1907 Scherzer Rolling Lift Bridge CAD designed and 3D Printed

[Jim Donovan]

WOW. What a great project!
Good stuff.
Looking forward to seeing more.

Suggestion
Us old guys have trouble with the green font on blue background.
Black & white is better.

MJinTN

Thanks for the feedback, I will make the change. We will see how this project goes.

Jim

[Jim Donovan]

I'm curious and have a place for a large, complicated swing bridge on my layout, so I'll be following along.

Thanks for following, hope the thread helps.

Jim

[Jim Donovan]

Jim very interesting how you do this.  I'll be foolowing along also.

Jerry

Thanks Jerry

[Jim Donovan]

Jim not that I ever intend on 3D printing but this project seems fascinating both on design and approach; I'll be following along and see how things develop.

Thanks Larry;

I am going to try and push the equipment and myself to see if we can make a realistic copy of the original bridge. Thanks for following.

[Jim Donovan]

I'll be following along on this adventure. I've always fancied Scherzer Rolling Lift Bridges. I'd like to build one using brass and animate it someday.

Do you plan on animating the bridge?

Bernd

Thanks for following Bernd. As a matter of fact I do indeed hope to animate the bridge, in the same manner as the original bridge operated gear wise. I have a couple of 30 rpm geared motors that should fit where the actual 25 hp electric motor was located so we will see if we can repeat how it worked.

Jim

[Jim Donovan]

Well presented, I might get around to showing off my printing plant one of these days, too. 

I did finally get a handle on printing, now to find something useful to print.  I'm back to negative territory in CAD.  Fusion360 passed me by like an express train in the night.  Still in sub beginner with the FreeCAD.  Most tutorials list themselves as beginner but few really are. 

Love the bridge project, Jim, coming along well.

KarlS

Karl, thanks for following along. Hope you get something out of it that helps your own 3D printing.

Jim

[Jim Donovan]

I will be checking in. Bridges fascinate me. I just finished a Swing Bridge kit for a friend and am now kit-bashing the approach bridges to it. Watching a 3d built bridge come together will be great

TomO

TomO thanks for following along.

Jim

[Jim Donovan]

Jim,

This is going to be a very interesting project to follow along.  I personally don't use Tinkercad as I use Fusion 360.  I use Fusion 360 as I make my 2d patterns in Autocad, import the dfx file into Fusion 360 and then extrude the 2d pattern.  While Tintercad seems to be a basic program I see you can get some very complex parts out of it.

Looking forward to the next update.

Ron;

How you are using Fusion is interesting. I will indeed be pushing Tinkercad and using all the tricks I know but so far it is handling the file size complexity so I should be good on this one but I will be learning either Fusion or FreeCad next. I want to do more than Tinkercad was ever designed for. Th.anks for following along

Jim

[Jim Donovan]

Jim, I don't have any plans to do 3D printing but I do find the process interesting.
Thanks for sharing your setup, what you plan on printing and how you're going to do it.

Rick thanks for following along, hope you enjoy the ride.

Jim

[Jim Donovan]

OK, time to start working my way through the various steps. Before I can print or even design a part I need to understand how the bridge was made and how it looked. In this case I also need to know how it operated since I want to recreate a working model. I saw a photo of the bridge years ago and kept it on file. It was one of the previous photos shown and on Monroe street in Toledo Ohio. Going on-line I hit the jackpot finding a  tremendous amount of information from the Toledo Museum and the Toledo Historical Association's websites. I printed all the information and placed it in a 3 ring binder for easy reference. The photos are especially helpful. I was even able to get the blueprints, many have been blurred or reduced in size during the past so when I enlarge them to see the details often times I can't read what is written. Still a big help. Finally I found a book at Amazon detailing the history of this type bridge including documents (and photos) of many of the actual Scherzer bridges in the world. All in all I think I have enough to make a reasonable replica. located

[deemery]

Are you worried about the strength of the 3D printed parts when the bridge operates?  Certainly the engineering of the bridge should help mitigate that risk.  One clever thing I remember seeing before 3D printing was on a Silver Crash tank car kit, the railing posts were a composite part.  There was resin castings for appearance with a slot for thin brass strip for strength.

dave

[Jim Donovan]

A quick note, I am not a mechanical engineer so my determination and use of dimensions are simply my best guess based on observation. I also adjust as needed in order for the model to be structurally sound. In other words the dimensions are a SWAG and good enough for government work!

So now I need to make a list of the various beams and other parts that make up the bridge so as I design the parts I will have a starting point and goal for the CAD model. I will do this one section at a time, the first being the lift section of the bridge beginning with the two side trusses that support the roadbed. 

Reviewing the photos and diagrams I settled on the following dimensions:

 Since HO is a metric scale with 3.5mm = 1 foot all measurements are in metric for printing purposes. I have converted each to scale inches to show what they would be if 1:1 in scale.

