Helical staircase dilema

SledDriver

I have produced a drawing which makes a spiral staircase using the variables CoreDiameter, OuterDiameter, StaircaseHeight, StaircaseRotation, StepNumber and TreadOverlap.

https://cad.onshape.com/documents/1711a00820d4382187710129/w/6a85f1dcbda4ec6409b8a4c6/e/0828299211e39ea005a0f62a

This works fine.

Apart from, due to the nature of the Curve Pattern command it is:

a) impossible to avoid having one step too many at the top of the helix. Staircases and the like are defined by the difference in height between floors. Not the difference "plus one step". Has anyone found a way around this without manually later editing the parts (which would negate the benefit of the variables automation)?

b) The Curve Pattern command produces a multitude of new parts. It seems impossible to boolean combine all the parts produced, including the original part, at the time of doing the Curve Pattern command. So after making the stairs, each stair is a new part, which is kinda messy. Anyone know a better way?

Jake_Rosenfeld

Hi John,

If your Helix starts at the top of the first stair rather than the bottom, the pattern will come out as you intend.  To do this you can Extrude-remove the bottom of outerColumn up-to-face of the top face of the first stair before you create the helix and do the curve pattern (or just edit the outerColumn extrude to have a 'blind' second direction that goes #stairHeight distance towards the top of the inner column; there are lots of ways to accomplish this).

As for b) Are you doing a feature pattern of the extrusion of the first stair?  If you do a part pattern you should get the boolean step tabs (new, add, remove, intersect) as a part of the curve pattern feature dialog.  If you are not seeing these as an option (in part pattern but not feature/face pattern) it is a bug.

owen_sparks

If you enjoy coding then featurescript is for you.  You could build this as single feature in the feature tree, with a user form that takes in all your inputs, then does the building and boolean operation in one hit.

Owen S.

Jake_Rosenfeld

Hi John,

If your Helix starts at the top of the first stair rather than the bottom, the pattern will come out as you intend.  To do this you can Extrude-remove the bottom of outerColumn up-to-face of the top face of the first stair before you create the helix and do the curve pattern (or just edit the outerColumn extrude to have a 'blind' second direction that goes #stairHeight distance towards the top of the inner column; there are lots of ways to accomplish this).

As for b) Are you doing a feature pattern of the extrusion of the first stair?  If you do a part pattern you should get the boolean step tabs (new, add, remove, intersect) as a part of the curve pattern feature dialog.  If you are not seeing these as an option (in part pattern but not feature/face pattern) it is a bug.

SledDriver

Thanks to you both. I'll do some more testing.

FeatureScript does look kinda useful! :-)