construction of constant radius spline?

Model Railroader Layouts and layout building
1

i need a constant radius dia 56" loop at the end of a 32" wide pennisula. i was planning on building the loop as a spline rather than using up a sheet of foam and dealing with supporting the outer edge.

planning on using 1/8" masonite, probably with softer and thicker material between layers of masonite.

wondering how to maintain a constant radius, assuming a curved wooden template cut at the inside radius for a portion of the circumference

doesn’t need to be perfect if the spline is ~2" wide. an accurate center line can be drawn when completed to locate the track

2

Is the 56" the radius or the circumference ?

I guess that I would build a jig that might be just part of the curve.

Start the build and just move the jig has a section is completed.

Either way that is a big circle!

3

One of the nice features to spline roadbed is that it creates a natural easement curve. But I do see the need to control things so that your desired minimum or “real” radius is maintained. I think the idea of constructing it within a jig makes sense. I assume that the finished spline roadbed will actually have some degree of flexibility when completed.

Dave Nelson

4

If you have a suitable surface on which to work, you could simply draw the curve in pencil, then use nails spaced-out along the line to act as a form, then add less-closely-space nails to keep each consecutive strip properly spaced from the previously-applied one.

Wayne

5

Ya, it will be as flexible as cement.[swg][(-D]

I put a nail where the centre spline was to go and proceeded to ad the three 1/4" splines to one side, then pulled out the nail and added the other four. Initially I just clamped the uprights to the grid as there was no set distance between them. Once the spline was in place I adjusted the uprights for height to adjust the grade by using a tailors measuring tape to measure the distance between them and doing the math.

I beveled the outside splines for that angled roadbed look, no need for cork roadbed on top if you do that, thus reducing the cost even more.

The curves in my spline were so far above the minimums that I did not need to worry about the radius, just the grade change. I just routed the spline as I went. The bench is 6’ wide.

This 4’ span without support has been there for 14 years and has not sagged so much as a mm. Someday a bridge will go in there.[(-D]

I used 1/4" hardboard cut into 1" wide strips. Making them 1" wide makes the math easier when calculating grades. With no roadbed required this is very economical, you can get a whole lot of 1" strips out of a 4’ x 8’ sheet.

As far as mapping out the radius, when required, I use an old wooden yardstick with holes for the pencil tip at one end and a nail at the other. Close enough works for me.

https://www.youtube.com/watch?v=KbUhA2_F-7M&ab_channel=BATTRAIN1</

6

You can use the usual techniques: a trammel, pencil, on a surface.

The idea of drawing the centerline through the arc you need, and then using dowels or nails driven into the surface at the appropriate distance from that depicted arc that would allow you to form the arc out of splines with the nails/dowels acting as fulcrums should work.

MDF splines worked well for me formed around screws driven into the tops of risers. If you’re not fixated on precision here, and are satisfied with an approximation of a specific radius, that’s the way to go. Glue an initial three splines on the outside of the screws, lapped and clamped, and when they’re solid, another three lapped and clamped to the first splines, but on the inside of them along the curve.

And Brent knows from experience that splines are like concrete. No sproing, unless they come unglued, no give, not in any axis. They’re like 3" steel pipe 18" long. Good luck bending it without significant mechanical help.

7

I’ve wondered, why spline? It seems like a lot more work.

8

I love spline as it was so much fun to lay/install? It was over way too fast for my liking. You can get 64 linear feet of subroadbed for the cost of a sheet of hardboard, so if you are on a budget you can’t beat it. There is not the waste you get with cookie cutter. You do need a saw to cut it up though. I have a table saw and a radial arm saw. I wheeled the radial arm saw outside and used that. I cut the sheets in half lengthwise with the circular saw and fed them through the radial. Don’t forget to bevel/taper some of the cuts for the outside pieces.

I used a combination of spline and foam for subroadbed. Next time I will put spline everywhere under the mainline as it is more solid and stands up a little better under the mains. Don’t get me wrong, if you want to lay your track on foam go for it, I have had no issues doing just that. The spline just gives that little edge over foam for a subroadbed.

