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Switches page 1
Nn3 Switch Conversion
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This project uses a Micro Engineering code 55 left hand standard gauge N-scale switch and converts it from standard gauge to narrow gauge. (Picture) Do the left hand switch first as the right hand one is not a mirror image and there are complications with the throw bar and snap spring to be considered. Naming the parts of the switch look at this (picture). This is an expanded article on the process as first written up by Dave Varney on a single page flyer, entitled "How to Narrow a Micro Engineering turnout in Nn3" which was distributed by Republic Locomotive Works to interested parties in Nn3. The first chore is to remove the snap spring from the back of the switch points. Turn you switch over and behind the points you will find a plastic piece that has been added to the switch with ACC glue. With an exacto knife you want to carefully pry this piece loose without damaging it. (picture) Once the "E" shaped piece has been removed then take the spring out of the switch. While you have it in hand straighten the end pieces that go through the throw bar and switch body, so that it can be reinserted into the regauged switch later on. Once removed save these pieces as they will be used again later. Turn the switch over and modify the keeper that holds the throw bar in place in the switch. (picture) Next chore is to remove the remove the points from the switch, do it carefully so as not to damage the keeper. (picture) But the points aside as you will need them later. The following two steps were considered after we had completed our first switch and we feel are significant enough to be included here. (Picture1)(picture2) The next step is to remove the ties which will be replaced with PCBoard ties to hold the rails in gauge at Nn3. The idea of this conversion is to not move the frog section of the original switch in the plastic ties. (picture) Then I removed with needle nose pliers the two guard rails located opposite the frog of the switch. The guard rail is a casting which has two feet cast into the bottom of the guardrails. These feet extend out and under the stock rail, so to remove the guard rail grasp them one at a time by the open end of the rail head and gently twist them guard rail rolling it over the stock rail. (picture) Now we need a good exacto knife blade again and we are going to cut the cast spikes on the plastic ties from the inside of the straight stock rail all the way through the switch. Then we cut the spikes from the inside of the curved wing rail. (picture) Now we are ready to remove the straight stock rail completely and put it aside for use later. (picture) The curved stock rail needs the spikes removed from the inside edge of the rail from tie 29 moving past the frog to the end of the curved stock rail. Do not remove this rail. (picture) Now we start to regauge the turnout and install the PCBoard ties. (picture) I used a 15 watt pencil iron with a fresh tip well tinned. If you use a larger iron you can cause yourself a lot of trouble. To much heat on the PCBoard tie and it will delaminate to copper surface and the tie has to be replaced. Worse still the excess heat can metal the plastic ties and small cast spike heads and then you really have problem. The first tie to be installed is no. 27. Refer to the picture we are going to solder the tie once aligned the the wind rail at the red dot. Remember that this is the inside of the rail flange way to you do want a lumpy joint. Now you need to gauge the curved stock rail to the curved wing rail and solder the tie at the brown dot to the curved wing rail. Next is tie 20, a similar process of regauging the curved stock rail to the curved wing rail and soldering the tie first to the straight wing rail and then to the curved wing rail and the curved stock rail. This time you should be soldering on the outside of the rail or non flange side of the rail. (picture) The last two ties to install are 9 and 4 or 5. (picture) This completes the curved side of the switch. To install the straight stock rail I started at tie 4 or 5 and soldered the rail in place. Make sure you have the rail the right way around. (picture) Then progress along the switch to tie 9, then 20 and finally 27. I did not install the tie at 42 as there is quite a bit of fitting required to complete the points and get them fitted properly. The modification of the points is next and is the most difficult part I found, as you have to keep several pieces in place while applying heat to unsolder other parts without disturbing the parts you do not want to change. I used two haemostats and a small portable vice to accomplish this task. First I attached a haemostat over the curved point rail and the tie bar clamping them in place with the fingers of the haemostat in line with the tie-bar. Then I clamped the haemostat in a small desk vice. I also use several helping hands made by soldering large alligator clips to both ends of a 4 to 6 inch piece of a No. 12 solid cooper wire. They can be bent to any shape I need and provide support for work item I want to hold and are stiff enough not to be deformed by the weight of the haemostat. In this instance I want to hold a second haemostat. This haemostat is clamped in the center of the tie-bar at 90° to the tie-bar. I use two of the alligator clip affairs to hold the end of this haemostat and take the weight of the haemostat so the tie bar is not distorted. Another portable vice could be used instead if you have a second one. Once you have secured the tie-bar then using a soldering iron, remove the