spiral staircase (going mad!!)

[uni1]

hello people,
i have to draw this spiral staircase in AutoCAD but its pretty messy even on the architect manual: looks like every method i apply is wrong! (since i have to check a certain distance on a certain point and its not matching)

so im NOT asking about blocks and stuff, just if u know some page/site/link or w/e comes to your mind that may help, some scheme...i dont know...showing how to geometrically construct the staircase.

i underline that the spiral staircase with all the steps aiming to the center of the middle pillar its not my case.

thanx in advance

 

[chicopee]

I am assuming that you are drawing this in 3Dsolid, so what I would do is draw one tread with a portion of the center post and railing (inside and outside);the railing will have to be rotated along a certain axis to get a little bit of elevation; then do a polar array for a number of treads calulated for one pitch of the spiral; then move each tread a cetain amount so as to get a complete revolution in one pitch; union every thing in that spiral pitch; then copy this unionized solid portion to make you complete circular staircase.
Obviously, you'll have to calculate the pitch; the amount of center post that each tread will need and even make it a little longer than the calculated value since when you UNION the excess will be incorporated in to the center post.
The tricky part will be to draw the circular handrail; so draw it a little longer for one tread in the X-Y plane as a solid and rotate it about its lower end in the X-Z or Y-Z plane a calculated angular value.

 

[chicopee]

Thinking back about drawing the circular handrail,it will be better if you drew an ellipse in the x-y plane whereby the minor axis would the diameter of the stairway when viewed perpendicular to the x-y plane and the major axis would be equal to the above diameter value divided by the cosine of the lead angle. This lead angle is equal to the arctan(pitch/(circular diameter*pie))
Once the ellipse is drawn in the x-y plane only take a portion lining perpendicular to a typical tread whose center will line up to the minor diameter of the above ellipse; then rotate that portion of the ellipse about the center of the ellipse a value of the lead angle. make sure the portion of the ellipse you select to rotate is sufficient to union with other arrayed tread as mentioned in the previous post.
A little complicated and if you are not familiar with the math mentioned above get help from an engineer. Once you complete this project, the experience will be gratifying.

 

[MechEng2005]

I think I follow what chicopee has suggested and agree. Another option for the handrail might be just to include a point with the intitial drawing of the single tread. Say a point at the center of the tread, up 42" vertically on the left and right side.

Then when you copy/array this tread, do the same with the point. Then, when you are done you will have all the treads and a series of points 42" above each stair. Put a spline through the points to get a path for the handrail.

-- MechEng2005

 

[IFRs]

Part of the issue, at least for me, is that I need to give the fabricator a roll radius for the handrail. A spline certainly draws it OK but does not help with fabrication. Same for an ellipse - hard to roll one!! Think of a Slinky (remember that toy?) - when you stretch it, it forms a spiral band that has a constant radius. So, you should be able to roll or draw a handrail to some radius for any spiral stairway configuration. My efforts a finding an equation for this radius have failed. I have dreamed up a method for figuring out the radius of such an arc and am currently trying it out on a couple of projects.

 

[MechEng2005]

Hmm... I might try creating the ellipse or spline, then use the LIST command to get the length for one revoloution (circumferance) of the ellipse/spline. Take the length, divide by 2*pi, and that should be the constant radius...

 

[dinjin]

isn't the technique for drawing screw threads the
same concept?

 

[feedmenow]

This is the way I would do it.
In Autocad use the Helix command and draw 1 revolution, diameter x Height.
Then use list and it will give you all the information you need.
If you want a 3d model of the handrail, rotate the UCS and put it on the end point and draw a circle, explode the Helix just once, then extrude the circle and pick the Helix as the path. This will only work with a circle any other shape will twist as it goes around the Helix.
As for the fabricator all he needs to know is the diameter, height and length.
Its a bit of hit and miss getting the first one right, the tube has to be rolled and twisted at the same time, not a easy job,
Best of luck.
I hope this helps.
Regards
Dave

 

[IFRs]

The methods of drawing the helical handrail work well. Does anyone have a formula to calculate the roll radius of the handrail without drawing it and dividing the measured length by 2PI? Does dividing the measure length by 2PI really give the proper roll radius?