I have added turnouts and sidings in a couple of spots and all it took was to glue some more splines onto the existing ones which took no time at all to do.

For terrain, you can butt foam up against the spline, staple or glue screen, or cardboard strips to the side of it. Choose your favourite method.

Here I had a change of plan in the terrain and glued cardboard to the side of the splines with the glue gun. The double track is splines with spacers in between.

Depending on what tools you have, there is more than one way to build a layout.

9

less material and hopefully stronger structure in a more exposed location

10

It does seem like a lot more work, and that was my orientation when I did it on my second layout. I was surprised, though, at how quickly it went. The thing we all seem to miss is that, if you slat up a sheet of 1/4" MDF, a full 4X8 sheet of it, you’ll end up with about forty-five 8’ long slats. It might take you a couple of days or four to layeer four or more splines for your main, waiting for the glue to dry each time, but inside of three/four days you have 50’ feet of nicely flowing roadbed. The splines naturally curve in any axis as you lay them, provided you take care to position your supporting risers correctly to help orient them according to your plan.

Once I closed my loop, I think inside of three days for the layout pictured below, by far the heaviest workload was forming the terrain over sheets of window screen by mixing and dying successive, many, many, successive 8 cup batches of ‘ground goop’ using that formula that Joe Fugate shared with us here back in 2004/5. But the mains, fashioned from 5-6 layers of 1/4" X 15/16"X 8’ splines went at a torrid pace due to their 8’ lengths.

Again, once they’re dried, they’re amazingly robust and rigid. At that point, the limit to their durability lies in the strengths of the various supporing risers and how they’re anchored (normally, top predrilled down into the top of the riser, countersunk enough to bury the head of a simple 1.5" wood screw).

11

Crandell, what glue did you use, just curious? I used a hot glue gun, I would glue and clamp about three or four feet at a time and of course, it was set in under a minute and I moved on. After it was all together I used drywall screws every foot alternating sides. It is very important to drill pilot holes for this. I also used drywall screws down through the top into the riser.

It has been in place 14 years without showing any sign of failure.

I also put a little superelevation in by using a rasp. That was very easy.

Went to a steel stud and cement roadbed over the fireplace to avoid expansion and contraction issues.

12

I have been watching this with some interest. I have built a lot of layouts, both for myself and for/with others.

I have never used spline roadbed.

On the other hand, I have never used foam either…

I get the idea of the free flowing more natural path, I just never saw an easy way to establish that path?

My other built in bias - I don’t like Masonite.

Other concerns/questions - underside clearance, roadbed thickness for switch machine rods, clearance for hidden trackage below?

AND, a great many of my layouts have had lots of double track - or more - that’s a wide spline…

I’m with Jim at this point, it seems like a lot more work?

AND, I always viewed it as something for layouts with very large radius curves, potentially larger than my 36" to 48" curves.

Surely not for 28" radius curves? But what do I know? Not much about this method of construction.

For what it might be worth, I have seldom cut large curved sections out of plywood either, there are strenght issues with that.

I have used a biscuit joiner to join sections of roadbed cut from 3/4" lumber. I have laminated 3/8" plywood into 3/4" “seamless” curved roadbed.

While the detailed civil engineering of my trackwork is done during construction, I do often desire or need to follow the “plans” pretty close to make everything work, track centers, easements, etc.

Thoughts please.

Sheldon

13

I agree that masonite is a weird product and I am not even sure why it is made. I have used it for the spline roadbed and my backdrop and have not had the slightest issue with either one, however, I can’t think of anything else I would ever use it for.

When I went with foam and spline it was just to try something different. I am not in the same league as most on this forum, for every hour I spend at the hockey rink with minor hockey and other community activities I spend seconds on the layout. After fifteen years my photos show not much progress.

I have not had any issues with using foam or spline. I am just getting to the point of installing switch machines and I am using Rapido switch machines that are installed topside. Rapido has an installation video that shows how to install them in foam or wood.

