compound angle question

[Greg Mann]

I don't mean to open the "old wound" again but I was watching Woodworks' tapes this weekend (relaxing you know ) and I caught Mr. Marks making a pyramidal umbrella stand. According to the show, David simply cut 45 degree angles to mate the 4 tapered edges.

Check out the posted show on DIY network: http://www.diynetwork.com/diy/shows_..._26926,00.html

I dunno...just seeing what y'all think about this compund angle stuff.... I would've thought David would've said something if the angles were different than 45 degrees. Man, one of these days I just gotta cut some scrap and see for myself I guess!!

Chris, This works because David is making the 45 degree miter cuts while the workpiece is still laying on its base surface, not on a surface that will become a side of the pyramid.

Greg

[Chris Padilla]

Chris, This works because David is making the 45 degree miter cuts while the workpiece is still laying on its base surface, not on a surface that will become a side of the pyramid.

Greg

Greg,

Color me clueless here but I really don't follow at all. Near as I can tell, the umbrella stand is simply an inverted pyramid.

Either I don't understand what this whole thread is about or I'm as thick as they come...probably both!

[Randy Moore]

Greg,

Color me clueless here but I really don't follow at all. Near as I can tell, the umbrella stand is simply an inverted pyramid.

Either I don't understand what this whole thread is about or I'm as thick as they come...probably both!

Chris,
I was no good in math in H.S. some 30+ years back and now this whole thread has me so confused that I am tempted to get the boat out of the garage and go fishing for the day.
I am with you, Chris. It seems the umbrella stand is the same as what would go up on the ceiling. I guess someday I will get around to trying this.
Thank you Chris for admitting you are you ain't the smartest person in SAWMILL CREEK. Makes me feel a little better.
Randy

[Bill Arnold]

... I dunno...just seeing what y'all think about this compund angle stuff.... I would've thought David would've said something if the angles were different than 45 degrees. Man, one of these days I just gotta cut some scrap and see for myself I guess!!

The actual angle depends on height and tilt. I ran the numbers on the umbrella stand and got these results:
Height: 24 3/4"
Tilt: 8.5* (approximately)
Actual bevel angle: 44.389*

If the bevel is cut to 45* rather than 44.4 (rounded), the outside of the miters will come together first. Under clamping, the slightly over 1* error will be masked or just go away.

Regards,

[Chris Barton]

Very interesting question but, if you consider the gometry of this there is only one correct answer: 45 degrees to the perpidicular plane of cut. If you were to take the pyramid adn bisect it at any point on the perpidicular plane and look at the cross section (as shown to the right in the original post) the points where perpindicular side meet have to be 45 degrees. Now, usually one slightly over cuts the angle so that the outside of the angle will meet closed first. I would expect the error the finish carpenter is having is with less than perfectly precise tools.


Chris

[Richard Wolf]

Chris, your thinking is correct but to cut the angle at 45 degrees you must hold the piece at the taper angle, unsafe and difficult to do. I suggest that people that don't understand this problem, head into your shop and build a tapered box from scrap. Make the taper servre enough that you don't come away with results like David Marks did. Once you do this exercise you will not forget the need for compound angles!
Its exactly like cutting sprung crown molding flat on your miter saw, sure the corners of the room are at 90 degrees, but when setting the compound angles, neither is at 45.

Richard

P.S. To my friend Per; I know, the corners of the room is never at 90 degrees.

[Chris Barton]

Hi Rich,


I agree. When I have done this sort of thing before I have used the tablesaw to cut the tapers and then have used a 45 degree champhoring bit in my router table to cut the angles. Seems to work every time for me.

Chris

[Ralph Barhorst]

Chris, This works because David is making the 45 degree miter cuts while the workpiece is still laying on its base surface, not on a surface that will become a side of the pyramid.

Greg

I saw that episode of Woodworks and Greg is correct.

One way to look at this is to think of three different four sided boxes.

The first box is a simple square box with mitered corners. In this case the sides are square and the blade is tilted at 45 degrees. No compound angles are required.

The second box uses trapezoidial sides with the angles cut at 45 degrees. With the angles cut at 45 degrees you will end up with a flat box with the height being equal to the thickness of the material. The blade does not get tilted at all (0 degrees).

The third box is half way between the first two. The 2 dimensional side view of this 3 dimensional box shows that the angle of the trapezoid is 45 degrees. However the sides cannot be cut at 45 degrees since the side is also tilted in toward the center of the box. The actual cut would be 54.74 degrees (table saw miter guage setting) with the blade tilted 30 degrees. See the chart that I posted earlier in this thread.

[Keith Christopher]

Well here is my go at illustrating this. I didn't taper the whole thing as I felt it was a more dramatic view this way

[lou sansone]

here is an example of the compound miter in action

http://www.sawmillcreek.org/showthread.php?t=18743

lou

[Carl Eyman]

Yeah, still beautiful, but how did you finish it?

[lou sansone]

Yeah, still beautiful, but how did you finish it?

here is what I have found to work for curly maple, after lots of experimentation - You have to have decent maple or else the rest is not worth a hill of beans.

I call this my "double dye process" I am not sure that I have ever seen anyone else use this exact method, but for all I know every one does but will not tell anyone how they do it.

1. sand to 220 grit
2. use a water base aniline dye - I use a mixture of honey amber maple and pilgram maple. mix to suit your taste. I think darker is better than lighter on the color. I make my dye the strength of very very strong tea. I always wear rubber gloves because it will stain your fingers brown.
3. brush on the dye. lots of it. rub it into the wood with a rag.
4. let it dry overnight
5. sand to get rid of the raised grain. Do not sand off the dye. Some folks do that, but I do not. I also do not play games with using different color dyes and sanding them back. If you have decent wood and the right base color the wood will do the work and not the chemistry lab.
6. brush on the dye again- same strength or possibly a little weaker or stronger depending on the first try
7. let it dry overnight
8. coat the whole piece with BLO thinned with turps or mineral spirits- soak it on and if you want you can use a sanding sponge and make gravy with the dust and BLO. Be carefull here - use super fine sponges
9. wipe off the excess
10. let it dry a few days
11. put 1 or 2 coats of orange or garnet shellac 1/2 lb cut on with a brush and sand between coats carefully - this is where you can ruin the piece by sanding through the dye
12. top coat with what ever you like - tung oil, poly soup mixture, more shellac- but use super blond , nitro lacquer, ....
13 put a few coats on of the top coat until you like the build
14. let the finish set a week
15. rub it out with 0000 steel wool and wax or what ever else you like to rub stuff out with
16. make a nice pot of coffee and sit and look at your piece for a while - think nice thoughts and all of that rot.
17. post a picture for us to look at on SMC