Track basics Track Joints When laying track, it is a good practice to alternate which way the bolts head through the rail. The full size does this as if a car or engine derails, the nut side can be sheared off and the bolts with the heads will be passed over, keeping the rail joint intact. Having a tie under the joint is helpful to support the joint, but there are times where it doesn’t work out and that is fine. The joint should have an expansion gap to give space for the rails to expand as the rail heats up. When spiking the ties, the spikes should not be straight across from each other as the tie will be free to twist. The spikes should be staggered from the outside to inside of the rail. But should not angle the same direction as that can cause the tie to twist and change the gauge. The rail should be spiked so the spikes that are on the inside of the rail are towards the same edge of the time and the spikes that are on the outside edge of the rail are on the opposite side of the tie. If the tie shifts, this will help keep the tie from twisting. (The top tie in the picture is done poorly. The bottom two ties are done properly.) Guard rails for bridges/trestles/etc. The guard rail should be placed inside the gauge far enough away from the main rail to allow the widest wheel to easily pass between the main rail and guard rail. If it is too tight, the wheel might not be captured but skip right over the guard rail. If a guard rail is used on a curve, it should be placed along the inside rail of the curve as if a car/engine derails, it will head towards the outside of the curve and the guard rail along the inside rail will keep it from doing that. Guard rails on switches The guard rails on switches should be set so that the wheel set with the largest back to back does not pick the point of the frog, but if the wheel set is up against the guard rail, the other flange has clearance with the point of the frog. If it is not set up this way, a wider axle set could pick the frog and derail. If the guard rail is too far away from the stock rail (or is not there at all) that axle set will be allowed to wander and pick the point of the frog. The wing rail is then set so the narrowest back to back axle set does not ride up on the wing rail. The pictures show a guard rail that is properly positioned and the flange at the frog and then shows what happens if the guard rail is missing or is too far away from the stock rail. Points on switches In full size, the point starts below the stock rail height and catches the flange. Then the point rises so it is 1/4 above the stock rail so if wheels are hollow (from being worn) the outside edge of the wheel wont interfere with the stock rail. The point is then back at stock rail height when it connects at the heel block. In 1:4 scale it would be a good idea to have the point rise so it is 1/16 above the stock rail and in 1:8 scale maybe 1/32 above the stock rail. The stock rail for the diverging track in full size is also kinked right at the point (the kink depends on how sharp the curve is) and the points are straight. The frog is straight and the stock rail curves at the desired radius/curvature and the rail heading into the frog is curved slightly tighter to account for the frog being straight. The angle of the frog is a tangent to the desired radius. For each radius, the frog will have a different angle. Ballast and Tamping Ballast (crushed stone) is used to give a good stable basis to support the track, anchor the track so it doesn’t move freely out of position and to allow drainage. The ballast should have rough/sharp edges as rounded stones (such as found in rivers) won’t interlock very well. To allow for proper drainage, the ties need to be sitting on ballast and not on the bare ground. Once the ground is graded, a decent layer of stone should be laid down and then the track on top of the initial layer of stone and then more ballast added on top. When tamping, do not tamp in the center of the tie but both sides of the outside ends of the tie and both sides of the tie just inside the rail. When tamping use a solid bar (I use a steel bar) and pound it into the ballast near the tie. This will force the ballast under the tie to support the track. The reason why the center should not be tamped is it may be possible to pack the ballast under the center of the tie tighter than the two ends which will give more support in the middle causing the tie to rock and bend and raise the risk of breaking the tie. Once the ties are tamped, more ballast can be added to level up the ballast and make the track look neat. Grades, straights and curves On a full size railroad a 1.2% grade (a 1.2’ rise in 100’, 1:83 grade) is considered a normal maximum for a main line. The steeper the grade, the less an engine can pull. If what an engine can pull on straight, level track