Unitrack 718 curves

[Kiran]

I want to make some gentle curves in my double track main line using R718 curves. If I use R718 on the outer curve, is it possible to make an inner curve with some existing track pieces without resorting to cutting or flexing? The spacing may not be uniform throughout butas long as it is not too close, I might try it.

 

On an unrelated note, any idea why Unitrack doesn't do single track pieces with concrete ties? If I am using mostly double track pieces with concrete ties and have to use some 718 curves or even 481 curves in the middle, I will end up with odd wooden ties here and there.

[Ochanomizu]

Hello,

 

For gentle curves I would recommend abandon Tomix and Kato track systems for that length of track and use long-length flex track.  This enables more realistic parabolic shapes.

[cteno4]

The Kato track geometry is based on 33mm radius increments. The 481 and 718 single track pieces are meant to be used with #4 and #6 points. 
 

for an inner curve with out curve or 718 you would need a 685 that doesn't exist. for large radius double curves, Ochanomizu’s suggestion of using concrete tie flex track. 
 

Kato track has a long legacy and they slowly expand the track offerings, but have not gotten to having all the single track pieces in concrete ties.  There are a few like some straight pieces.
 

jeff

[lighthouse]

If you use curve R718 as an inside curve, you can build an outside curve with the help of the S33 and R718. For 90 degree curves the following would be possible:

Inside = 6x R718-15 °
Outside = 1x S33 + 6xR718-15 ° + S33

But you have a significantly larger distance between the tracks in the area of 45 °. You can also find this larger distance in Japan :)

 

[Kiran]

15 hours ago, lighthouse said:

If you use curve R718 as an inside curve, you can build an outside curve with the help of the S33 and R718. For 90 degree curves the following would be possible:

Inside = 6x R718-15 °
Outside = 1x S33 + 6xR718-15 ° + S33

But you have a significantly larger distance between the tracks in the area of 45 °. You can also find this larger distance in Japan 🙂

 

Thank you. I am not making a 90 degree curve. I was only looking at using 1 718 curve. I am guessing using S33 won't work with only 1 718-15.

[cteno4]

could always just make a custom piece of flex track on a roadbed base to fit in if needed.

 

jeff

[Takahama Trainwatcher]

R718 travels a distance of 188 mm along its arc for 15 degrees. (15/360 * 2 * pi * r [718] ).

If you used the R718 inside that to try to emulate a radius of 685 mm for 15 degrees, the required arc length of 179 mm (15/360 * 2 * pi * r[685] ) would be exceeded by around 9 mm. The track separation would be slightly off 33 mm but would probably be easy to fix gradually in subsequent tracks; the question would be if there is a way to compensate for that 9 mm in the following (straight?) track lengths.

 

A pair of 29 mm straights against a pair of 33 mm straights would compensate 8 mm. Might be enough?

Edited August 26, 2020 by Takahama Trainwatcher
Additional info

[Kiran]

1 hour ago, cteno4 said:

could always just make a custom piece of flex track on a roadbed base to fit in if needed.

 

jeff

That's the fallback.