Hi, I've got a 5x9 foot bench I'm building an oval on and want to know just how big a curve I can use in HO. What's a good margin from the edge of the track to the edge of the table? That will tell me the max radius of the curve I can build. Regards,
I think the closest you can put the track from the table's edge would be about 3 inches, but about 5 inches would be better. For such a small layout I would go with 24" radius curves, Atlas makes 24" radius snap-track in both a code 100 and code 83. If you have enough room for a 5x9 you might as well build a better layout in the same space. You should read this before you get too set on building a loop. http://www.layoutvision.com/id28.html
It would depend on a few variables of your wants/needs. I always push my radius to the max to enable the smoothest possible operation, however I'm of the type willing to sacrifice an inch or two of radius (except below my absolute minimum) in order to keep a 3"+ buffer from the edge of the layout (I'm in N Scale btw, so ~6" in HO). I use that buffer not as a safety for falling equipment (though it does help), but as a scenic buffer so that it does not appear that my trains are running on the edge of the universe. That being said, in the past I would never go below 11" (Absolute Minimum), and now that I'm putting much much more time into the planning stages, my absolute minimum radius is up to 14" (Again, for N scale). So if my design hit a snag where 14 inch radius travels less than 3" away from the edge I would re-design as much as necessary to avoid that.
If you ever want to photograph your trains in that section of the layout, the 3 inches (6 inches in HO) that Mark mentions will be a bare minimum. However, you may be able to rig a temporary sceniced surface in front of the layout fascia to hid the "edge of the universe" in a photograph. As far as operation alone, as long as the track is supported and the cars and locos can negotiate the radius reliably, you can go to the edge of the layout. How close to the edge you can go will depend on what you want for your layout: 1. The idea of setting the largest radius for the most reliable operation could support going right up to the edge of the layout. 2. Appearance to the operator--Minimum acceptable distance between the track and the edge of the universe is a very personal issue influenced by: a.viewing height (bird''s eye level vs scale railfan's eye level), b. type of scenery between the track and the edge (trees or buildings rising above both the track and fascia edge versus relatively level and open surface between track and fascia versus falling scenery like a 4 inch high retaining wall or steep hillside or trestle bent from the side of the track down to the top edge of the fascia board), c. colors and textures of the scenery compared to the fascia (is your eye drawn to the scenery or to the facsia), and d. your own willingness and capacity to pretend the layout extends beyond the fascia. 3. Appearance in the camera's eye --I recently took a number of pics for the TBX 3401 traveling TrainBoard gondola thread and found that 6 inches between track and fascia was often not enough...even in N-scale... because a camera does not have the ability to ignore flaws or replace flat fascia or blank spaces with imagined details (although PhotoShop can certainly come close, in some instances, and--as mentioned above--you can sometimes put up temporary scenery in front of the fascia).
