Proposed Tangent Handrail Lesson

[Baldwin]

OK, I need a cutting and face mold for a spiral handrail with these parameters...

Center-line radius = 29"
Unit rise = 9.04
Unit run along the center-line = 15.71"
Floor plan = 360 degrees
Number of segments = 6

handrail width = 2.75"
handrail height = 2.875"

I don't care how or which method or book you choose to use but any of the face molds from any of you, must look alike and with the same bevels or be in error.

FYI, this is no practice exercise for me but a typical order and one which I'm working on now.

[bellchippy]

Re: Proposed Tangent Handrail Lesson

Jim

Good project I'm in, I'll make a start tomorrow.

Brian

[Keith Mathewson]

Re: Proposed Tangent Handrail Lesson

Here it is. Searching the waterline for holes...

[Baldwin]

Re: Proposed Tangent Handrail Lesson

Keith ,
Your drawing looks pretty good and pretty close but a few things to check...

The pitch of the tangents in elevation is not established by the unit rise and run of a step. The given rise/run does establish the center-line pitch of the rail which is then used to determine the height "H" in the tangent elevation.

You are correct in drawing this as an obtuse plan with equally pitched tangents but let's get that pitch correct.

[Albert C]

Re: Proposed Tangent Handrail Lesson

Here is something that may be of help to those of you in the tangent handrail business.
Definitely, a subject that only a few can master.

http://www.sbebuilders.com/tools/geo...on_tangent.php

[Keith Mathewson]

Re: Proposed Tangent Handrail Lesson

It is my understanding that in plan view tangent BC equals tangent BA and since BF is the stretch out of BA then BC would equal BF. With equally pitched upper tangents it appeared to me that point F would be the point where the inclined tangent touched the baseline and the starting point for the upper tangent at the given incline angle. This seemed like it fit together nicely, given two sides of a triangle to obtain the pitch. Apparently there is another process to obtain those values but I haven't sussed it out yet.

I was perplexed as to the rise of 9" and a run of 15.7". I first assumed it to be either two treads on an inside stringer or one on an outside stringer but then a 9" rise made me think that it may be 1 riser and a percentage of another.

[Baldwin]

Re: Proposed Tangent Handrail Lesson

Keith,
9 and 15 are common units of rise/run for spiral stairs along the outside radius (spiral stairs supported by center pole.) And no,. I didn't make this exactly clear.

SOME DISTINCTIONS: Straight, plan-tangent lines are "unfolded" or "rotated" into the vertical plane at B (the vertex) and not "stretched-out". Circular, center-lines on the other hand, are "stretched-out" or "rolled-out" as in the circular segment AC. (In this case, dia X pie/6=roll-out length.)
____________
Stair and handrail pitch is always determined by rise/run of a tread and not any lines drawn tangent to a curve. (Rise/run inv tan=pitch)

Remember that unfolded tangent lines and oblique planes etc. are just imaginary, geometric constructs which enable us to draw patterns. Customers know nothing of these things and provide no information regarding layout lines or procedures. Customers do provide stair plans and specifications including rise/run etc.

Tangent height "H" is determined by stair layout or trigonometry of the right triangle. The base of the triangle is the roll-out length AC while the pitch is specified by rise/run. This is all we need to know in order to determine H (pitch tan x base=H)

While it's possible to draw everything out, right-angle trig functions are basic to modern stair calculations and I'm ass-uming that most everyone is familiar with this.

Hope this plugs a few holes.

[Gotstairs]

Re: Proposed Tangent Handrail Lesson

Jim,

Can you check the layout, I have the unit of run at 15.184.

[bellchippy]

Re: Proposed Tangent Handrail Lesson

Here's my attempt, had do it half size but to scale took about four hours,I suppose the more I do the quicker i'll get. Don't know if you can see everything needed to make a judgement, if not I can supply close ups and information.

Brian

[bellchippy]

Re: Proposed Tangent Handrail Lesson

A bit more

[Baldwin]

Re: Proposed Tangent Handrail Lesson

Gotstairs,
Yes you're right as the customer actually furnished the unit run based on something other than the handrail center-line. I discovered that as well and made corrections. Use your number.

[Baldwin]

Re: Proposed Tangent Handrail Lesson

Brian,

I think we're going to need to see more of your drawing and perhaps some dimensions and angles in black marker. What I can see looks good.

[bellchippy]

Re: Proposed Tangent Handrail Lesson

Jim

Hope you can see this better, taken with iPhone so can't get back far enough. It's half scale, level spring lines are 60 deg. Base line pi x dia(29)divided by six. Hope that's correct, I did cheat, I probably would have done the same as Keith.

Brian

[Keith Mathewson]

Re: Proposed Tangent Handrail Lesson

Not seeing how H is not the height of two risers, In plan view the rail travels two tread lengths.

[Baldwin]

Re: Proposed Tangent Handrail Lesson

Keith,
H does happen to be the height of two risers but the length of the tangent lines in your plan should not be 15.7 but 16.7 and the vertical line at vertex is not 9.04 but 8.7. Neither should the pitch angle of the tangents in elevation, coincide with the center-line pitch of the rail.

I'm also seeing a line radiating from the center of the plan circle which does not intersect the vertex in plan. This line should be parallel to the level ordinate line (if it is then the level ordinate is wrong). Both you and Brain seem to have this issue.

This drawing should appear as plate 78 in every respect.