Thread: How Do I Calculate Angle of Uneven Stairs for Handrail Angle to Calculate Balusters

quick note for me:

Stair Baluster Calculations using COS (CoSign)
http://www.youtube.com/watch?v=b2jgpO8JYyM


Not for stair balustrades
http://www.youtube.com/watch?v=T54qZpez0s8



This one:
How to calculate and build stair balisters (mis-titled How to Build Deck Stairs)
http://www.youtube.com/watch?v=IYs7XWSYDRA


Mathematical definitions:
https://www.khanacademy.org/math/geo...ne-and-tangent


FYI...a comfortable stair angle is 32 degrees. There is a formula called the 7:11 guideline. you take your "unit rise" (pre-calculated using your total rise divided by number of risers)... multiply it by 11 and divide it by 7. This will give you a comfortable "unit run". This should keep you within code, however check your local building codes online to verify.

wood solutions Design_Guide_08_Stairs_Balustrades_and_Handrails_5-6_MB.pdf
http://www.woodsolutions.com.au/fwpa...ils_5-6_MB.pdf

I've got a few days before the new posts are ready.

So I thought I'd go ahead and sort out the spacings.

Stirrups are already painted and fixed in place permenantly.

The bottom rail has to be 125mm Max above all step noses.
So I setup as pictured.
And measured and measured and measured.

Some steps measurements were 120mm and others were 125mm

None over 125mm

Aren't apps fantastic!
Couldn't find a protractor to measure angle.
And didn't want to mess around trying to transcribe to the drop saw.
So grabbed a few plum bob apps from the store.

IMG_1134.jpg IMG_1135.jpg IMG_1136.jpg IMG_1137.jpg IMG_1138.jpg IMG_1140.jpg IMG_1141.jpg Untitled 4.jpg Untitled 5.jpg

Measured the slope at 1660

Then back to block layer and searched around for a calculator.
Found this one but it needed the Run as I had the slope measurement of 1660 and the Angle of 30.6.

So returned to my setup and clamped a vertical board high enough to laser measure to the top post.
Exactly 1440. Who knows why it was so exact.

Played around just a bit and 30 degrees fitted in with my measurement better than 31 or 32 as the original post suggested.
Over 2 degrees the slope changed about 35mm

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

Ended up cutting top and bottom rails at 32 degrees.

Ended up cutting everything at 32 degrees.

It was a lot easier formula than I thought.

After getting the wrong help measurement from the supplier.
I don't trust anyone anymore even with written instructions.
Laid it out 3 times before proving his measurement was wrong.


My calculations that worked the first time after research and thought from my previous posts above.

42mm balusters cut at 32 degrees is a 50mm slope
90mm balusters cut at 32 degrees is a 106mm slope

2 x 106mm (motifs) = 212
9 x 50mm balusters = 450
===
662 mm of balesters

1660mm (32 degrees) slope between newels.

1660
-662
===
998mm of left over space

I have 11 pieces to space out evenly between the newels with spaces next to the newels.
Add 11 and 1 (another space to the end).
Giving us 12 spaces to divide up from the 998.

998 / 12 = 83mm

Laid this out again and exactly right the first time.



-------

An additional procedure to get everything balanced when coming up short:
even number of motifs. don't centre a motif on a run.
start form the left and layout to and including the first motif.
move to the far right and layout to and including the first motif.
measurements the space left between the the two motifs and recalculate.

That way you spread out the inaccuracies towards the middle.
And don't end up with a baluster too close or too far from the newel at one end or the other.