Compound miters can be made on the bench saw by setting both the miter fence and the blade bevel.
Generally, however, the accuracy in the angle indicators is not that good so compund miters will be tough to get right.
Instead of compound mitering, you can prop the piece up at the angle that it will normally be at when installed and then cut a simple miter instead of a compound miter. This eliminates one of the variables and makes it easier to make.
What exactly are you making? How did you determine you need 38° and 38°?
The last time I cut a bevel and needed it to be *DEADON* I made a practice cut on a piece of scrap. Then I took a piece of scrap plywood with a factory edge and put that against the fence. Take the bevelled piece and place that on edge tight to the fence with the toe (point) of the bevel towards the fence. Now take another small piece of stock the same width and hold it flat against the bevel. Draw lines from the inside corner where the two pieces meet out against both pieces.
Since the bevelled piece is flat to the fence and the edge of the ply is also flat to the fence, the one line and the edge are parallel. Use your square to complete as large a triangle as you can. Carefully mark and measure the sides.
Remember that the great indian chief of trig is SOHCAHTOA, and you'll be able to recall the trig formula's.
Sin = O / H
Cos = A / H
Tan = O / A
Bring up your trig calculator on windows (the standard windows calculator has a "scientific" mode - Click on View/Scientific)
Take any two of your measurements, say Opposite and the Adjacent. Plug in the Opposite, divide by the Adjacent, click the [Inv] box and then click the [Tan] button. The result will be your miter angle in degrees!
It's taken much longer to type this than to do it. If the answer isn't *EXACTLY* what you're after, fiddle the saw and repeat.
You really can't trust the angle graduations on most saws. They'll get you in the neighborhood, but if you really need it close, measure it out.
Nice tip. There are also compound mitering charts you can find on the internet. Here's one: http://www.scrollsaw.com/miter.htm Usually they will include most angles ou will need.
I've got a project coming up that will have some compound miters, and I have a different question about it. I've already figured the angles needed, what troubles me is putting the pieces together. Has anyone out there figured out a good way to clamp compound mitered joints together? I've done some in the past, but the clamping part always seems to be such a screwy thing that I don't think I've ever gotten quite right.
I've found band clamps to be helpfull with multiple sided mitered objects, but with the *compound* miters they just slip off because of the tilt of the sides relitive to each other.
What I am doing is a 4 sided object with the tilt of the sides at 30 degrees. So the 45 degree miter plus the 30 degree till make for cut settings of 49.11 degree miter gauge and 20.7 degree blade tilt. Just think of it as a 4 sided rectagular bowl with the sides sloping up at 30 degrees. Or if it would be easier to visualise thinking of it as a truncated pyramid with a low slope.
Sorry I don't have a web site, so I don't have the ability to post a drawing. :( It would be much easier to describe it with a visual, particularly since I am a more visual than verbally oriented person.