to 3 decimal places, so it's nice to get confirmation for my calculations. I usually triple check my efforts because it's all too easy to make a small error leading to a major screw up, ha, ha. I didn't even double check my calculations last night so I came back in to do so. Joe's chart saved me some time. Slainte, RJ.  RJFurniture

1. 
   albee104 | Jun 11, 2002 01:54am | #5

   Thanks again for your help in solving my miter problem. The numbers you gave me were on the money. I kind of left it vague, as to what it was that I was actually doing. The backs of the benches were made from 2X6's run horizontaly, with the numbers you gave me, the miters fit together perfectly. When I have a little more time, I will use the information you gave to learn how to figure this problem out for myself.  Again, many thanks.                                                                                                                                  

2. 
   Joe_Fusco | Jun 06, 2002 11:21pm | #4

   Albee,

   I'm having a hard time conceptualizing just what it is you are doing, but in any case these two links might be of some help if all else fails.

   1. Miters & Bevels. . .
   2. Dihedrals. . .

   View Image