In this Instructable I will go through the process I took to make a small table with Surcrete. In this case, in the form of an mini ironing board. This was an exploration in form and the process from digital to physical. I will gloss over the earlier steps to concentrate on the actual mold making and pour process.
Step 1: Going From 3D Model to 3D Print
Using Fusion 360, I drew up a shape that I felt best represented all of the conditions I was looking to test both in structural geometry but also to learn for mold placement and breakdown. Using long axis symmetry when setting up the model allowed me to quickly test out the form. I generally like to consider what the underside and profile shape look like. Once I was happy with the look of the form I flattened the bottom to serve as the entry point fot the concrete to be poured and ultimately harden flat along the base when upside down.
Step 2: Post Processing the 3D Prints
Orientation of all the prints did have an impact on the post process work for the mold. I found the ideal scenario is where the least amount of post process work has to happen within the molds surface no mater what orientation is preferred on the printer. After all the molds were printed, I filed and sanded down the inside surface of molds where needed. I found it best to sand first before the pour so you don't have to add that much more sanding time to the final product.
Step 3: Prepping the Surface
Next, after sanding I covered all of the interior mold surfaces with one smooth coat of XTC-3 (This was my favorite surface treatment product from my previous Instructable). With this many pieces I wanted to get the best bang for my buck so I laid them all out nearly on top of each other to be easily able to cover all the surfaces as fast as I could before the Epoxy cured. Within 5 minutes of mixing you can start to see the liquid get heavier and once you see the steam coming off of it, you have less than 30 seconds left. For this amount surface area I used (2) rounds of 30 ml cups. Be careful with this stuff because it does get pretty hot.
Step 4: Assembling the Molds
After all the pieces were dry I began to assemble them with mini hex bolts that for the most part could be finger tightened. These do take patience but were worth it in the end to get a good solid seal to the molds. Once all the pieces come together you can get a really good feel for how large the mold is and how sturdy it will be during the pour.
Step 5: Ready to Mix
I find it really important to make sure to clear anything that you will not be using from your work space and layout all the necessary tools you will be using (See previous Instructable). I also measured out all the concrete and mix activator I was going to use so that I would not have to make any calcs on the spot. Mixing concrete can be very nerve racking so having a solid game plan can help you perform a mindless mix process where no improvising is necessary. Like most bags of concrete the manufacturer give you measurements in 50-80 lbs bags. In this test I had a set volume I was aiming for so the mix calls for 4 to 1 to 1/32 - XS Surcrete to mix activator to 1/32 of water. Adding a touch more water can help make the mix more easily pour-able but be careful not to over add too much with this ratio.
Step 6: The Pour / Mold Fails
One very important thing to note when make these types of non traditional geometry pours is that there can be many areas where concrete does not naturally flow into. For this I had placed these on a table with a paint shaker that I used to vibrate the table after the pour. Once finished, I noticed the PLA plastic was cracking and splitting mostly in the corners of the molds. After looking over the broken pieces I discovered that the cross connection point of the mold was overly stressed in tension with all the weight and the paint shaker certainly helped the bubbles surface but also added much more bouncing to the mold which caused the shattering. All in all it still kept its form.
Step 7: Time to Demold It
For the most part, my choice in the breakdown of molds went well for removal but the area around the centralized leg gave me some difficulty with all of the complex curves that held on to the plastic more.
Step 8: Taking a Closer Look
From the looks of it, all of the air bubbles were not able to escape properly from the underside of the form. I figured this much which is another reason I poured it upside down in hopes to achieve a much finer surface below.
Step 9: Final Look
Here is the final look of the piece without any post processing work - I am almost ready to iron that shirt! I plan to create a Sand and Stain Instructable next to go through the process of this and the variations of surface treatment. Thanks for reading and stay tuned for the next Slice Lab Instructables.