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'xplain me a spline helix

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  • Member since
    February 2001
  • From: Wyoming, where men are men, and sheep are nervous!
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Posted by Pruitt on Monday, September 24, 2007 11:06 AM

The KCT helix looks good, but it sure looks like a LOT of work!

Here's my own helix:

I cut semi-circles from a sheet of plywood, and spliced 24" straight sections (to reduce the grade) between. I used a lot of sheets of plywood, but all the excess left me with plenty of subroadbed for other trackwork and bases for structures.

  • Member since
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  • From: Eastern Massachusetts
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Posted by railroadyoshi on Sunday, September 23, 2007 4:29 PM
They have come up with a great concept, haven't they? From the site, I believe the radius is 34".
Yoshi "Grammar? Whom Cares?" http://yfcorp.googlepages.com-Railfanning
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  • From: PtTownsendWA
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Posted by johncolley on Sunday, September 23, 2007 4:03 PM
Yoshi, Way Cool! Thank you for sharing! Q.: What is the centerline radius ? What a neat concept. I am always impressed with the simplicity of solutions that should be obvious, eh?     jc5729 John Colley, Port Townsend, WA
jc5729
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Posted by Anonymous on Sunday, September 23, 2007 1:23 PM
 ericboone wrote:

Spline roadbed may not be the best choice for a helix because of the vertical thickness of the spline.  You have to add that thickness to the vertical climb of each loop.  Spline is typically 3/4" or even 1" thick.

If I was going to build a helix, I would use a method I learned at the last club I was at before moving.  1/8" thick plywood was cut into 45 degree arcs of the appropriate radius.  Those arcs were laminated into a 1/4" thick sub-roadbed with the joints staggered by about 20 degrees.  This resulted in a strong, kink free, 1/4" thick helix sub-roadbed.  The track was laid directly on the sub-roadbed to help keep the thickness down and keep the grade minimized.  Roadbed (cork, Homabed, foam) isn't necessary as the helix is hidden track anyway.  The helix was held in place with 1x2 columns with notches every 45 degrees on both sides, although using nuts on threaded rods would work well too.

That sounds like a beautiful helix. I can almost see it in minds eye now.

  • Member since
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  • From: Minnesota
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Posted by ericboone on Sunday, September 23, 2007 1:04 PM

Spline roadbed may not be the best choice for a helix because of the vertical thickness of the spline.  You have to add that thickness to the vertical climb of each loop.  Spline is typically 3/4" or even 1" thick.

If I was going to build a helix, I would use a method I learned at the last club I was at before moving.  1/8" thick plywood was cut into 45 degree arcs of the appropriate radius.  Those arcs were laminated into a 1/4" thick sub-roadbed with the joints staggered by about 20 degrees.  This resulted in a strong, kink free, 1/4" thick helix sub-roadbed.  The track was laid directly on the sub-roadbed to help keep the thickness down and keep the grade minimized.  Roadbed (cork, Homabed, foam) isn't necessary as the helix is hidden track anyway.  The helix was held in place with 1x2 columns with notches every 45 degrees on both sides, although using nuts on threaded rods would work well too.

  • Member since
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  • From: Eastern Massachusetts
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Posted by railroadyoshi on Sunday, September 23, 2007 1:01 PM

Dustin and Electro, thanks for your replies.

 http://www.bnsfchillisub.com/Local%20Layouts.htm

Helix photos are buried just a little ways down on that page, but "KCT Helix!" is pretty easy to spot as you scroll. The idea is definitely something to try.

The primary reason I was interested in using spline is that there are 2 points mid-helix where tracks must enter, and I thought that making these connections would be easier in a spline design. 

Yoshi "Grammar? Whom Cares?" http://yfcorp.googlepages.com-Railfanning
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  • From: Sweden
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Posted by electrolove on Sunday, September 23, 2007 12:41 PM
Spline roadbed is very sturdy when built the right way. I'm sure you can use it in a helix. My splines are 20 mm in height. Try to calculate if your trains will fit with the radius you will use. You must stagger the end of spline to glue it to another one. The joint will be very strong. Can you please post some pictures of the BNSF Chilli sub, I'm interested to see how it's done. I plan to build my helix with spline roadbed.

 railroadyoshi wrote:

Hello everybody. Here we have it, another topic on spline roadbed.

After reading more about spline roadbed here and the numerous endorsements, I had a question for you all.

Can spline also be applied effectively to a helix? It would seem that this could be the ideal way to create a helix, as all it would require are a few pseudo-joists spanned from a circular support structure, on which thin splines could be laid.

What issues could you see with such a plan? The splines would no doubt have to be thin in order to maintain maximum clearance, requiring a closely spaced support structure.

I had seen another idea from the BNSF Chilli sub using double layered angle pieces as well. Any thoughts as to which would work better from the perspectives of time, cost, and margin for error?

Rio Grande Zephyr 5771 from Denver, Colorado to Salt Lake City, Utah "Thru the Rockies"
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  • From: Victoria, BC, Canada
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Posted by Dustin on Sunday, September 23, 2007 11:01 AM

 

I am very close to using the BNSF Chilisub idea of helix construction... it would be way faster in my opinion as it can be built in short segments and the screws hold it as the glue dries; you have a level surface to use right away for track laying.

With the spline method, my expectation is that the strips need to be fairly long to get the true benefit of the spline rigidity and trueness. When building a helix, keep in mind that you need to lay track, add feeders etc. as you go. Depending on the spline length, one piece may overlap itself making subsequent track laying difficult.

Also, I'm not sure how much vertical deflection spline roadbed allows.... ie. how much grade can it flex to, or how easily it can transition from say flat track to 2-2.5%?

The purpose of spline, I believe is its vertical rigidity and lack of deflection in the x-axis.

I have never used spline though.... anyone else have any yeah or nay's on what I have said?

Hope I've helped somewhat!

Dustin CN- Par for the course!
  • Member since
    March 2005
  • From: Eastern Massachusetts
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'xplain me a spline helix
Posted by railroadyoshi on Sunday, September 23, 2007 9:39 AM

Hello everybody. Here we have it, another topic on spline roadbed.

After reading more about spline roadbed here and the numerous endorsements, I had a question for you all.

Can spline also be applied effectively to a helix? It would seem that this could be the ideal way to create a helix, as all it would require are a few pseudo-joists spanned from a circular support structure, on which thin splines could be laid.

What issues could you see with such a plan? The splines would no doubt have to be thin in order to maintain maximum clearance, requiring a closely spaced support structure.

I had seen another idea from the BNSF Chilli sub using double layered angle pieces as well. Any thoughts as to which would work better from the perspectives of time, cost, and margin for error?

Yoshi "Grammar? Whom Cares?" http://yfcorp.googlepages.com-Railfanning

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