I have to make a 75-degree bevel and I just cannot figure out how. I have a table saw and a sliding compound miter saw that don't go higher than 45. This is for the roof of a bird feeder. Even if I could hold the wood upright, I would still need to set up at 75, right? It's a scarry thing to do anyway. I hope I won't have to do it with a hand saw.
I used a protractor to see on paper what you suggested. I do understand that 15 is compliment of 75 but in practice? I don't get it at all. I have to make the bevel on the width of the board which is 7-1/4 wide x 3/4 thick. The 2 parts of the roof (18-1/4 long each) meet at the bevel. A 15-degree bevel will be very short, won't it? Unless I have to set up the board a different way? A drawing would be very much appreciated. I'm lost.
Think like this. The 15° piece is the cut off. What is left is the "INCLUDED ANGLE" of 75°.
Lay the roof board top side of the roof down on your SCMS saw. It will be on the left side of the blade. Have the blade set at a 15° bevel to the left. Make your cut. Repeat with the other half of the roof. Flip them over and join the two beveled edges.
Now if the roof is really steep and the included angle has to 15°, we have a whole different kettle of fish.
I am not sure I understand your instructions. I will make some test cuts and see. My SCMS tilts on the left only. So if I set at 15, tilt on the left, place the board on the left also, below the blade, I should be able to do it, right? The roof is really steep. I'll let you know how it turned out.
I did some tests and always ended up with the wrong angle. I don't know if it makes a difference but the 75 is an inside angle. I tried like you said with the miter saw, also with the table saw but the inside angle is way too big. Then I put the board upright on the table saw, using another board behind so the blade was not in contact with the fence, and set the bevel at 37.5. I made several cuts until the blade cut all the way through the board from the edge. The angle was way too steep. My husband came up with the idea of a jig for the SCMS, setting the bevel at 45 and the jig at 30. It would work but it's too much trouble for just 2 cuts. Finally, I cut two 37.5 and overlapped the right side. I don't particularly like it but I get a 75 inside angle. I tried to include a picture of the feeder but it doesn't work even if the jpeg file shows in the attachments window.
OK, here is what I understand. The included angle of each roof board is 37.5°. When you put them together, you have a 75° inside angle to the assembled roof.
Now I see your problem. You would have to be able to tilt the blade 52.5° and you only can go to 45°.
What I would do under these circumstances is build a ramp 7.5° up off of horizontal to hold my board. I am still thinking SCMS. Tilt the blade to 45° and make your cut.
To make making the ramp easy, draw a side view as long as you want the ramp to be. Measure the distance up on end would need to be to make it angle at 7.5°. So your ramp has a surface and a leg raising one end. Clamp your roof board on the ramp, with the end to be cut touching a horizontal surface. Place the assembly on your SCMS with the blade tilted to 45°, hold in place and make your cut.
I just drew it out on CAD. Should work. I'd post a picture, but it seems I need a picture posting tutorial again. Sigh.....
I don't know how you did it, how you figured it out, but it worked!!! I drew everything on paper like you suggested. It was a good idea to visualize first. We made the jig at 7.5 and, Voila!
There is a part of your brain that is missing in mine :-)
Thank you so much for your help.
I was sooooooo wrong. I mixed up the angles. I don't know how I ended up with a 75-deg. angle. It was not steep enough. It just didn't work. Even with the jig for the miter saw. I don't understand that whole angle thing at all. I got so aggravated that I put everything away. A couple of days ago, I went back to work on this project and read the instructions again and again. I needed a 15-deg. angle. This si so steep! There is no way I can do that without using the table saw and seting the board upright. I don't have a jig for that. I tried anyway with a thick piece of wood behing the board so it doesn't touch the blade, but seting the blade at the right angle and depth to get that 15-deg. was too complicated. I gave up. I cut 45 and ovelapped the boards. Too bad, the roof is now much shorter. Anyway, it looks good. I can't send the picture. I still don't know how it works.
Thanks again Carol. I learned about jigs for miter saws. It will be helpful in a near future...