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Make a plastic phone cover using CNC milling

  • This topic has 76 replies, 22 voices, and was last updated 2 years ago by Reter.
Jerry de Vos jerzeek

Make a plastic phone cover using CNC milling

11/11/2017 at 21:32

Hi Guys,
I made an instuction video on how to make this, and in this thread i want to reply on questions that you guys might have!

Why not design the injection point on the inside of the phone cover? – by @jegor-m
This is cause the inside has an insert to mold around, and in general you want to prevent injecting through inserts.

Where does the air go
Yes on big injection machines this is a problem, but here the tolerances are not so thight, one scratch and you will have plenty of ventilation…

What material did you use?
The mold is made out of Aluminum

How much did the mold cost?
We paid €400 for the mold, €50 for shipping

I used Solidworks mainly because i know the program very well and the iPhone can have difficult radii. you can easily use fusion360, thinkercat or any other (free) program, but im still learning those πŸ˜‰

Where to find the mould files?
Mold files are in the download pack:https://github.com/hakkens/precious-plastic-kit/archive/master.zip
In this path:Β Β  5.create -> iPhone 7-8 mould -> STEP files 😃

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27/04/2018 at 10:12


Don’t worry it’s not the end of the world, small problems like this are fixable, there’s enough metal in the mould to make adjustments.


Yes, the reworked files look like they line up fine now.

30/04/2018 at 21:24

i had the same problem at the mould!! i put the one part back to the cnc and i milled that perimetrical line !after that used the mould just with the screws! i thought that was my mistake when i exported the cam thats why i didn’t mention it!

01/05/2018 at 09:25


I still feel bad about this.

Maybe I can help you a bit, it should be possible to change the top halve of the mold in order to fit your bottom halve, then you only need to remake the top halve.
Would you be interested in this?

Greetz, Jerry

01/05/2018 at 12:55


It’s not necessary to remake half of the mould, it’s possible to just remove the lip, drill holes for dowel pins to correctly align the two halves, and enlarge the clamping holes so they line up.

I’ve already suggested this fix to Manuel and he knows somebody who can do this for him.

02/05/2018 at 15:09


Even better!

13/05/2018 at 20:51


It all worked very good i milled the lip away and know it fits with bigger holes for the screws.

So we tried to inject PP in the mold but also with me (84 kg) hanging on the lever arm it only injects as much as you can see on the picture.
What would you suggest me to do ? I think the temperature looks pretty good while injecting its at 260 deg. πŸ™‚

And my second question is about the stamps you have created πŸ™‚ We`d like to make our own stamps with an other logo πŸ™‚ where did you let them produce? It would be great if you could tell me a bit about making those stamps πŸ™‚

greets Manuel.

14/05/2018 at 08:44


One suggestion would be to may be increase the mould temperature, to have plastic to cool slightly slower.
Another thing: how do you know the temperature of plastic? Could you may be share a photo / sketch of the orientation of the heating elements + the thermocouple location. It could be that your reading is taken from the heating element and that doesn’t represent actual plastic temp.

14/05/2018 at 21:33

@manuelmaeder Try to use another type of pp , tryΒ  also lpde and i believe for cases is the best!

20/05/2018 at 00:42

Did you try with ldpe or by warming the mould?
Pictures of the whole installation?
Thanks for the sharing
Precious regards

21/05/2018 at 22:08

@jerzeek Hey Jerry πŸ™‚ everything works great with the mold. We want to accelerate our process and therefore we d like to Know what that you used for clamping the mold halfs from the fish mold. It looks like 50 Times faster than using screws for mounting the mold halfs together πŸ™‚ i hope you know what i mean πŸ™‚

21/05/2018 at 22:12

Hi @manuelmaeder,
I’m not sure if this is what you’re after but have a look at this topic: http://onearmy.world/community/forums/topic/injection-mold-quick-release/

22/05/2018 at 12:51



They look like over-centre toggle clamps, like this.

They are quick but do stretch/give a little under pressure, so you might get more flash along the mould parting line.

22/05/2018 at 12:56


Yes, those ones look much more heavy duty, probably better for a larger mould.

22/05/2018 at 17:02

Thanks for all your answers πŸ™‚ yes thats what im looking for

23/05/2018 at 17:52

Hi guys!

