this week the assignment was to design an object to be casted and molded that could fit within a 3" x 3" x 7" piece of wax. the milling was to be done via CNC (in our cast the roland srm-20 that we also used for pcb milling) in the electronics week.

we run two passes for the milling: a rough cut with 2.5 axis controls, and a finish cut using 3-axis machining and a finer step size. see this guide from leo. again we use the mods project for toolpath generation. this might be an unpopular opinion at the harvard lab this week, because it was a quite grueling week all around, but i really like the roland and i really like mods.

there were also many eventful moments this week!

i found a bat under my bike tire, cold, and wet and almost dead and we brought it into sec to feed it water (no humans are allowed to drink water in there, but they didn't say anything about bats???)

ok before the project, this week was really a bit of a pain. the machines were broken (?) i didn't experience this myself, except some minor bed unevenness, but it resulted in long lines long lines for the machines this week. so i started out by designing in fusion360. i wanted to do something with light and with drystone to see if i could illuminate through the drystone. i was inspired earlier this week by a video i saw on instagram and i wanted to see if i could achieve a similar effect with machining.

i designed a little orb on a tiny stand. because it needs to fit inside the 3" x 3" there is no way that it can be bigger. and in fact, in the end, there were some milling issues with the gap sizes so if anything it should have been smaller.

in order to mill properly, the object needs to be placed properly inside the wax as a positive print. the process here is to mill the wax to the positive impression, cast a mold in the wax, and then use the now negative mold to cast the positive again. there is some brain flipping required, and at least two tricks here to note:

1. make sure to create a register to align the prints if there are multiple parts. since i wanted to do a sphere that's symmetrical i only need to mill half, but i made a register that would align the pieces perfectly.

2. leave either a funnel, or a wide entrance for filling the mold with. if you "close" the wax off entirely, it will be impossible to close the mold. since i actually want to try to achieve a hollow mold which is quite difficult with spinning, i chose to merge the bottom with the edge (effectively making the whole thing a funnel) rather than creating a small funnel that can be easily cut off and sanded in post.

the final cad files came out like this.

thanks to claire for the advise, help, and review of cad files. her htmaa site for this week is really helpful.

then i had to wait approximately 1,000 hours to use the roland, but then, boy oh boy, was it my turn!

i started by milling my rough cut which went perfectly. it was super fast and easy and looked pretty great.

then i went for the finish cut and that was a bit worse. i started with the 1/32" endmill which was a huge mistake because my cut depth was too high and it bit into the edge. huge and silly mistake! dumb. but anyway it was fine because i was a very active observer (leo too) and stopped it immediately. roland tv = only tv.

i restarted with the 1/8" ball endmill and ran the full cycle but the step size (0.5) was way too big for a final cut, and it looked terrible. this second image is supposed to be the button cover for the lamp and it's really not good...

i reran with a (0.2) step size and it was much much slower (~2 hours) but much cleaner and the piece was starting to look good. although still not perfect. unfortunately, the my design was too tight for the 1/8" endmill which i just didn't account for. i cut out some of the easiest parts, but i'm hoping i can sand it out!

[add photos when the oomoo is removed]

even though i had been in sec all saturday, sunday, and monday, by now it was tuesday at 11:50 pm so i quickly poured my oomoo and got out of there!

the mold came out with some issues which we knew would happen but at midnight i wasn't really internalizing how much of an issue it could be. you can see how many issues are noticeable on the mold. the biggest issue is that because i was hoping to make this hollow, there are serious issues with the one gigantic hold that was formed from the wax not being fully cut through on that edge, and the poor quality cut on what was supposed to be the rounded base (that sticks through a corresponding hole on the base).

i chose not to cut out the wax manually last night to prevent this (and so that i could test the casting before i damage the wax) but i'll do another round where i clear it out first, and it should work ok, with the exception of the register which can't be subtractively changed.

the final casting looked pretty good, the stand came out perfectly and felt quite nice - the thickness (3mm) was about perfect for the hydrostone.

the final casting looked pretty good, the stand came out perfectly and felt quite nice - the thickness (3mm) was about perfect for the hydrostone. the pieces fit quite well together.