(over) stimulated by the discussion on another thread about Flyer curved track, I rummaged around in my notes and miraculously found some measurements I had made a few years ago of a circle of Gilbert flyer track (the only track I have is the original flyer track).  I then supplemented these with additional measurements shown below.  I figured if I posted the results here I'd at least be able to find them again via the search function...!

Gilbert Flyer curved track

My original measurements were done in millimeters, so I'll give all these in mm first and then convert.

The diameter across the circle, from the inside of the inside rail was 950 mm - that's probably good to +/- 4 mm.  I'm sure I "squared" the circle, so I got similar measurements across several directions, but my notes only report one value.  I should have made and recorded several measurements, then averaged, but it appears I didn't.  Today I measured D, the distance across the rails from outside to outside, 27.1 mm, and T, the length of the tie, 47.4 mm.  With all that, here's what you get.

R = 475 mm = 18.7 in. ~ 18 11/16 in (to the nearest 1/16 in.).  So the diameter is 950 mm = 37.4 in ~37 3/8 in.

D above is 27.1 mm, so the radius to the track centerline is 475 + 13.55 = 488.6 mm = 19.2 in ~ 19 1/4 in and the radius to the outside of the outer rail is 475 + 27.1 = 502.1 mm = 19.8 in ~ 19 3/4 in

T above is 47.4 mm, so the radius to the outer edge of the tie (not the roadbed) is 488.6 + 23.7 = 512.3 mm = 20.2 in ~ 20 3/16 in

Just for giggles, the radius to the inside edge of the tie is 488.6 - 47.4 = 441.2 = 17.4 in (so that's not how Lionel gets S36!)

BTW, for those of you who remember high school geometry (or can google 'chord to radius'), I used that method as another way to estimate the track radius (to the inner edge of the inside rail) and got ~477 mm...

In any event, there doesn't seem to be any dimension that is 'exactly' 20 in (or R20, as Lionel sez) and certainly nothing even close to S36 (or R18).  Still, Tom (AMFLYER) on the other thread got it right, that the values for Gilbert's original 20 in radius, 40 in diameter curve is approximately the dimension of the table top that would (just) hold a circle of track.



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Original Post

A major problem with trying to determine original Flyer radius from track is the lack of consistency with the curve track. The metal is ‘springy and no two pieces are exactly alike. If you want to use your method, try making a circle from Flyer switches. The thinking is the plastic should be reasonably stable, at least as far as holding the metal rail.

I’ve attached some old drawings I did some time ago. The stated radius of the SHS S-Trax came from a post by Don Thompson, however I don’t think the info was correct even though it is documented. Maybe he was thinking the inside edge of the roadbed?

5” centers for Flyer track also yields a radius which is too small. If you measure the parallel track from a cross-over made from two Flyer switches you get 5 1/8” centers and that results in a roughly 19 1/8” radius. I believe somewhere Gilbert said the radius is 19”.

Let me know what you think…

Tom Stoltz

in Maine

Am Flyer Curves B&W


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Wow! Thanks for all the careful and detailed measurements. I see in your picture the track is in a piece of rubber roadbed. I know from 55 years of building layouts with Gilbert track that a circle of track plus one 10" straight will just fit on a 50" board if all the track joints are perfect. When I started using the rubber roadbed that 50" became 50 1/4" no matter how hard I tried. The rubber roadbed impacts the track joint fits ever so slightly. In any event Gilbert intended their sizes to equate to table sizes rather than track centerlines as you so capably proved.

Interesting, Tom. In my experience the SHS track has the same centerline diameter as the Gilbert track plus or minus about 1/8". I round it off to 19" but in all honesty when using the Gilbert track I only care about the outside dimensions to the edge of the ties. As you said, the Gilbert track is not completely rigid. I have not tried the "all turnout" approach.

I'm all on board for metric, but this is a discussion about American Flyer from the 50's ; should be talking inches.

Tom (the AMFLYER one) -- that Johnson rubber roadbed measures 66 mm across, so using my value for the centerline radius of 488.6 mm plus 33 mm one gets a radius to the outer edge of the rubber roadbed of 521.6 mm or 20.5 inches -- so I can see how you'd have trouble getting track with the roadbed plus a 10 inch straight into 50 inches -- 51 would be tight.

I add 2” to the calculated Gilbert layout dimensions when using the rubber roadbed, it fits with a bit to spare. i was commenting on the slight increase in just the outside tie dimensions when using the roadbed. It is too bad the Johnson roadbed is no longer made.

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