Phillip Taylor describes how he adapted a MODRATEC interlocking machine to link with a set of 14 MSE levers.
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ADAPTING MODRATEC INTERLOCKING TO THE MSE 14-LEVER FRAME
© The content of this article copyright 2007 Phillip Taylor. Send email for Phillip Taylor via MODRATEC.
Several years ago I had built an MSE 14-lever frame to control the points and signals on my P4 model of Newick & Chailey, on the LBSCR line between Lewes and East Grinstead. The lever frame design is based on a simplified version of the original signal box diagram as published in the 'Brighton Circular' Vol. 15 No. 2.
At the time I had the vague notion that I would one day fit interlocking, without any firm idea of how to achieve it! In the meantime I built a couple of MODRATEC interlocked lever frames for other locations and found the process to be satisfying and straightforward. Their computer program (SigScribe4) that allows you to design your lever frame and which calculates all the required interlocking for you is very clever indeed. Having checked the lever spacing and required throw to operate the tappets (about 9mm) it seemed feasible to adapt the MODRATEC interlocking to suit. I therefore made the necessary design using SigScribe4 to suit the existing lever layout. The MODRATEC system is based on 6 lever groups, and as the MSE lever frame has 14 levers it was necessary to make a design based on 18 levers, with the outer two at each end spare (in fact these tappets are simply omitted). I then contacted the ever-helpful Harold at MODRATEC to see if he would help. With a positive response and a substantial discount from the normal (already very reasonable) price because a significant proportion of the parts (such as levers, lever brackets, etc.) would not be required, an order was placed.
Normally the MODRATEC locking frame is located to the front of the levers. However, to suit my installation I placed it behind them. This is OK provided that the lever sense remains the same, i.e. back for normal. This could be reversed if necessary by putting the attachment points for the tappet links below the lever fulcrums. In order to gain easier access to the locking frame when in situ, I did toy with the idea of building it upside down, but decided against that as the risk of a disastrous construction error would be high!
The parts as received are basic pre-cut lengths of various kinds of brass section plus assorted brass fixings and Perspex plates (Photo. 1). I should emphasise here that it is essential to take care, work methodically, and follow the instructions exactly. They are written without assuming any previous engineering knowledge on the part of the builder, and are easy to follow provided sufficient care is taken. I would also recommend using new drill bits of exactly the recommended sizes, whilst a vertical drill stand makes the job much easier. Various 'tools' (actually simple pre-drilled jigs) are provided to enable the holes to be drilled in the correct positions. As the instructions are comprehensive, I will only describe the adaptations. Obviously all parts relating to the levers can be ignored. It is important to note that when drilling the bearers it is essential to keep the bearers at the full length until after the holes are drilled, because the holes are referenced from both ends. Once the holes have been drilled it is OK to remove the redundant rear sections where the levers would normally be mounted.
It is necessary to provide a firm mounting for the locking frame with no free-play or movement between it and the lever frame. I had already mounted my lever frame in a purpose-made MDF housing, and I fitted two cross-pieces of 20mm square softwood secured by screws from each end (Photos. 2 & 3). When fitting the assembly, make sure that the horizontal mid point between the upper and lower tappets is approximately in line with the tappet link take-off points on the levers. This will prevent the tappet links from taking excessive vertical angles. I had originally drilled 0.9mm holes in the MSE levers prior to assembly with the possible use of additional links in mind. Of course, such a small diameter would not be strong nough for the tappets links themselves, so rather than dismantle the lever frame to re-drill I used 2.1mm dia. steel wire (from coat-hangers!) with a piece of 0.8mm steel wire soldered at the point where it entered the lever (Photo. 4—note that the bend in the larger diameter wire is increased prior to fitting). I made a simple jig with a nail and a hole in a piece of wood to ensure all 14 links were identical—the bend at the tappet end and the soldered wire are perpendicular to each other. The tail of the small diameter wire is bent back after fitting to retain on the lever. Normally piano wire is provided for this function, and if I was starting from scratch I would drill the levers to a suitable diameter for this.
The lever spacings of the MODRATEC and MSE frames are not identical, which means that the tappet links become progressively more angled nearer to each end. In order to minimise this I drilled the holes in the tappets for the tappet links off-centre (Photo 5), which also prevents the upper and lower links interfering with each other. This does not affect the function. Some of the links were bent in the horizontal plane to allow a better fit. All adjustments must be completed before marking the notches on the tappets. (Underside view, Photo 6. The levers without slide switches are for the facing point locks, which perform no function on the model).
Although it is necessary for the tappet travel to be of the same order as the standard MODRATEC design (about 9mm), the exact travel is not critical because it is automatically taken into account when notching the tappets. Similarly, if the angled tappet links give rise to a slight variation in travel from the ends of the frame to the middle, this is likewise catered for.
Assembly of the locking frame can then proceed exactly as per the instructions (Photo 7), allowing for your chosen design of tappet link. The tappet links are retained in the tappets by their ends being bent back beyond 90 degrees, and here I must confess to a stroke of luck! In order to connect the links to the lower tappets it is much easier if the tappets can be tilted downwards at the end further away from the levers. By removing the fixing screws from the rearmost wooden cross piece and loosening those on the front one, this was easy (Photos 8 & 9).
As a result of the restricted access to the upper side of the locking frame caused by my installation within a semi-enclosed box, it was necessary to be very careful when marking the tappets for their notches to avoid parallax error.
I was a little concerned that the fulcrum rod of the MSE lever frame allowed too much movement in the levers when under load and considered adding a central rigid mounting point. However, in fact this was not necessary and the assembly worked fine without it. [MSE points out that with their 7-lever units, the fulcrum rod is supported every 7 levers, irrespective of frame length. ED] (Photo 10 shows the lever frame, the distant levers are green as per LBSC practice. Photos 11 & 12 show the finished installation from above and below respectively.)
In all this adaptation proved rather easier than I had anticipated and I now have a fully interlocked lever frame. All I have to do now is build some signals!
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Thank you for producing a great kit. (Chris)
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