[Arm-netbook] CNC milling of plastic lumber instead of 3D printing?

[Hrvoje Lasic]

just a few notes below

Heya,
this idea is too late for the current batches of laptops, but I was
wondering if it wouldn’t be easier and faster to mill the laptop plastic
parts out of recycled blocks of plastic (“plastic lumber”) with a CNC
mill.
* suitable plastic lumber can be made from a wider range of plastics
than 3d printer filament
* plastic lumber can be made from readily available plastic waste. HDPE
from plastic bags make for cheap sturdy blocks of material.
* a CNC mill cares much less about the melting point of the work piece
during operation than a 3d printer

actually during milling you also develop heat, potentially much higher then
during 3d printing. You will need to test speeds, bits etc...

* there are fewer concerns about material shrinkage at construction
time, because the work piece isn’t partially liquid at any time of the
CNC operations.
* processing the work piece is faster because it doesn’t require as much
motion as printing sturdy zig zag patterns.
* even rather unsophisticated CNC mills can be used as the work piece is
rather soft compared to the usual CNC mill work pieces such as
aluminium.

Actually, first of all not all parts can be milled. It totally depend on
specific parts, so each part is separate problem.Also, if plastics are soft
it does not mean that you need unsophisticated milling machine. You still
need some range of precision and depend on parts 4 or 5 axes. So, it may
turn to be very expensive. Also you are talking quite small parts that you
need to hold&process somehow. I would say it is a project within a project.

Then, if all these is doable in theory. Then you need a person who is very
knowledgeable about processing materials (specifically plastics), one need
to know a lot about processing speeds, depth cuts, tooling types etc and
must be able to create tool paths on some kind of CAM software and this
include trial & error process for each part.

Then, lets imagine you found person that have that kind of machines,
knowledge to do it, I guess it would be cheaper to create mold tooling from
aluminum for each part and easily produce each part in thousands.

* there seem to be much fewer vendors of plastic lumber than there are
vendors of high quality 3d printer filament
* this approach isn’t quite as common, so it may be harder to find
good advice from experienced people.
What do you think?
(I’m currently in the process of setting up a plastic recycling work
space for my plastic lumber needs.)
--
Ricardo
GPG: BCA6 89B6 3655 3801 C3C6 2150 197A 5888 235F ACAC
https://elephly.net
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[Luke Kenneth Casson Leighton]

Heya,
this idea is too late for the current batches of laptops,

it isn't

but I was
wondering if it wouldn’t be easier and faster to mill the laptop plastic
parts out of recycled blocks of plastic (“plastic lumber”) with a CNC
mill.

ok, so some of the parts are only 0.7mm thick in places: i'd be
concerned about fibre chunks / variations.

also it would mean a lot of software work writing a library (backend)
for pyopenscad that outputted formats suitable for CNC machining.

also it would be quite likely that the actual machining time would be
far, far longer than 3D filament printing.

i very much appreciate the idea though.

l.

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[Ricardo Wurmus]

Post by Hrvoje Lasic

* a CNC mill cares much less about the melting point of the work piece
during operation than a 3d printer

actually during milling you also develop heat, potentially much higher then
during 3d printing. You will need to test speeds, bits etc...

That’s right, but that’s a solved problem (for a given material and a
range of tool speeds). The bit obviously shouldn’t rest and it should
not rotate nearly as quickly as required for metals.

Post by Hrvoje Lasic

* even rather unsophisticated CNC mills can be used as the work piece is
rather soft compared to the usual CNC mill work pieces such as
aluminium.

[…].Also, if plastics are soft
it does not mean that you need unsophisticated milling machine. You still
need some range of precision

That’s right. I just meant that it doesn’t have to be these fancy
industrial CNC machines. The requirements for the milling tool itself
are much more reasonable when dealing with plastics compared to
aluminium.

Post by Hrvoje Lasic
and depend on parts 4 or 5 axes. So, it may
turn to be very expensive. Also you are talking quite small parts that you
need to hold&process somehow. I would say it is a project within a project.

Possibly. I haven’t taken a look at the parts myself. Obstructed cut
outs won’t be possible with a simple CNC mill, obviously, but I wouldn’t
expect one to use the designs that were made to target 3d printers to
produce parts on a CNC mill.

But you are right, that it wouldn’t be a simple decision to “switch”
from 3d printers to CNC mills, which is also why I think that the idea
came a bit late.

--
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6 2150 197A 5888 235F ACAC
https://elephly.net


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