My layout is pretty simple and straightforward, built for running trains and modeling the vastness of the landscape found through the Rocky mountains. There is a very good chance there is another layout in my future when we move. I have been exposed to all types of layout construction since I was a small boy. I am convinced there is not a one size fits all for that. I would bet I will use a combination of all types of construction on the next one. Any mainline will be on spline and/or plywood, yards will be on ply or foam. I will certainly use foam for terrain as it is so versatile.

People generally do not like change and the rhetoric and reasons for not doing something different always jump to the forefront without any consideration that there might be benefits to making that change.

Way back when I joined this forum there were some pretty intense conversations about how people were moving away from L-Girder construction that I frankly could not get my head around. In all aspects of life change is growth, sometimes it is for the better sometimes not so much.

14

I fear we might be hijacking this thread. Although, it’s partly relevant. Sorry to Greg if we are doing so.

My first layout was mostly foam. It worked, but as you might imagine, me being wholy green, it was not a great effort or result. Next, I thought I’d give splines a try, and I think it went swimmingly. Third was cookie-cutter and I made a large helix with a mountain cover. Again, success.

So, like Brent, I like to try different things. The splines are no more spendy on time than any other method I have tried, and I’m going on three different methods now. Fashioning vertical and horizontal easements are a breeze with splines. If you situate your risers at the appropriate heights, they’ll bend naturally, just like flex track. Probably the trickiest part is walking away only after you’re sure the splines are all lined up against each other when you clamp them. Otherwise, you have a lot of shaping to do later with the surform file.

Brent, I used aliphatic resin, or yellow glue. I only used the hot glue to affix the window screening swatches to the sides of the splines. I don’t know that I trusted the hot glue with the splines, and maybe, I forget now, the instructions I followed said to use wood glue. It was somewhat messy, as you would assume when clamping the splines, but paper towels or newsprint took care of that problem.

15

Brent,

Thanks for your thoughts.

I’m an engineering kind of guy, so show me way something is better and I am all in. One example for me was gluing down track with adhesive caulk.

BUT, I don’t imbrace change for change sake, new is not always better, often it is just different.

I’m already heavily invested in Tortise machines, Atlas switches and track, and a few other things.

Nothing has come along to justify replacing those investments, at least not as it relates to my specific goals.

But back to benchwork. I have always built some sort of hybrid open grid/L girder benchwork combined with table top for areas like cities and yards.

One of the first questions I have with spline is how to transition to table top areas?

For my purposes these days, I see L girder as pointless - it is for people who plan as they go and who are likely to make changes - neither applies to me.

Spline seems hard to plot the exact curve or location, that is the part I don’t get?

Thanks again,

Sheldon

16

???

17

Read on! The rest of Sheldon’s post explains these remarks.

Rich

18

sorry. i didn’t see the better any other approach being suggested

19

Sheldon - " …But back to benchwork. I have always built some sort of hybrid open grid/L girder benchwork combined with table top for areas like cities and yards…"

Sheldon, you asked how to transition splines to level surfaces, like to a yard throat or something similar where the expanse opens for ladders, caboose tracks, etc. It’s the same philosophy as you state in my quote of your text. You figure it out, you engineer it, you nip 'n tuck, cut out, shim up, that sort of thing. You bring the splines down to level by fashioning them to meet, at grade, with the yard surface. That could be with a shorter riser to accommodate the spline’s vertical depth, or notch a joist…whatever seems to work and will bear weight sufficiently.

20

I have never used Masonite as spline, but I have spanned a 6 foot distance by laminating three 1x4s together with glue and screws, then capping it with a traditional board, in my case a 1x6 for an extremely narrow shelf over the span.

If I wanted a wider subroadbed table top, I could use two 1x4 lam-beams spread 16 inches apart.

I could see using the masonite for making curves, as a support for traditional plywood subroadbed. Cut out plywood at the precise curve, then use it as a template for the masonite spline, and as a final cap so traditional caulking or nailing roadbed and track to plywood would still happen.