Staircase Wall Frames - Woodworking Talk

itstonye · 10-21-2008, 06:04 PM

I am having trouble finding the formula for making acute and obtuse angle cuts on a mitre saw for wall frames that are parallelograms.
I was told to make a 45 degree block and attach it to the left fence. Can anyone shed some light on this for me. assuming the angles are: 50 degrees and 130 degrees.

I found some on the internet but they called for using a scientific or graphing calculator. there was a trim carpenter i knew and he used to say: subtract the angle from 180, divide by 2, add 45 .. .. .. or somthing to that effect but i can't remember obviously. if any one can help i would appreciate it. itstonye@comcast.net

firehawkmph · 10-21-2008, 06:18 PM

Tony,
couldn't you draw one out on the wall and use a protractor to measure the angles? Divide the angle by 2 to get your saw setting. If your saw doesn't allow that setting, then make up a 45 degree block to set against your fence and deduct that from your angle to find the setting, or something like that.
Mike Hawkins

pianoman · 10-21-2008, 06:21 PM

I really need more information, are you talking about the slope or the angle one landing leaves the other. If you are trying to make a cut which a saw buck or what ever ...that won`t tilt that far, you`re right about the 45 degree block. Rick

Daveb · 10-21-2008, 06:22 PM

I've never done this, but I do understand geometry - to some degree. Hey, I made a funny. For each corner, wouldn't you just divide the angle by 2 (130 = 65+65). So you would cut each mating end to 65 degrees? Then cut the other ends at (50 = 25 + 25) 25 degrees? But I am not sure if I am missing something. That's what scraps are for!

Edited - I'm too late on the "enter button". these guys beat me.

itstonye · 10-21-2008, 10:05 PM

it seems to me that the formula for the acute angle is:

angle = 50 degrees

50/2 = 25

For the obtuse angle I figured this formula but im not sure if im right. Some reassurance would help:

angle = 130 degrees

130/2 = 65

90-65 = 25

25 - 10 = 15

set saw at 15 degrees with a 45 degree block and cut .. .. ..

or is the formula:

130/2 = 65

65 - 45 = 20 degrees

set saw at 20 degrees with a 45 degree block and cut.

Handyman · 10-21-2008, 10:10 PM

Quote:

Originally Posted by itstonye

it seems to me that the formula for the acute angle is:

angle = 50 degrees

50/2 = 25

For the obtuse angle I figured this formula but im not sure if im right. Some reassurance would help:

angle = 130 degrees

130/2 = 65

90-65 = 25

25 - 10 = 15

set saw at 15 degrees with a 45 degree block and cut .. .. ..

or is the formula:

130/2 = 65

65 - 45 = 20 degrees

set saw at 20 degrees with a 45 degree block and cut.

joesdad · 10-21-2008, 11:57 PM

If you guys saw how I do the cuts for stair panels you'd tell me I'm nuts. But they come out perfect every time. You only need to make one perfect set of miters and then build a jig from there which can be mounted to the fence and deck of the saw. Impossible to explain, but next time I do a set I'll take some pics. It's the long point of the box that make everyone nuts, which is what I assume you're talking about.

Oh...and you don't need all of those mind bending formulas either.

-Armand

itstonye · 10-22-2008, 09:16 PM

Ureka!!!!! I've got it!!!! I tried it today and all is well.

for the obtuse angle subtract it from 180 and divide the remainder by 2 set you saw at the result and cut.
EX: angle = 130 degrees

180 - 130 = 50 , 50 / 2 = 25 degrees

for the acute : subtract the angle from 180 and divide by 2 then subtract 45 degree's for the gauge block that has been pre made set saw at result and cut away.
EX: angle = 50 degrees

180 - 50 = 130, 130 / 2 = 65, 65 - 45 = 20 degrees

using a 45 degree gauge block and the saw to 20 degrees you'll have perfectly bisected angles.

Thank you to all that helped or tried to help i appreciate it. I guess i just had to do it a few times to get the formula right. i hope this helps anyone with similar problems.