FAQ

Collapsible content

How do I select my helix from the table below?

The table below lists PMR helix solutions which have the vertical rise shown at the top of each column.

  1. Find the column with your desired vertical rise in the heading row.
  2. In that column, review the grade options for each radius. Don't go past the maximum radius for your helix footprint. (see Space Required column)
  3. Click your preferred grade for details of your helix.

What do the blank cells mean?

Blank cells means there is no mathematical solution for a helix with that rise and radius (if there was, PMR would offer it!). This is because of one or more reasons:

  • The grade to achieve this rise would be too steep for model railroads.
  • The vertical clearance between the rail head and the lower surface of the next loop of the helix would be too low.

Helix Kits - N, 1 track

Helix kits with 16" to 18" of rise, and even number of turns between entry and exit:

Vertical Rise 16" 406mm 16 1/4" 413mm 16 1/2" 419mm 16 3/4" 425mm 17" 432mm 17 1/4" 438mm 17 1/2" 445mm 17 3/4" 451mm 18" 457mm Space Required (l x w)
Radius 13.5" 343mm 3.0% 30" x 30" 76cm x 76cm
14.0" 356mm 2.9% 31" x 31" 79cm x 79cm
14.5" 368mm 3.0% 2.8% 32" x 32" 81cm x 81cm
15.0" 381mm 2.9% 3.0% 2.7% 33" x 33" 84cm x 84cm
15.5" 394mm 2.8% 2.9% 3.0% 34" x 34" 86cm x 86cm
16.0" 406mm 2.7% 2.8% 2.9% 3.0% 35" x 35" 89cm x 89cm
16.5" 419mm 2.6% 2.7% 2.8% 2.9% 36" x 36" 91cm x 91cm
17.0" 432mm 2.5% 2.6% 2.7% 2.4% 37" x 37" 94cm x 94cm
17.5" 445mm 2.9% 2.5% 2.6% 2.7% 38" x 38" 97cm x 97cm
18.0" 457mm 2.4% 2.9% 2.5% 2.6% 39" x 39" 99cm x 99cm
18.5" 470mm 2.3% 2.8% 2.4% 2.5% 2.2% 40" x 40" 102cm x 102cm
19.0" 483mm 2.7% 2.3% 2.8% 2.4% 2.5% 41" x 41" 104cm x 104cm
19.5" 495mm 2.6% 2.2% 2.7% 2.3% 2.8% 2.4% 2.1% 42" x 42" 107cm x 107cm
20.0" 508mm 2.6% 2.2% 2.7% 2.3% 2.8% 2.4% 43" x 43" 109cm x 109cm
20.5" 521mm 2.5% 2.1% 2.6% 2.2% 2.7% 2.3% 2.0% 44" x 44" 112cm x 112cm
21.0" 533mm 2.5% 2.1% 2.6% 2.2% 2.7% 45" x 45" 114cm x 114cm
21.5" 546mm 2.0% 2.1% 2.6% 2.2% 1.9% 46" x 46" 117cm x 117cm
22.0" 559mm 2.3% 2.0% 2.5% 2.1% 2.6% 47" x 47" 119cm x 119cm
22.5" 572mm 1.9% 2.3% 2.9% 2.0% 1.8% 48" x 48" 122cm x 122cm
23.0" 584mm 2.2% 2.8% 1.9% 2.9% 2.0% 2.5% 49" x 49" 124cm x 124cm
23.5" 597mm 1.8% 2.2% 2.8% 1.9% 2.3% 2.9% 2.0% 50" x 50" 127cm x 127cm
24.0" 610mm 1.8% 2.2% 2.8% 1.9% 2.9% 1.7% 51" x 51" 130cm x 130cm