is considered to be 100%, a 0.2% grade (2.4” rise in 100’) cuts the train down to 50%, a 1% grade cuts a train down to 16.6%, a 2% grade cuts a train down to 9% and a 3% grade cuts a train down to 6%. (As an aside, most roads are marked as a steep hill at a 12% grade or more.) The bigger danger is the steeper the grade, the greater the risk of having a run-away train. Most scale equipment only has brakes on the engines and the cars don’t have any. This minimizes the braking power for coming down the hills, especially if the hill is on a long straight of way (curves add resistance which helps keep the speed under control when heading down hill). For most scale railroads I would recommend a 2% grade maximum. There are times when up to a 3% grade is needed, but I would use that sparingly. On straight track, the rails should be level with each other whereas on curves, the outside rail is picked up above the inside rail to give the curve superelevation. The tighter the curve and the faster the train is to run over the curve means the more superelevation the curve needs. I have around a 50’ radius curve and the superelevation is around 1/8”-3/16”. When transitioning from a straight to a curve, the full size slowly decreased the radius to the desired radius (slowly tightening up the curve) instead of going directly from a straight to the curve. This is a good practice for miniature as well and as the radius decreases, the superelevation increases. Once the track is graded, tamped and ready for service, riding an engine or car over the track will let the rider knows how it feels. If it doesn’t feel right, then the track may need to be adjusted. The track should feel smooth and natural and not like the car wants to tip over on the curves or is bouncing/rocking down the track. The best practice is to use the greatest radius of curve that is possible and to use the smallest grade as possible. This will minimize the resistance that the track will have on the train. Gauge All of my equipment is 7.5” gauge and my track gauge is 7.530” max on the straights (1/32” over) and 7.562” max on the curves (1/16” over). In miniature and full size the practice is to have a slightly wider gauge in the curves than the straights to allow extra room for the wheel sets, especially with long rigid wheelbases, on the curves. I do urge caution about making the gauge even wider as the wider the gauge, the more room the wheel sets have to hunt/more room the wheel sets have to move laterally. With 1:8 scale equipment, the width from the outside of one flange to the outside of the other flange is about 1/16” less than the nominal gauge. For 7.5” gauge equipment, this means the flange to flange measurement is 7-7/16”. On a curve that is set at 7-9/16” there is an 1/8” difference between the flange to flange measurement and the track gauge. If the track gauge is set at 7-5/8”, the difference is now increased to 3/16”. If the gauge on straight track is set at 7-5/8”, the equipment can move laterally/hunt by 3/16”, which I believe is excessive as this means that the cars can be nosing as they run down the track with the front of the car going one way and the back going the other way with up to 3/16” movement. 7.5” gauge equipment is meant to run on 7.5” gauge track. “Grading the Track A transit is really useful when laying out and grading the line. Height differences in the land and grade can be measured and the grade can be calculated. Since I didn’t have a transit but knew the approximate height difference of my land (about 63”) I knew that for my 485’ loop I would need a 3% grade which would also be on a 52’ radius curve. I used a string line to plot the basic curve and used a board with a level to figure out the grade. With a 48” level, I needed to place 1” high spacer under the level at the 33” mark on the downhill side of the level. Once the level read level, I had my grade. (For a 2% grade, a .96” spacer would need to be under the 48” mark on the same level). Once the track was laid I had to grade the track and level up the rails on the straight and get the superelevation the curves. I laid on the ground and sighted down the rail to see where the low spots (and high spots) were and then picked up the low spots and tamped them. On the straight track, I then used a level to raise/lower the opposite rail so it was level with the firs rail I tamped. On the curves I sighted down the inside rail first and then raised the outside rail to the superelevation that I wanted. When care is taken in laying, grading and leveling track, a very good running track can be made. This will also create a much more stable and comfortable ride. Track work is a lot of work and regular maintenance will need to be done to keep the track in good condition.
Posted on: Fri, 26 Dec 2014 21:45:29 +0000
Trending Topics
Recently Viewed Topics
© 2015