Dan/John/Mark/Tom,
Here’s some comments I made to a friend. Please let me know if I’m close or way off base.
I believe there are 2 things at play with easements. The 1st is the front (or rear for that matter) hitting the track. The 2nd is what looks good, particularly with large engines.
I understand the 2nd one more than the 1st. The way I see it is if an engine can go up 1/8”, then 1/4”, why can it go up 1/4” to begin with? Doesn’t 1/8 become 0 for the next section so you 0 to 1/8, then 0 to 1/4, 0 to 1/2, and so on? I suppose there’s some geometry involved with how the rear moves as the engine climbs, so the 0 isn’t really 0.
One thing I always thought was that those using L-girder simply cookie-cut a length of plywood sub-roadbed and used risers to raise it at regular intervals until they reach their desired grade (2.4%-2.6% or whatever) rather than use a bunch of shorter tracks. Dan used 35” segments and 1/8, +1/4, +1/2, etc. L-girder is often 16” centers, so the intervals and amounts would be different.
As far as bending goes, if you tack the end of a 40” straight to the sub-roadbed, then raise the sub-roadbed X”, the track should bend to match the sub-roadbed as you tack it down. The same should happen to the pin when you add the next track, though the pin might be too strong and need a little help. The technique is probably the opposite of using a hammer to straighten a bent nail. I really don’t think it should be necessary to use shorter tracks. It is in the software if you want to get a more accurate representation of the easements and actual grade. If you put 3% in SCARM, then add the beginning and ending easements during construction, the section between the easements will end up being greater than 3%.
When trying this out with Dave’s layout, I put together a Ross 20 track plus 2 Ross 15 tracks to get 35” sections. Then I raised the first 1/8, the 2nd 3/8 (1/8+1/4), and so on until I hit my desired grade. At that point I added more sections using that same added height. Once I got to above 2%, I lowered the rate of incline in reverse order. As you can see in the photo I posted, I reached 2.5% with the 4th section. Unfortunately, I only had 2 more sections to work with, but needed 4, so I’d have to back off to 3 sections for the beginning easement and 3 for the ending. That means I couldn’t rise as high.
If it were me, I wouldn’t use shorter tracks. I’d use the longest tracks that fit and just place the shims at the correct intervals. If your bench work has 16” centers, risers could go 1/16, then 1/8 to get the 0.3% initial easement.
