Replies

1. 
   jackplane | May 05, 2005 11:17pm | #1

   With these types of compound angles, I prefer to use math equations involving logarithms(sine, cosine etc.)

     I don't have the reference book at hand(Pocket Ref, Sequoia Publ.), but a good math book with trig tables will suffice. Just plug in the values.

    

2. 
   MarkRD | May 05, 2005 11:36pm | #2

   I'm confused with your dimensions. Can you include a pic. I'll gladly do the math but I need to see the shape.

   Thanks,
   Mark

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

1. 
   tas | May 06, 2005 04:05am | #3

   Mark,

   I do not have a camera so pics are not an option. The pieces are 4 1/2" across on the top and 9" across on the bottom. They are 51/2" high and 7/8 Thick. I hope that might help.

   Thanks For your efforts!

   Tom

1. 
   MarkRD | May 06, 2005 05:20am | #5

   Tas, that was what I needed. The pictures below should help.

   View Image

   The end view is the end of one of the roof tiles. Since there are 6 roof pieces, there are 12 edges. 360 degrees divided by 12 = 30 degrees.

   View Image

   Hope that helps,

   Mark

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

1. 
   MarkRD | May 06, 2005 05:39am | #6

   If I were doing this on my power miterbox (It cuts 6" deep) tilts right up to 45*, pivots left 60* and right 45*.I'm not standing at my saw as I think this through so your mileage may vary. :-)I'd put the top of the tile against the fence. Tip the saw 30* to the right and pivot 23* to the right and cut one side. Flip the board around and put the bottom against the fence, then pivot the saw 23* to the left and cut the other side.This hurts :-)Mark

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

2. 
   tas | May 06, 2005 05:36pm | #7

   Mark,

   Thank you for your Help! I plan on finishing this this weekend I will let you know how this turns out.

   TAS

1. 
   AlanWS | May 06, 2005 07:38pm | #9

   The answers you've gotten are not quite right.Mark's answer is helpful, but it's incomplete. The angle of the piece (what I might call the miter gauge angle for a tablesaw cut) is correct, but not the bevel angle (what I'll call the blade tilt angle.) The bevel at the edges is 30 degrees, but only if you are looking at it from the top -- that is not the blade tilt angle. To recognize why, imagine that you were making a flat roof of 0 pitch. Then the 6 pieces could each be cut with a 0 bevel (square) edge. If you imagine a roof with a 90 degree pitch (essentially a hexagonal column without any taper that won't keep off the rain), then the bevel on each side _would_ be 30 degrees. For any reasonable roof pitch between 0 and 90, you will have a bevel between 0 and 30. So the confusing thing about these compound miters is how much we must tilt the blade.If you know the roof pitch, you could place the board at that slant against a mitersaw fence, turn the saw to 30 degrees from the fence, but square to the table, and cut. If you can't cut all the way through, you could use the partially cut piece to set up mitersaw or tablesaw for the rest of the cuts in a more convenient manner. Actually, this method will work no matter what the pitch, so you could just do it and take the pitch you get.You can take off points for not showing my work, but given the 23 degree angle Mark determined for roof parts (the miter gauge setting), and the 30 degree angle between pieces seen from the top, trig gives me a bevel angle (blade tilt) of 21.4 degrees.

2. 
   MarkRD | May 06, 2005 07:58pm | #10

   Alan, you are right I did take the "top down" view to calculate the 30*.What slope angle did you assume for the tiles when you did your calculation? 45* MarkMeasure it with a micrometer, mark it with chalk, cut it with an ax.

   Edited 5/6/2005 3:28 pm ET by Mark

3. 
   lwj2 | May 06, 2005 04:44am | #4

   TAS, if you've got six pieces sounds like you're making a hexagonal piece. Angles should be 60°, so half of that is 30° per side.

   Not certain what the compound angle should be, depends on the run/rise factor.

   As was mentioned, a PocketRef has just about any formula you could need -- mine ran about nine bucks (US) several years ago. One of the handiest books I've acquired in fifty-odd years of book buying.

   Leon Jester

   
   

   ---

   Edited 5/5/2005 9:50 pm ET by Leon Jester

1. 
   tas | May 06, 2005 05:40pm | #8

   Leon, Thank you for the tip on the Pocket Ref, I'll Pick a copy up next time I see one.

    

   Thanks!

   TAS

4. 
   bladeburner | May 06, 2005 08:44pm | #11

   You may find this helpful, as well.

   http://www.csgnetwork.com/sawmitercalc.html

   Joe

5. 
   Harryd | May 07, 2005 07:04am | #12

   TAS,

   I have the math formulae, but this link is much faster:

   http://www.woodworkersguildofga.org/ShopHelpers/MiterCalculator.htm

   I  derrived the formulae I once used.   I could cut twenty staves for a 30 deg slope from hard maple that fit without error. I made a bunch of staved bowls and a few cypress planters, all on the table saw. That was some years ago.

   The angles are almost impossible to measure with a protractor.  A tenth of a degree is a WAG. An accurate way to get the angles is to use a machinist's guage block or a reasonable sub -I used a piece of one inch precision square bar stock that miked accurate to about .ooo5 inches. Get the tangent of the desired angle, use the guage block for the rise and calculate the corresponding run. Set the block to the run on a taper jig.  For small angles and using a precision steel rule to set the run, accuracy of about a tenth af a degree is possible. Cut a hardwood taper for the saw blade angle and one for a dedicated taper gig to rip the "staves."  Use a square on the table top and the blade taper piece to set the blade angle.

   Consider an  upright  "cylinder" hexagonal in cross section, and then consider six trapezodial pieces arranged in a hexagon flat on the table.  The angle of the sides of the pieces for the upright form is 30 deg, and for the flat it is 90 degrees. For any intermediate taper the angle must be between 30 and 90. This is not intuitive but a few  3-d schetches makes it clear.

   HarryD

1. 
   chills1994 | May 07, 2005 02:19pm | #13

   this book would help.  it has chapters dedicated to staved and tapered construction.

   http://www.woodcraft.com/family.aspx?familyid=4862

   also try that book's website http://www.compoundmiter.com

    

6. 
   Steinmetz | May 09, 2005 02:16am | #14

   Metod, Am I the only one to 'get'your crack about Tas' wife and kids eating out of a bird feeder? How do you know his wife and he are not birds?
   I had to deep six my similar bird feeder, because it was 'Squirrel proof'YEAH RIGHT!!

   Those bushy tail rats would take a flying leap and knock all the seeds out and scatter them around for a picknic in the grass.
   Bought a metal cage type that holds a block of suet and seeds. They managed to open the friggin cage and cart off the block.
   I padlocked the cage; now I think they're picking the lock
   Stein