Mark

Next time I look at the drawings I will check the date. I have some copies of some pictures taken by Mike Longridge which show the new bridge in its final stages of construction. Shows people walking along the top with no safety equipment whatsoever and the line was clearly open to traffic. There is some stock in the background which suggests early post war. Regards Mark Humphrys

I am slowly working through my list of corrections. Nearly there now! Regards Mark Humphrys

Here are the final images of the bridge taken at the end of September. It won't be painted as it was a test build, but I now need to make the changes for the production etch.

I should be there for the day on Sunday, but I will ask Paul to bring the bridge on Saturday to go in the display cabinet. Regards Mark Humphrys

Thanks Mike. Did the 45xx beading work? Today I have finished glazing the west side of the bridge and the photos show the steps to get there. It was actually a lot easier than I thought it would be. The only serious issue is I don't think the frames are high enough, but the concept works, so it should be a simple mod. The first images are of the inner and outer parts of the frame being assembled and then a piece of clear plastic frosted with a glass fibre brush is slid between the frames. The images on the bridge show all the windows loosely positioned. Regards Mark Humphrys

Funnily enough the next job is to put the windows on the back of the bridge, hopefully this evening. They are etched as part of the kit, but only for one side since Brent only had them on the West side. The legs were enclosed on the bridge at Brent but this was removed sometime in the 30's. I have drawings for the panels, but I haven't included them in the kit. That is the reason the diagonal braces are only fitted to 3 sides of the support tower, because the entrance was under the bridge. Thanks for the positive feedback. I am hoping to have this built in time for Scaleforum. Regards Mark Humphrys

Thanks for all the comments guys. Not posted anything for a few weeks due to work commitments. I have done a fair bit now and have got the main superstructure soldered together now. I have also added the smoke deflectors and a few other small details. Regards Mark Humphrys

I have spent the last few sessions working on the second staircase and made a start on some of the details. The photo's show various bits being assembled and then the key sub assemblies balanced together, or temporarily stuck with Pritt Stick to hold in position. Another few sessions and I can start soldering together all the main components. The jig is for forming the stiffening braces that go under the main span and the image shows the tags that locate the bar for forming the bend followed by the web of the brace and the locating slots. The valences have some beams to go between them and the frame which holds them further out than they are on the photo's, but these can't really go on until the structure is fully soldered together. So far I have not come across any major issues with it. Regards Mark Humphrys

I haven't found too much difficulty with folds that are in full thickness etches where a half etched line suffices. The problems were with the legs, where the actual leg is half etched. I put a line of small holes in to weaken it for bending, but it was still too stiff, which increased the risk of bending the diagonal braces as result of excessive force so this will be modified to fold along a dashed line rather than a dotted line. Also the small holes etched on the half etch 180 degree fold on the steps needs to be weakened as well to speed up the process of folding 40 individual steps, so I will probably do this with dashed slots as well. Regards Mark Humphrys

I have been asked by others if I would consider a 7mm version. It is quite possible, although I would have to adjust some parts to make sure it scales properly. I think I will get the 4mm version sorted first and see how it goes. I would need four new tools for a 7mm version, so I would need to be confident that I don't end up out of pocket on it. Regards Mark Humphrys

Thanks for your kind comment comments. The bridge is made from Nickel Silver and is intended to sit below the surface of the platform by 4mm. I have had a quick look at the thermal expansion for Nickel Silver and it seems to be around 1.6e-5mm/mm/degC. The total width of the bridge is 240mm, so on the assumption that you have a temperature range of 45deg C, then the total expansion is 1.6e-5x240x45 which gives a total deflection of 0.17mm. I suspect the reality is the temperature when the bridge is installed would be around mid range, so you have a deflection of +/-0.085mm. I can't see this being a significant problem. I have probably spent around 100 hours over the last five weeks working on this, but a fair chunk of that time has been spent making notes and maintaining a list of minor things to change for the production tool. The good news is that so far I haven't found anything that requires a radical redesign. Most of the issues revolve around the ease of bending parts, which is easily addressed by making the fold lines less stiff. I would expect to spend a similar amount of time on a loco kit and I am on a learning curve with this as well. Tonight I am planning to build up the staircase on the other side of the bridge. After that, there are some braces to go on the main span before I contemplate soldering the sub assemblies together. After that I can start on the valences. Regards Mark Humphrys

I have spent the last week soldering together the main span girders onto the floor and assembling the first staircase sub assembly. The photos show various stages of assembly and then the sub assemblies loosely put together. Each step is individually soldered into a slot in the wall. I was concerned about it going banana shaped, so I soldered small groups on either side to even out the expansion. In the event, I don't think this would have been a problem. There are a some gaps between the landing and the main staircase, because there are dowels that locate it into the landing tower, which are intended to file flush with the inside before the main span is fitted. I haven't the staircase to the landing yet, so the main span is pushing against one of the dowels and forcing the staircase away. The staircase assembly is locked to the landing tower with tabs that locate in slots under the floor. Regards Mark Humphrys

