1907 Scherzer Rolling Lift Bridge CAD designed and 3D Printed

[Jim Donovan]

Thanks for following along, I have finally made enough progress to share. 

I ended up creating 14 various sections and used thick CA glue to assemble the sections together creating the lift section. 



Here you see a couple of the diagonal truss sections still on their supports having just come out of the printer. An important consideration in 3D printing is where, how many and what size of supports to use when preparing the design for printing. All major 3D print programs have an automatic support function where the program will make and set the required supports. I use this feature to see where the computer thinks the supports should go then delete them and go to manual support. Almost always the program will overdo the supports needed, the fewer supports you can use and the less thickness at contact with the part, the less clean up work you have removing the supports and better finish the part will have. That said you must have enough support, and the right type in order for the part to print correctly. Not enough and the part will fail and oftentimes make a mess in the print tray. Cleaning the mess is not hard but it must be done. Learning to find the right mix of number and size of supports is definitely a learning process.


..
I will often test making a part using the absolute minimum supports I think needed. If it fails I look at where and why it failed, have the machine clean the tray bottom, correct and try again. I alway have 'anchor' supports, these are either medium or heavy supports located where the most stress and weight will be on the part as it is formed. The further a support is needed  away from the printing plate the smaller the support I use is as it will not need to carry the weight or have the stress of the bottom sections. If you look at the above photo of an Adirondack Chair (I am making these for the winter challenge) you will see there are only 10 supports used, 1 medium in the middle and the rest light supports. I was able to simply grab the chair gently with my hand and pull the chair off the supports. For the O scale version I was able to reduce the number of supports to just 6.

The parts are removed from their supports after having been washed in an alcohol bath but before they are placed in a UV dryer to complete the curing process. When you buy 3D resin parts make sure the supports have been removed . Finished parts can be brittle and may very well break if the supports are cut off after the part has been cured.

[labdad]

Thanks for the "lesson". Good information for those of who think we want a printer.

MJinTN

[Jim Donovan]

Above are the Rolling Section Trusses glued together on the left and I was able to make the under road support section in one shot, it is seen on the right.


 
In the above photo you see the completed lift section of the bridge. I place a couple of 3 x 12 wood boards in place to make sure I had the clarence correct. The original bridge had diagonally planks as the road surface. The planks were two high and each layer was placed in the opposite direction of the other. Wood was used to keep the weight of the bridge down. If each board went completely across the bridge they would have been about 36 feet long. The diagrams and blueprints I am working from are silent on the issue of if the boards were this length or spliced together. The bridge had asphalt put down sometime much later when it no longer opened so I can't determine the length of the boards. If anyone has an idea on the matter let me know. 

Having a wood board surface with the ends of the boards locked under the steel truss was one of the neat features I want to capture of this bridge.



Here is a look at the section from the front.

[Jim Donovan]

Thanks for the "lesson". Good information for those of who think we want a printer.

MJinTN

Thanks for stopping by. I enjoy 3D printing and especially its ability to create items not usually seen in train modeling, like this bridge. In the beginning I simply made items from files I had downloaded at websites like Thingiverse.com, then as I understood the process better, I started to design simple items like barrels, sacks and such. Today I have a pretty firm understanding of Tinkercad along with the time and patience needed to do CAD design. I'm retired, my layout is a small shelf set up so I use my time to build details. However, 3D printing is definitely not for everyone, if I did not have a vented climate controlled garage to keep it in I would not be printing

Jim

[Jim Donovan]

With the lift section finished as far as I can go for now I have begun designing the rolling mechanism part of the bridge.



In the above screenshot you can see the lift section in gray and dark blue. The parts making up the rolling lift section are to the right. The key to getting the bridge to rotate upward correctly is to make sure it pivots around an imaginary center of a circle of which the light blue curved sections seen in the picture is part of. The center point will be where the gearing and shaft will go so when the bridge 'lifts' the shaft will turn, the gearing will cause the shaft to track backwards which makes the rolling section turn as well raising the bridge. Because everything pivots around the center point and there is a counterweight on its 'backside' very little horsepower is needed to accomplish the raising and lowering of the bridge. The actual bridge used a 25 hp electric motor that was housed on top of the red flat section seen in the picture. I will be using a very small geared electric motor that will turn at 30 rpm. Hopefully I can make it work.

[Jim Donovan]

In addition to designing the next section of the bridge I have started making the diorama part it will go into. The above photo shows the lift section across the canal with pink foam on either side. This rectangle will be the bridge diorama scene when complete. It is obvious that I am going to have to make changes to the layout to make this all work. First the train track on left will need to be moved away from canal and instead be placed against the back wall of the layout. All the building to the right will be moved out (urban development in 1910!). The gray tray the bridge crosses will be filled with epoxy resin to match the rest of the canal and hopefully I will be able to feather the resin in a way so the seam is not apparent. If it is I will think of something to hide it. The gray tray was easy to design and 3D print. It will easily contain the epoxy resin and ensure no leaking occurs. 



Here you see the section pulled off the layout and some more foam work accomplished. The cut out on the right will end up being an underground walkway for the mules and mule handlers that pulled the canel boats in those days. On the left side you can see I will have a pretty large slope going up to the bridge. While not ideal it was not uncommon back then for roads to be narrow and grades more severe then we see for the most part today. The road will be brick. On the far left you see the flat area where the new track will be located.

[Jim Donovan]

I will finish this update with a couple of quick comments on how I cut and shape the foam board for this project. A couple of years ago I treated myself to a MicroMark foam cutter. Above you can see it with a sheet of foam board about to be cut. I thought I was buying it just because I could but it sure has come in handy. Truly straight clean lines are easy to achieve with the hot wire cutter. There is a variable temperature knob with 5 settings but I keep mine at 3 and it works fantastic. You can see there is an adjustable bar, note that I put a heavy block weight on the far side so that the aluminum bar does not move as I put pressure on it while cutting.



In addition the wire cutter can make free form cuts just as easy. No more ugly cuts and foam pieces everywhere. What is really neat is taking the 1 inch foam board and slicing it to 3/8 thick, straight, neat and ready to be used. I used the cutter to create the slope grades on this scene. Overall a great tool.

Until next time, thanks for visiting, I hope you got a idea out of the report.

Jim

[Jerry]

Nice machine Jim.  Looks like it really can do some nice cutting.

Jerry

[Rick]

Jim, your 3D printed parts look outstanding.
I can see how that foam cutter would come in handy.

[Bernd]

Jim,

Been following this project since it's inception. Nice job on getting it printed in resin. I look at that bridge and wonder what it would look like in brass.     

Bernd

[KentuckySouthern]

That is quite a complex bridge project, Jim.  The printing is well done and your CAD drawings are more artistic in themselves.  CAD is where I've fallen short in my 3D endeavors. So far I've found enough drawings online to keep printing as much as I can. There are some nice projects ready to slice and print available.

[jbvb]

I've also been following. Congratulations!

[friscomike]

Howdy Jim,

Wow, the bridge looks amazing.  It's well-engineered and printed.

Have fun,
mike