From: hanss@microsoft.com (Hans Spiller)
Subject: Re: Helix Calculation
Date: 08 Oct 92 06:35:59 GMT
Organization: Microsoft Corp.
Summary: building helices--several methods

In article <1992Oct7.003433.26720@Princeton.EDU>, jsm@phoenix.Princeton.EDU (John Scott McCauley Jr.) writes:
> In article <1992Oct6.153144.2134@magnus.acs.ohio-state.edu> cwatters@magnus.acs.ohio-state.edu (Coyt D Watters) writes:
> >Does anyone have a method for designing a helix?  I am building a 
...
> >Space restrictions dictate that the radius be MAX 22".
> >
> 
> I've also thought about building a helix. I think the usual method is to form
> the roadbed from 90 to 360 degree cuts from thin plywood or foam core board.
> 
> However, using the above method you might wind up with lots of waste material
> and nasty joints where the cuts meet.
[clever method of laminating foam core deleted]

N Scale magazine had an article on building tapered helices out of plywood
a couple of years ago.  you can still buy the back issue--check your hobby
store.  the author's points were that
o  smooth running inside the helix is really important, as it's hard to
   access.
o  the tradtional method wastes a lot of wood and still leaves a lot of
   joints to make bumpy running
o  it's difficult to rationalize a large cylindrical mountain, where a
   tapered one is easier

the technique is basically to make a continuous spiral out of a single
disk of plywood with a jigsaw.  the levels are suspended by the usual
sort of risers you'd expect to see in a cookie cutter or L-girder layout.
he came up with a clever arrangement that makes the whole structure very
strong.  he also found that it was pretty important to put a guard rail
(made from light cardboard) all the way around both sides, especially when
running long trains upgrade.  obviously, given the dimensions of american
plywood, your max radius of 22" is pretty easily done.  what's your min
radius?  will you need to stack two tapered helices in order to reach your
desired height? (I imagine them arranged like an hourglass...)


as an extension of scott's approach, making roadbed out of several pieces
of thin wood, oriented vertically so it's easily bent, with spacers between
the pieces, is very old.  just about any of the books that explain benchwork
and roadbed mention it.  no reason to not apply it to a helix that I can
think of.

Rick Rideout (owner of Rix products) has another approach.  he makes his
roadbed out of two strips of 3/8" plywood, cut the width of his roadbed.
when he wants to bend it (he's one of those guys that puts curves in all
track to make it seem longer) he puts a whole bunch of sawkerfs in it, most
of the way through.  the "intact" sides are arranged opposite and because
of the kerfs it can easily be bent to shape.  once he's satisfied with
the curve, he glues the layers together, which makes the whole thing very
rigid.  obviously a table saw or radial arm saw ("radical harm saw" :-) is
pretty crucial to doing this efficiently.  you can make the "before" pieces
more flexible by cutting more kerfs.  by making a whole bunch of these
things at once, you can save a lot of effort by ganging a bunch of them
together and cutting kerfs in all of them with a single pass of the saw.

the ascii drawing below shows a top view of the two pieces before
and after glue up.  imagine a curve in the "after" piece.  straight
lines are hard enough in ascii...


		Before glue up
  _____________________________________________________________
  |							      |\
  |  |	|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  ||   Top
  |__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__||
  \__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\|

   __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ 
  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |\ 
  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  ||
  |___________________________________________________________||  Bottom.
  \___________________________________________________________\|
  							      

  
		After glue up
  _____________________________________________________________
  |							      |\
  |  |	|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  ||\ 
  |__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__||| 
  \__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\__\||
   \___________________________________________________________\|

I havnt tried any of these techniques, and using either of the lamination
techniques in a helix is my own idea, so probably no one knows what
difficulties you'll run into.  I've tried to give credit where it's due,
and I definitely recommend the N-Scale article on tapered helicies.  find
a recent issue in a hobby shop, look in the back issues ad, and send away
to hundman publications for the one with article on making a tapered
helix.  I got a box of back issues from them with about a two week turnaround,
earlier this year.

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	|   | |----|------------		-Hans
	|   | |    |   //       |		hanss@microsoft.com
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