The U channel main beams are being sized at .5mm thick, 1.5mm wide and 3.5mm high. This makes the beams 1.7 inches thick, 5 inches wide and 12 inches high for HO scale. They are used for the side bottom and side top trusses.

The plates used to tie the main beams together are .75mm wide, .2mm thick and 6mm long (rounded ends). This would work out to .69 of inch thick x 2.5 inches wide and 6 inches long. Each plate is tied to the beams and each other by rivets. I designed the rivets to be .3mm diameter by 1mm long resulting in 1 x 3.5 inches. Still close to original just a little higher to stand out.

The diagonal beams are 1mm wide x 3mm high and .3mm thick. In 1:1 scale they are  3.4 inches x 10 inches x .3 inches. The diagonal plates and rivets are same as used on main beams.

Finally, the upright beams that hold the diagonal beams together are .4mm wide x 3mm high and .2 thick, or 1.4 inches x 10 inches x .7 inches thick. The diagonal plates are the same .2mm thick and sized as needed.

Not exactly the original sizes  but they are in the ballpark and allow the model to be sound and printable by the 3D printer.  .2mm thick parts are right at the limits of my 3D printer converting to .00787 inches, really thin.

These are no means the original specifications just where I ended up in the end. In the beginning I attempted to match exactly what I saw in the diagrams and photos. Then, through trial and error over the past week I test printed each part comparing it to the information I had. Some parts like the rivets ended up having to be larger than original in order for the detail to be seen. Some of the beams needed sections made thicker in order to offer proper support for the model.

I wanted to capture as much detail as possible. The real riveted plates in the V formation consist of flat iron plates overlapping each other and held together by a single large rivet at each end of the plate. So three rivet were needed for every two plates. These rivets also passed through both U channel beams to created a complete truss the upright trusses attach to. To simulated this I offset the V of the plates so they look like one is over the other (but still part of each other for model support) and the rivets are long enough that when dry brushed they will show up against the background. 

Here is how the parts look like in the Tinkercad CAD program when put together on these specs:

[Jim Donovan]

With the design finalized I export the items one at a time creating separate .stl files. This is a file type commonly used when dealing with three dimensional objects. In order to print the file I need to imported the .stl file into an application called a 'Slicer'. These applications take the .stl file and allow you to make the item 'printable'. The application has the parameters of the 3D printer being used as well and the liquid resin type (you tell it what you have). Further it allows you to set up the necessary supports to hold the item in place while it is made. You can use the program to do this for you, do it yourself or a combination of both. I use a slicer application from a firm called Chitubox. The version I use is free but still has way more ability than I need.  After importing I orient the object in the manner I want to minimize the number of supports needed versus the time needed to print the item. It is a trade off, the more vertical space the object takes up in the print space the longer to make but the fewer supports usually required. For example if I printed these trusses as shown in the CAD photo they could be made in about 30 minutes but would require a whole row of supports across the bottom to keep the part in place. Maybe 50 supports each needing to be removed and each might leave a blemish on the item. If I print them on end vertically I can reduce the support count to just 4 but it will take almost 8 hours to make. Since I am more interested in great detail and not time on this project I went with the vertical option. A side note, the slicer programs are getting better but learning how to place supports manually is still a great help. I usually have the program place the initial supports and then I make adjustments. However for complex or really detailed items I add the supports one at a time by myself. This allows me to adjust support size, placement and type.

OK, a lot of explanation. Here is how the trusses look in the slicer program after all supports added and everything checked to make sure it will print:



I sent the file to the printer and here is how those parts came out:


Removing the parts from the printer using a plastic scraper I wash the parts in isopropyl alcohol to remove all excess resin, Supports are removed with a sharp sprue cutter, making sure I don't break any of the soft fragile parts since at this point the part is very pliable and easy to tear. Finally they are placed in a UV dryer to complete the hardening process and we have a finished part!



So that is today's update. As I write the printer is busy making the other parts I designed for the two bridge side lift sections. I am now designing the roadbed girder system. Till next time.

[Jim Donovan]

Are you worried about the strength of the 3D printed parts when the bridge operates?  Certainly the engineering of the bridge should help mitigate that risk.  One clever thing I remember seeing before 3D printing was on a Silver Crash tank car kit, the railing posts were a composite part.  There was resin castings for appearance with a slot for thin brass strip for strength.

dave

Dave that is a great idea for something I have been worried about. I will slide cut to shape brass plates though the bottom trusses to improve strength when I get to the construction part. Great idea and thanks for the tip.

Jim

[Philip]

Great looking parts Jim! Tinkercad is finally beginning to raise the bar with the new latest functions. I wish they would add Bevel/Chamfer on path.

Philip