3D printing parts
for the Thornbury dam

thornbury damPhotos of the Thornbury dam in the 1950s

My next project for our NMR club is to build the Thornbury dam that is behind the railway bridge that I constructed.  I began with a rough sketch on cardboard based on a photo that we found in a book. We had to use our imagination to work out the sizes of the various features. We wanted to get as close as we could to the original. We acquired some photos of a rebuild in the 1960s that we could use as a guide but the rebuild had changed the shape of the abutments by making them smooth instead of stepped. While we were figuring out how to build the dam and what medium to use (cardboard, styrene, wood, etc) eight of our members formed a consortium to buy a 3D printer and to learn how to use it. It was decided that the Thornbury dam would be a good project to use for experimenting.  John Houghton took the lead as he has the most experience with CAD-type computer programs.  This is way beyond my knowledge-base so I handed over the construction phase of the dam to him.  I'll leave it to John to explain how the experiment in 3D printing parts is going. The printer was bought from DigitMakers in Markham, Ontario (digitmakers.ca). 

"To do my drawings, I bought ViaCAD2D/3D. It is more to my familiarity from when I was drawing at work. Others are using SketchUp, which is free.

To generate the files that the printer will read, I use the slicer software Cura, which is free. There are many freeware Slicer programs available and some very powerful paid programs.

 The consortium [at the club] has purchased the 3-D printer and it is set up in my basement. I have been testing out how to print and we have at present 3 materials that I am experimenting with. PLA, a rigid white plastic, ABS, also white that is similar to styrene, and wood filled PLA, a brown PLA that is a little softer than the regular PLA. The wood can be stained with wood stain and is a bit easier to sand as compared to regular PLA. 

 For those venturing into designing their own parts to be printed, the software we are recommending is Sketchup.  You will need to install the STL plugin for Sketchup, but both items are free to use. If this info is over your head right now, ignore it. 

 After making a sketch it has to be converted to an STL format drawing. PLA costs at a rate of about 20 cents per meter and the program that I use to get a drawing onto the printer tells me how many meters of material will be used so I can estimate the cost of a part. The wood filled PLA is about 30 cents per meter. 

 Material costs will vary and I am finding different settings to use that affect those costs. It will depend on how smooth a finish you will want for the final print and I am experimenting to learn what can and cannot be done on the printer. 

 The first project I am working on is the Thornbury dam. I have printed out a couple of test pieces to try to get the "look" of the dam as we do not have dimensions, only a few photo copy pictures of the dam pre the 1960's refurbishment.

 Even at the best printing, the surface of the final parts will need work. The surface is not glass smooth. Some sanding and filling will be required before painting if a smooth surface is required. I have experimented with different fillers and all of the plastic model fillers that can be bought at a hobby shop work fine. All those are an acetone based product and stink. Laying it on, then sanding it smooth gives a good surface and the fillers stick well to the PLA. I also played with acrylic resin fillers and they also adhere well to the surface, sand well and do not produce odours as they are water-based. 

 I then tried acrylic paints, like the dollar store stuff, especially the thick stuff. It works as well. I also tried acrylic paint in a tube that you purchase at an art store. It is thick, so I spread it on with a spatula, let it dry and sanded it. All acrylic materials are sticking well to the PLA and wood-filled PLA, so I would recommend a light grey acrylic thick paint in a tube as the best solution. Once the surface is finished to your liking an air gun finish with acrylic paints should work very well. 

 On the PLA there needs to be some extra finishing. I played with fillers and found all the hobby shop plastic fillers stick to the PLA and sand well after. I also found that thick artist acrylic paint that comes in tubes from Curry's, works just as well as the fillers. Doesn't smell, sands well and you can get a specific colour that comes close to final product finish, or a light grey to act as an undercoat before painting. 

 I figured out how to make ABS stick to the build plate, I think, so I plan to build in ABS. Just tested how to glue it to itself and solvent ABS styrene glues work just fine, so styrene sheet and parts can be mixed with the ABS printed parts. 

 ABS seems to have a smoother finish on the printer and a smoothing procedure some use is to dunk the part in acetone for a second or two to dissolve the rough surface. Going to be stinky though. I will try the artist acrylics on the ABS as well see how it works."

3D printing of abutment with PLAFirst attempt; abutment in PLA
model abutment in PLAAbutment with filler added
front view of 3D abutment printFront view of 3D printed dam abutment
3D print of dam spillwayThe spillway sample 3D print in PLA
3D print of spillway sideviewPLA sample of spillway side view

3D printing of dam partsCardboard and styrene sizing mockups and first test samples of 3D parts in PLA

Printing the dam in ABS

"On my first attempt the initial layer did not stick to the bed even at 105C, so I aborted the print. This is a large area of the bed that the item covers and I was anticipating there might be an issue with sticking as the edges of the bed don’t get the same even heating as the center where the smaller test box worked yesterday.


I had read about some using glue and acetone but that was on a glass plate and ours has the plastic heat sheet original cover on the bed. It is definitely affected by acetone so that is a no-no. Acrylic seemed like an option so I tried some acrylic medium I had on hand. Matte Medium would also work but I didn’t have any. Anyway, after the bed warmed up, the acrylic was a bit sticky and so far, after about 8 layers everything is sticking pretty well. We will see as the print progresses and I will probably reduce the bed temp after about 50 layers get printed, to make the ABS a little harder.


I joined the abutment and the spillway into one unit so it is going to take 8-1/2 hours to print according to Cura. Also will use up 21.75 meters of ABS. Cost of one abutment + Spillway $8.70. X 4 units. Then there will be one extra abutment needed. Maybe $50.00 CDN worth of material in total."


Here are the ABS plastic samples of the spillways ready for assembly. John has done some sanding and filling to the ones on the left. The cardboard template was only a guide.  We're using creative license to make the dam pleasing to the eye so that it "feels right".  

3d abs plastic dam spillway partsThe ABS plastic spillway parts ready for assembly.

First spillway with water effect

dam spillway with water effectFirst sample of painted spillway with water effect.

After John had printed and assembled one spillway in the size we planned to use I painted it with PollyScale concrete, dry brushed on some black and brown weathering, and added Woodland Scenics water effects. I had never tried this product before. I found a good tutorial on the Internet that I could use as a guide.  The method is to lay down beads of the water effect on a non-stick surface, dapple it with a stiff paint brush, let it dry and then add highlights with white paint. All of this can be done on a flat surface. The dried effect is still supple so it can be removed from the backing and added to the dam (or waterfall) as a single unit. My test strip was done on wax paper. Next time I will try Saran wrap. I had trouble peeling the water effect off the wax paper. I left it in place because the opaqueness seems to be OK.  We plan to assemble the entire dam on a piece of masonite so it can be completed at the workbench.

The Craigleith Station project

3d printing of craigleith station wallsSample of the walls for the Craigleith station as drawn in Sketchup.

Meanwhile Martin Alborough is working with John on another 3D project: the station at Craigleith.

Martin has been drawing the parts using Sketchup on his PC while John concentrates on the printing function. The detail is quite incredible. Martin and John were explaining that the process of drawing the lines involves multiples of 4mm and the end product in the drawing must be an even number (integer).  The trick is to avoid gaps between lines as the printer lays them down.  We're on a steep learning curve.  Here are some first samples of the walls and the base of the corner tower. (I have a separate page about the prototype building at Craigleith.)

I'll do a separate page about the station as Martin continues his experimentation. You can also follow our progress on the NMR club website.

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