The clean way look a bit too complex for me.
It's not that difficult if you understand that a cutout just is a path that goes vertical and horizontal in percentages.First rotate and mirror the staircase as in your plan. Export and import it so it is in that position after import.
Note the width and depth. Measure each staircase part using the dimension lines. Notice that the shorter horizontal dimensions add up to the width and the shorter vertical dimensions add up to the depth.
Now to calculate the SVG Path cutout. Understand that width is 100% represented as 1 and depth is also 100% represented as 1. The shorter dimension are fractions of 100% (1).
If you positioned the staircase correctly the start point is easy: top-left = 0,0 or 0.0,0.0 .
So the first part of the path is 'M0,0'
Now we have to go vertical to reach the 97.7 length. The calculation is really simple: 97.7/228.3 = 0.427945686.
97.7 is the length we want to go vertical and 228.3 is the depth of the object, i.e. 100% or 1. To go vertical we use 'v'.
The vertical number for the path is v0.427945686 but using 3 or 4 numbers after the decimal point is usually more than enough precision: v0.4279.
We now have "M0,0 v0.4279".
Now we need to go horizontal. Basically we do the same calculation but now with the horizontal numbers: 129.4/225=0.575111111 or 0.5751.
To go horizontal we use 'h': h0.5751.
We now have "M0,0 v0.4279 h0.5751".
Vertical again: 130.6/228.3=0.572054314 > v0.5720
Horizontal again: 95.6/225=0.424888889 > h0.4249
Vertical again: 228.3/228.3=1. Because we want to go up instead of down the number is negative: v-1.
And back to the origin is 'z'.
Notice that v0.4279 + v0.5720 = 1 (or should be 1, I missed that
At least h0.5751 + h0.4249 = correctly 1).The full cutout: "M0,0 v0.4279 h0.5751 v0.5720 h0.4249 v-1 z"
Import the staircase in a Furniture Library. Modify the staircase in the library. Check 'Staircase' and replace the "Cutout Shape" with the SVG path we created: M0,0 v0.4279 h0.5751 v0.5720 h0.4249 v-1 z
Save and save the library. Import in Sweet Home 3D and you will find your staircase with the correct cutout.
The library with the staircase: https://dodecagon.nl/upload/staircasecutout/staircase.sh3f
Extra: You can shorten the cutout a little where the start of staircase (bottom) is by shortening the second vertical number. Just make sure that the vertical going back up (the last negative one) is the same number as the two verticals going down.
You can go beyond 1 to create a cutout that is larger than the object itself, for example if you want a little space around the staircase. Most likely you want start with M not at 0,0 but with one or both numbers a small negative. If you create an image with the dimensions before starting to calculate that is not so difficult.
Don't forget the MiniManual I linked to in my first answer. It explains the same but with more options for navigating points.
----------------------------------------
Dodecagon.nl
1300+ 3D models, manuals, and projects
