StanFoster
Active Member
- Joined
- Nov 16, 2003
- Messages
- 17,139
- Location
- Paxton, Il
- Aircraft
- Helicycle N360SF
- Total Flight Time
- 1250
I am laying out a 90 degree stairway this morning in my stairshop. The first thing is I need a dead on accurate 90 degree angle layed out for the beginning and ending of my curved stairway.
I have seen many different ways of doing these....some use a 3-4-5 foot triangle.....some let a laser do it for them, some just take a framing square and use long straight edges.
The laser method is ok if you can verify its sends out laser beams that are 90 degrees apart.
The 3-4-5 foot triangle is ok, but you have to be very accurate projecting the lines out from the right angle of the triangle.
I simply use my calculator to draw it as accurately as I can.
This is simple trig for many here...but there are some that could learn such a simple yet most accurate way to lay out a large 90 degree angle.
The stairway I am laying out has a 124.5 inch radius outside stringer that must be marked off exactly at 90 degrees.
The first picture shows some poster board stapled to the plywood in an arc. I drew the 124.5 inch radius arc on that poster board...and picked a point near one end where I wanted one side of the 90 degree angle to be.
I am simply figuring a right triangle whose 90 degree sides are 124.5 inches long. If you square 124.5 you end up with 15500.25. Double that and you arrive at 31000.5. Take the square root of 31000.5 and you come up with 176.069 inches. That is the one and only length that when both ends of the 124.5 inch legs are apart....will the legs be right at 90.000 degrees.
The 2nd picture shows a small drawing of what I have drawn out full scale for the stairway.
I place a small nail on one end of the 124.5 inch arc....and make sure its adjusted to allow for the hook on the tape. I simply draw an arc of 176.069 inches....rounded off to just 176 and 1/16 inch....and where this arc intersects the 124.5 inch arc.....its exactly 90 degrees.
The last picture is a stretched line that falls right over the intersection. That string is dead on 90 degrees from the other side of the triange.
Quick and very accurate.
Stan
I have seen many different ways of doing these....some use a 3-4-5 foot triangle.....some let a laser do it for them, some just take a framing square and use long straight edges.
The laser method is ok if you can verify its sends out laser beams that are 90 degrees apart.
The 3-4-5 foot triangle is ok, but you have to be very accurate projecting the lines out from the right angle of the triangle.
I simply use my calculator to draw it as accurately as I can.
This is simple trig for many here...but there are some that could learn such a simple yet most accurate way to lay out a large 90 degree angle.
The stairway I am laying out has a 124.5 inch radius outside stringer that must be marked off exactly at 90 degrees.
The first picture shows some poster board stapled to the plywood in an arc. I drew the 124.5 inch radius arc on that poster board...and picked a point near one end where I wanted one side of the 90 degree angle to be.
I am simply figuring a right triangle whose 90 degree sides are 124.5 inches long. If you square 124.5 you end up with 15500.25. Double that and you arrive at 31000.5. Take the square root of 31000.5 and you come up with 176.069 inches. That is the one and only length that when both ends of the 124.5 inch legs are apart....will the legs be right at 90.000 degrees.
The 2nd picture shows a small drawing of what I have drawn out full scale for the stairway.
I place a small nail on one end of the 124.5 inch arc....and make sure its adjusted to allow for the hook on the tape. I simply draw an arc of 176.069 inches....rounded off to just 176 and 1/16 inch....and where this arc intersects the 124.5 inch arc.....its exactly 90 degrees.
The last picture is a stretched line that falls right over the intersection. That string is dead on 90 degrees from the other side of the triange.
Quick and very accurate.
Stan