Replies

1. 
   Senomozi | Nov 16, 2007 08:50pm | #1

   Hello exmgrnc,

   The fact you have a taper does not have any effect on the angle of the miter.  If the bird house has 4 walls then you need a 45 degree miter along both vertical edges of each wall.  If the bird house is hexagonal then the miters need to be  30 degrees.  If the bird house is octagonal then the miters are 22.5 degrees.

   The taper only affects the top and bottom edges of the walls.  You need to miter these edges to match the angle of the taper.

   Regards,

   Senomozi

1. 
   saschafer | Nov 16, 2007 10:11pm | #3

   "The fact you have a taper does not have any effect on the angle of the miter."

   Actually, it does. (Ask anyone who has tried to install crown molding.) The projected angle (the apparent angle when you look straight down on the assembly) remains the same, 45° or whatever, but the angle at which you have to cut the miter, assuming the boards are lying flat on your saw's table, changes. You didn't notice a problem with your flower pot because your tilt angle was small (the discrepancy increases rapidly with increasing tilt angle), and the number of sides was large (so that the error was spread out over more individual joints). Trust me, if you tried to make a four-sided box where the sides flared out at 45°, cutting the miters at 45° wouldn't have come even close.

   -Steve

    

1. 
   Senomozi | Nov 16, 2007 11:28pm | #5

   Hello Steve,

   What you say about crown moldings is correct but only because you use the back of the molding as the registration point, or reference if you wish.  If instead you install the molding "in-position" in the miter box, you only need to perform 45 degree miters to get perfect 90 degree corners.  Please refer to FWW#178 for more details on this method of work. 

   The approach I suggested is similar in concept in that after the taper has been done, you use the tapered edge as the reference face to cut the 45 degree miter.

   Sounds like its time to make a small prototype!

   Regards,

   Senomozi

1. 
   saschafer | Nov 17, 2007 12:01am | #6

   "The approach I suggested is similar in concept in that after the taper has been done, you use the tapered edge as the reference face to cut the 45 degree miter."

   First of all, that's not equivalent to the technique discussed in FWW #178, which is to cut crown molding "in place," and which is relatively easy to do because most crown molding isn't very tall. Second, as I said before, it only worked for you because your taper angle was very small--the discrepancy in the case of a 12-sided flower pot whose tilt angle is 2.5° is miniscule, a small fraction of a degree. But try to replicate the shape of the Great Pyramid of Giza that way, and it simply won't work.

   -Steve

    

2. 
   oldusty | Nov 17, 2007 12:34am | #7

     Hi Senomozi ,

                    There is more than one way to do this but ,,

              In making tapered 4 sided columns of various sizes , first I make the taper jigs to make the rt and a modification for left often times is needed too . Then  cut out the blanks , 45 off the tapered edges and while the saw is set for 45 lower the blade and run the parts on edge to cut the splines .You are running the knife edge down . comes out good the first time or your money back .

                may the wood lords be with you                  dusty

2. 
   Senomozi | Nov 16, 2007 09:15pm | #2

   Hello again exmgrnc,

   I attached a picture to show a similar situation I faced when I built a flower pot out of cedar.  I cut 12 pieces like the ones the picture shows using a tapering jig in the table saw.  Once they were all cut I simply mitered all the long edges at 15 degrees on the table saw.  Getting the tapering jig to exactly 2.5 degrees was not important for me because I did not care if the pot flared a little more or less than the plan called for.  As long as all the pieces are tapered exactly the same you will get a good fit in the end.

   Regards,

   Senomozi

       

    

   
3. 
   saschafer | Nov 16, 2007 11:13pm | #4

   You can find a decent discussion along with formulas here. The terminology used is crown molding-centric, but it should be pretty straightforward to see how to apply it to the more general case.

   You can also download an Excel calculator that does the work for you here.

   I have not verified that these sources are error-free!

   -Steve

    

4. 
   QCInspector | Nov 18, 2007 07:26am | #8

   Something like this.

   http://www.josephfusco.org/Calculators/Advanced_Box_Cutter.html

5. 
   saschafer | Nov 20, 2007 07:16am | #9

   I knew that there was an article in an old FWW that discussed a geometric construction method (using compass, straightedge, etc., just like in high school geometry class) for figuring the angles for compound joints: FWW #76, p. 65. Unfortunately, a PDF of that article does not appear to be available.

   Be prepared for some heavy-duty geometry if you decide to look at the article.

   -Steve