Week 9 - Molding and Casting

Just as fun as the previous week! Molding and Casting. This will involve making yet further use of the Roland Modela to mill a design which can then be used to make a cast and subsequently mold parts from it. You could say the Modela is the swiss army knife of the Lab!

Assignment:

Design a 3D mold, machine it, and cast parts from it


  

25th March 2015 - What do people like to cast?

A slight struggle for me is thinking of what to make for this assignment. I want to make sure the thing I design is functional and hopefully practical. I hate designing pretty objects which end up being clutter. This is going to take some thinking.


26th March 2015 - A practical idea!

During today's local class on the process of molding and casting and looking at the possibilities; I have decided to link this assignment to my 3D printing assignment. I will design a silicon case for the light that I printed. The advantages of this is that I have an accurate 3D model with which I can design the case around and it will be a practical item once made. The slight down side is the complex job of making a hollow object which cannot be produced by rotating the mold, a third part will have to be designed in addition to the usual two pieces. Time to get cracking!

28th March 2015 - Designing a mold is like being Leonardo in Inception!

One thing most of us have found is that designing a mold is extremely confusing! You don't know whether you are coming or going! Because the object I wish to make was hollow I am having to design a 4 piece mold. I had a good start in the sense that I knew what dimensions I wanted almost straight away. However, translating the shape into a mold is a brain zapping process. You have to think about whether the mold is correctly inverted. Do the "keys" that hold the halves of the mold together line up properly. Did you do the boolean differences and unions correctly. And so on. It took me about 4 to 5 hours of hard work but in the end I managed to get the parts of my mold designed and correctly inverted:



The next challenge now if grabbing enough machine time to do the job! My design is going to take a few hours to say the least. It will pay off though! (I hope...)


29th March 2015 - Discovering limitations...

After spending all that time on the design of the mould, it turns out that the Modela cannot accomodate the large depth of the design. Even worse, neither the shopbot or Modela have a long enough and thin enough tool to mill the wax. This led to some serious back to square one stuff. Instead of casting a mold for the centre, I will make the a 3D printed inner mold. All I then had to do was re-design the outer mold taking into consideration the tool width more closely. This wasn't such a long process this time thankfully.



I then decided to adapt my 3D printed light to make the inner mold. The plan is to make it water-tight with a thin layer of tape and laser cut some acrylic discs to enable it to sit correctly in the mold. The discs were easy to make the next challenge is gluing them together accurately.


1st April 2015 - Time for a re-think...

After seeing the trouble other students have had producing these molds, it seems like a good idea to do something much more simple. I am going to collaborate with Alex (our FabLab manager) to make a 3D printed Jesus nailed on a molded crucifix (as Easter is coming up!). The inspiration comes from my grandmother passing away. She is Irish so I will design a crucifix with Celtic patterns. Alex has already printed Jesus out and so it is just up to me to make the crucifix.




2nd April 2015 - A beautiful crucifix!

I stayed up until 3:30 AM plus more time this morning on designing the mold but it is finally complete! It just about fits into the Modela meaning I can use the really small milling bits and get some incredible detail. Below you can see the model of the crucifix with the 3D printed Jesus and the crucifix he will be fixed to and the mold that I will mill out:





The plan is to leave the machine running over night and by tomorow have a beautiful mold with which I can cast the rubber mold.

Picking the right tools:

While I wait for a slot on the Modela, it is good to take some time to ensure that my design will definitely be able to be cut by the machine. It is especially important to do this when the machine is being used to its extremities in terms of dimensions, which is the case here. My main concern is that the rough cut tool and collet will have enough room to move around. To do this I am looking at the milling tools I am likely to use and then looking at cross sections of my design:





It is a relief for me that the tools will be long enough and the collet won't get in the way for both the rough cut and finish cut.

Another preparation step is to cut a wax block down to size. This is easily done with a tri-square, a saw and a clamp:






7th April 2015 - Preparing the modela

Preparing the modela posed many challenges today. The first one being a serious issue with the fab modules. The software decided that it wanted to change the origin of my design so that it went outsie of the milling bed. As there is no way to change the origin of the job, I was left at a dead end. I ended up using Modela's own program instead which worked. I had spent the whole day sorting this out so I had to leave the roughing job to do its thing overnight and come back to it in the morning.


8th April 2015 - Disaster...

I came first thing this morning and something went very wring during the job. Initially I cannot think of what or why but the tool went stright though the design and stopped before the end.



After chatting to some fablabbers, it turns out that I was in such a rush that I forgot that the modela software was also having issues and we were told not to use it. SIGH!! However, I was also given an excellent tip to reduce the job time which was to make the outer edges of the mold fit closer to the shape of the crucifix. You can see what I am trying to get at below:



I will return to the machine tomorrow and get it going ASAP as the machine will then need to be used for the input electronics assignment which is a priority. Thankfully the fabmodules was no longer changing the origin of my design so I can go back to using that. The lab seems to be playing tricks on me!


9th April 2015 - Finally running the modela

I ran the desig through fab modules again today and it stopped rotating the PNG. So I went on to run the rough cut and this was the result:



More preparation was needed for the finishing cut as I needed to use the 1/64 cutting tool which is normally used to mill PCB traces. To reduce the job time, I exported a second stl file which only goes 1mm into the design as that was where all the fine details were.

I ran this through the machine but for some reason the finishing job was offset in the x axis by about 2mm. Hardly noticable at a distance but much more obvious when close up:



Time ran out today so I will pour the rubber tomorrow.


10th April 2015 - Pouring the rubber mold!

Today I set up the mold for pouring the rubber mold. First I removed any dirt from the wax and tried to get rid of any hairy edges (of which there was quite a lot). I also had to clamp an acrylic pannel to the mold as the job went slightly outside of the wax block:



I estimated that 350 millilitre of rubber would definitely be enough but in the end I only needed half of it. Pouring the rubber was tricky as it was a large area to fill but isn't very deep. The rubber used was Smooth On PMC-121-30 which needs to be mixed in equal amounts. It is also important to not mix it quickly as air will also be mixed in.

I will leave the rubber to set and come back to it once it sets:




12th April 2015 - Finally a crucifix emerges!

I took out the rubber mold today and thankfully there were no major air bubbles but instead just a few miniscule ones:



I had a felling that the top of the rubber mold (which becomes the base when used) wasn't quite level. To check this, I used a level. You can see below that there is a slight tilt. To rectify this, either another rubber mold needs to be made or I can try to level this one off.





I thought that I will use the mold as it is and see what kind of effect it will have on the final piece. I used Smooth-Cast 300 which has a set time of 15 minutes and mixxes on a 1:1 ratio. It is just as simple as the rubber mold but quicker. This was the cast half way through setting:



And these are all the elements together:



And finally here is Jesus on the crucifix:



Here are the design files for this assignment. This assignment for me has been a real headache from start to finish. It was difficult to choose what to design, mill and cast. I am fairly happy with the final outcome but it needs some refinement. The final cross has a slanted back which needs rectifying and not to mention the fine details being offset. Now I have acheived the minimum criteria for this assignment, I will come back to it another time.