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 Post subject: Easements?
PostPosted: Sun Jun 19, 2011 8:54 pm 
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Joined: Tue Mar 29, 2011 9:14 pm
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Hi Guys,
I was thinking about using SweepSticks to aid in laying my track and was wondering if anyone used larger radii SweepSticks to create easements and how much bigger to go? If I was making a 22" curve would it be best to use a 32" for the easement or would that be too big or small?

What would be great is if a easement kit was available. Maybe something like 2"-4" long segments of radii in steps of 2" or so you could create a spline??? If I were to have a 22" radii I could stack 4-6 sections to create an easement that started out at 30"-34"...if that's enough?


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 Post subject: Re: Easements?
PostPosted: Mon Jun 20, 2011 9:45 am 
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Joined: Sat Aug 13, 2005 10:48 am
Posts: 365
Location: East Texas - USA
Easements in my experience are best performed free flow. True easing is a continuous change in radius. Classical methods are the bent stick, using a bit of flex track, and the ever unpopular mathematical layout and plotting.

For a fixture - use any close approximation that pre-bends closely - but solder the PC ties on only one rail - gently lay in place - for second rail and use gauge to solder in place the second rail. Pre-bending a smooth curve in the rails.

Not exactly a cookie cutter approach - but far better operationally. It would be possible to CAD a series of segments giving easements and create fixtures - but the differing combinations of start and end radii and varying lengths would be a large number of combinations - making production (and option purchasing) an expensive nightmare.

-ed-

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-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.


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 Post subject: Re: Easements?
PostPosted: Mon Jun 20, 2011 7:22 pm 
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Joined: Tue Mar 29, 2011 9:14 pm
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I understand the complexity in making an easement but I was trying to think of a way to have the “look” of one with the ease of using SweepSticks and keeping it simple and fairly cheap. I drew up some radii in 5 degree arcs in steps of 4” and placed them out in a 30 degree sweep (6 pc’s) on my CAD-CAM software at work. It doesn’t look too bad to me and maybe with some tweaking it might be doable (see attached PDF). Maybe instead of 4” steps it could be accelerated like 4, 6, 8, 10, 12 or some other combination? All I would need is 10 or so different radii and it would handle a lot of what I’m planning on my layout.


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 Post subject: Re: Easements?
PostPosted: Mon Jun 20, 2011 11:03 pm 
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Joined: Sat Aug 13, 2005 10:48 am
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Location: East Texas - USA
The dean of layout planning - John Armstrong - had a similar suggestion of increasing radius using sectional track where modelers chose not to follow the bent stick approach. Your approach should work well and would provide improvement over having no easement. I note that you get a 1.4 offset in your CAD. A true cubic spiral would not have that much offset given the degrees of arc you are working with. You might try only a 2" geometric increase step (2-4-8-16-32) for 4 or five steps and gain what you are seeking. I'd plan the degree of arc to be equivalent to approximately 1/4 your longest car length - giving an easement of a worst case car length as a minimum. Its not just aesthetics - the coupler offsets issues are compressed with model curvature - easements do provide improved operational reliability.

-ed-

_________________
-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.


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