Need Help With Angles!

[john]

I have started making an octagonal shaped bird house but am having problems with the roof panels.

The triangular shaped panels need to have an angle where the sides adjoin to allow for the pitch of the roof. I have tried a couple with the sides cut at a ten degree angle and it looks close so I thought maybe the total should be 22.5 degrees but I'm not sure. I don't mind wasting a few, already done, but not too many. I'm not sure if there is a formula to calculate this angle or not.

Any suggestions?

Thanks

John

[JPG]

I have started making an octagonal shaped bird house but am having problems with the roof panels.

The triangular shaped panels need to have an angle where the sides adjoin. I have tried a couple with the sides cut at a ten degree angle and it looks close so I thought maybe the total should be 22.5 degrees but I'm not sure. I don't mind wasting a few, already done, but not too many. I'm not sure if there is a formula to calculate this angle or not.

Any suggestions?

Thanks

John

Is the roof sloped?

If not, 22.5(11.25?) is correct. Never mind I reread yer post. Tis a compound cut with a pitched roof. Need to know the pitch.

How are you cutting these?

[reible]

I've made a bird house like that, it takes a lot of wood!

You will be cutting compound angles and there is a table in the PTWFE. (The online version seems to be missing the table 3-1.) If you have the book look up what you need there. It will be some combination of miter gauge setting and table tilt.

Love to see it when it is done.

Ed

[reddog5362]

As JBG said you need to know the pitch to determine the angel of the cut. Here's a link to a hip rafter calculator. If I understand the question correctly, after you input the your info, the creeper side cut angle would be the angle your looking for. (Although thinking about it with an octagonal roof you would need to ½ the result)

http://www.blocklayer.com/roof/roofeng.aspx

[reddog5362]

Following the double post theme

here's a link to a gazebo calculator from the same site that will do 8 sides for you

http://www.blocklayer.com/GazeboEng.aspx

[charlese]

Tables are good, but so is the old method of cutting the 8 roof pieces out of cardboard or stiffened paper. you can do that by first cuttin the roof base then determine the height by the look you want. Use scissors to cut the triangle. After that basic angle is determined, make 8 identical pieces. Then all you need is a little slope to make the roof corner meet. You can do that with the sander.

[BigSky]

I have started making an octagonal shaped bird house but am having problems with the roof panels.

The triangular shaped panels need to have an angle where the sides adjoin to allow for the pitch of the roof. I have tried a couple with the sides cut at a ten degree angle and it looks close so I thought maybe the total should be 22.5 degrees but I'm not sure. I don't mind wasting a few, already done, but not too many. I'm not sure if there is a formula to calculate this angle or not.

Any suggestions?

Thanks

John

You need to determine the pitch or slope of the roof and then the tilt and miter angles can be determined. There is a table in Power Tool Woodworking for Everyone that gives the angles. I tried to link it here but it is not available in the online version of PTWFE. It is table 3.1 in my hard copy version of PTWFE. I have done this sort of project and I have only one word of advise. Precision is paramount. A fractional degree of error in a cut is compounded and does not present itself until assembly.


Here is a ink that will help you determine the "work angle" (aka slope) of the roof that you are building.

[john]

Hi guys:

Thanks for the replies. Angles have always been my downfall and it is again here. I had all the roof pieces cut but when I tried to lay them out for fitting, there is a gap at the top edge where they join. I tried taking pictures earlier today to show the problem, but both cameras have dead batteries:(

I think REDDOG5362 has identified the cut, creeper side cut.

I will be working on it again tonight and referring to PTWFE for help. The roof pitch is a 20 degree angle.

As soon as the camera is fired up I will add pictures. By then, I hope I have solved my problem.

John

[dusty]

Hi guys:

Thanks for the replies. Angles have always been my downfall and it is again here. I had all the roof pieces cut but when I tried to lay them out for fitting, there is a gap at the top edge where they join. I tried taking pictures earlier today to show the problem, but both cameras have dead batteries:(

I think REDDOG5362 has identified the cut, creeper side cut.

I will be working on it again tonight and referring to PTWFE for help. The roof pitch is a 20 degree angle.

As soon as the camera is fired up I will add pictures. By then, I hope I have solved my problem.

John

The links that reddog provided are excellent and are now bookmarked.

According to PTWFE, to build and octagonal roof with a 20° pitch set the miter gauge at 82°s and the table tilt at 21°s.

However, in Nick's "The Workshop Companion" Joining Wood, there is a different table. It says the two angles should be 68 3/4° and 7 3/4°.

[john]

I think I got it solved. Now all I have to do is make sure I can repeat it 8 times.

The first picture shows the problem gap. The second shows the adjoining edges cut at a 11.25 degree tilt. They don't quite match as I was pretty well doing it freehand with the previously cut pieces. Hopefully cutting new pieces using the correct angles will give me the results I want.

Thanks again for the help.

John