Staircase stringer to develop in 3D

[stevsmith]

Hi there,

 

I am trying to detail the stringers for a staircase I am developing in 3D.

The trouble is, I have hit a snag when it coms to devloping th curved riser section. See attached photograph.

 

The main issue is the break off point as it is situated on the curve and not on a straight section. I have attached a cad detail of what I am looking to achieve.

 

Any help would be gratly appreciated.

HELIX STRINGER.dwg

[shift1313]

Stev, im not sure i follow what you are trying to do. How will you actuall make the stringer? is this going to be metal or wood?(looks like metal from your drawing). Are you only looking to draw a curved stringer for the landing portion?

[stevsmith]

I managed to zip it.

 

This is the stair to get a twin stringer.

All steel construction.

 

The 1st flight of stairs was easy, but i need to figure out how to sweep the rest of the stringers to suit the tread positions referencing off the plan view.

 

The stringers are to be mitre cuts. no radii between joints.

425.zip

[shift1313]

so is sweep not working for you? It seems as though you already have the correct path with the red lines in the plan view. I copied your red outter path from the plan view and moved it off into space. i then drew a rectangle. SWEEP, selected the rectangle, hit A for alignment and select No for aligning to path. then select the red line as my path.

 

is the image what you are looking to do?

[stevsmith]

What you have done is correct Matt.

 

I have used the sweep on the Half Landing section like you have done, the problem lies with the 2nd flight on the staircase. As it comes down the 2 steps onto the half landing. the stringer has to curve around the line of the landing (the sweep you have just done) and intersect it so that it looks continuous.

 

Im at home just now and I dont have AutoCAD on my laptop. Im getting my new computer next week. So Im trying to explain it as best as I can mate.

 

Thanks for looking at it.

[stevsmith]

I actually had the half landing in place and took it out when I uploaded.

Stupid me..

[shift1313]

okay, when i first read it i thought you were having trouble with the landing. So you need something like this?

[stevsmith]

Hey Matt, I appreciate you taking the time to help me out.

 

I have attached a drawing showing what happens when I sweep both the half landing and the 2 steps. as you can see there is a collision that I need to turn into a mitre but as you can see, I cannot union the 2 stringers together.

As the images show the mitre is on the curve making the geometry complex.

 

Believe it or not but this stair has actually been made. all the developments were done in 2d which I can do no problem. This 3d is project for me to try and introduce it into or work.

[SEANT]

What if the stringers were fabricated like so? A bit more complicated, perhaps, but it would allow for consistent transitions.

[stevsmith]

Hi seant.

 

This is how the inner stringer was made. The idea was to connect the two stringers together using m12 csk's on site due to bad site access.

 

I like the idea that you have show, but because the stringers are made from stainless steel rather than mild steel, it is bad practace just to add segments on if you can undertand what im saying.

 

Also. If i was to go along this line, how would i develop the small additional radiused section that sits on the curve. If maybe I done it that way to start off I could somhow union the 2 segments together and then use a slice to complete what im looking to achieve.

 

That sounds plausable.

Helix stringer2.dwg

[SEANT]

Ah yes, on site fabrication does raise a whole new set of issues.

 

I was envisioning the stringers – certainly the spiral sections – as CNC parts (laser, waterjet, etc.), so the triangle piece could conceivable be cut in place. I’m not sure how practical that would be given that the pieces isn’t actually required, though aesthetically somewhat pleasing.

 

In general, I guess the tricky part are the seams that are not perpendicular to the “roll” direction, as the edge would likely end up as a spiral segment. Not impossible to match to a similar rolled edge, but would be impossible line up a Radius/Flat transition.

[stevsmith]

My thoughts exactly. As I have said previously the stringers have been made and rolled to shape. I done all the devleopments in 2d using the mean thickness of the steel. And it worked out well. But trying to do the developments in 3d is, to be honest a bit of a nightmare because of the transitions and geometry.

 

Plus, also. You cannot flat develop from 3d. It would be handy if you had an option like in solidworks where you could flat develop it and then roll it to the required radius.

[SEANT]

I re-read the thread again, and see where I was somewhat missing the primary gist.

 

It is an interesting modeling problem, though, so I tried to create that one piece at the inside corner of the curved landing/riser section. It is quite a challenge.

Stringer.dwg

[stevsmith]

How did you manage to get that?

 

I'm fairly new to the whole 3d drawing in Autocad.

Sometimes its trying to perceve how to draw things in a different perspective that throws me off.

 

Im trying to figure out the steps you took but im getiing lost. could you explain how you achieved it in a bit more detail please.

 

Thanks for all this help Seant and Matt.

It's very much appreciated.

[SEANT]

I started out by making a quarter round panel with the appropriate thickness. That’s the easy part but, as you may have noticed, I used the outside radius for the inside. I really should pay more attention to the details.

 

The tough part was generating the correct helixes to use as guides. The attached Excel spreadsheet has the calculations that I used.

 

Once the 4 pertinent helixes are created they can be used as guides for the two lofted surface. Those surfaces can be used with the SLICE command. I had to first make a horizontal slice to restrict the Surf-Slice to just a portion of the quarter round. The pieces were subsequently unioned back together.

HelixCalc.zip