Progress is being made on the bridge. The last few weeks have focussed on making the legs and I have started on the first flight of steps now. Again the images show the basic formation of the legs and various overlays to create the impression of 'L' section girders. I have also taken the opportunity to balance bits together to start to get a feel for the overall impression. The most important part has been to take plenty of time with each stage. There are some minor issues I have identified, mostly regarding the stiffness of the legs when trying to bend them, so I will make some minor alterations to the tool to make this easier. Otherwise, everything has fitted together remarkably well so far. Regards Mark Humphrys

The last few days I have been putting the external braces on the main span and doing the stairs and deck. The next job over the coming days is to assemble the legs and landing. The first image is the assembly jig for the staircase. On Brent, the stairs on the main span are enclosed behind wooden planks, so the jig incorporates these on the underside. If an open staircase is required, it can be done by removing the planks after soldering the steps in place. The second image illustrated one of the folded steps located in the assembly jig, followed by the stair case balanced on the bridge. The next image is tinning the metal strip that runs along the surface of the main deck on either side before fitting it to the floor, shown in the next image. The remainder are images of all the bits balanced together. Apart from some filling and adding the hand rails to the staircase this part of the main span assembly is nearly complete. Regards Mark Humphrys

That looks superb! Regards Mark Humphrys

Today's work has focussed on the upper web for the sides and a start on vertical stiffeners. Forming the upper web took around an hour and the first attempt at attaching to the first side was a bit difficult, because I had kept the part on the folding jig. For the second side, I removed the part before soldering and it was much easier to do. I have been trying to use the same side for the first operation of each stage so I have one with defects in it and one with improvements. The images are for the side with all the defects in. I have also included some rendered images from the cadds file that I created a few years ago showing the bridge in its intended setting. Regards Mark Humphrys

Thanks. I am planning to do it as a kit later on, but this is the test build of the etches. I have been working on this for the last six months, so hopefully I have flushed out most of the issues during the design phase. I have designed the kit to be for South Brent, or as a generic Great Western plate footbridge. The kit can be built with a hipped roof, curved roof, staggered entrances, with or without roof. I have also made it 4mm too high so the legs can be properly seated in the platform. Regards Mark Humphrys

Today's work has focussed on the lower web for the main span after fitting the overlays for the rivet detail yesterday. I have half etched these parts to make provision for the angle bracket that joins the sections together on the prototype. I have done a pair for the lower edge and another pair for the top edge of the sides. Being half etched, there are two ways of forming the bends for the staircase. One is to etch small holes where the bend is required, and the other way is to design a jig with the fold line half etched in the frame. The idea being that the bends are formed in the jig and the side can be soldered in place whilst still in the jig, which makes it easier to keep everthing square and not get burnt fingers!. The problem with this method is that the metal isn't fully supported when the bend is formed meaning you could get a radius bigger than required. The solution I came up with was to stick some brass shim on the surface of the part with Pritt Stick to bring it up to the same height as the frame before clamping it in the bending bars. The bend was then formed and the brass shim removed and used for the other end. The Pritt Stick stops the metal moving when it is being adjusted in the bending bars. Once the bends were formed, I had to use a broach to open the slots slightly to enable the tags on the side to locate properly. The sides were soldered into the lower web before removing it from the Jig one at a time. The final image is the assembled part after cleaning up.

This is the work from the last couple of days. Firstly embossing the rivets in the main span, tinning the rivet overlays on the fret and then soldered in place for. There has been no difficulty in removing the parts, or distortion when soldering. The etches are 0.3mm Nickel Silver, so they are more forgiving of heat than brass. In should complete the main spans tomorrow and then start on the legs.

Having been working on a kit for a Great Western covered footbridge, which I have designed specifically for Brent with additional parts to make it more generic, I have today received the etches laid out in the photo below, all eighteen sheets of them! I hope to use this thread to post images of the bridge as it develops over the coming few weeks. Regards Mark Humphrys

I thought the plan was for Fred to produce his D600 in gauge1 and then the Kernow model will be laser scanned from that. He had the body at Larkrail last year and emailed me some images after the show. I hope it scales easily when it is laser scanned! Regards Mark Humphrys

It is the foot bridge I am referring to. It has turned out to be a bl**dy nightmare to design, but I now have something that looks like the prototype and can be built as a generic Great Western footbridge as well with around six alternative configurations possible. Regards Mark Humphrys

Watch this space. I have been working on a kit for that since Christmas and it is in the final stage of checking before going to the etchers! Regards Mark Humphrys

Apart from the section around the buildings, a large part of the down platform at Dawlish is built on the sea wall and forms a cover over the path below. This area was totally rebuilt after the 1974 storm that caused serious damage as the waves come up from below and lifted the planks scattering them all over the track. A considerable amount of work has been done on other sections of the wall by Network Rail over the last ten years, which involved installing a concrete tongue along the base of some sections of the wall. The usual problem is caused by the sea removing the top sand and then scouring out the relatively soft sandstone underneath with the wall collapsing over the cavity. The path along this section of wall is just above sea level, so there is additional protection and the few pictures I have seen seem to show the path is still there, suggesting the sea literally demolished the wall. Regards Mark Humphrys