point rail from the straight side of the tie-bar. (You could use alligator clips in place of the haemostats but they are very poor heat sinks when compared to the haemostat) The next job is to take an existing piece of track and figure out where to cut the tie bar. It must be just short enough to fit between the rail heads of a straight piece of track. You want a very close fit not a loose one. The idea is that when the points are being shifted there is a point at which the two stubs of the tie-bar which stick out beyond the point rail are not contacting any rail. This prevents momentary shorts and sparks flying with you switch the points with power to the rails. When you have the length worked out then cut the tie-bar to the new shorter length. Now I put the tie-bar with the curved point rails back into the harness in the vice. Next I applied a bit of heat to the end of the brass tie-bar and using an exacto knife separated the brass shim stock from the tie-bar where the straight point rail will be reconnected to the tie-bar. I trim the shim stock so that there is enough room to get the point rail under the edge of the shim stock and in from the end of the tie-bar about 1/2 the width of the rail flange. This time I use an Alligator clip to the hold the point rail in place ready for soldering. I apply the heat to the shim stock at the flange of the straight point rail with a bit of solder flux and solder to re-solder the joint between the point rail and the tie-bar. Here is a picture drawing covering the modifications made to the point rail assembly before putting back into the switch. (picture) The last part of the job is to put in the PCBoard tie #42. I but it in place and soldered the curved stock rail to it first. Then using a track gauge find the correct position for the straight stock rail and soldered it into place. When soldering the rail to the tie do the soldering on the outside of the rails not in the inside where your wheel flanges run. Here is a peak at my switch after installing the points. (picture) The last job is going over the PCBoard ties and cutting the gaps to prevent short circuits. Each tie has to be cut between the point rail and the stock rail. There are several places where you have very close tolerances and a short could occur. The first is where the rail joiners for the point rails are located on the end of the wing rails. If you did not gauge your switch properly and the rail joiners are touching the stock rails then you have a problem until you get a gap between the two stock rail and the rail joiner. (picture) Now you have your switch how are you going to wire it. This is a power routing switch also known as an electro frog by some. It means that you have to isolate the rails on the frog end of the switch either close by or further away on one or both rails depending on how the track is wired before the next switch. If you have a passing siding totally within one block then the frog rails only need to be gaped between the two switches. If on the other hand the point end of the two switches receive their power from two different blocks then all four rails between the two switches have to be gapped to prevent a short circuit from occurring when one switch is thrown opposite of the other. Here is a picture of the standard gauge switch and narrow gauge switch side by side. (picture) Now to deal with the problems that will come up when you convert the right hand switch. What is the difference between the two switches. The location of the snap spring for the points is the difference. On the left-hand switch it is located under the curved stock rail and so does not have to be moved. On the right-hand switch it is located under the straight stock rail and so has to be moved. If you are not going to use the spring then it does not matter but if you wish to maintain the snap or locking feature then some extra work is required. On the right hand switch you will need to mill some of material from the back of the tie that holds the spring to make room for the spring. There is a mark on the tie where you have to drill the new hole for the spring on the other side of the center line. I used a #77 drill bit to do this. On the tie-bar there is a third hole on the opposite side of the tie-bar from the existing hole for the spring. I drilled this out with a #75 drill bit. (picture) On the reverse side you have to remove the "E" shaped piece to see the stepped part of the tie which was located under the open end of the center leg of the "E" shaped piece you removed. (picture) Starting at the new hole and working out to just under the inside edge of the rail flange, you need to remove the tie material to a depth equal to the low area on the other end of this tie. Try not to take out all of the center raised area if you can as you need it to support the "E" shaped piece when you reinstall it. Now you are ready to shift the spring from the straight side the the curved side of the switch. (picture) Now you are ready to re-attach the keeper plate, only this time you have to install it so the bar is over the spring in other words the "E" shaped piece will be turned 180° from it original position. The keeper plate has two small pegs which require new holes to be made in the new location. I used a #65 drill bit to make 2 blind holes for the "E" shaped keeper plate pegs to fit into. (picture) If you are going to convert the switch to narrow gauge then remove the spring and keeper plate and put aside for later use. If for now you are going to use it for standard gauge then install the keeper with a bit of ACC glue used very sparingly. (picture) |
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