Lessons Learned on Day 1 w Laser Cut Bowl Mold

Our goal was to work with what we had and see what would work.

Plastic; HDPE w some LDPE
Oven; Toaster Oven w imprecise temp control
Compression; A scissor car jack inside an old windown fram(failed) and C clamps (success)

Lesson 1 – Thickness of Steel Matters
We got 2mm stainless steel laser cut because we could not find 3mm steel in Yangon, Myanmar.  The mold bent along the edges since, in part because our compression system (a jack in a window frame) only applied pressure at the center of the mold.  However, the bottom of the inside half of the mold also flexed outward under the internal pressure.  The window frame was able to take a lot of pressure (enough to bend the metal), however it eventually started to fail.  Also, the guides that keep the inner mold properly aligned with the outer mold were not strong enough.  In the future the guides could be angle iron for both guidance and strength.

Lesson 2 – C clamps can work for Compression
This is a big money saver if you are just starting out. They will obviously not apply pressure evenly like a well made compression system but they can get the job done.  They also helped us apply pressure to the bottom of the inner mold to keep it from flexing outward.

Lesson 3 – Use Mold Release
We had a very hard time releasing the plastic from the inner mold.  The outer mold was not much of a problem.  Makes sense because the plastic shrinks toward the inner mold and away from the outer mold.

Lesson 4 – A toaster oven is OK for HDPE
Both halfs of the mold only fit in the compression oven toward the very end when the plastic was well melted.  It took 4 times of filling the outer mold full of HDPE and letting it melt until we had enough plastic. The toaster oven was cranked as high as it would go and there was no burning of plastic despite close proximity of the plastic and the heating elements.  Don’t count on this with all toaster ovens and all types of plastic.

Maybe you can weld a sheet of carbon steel in the out side to give de mould more recistence. Its going to be like a coating of stanle steel

That’s a good looking mould assembly :3

Any pics of the oven/heating system and demoulded bowl? Thanks for sharing, great to see the ‘minimal’ approaches

I think anytime thin plastic flakes or corners of chips have a direct view of the toaster oven elements there is a good possibility that they are significantly hotter than the bulk of the plastic. I would be very cautious if it is indoors. A simple heat shield would help even though it will slow things down.

Thank you for sharing the lessons learned on compression techniques