@manuelmaeder, glad to hear that it’s working! just like the the others i would suggest warming the mold, more pressure, hotter plastic, bigger sprue.

On the part of the clamping, indeed these clamps make the process much faster! But make sure you buy decent ones. The cheap one’s bend easily. also @kunststoffschmiedeΒ made moulds with quick releases : here


04/06/2018 at 16:10

@jerzeekΒ  Hey Jerry, we finished our own clamps and they work good. When Im looking at your phone covers they all look very good and they seme to have the same temp. We have some small problems right now with the prozess because it gets hot but looks like this.Β  In some places slightly burned and at some its good. Can you tell us which Temp. You used and your problems that You had with making decent phone covers :)? The heating elements did You place them in a specific way ?

Thanks for all the time you take to answer all of my questions πŸ™‚

04/06/2018 at 16:22

Ok, somehow i cant upload the image :/

04/06/2018 at 16:23

ok, this is the image

19/07/2018 at 13:07

Was wondering how you determine that 2.5mm was the thinnest you could go? And what would i have to change if i wanted to insert-mold an even thinner object to make it work?
Much appreciated!

19/07/2018 at 13:54

@manuelmaeder, i am running here a little service, offering mold machining as well, for volunteer prices (because we want to support PP success stories!!). However, we don’t design molds but do the machining only. the mold above would cost you about 150 Euro (material = 30 euro, 120 labor). It’s also cheap because it’s done by my PP students (but under my supervision).

about CNCs: you can build a quite good one (good enough) for 2500 euro in materials and about 2 weeks of full-time work, less is not really possible… I am posting the documentation of mine sometime here in the forum. in the picture below you see it what you can get for this money. working area 45x45x25cm, cuts steal and aluminium with no problems, precision 0.01 mm; it’s my 5th iteration of doing DIY machines and I am really happy now (after ‘wasting’ 1.5 years and thousands of euros).
Just as reference, there is story here in PP about some guys who made a mold for a sun-glass, they paid 3500 Euro for it….simple to make the math.

also, you will never regret to have paid for a CNC, i use it everyday, for all sorts of things, mostly using the xbox-controller or manual gcode only πŸ™‚ go for it !

19/07/2018 at 13:59

damn, i just realized that i answered to a post from long ago, sorry.

20/07/2018 at 04:08

Very much appreciated, @anne-barbier!

28/07/2018 at 11:09

@anne-barbier thanks for the offer and the information πŸ˜€ if i would have known that sooner i would have bought it from you πŸ˜€ πŸ™‚

Looks very cool your cnc machine. does it run with a programm on the PC ? Where did you get the programm for the cnc :)?

28/07/2018 at 11:24

Hey everybody.

Me and my colleague are looking for a PreciousPlastic Coin with Polypropylen
for marking our Phone Covers. This is the last step which we just got to have before we can sell our phone covers πŸ™‚ we have a decent storage right now of like several dozen forms and want to sell them on the bazar asap.

01/08/2018 at 17:09

@manuelmaeder I think the marking coins are out of stock in the bazar, but making them with a dremel or CNC should not be hard at all.
Another alternative is go the cheap route and make them this way:Β http://onearmy.world/community/forums/topic/hello-from-estonia/page/3/#post-131350

01/08/2018 at 17:12

@xxxoliverxx, i took care about manuel, he is getting that coin from us for free πŸ˜‰
problem is the size, it’s a long machine job to get through those 0.3 mm slots. I am doing a batch of it, in different sizes. pm me if you need one.

08/08/2018 at 20:59


Hi, sorry I didn’t reply earlier but I was on holiday..
Better late than never, I know there are still coins at PP HQ, but I think dave took it out of the bazar cause he is in 🇵🇹.
Did Anne already fix the problem or are you still in search of a coin?

Great to see the CNC service offering!

You can go thinner but then you need more force to inject it, now we already need 2 persons so then i would suggest to change te machine so you can apply more injection force

10/08/2018 at 05:19

Hey Jerry, Anne fixed the problem πŸ™‚ thank you

13/11/2018 at 22:09

hi @jerzeek
I am just getting into your stuff, and have an injection machine up and running. Now considering making and iphone case and wanted to use your mold. But it seems like the files are gone. Can you help me?

15/11/2018 at 14:10

Mould files are in the download pack:

5.create -> iPhone 7-8 mould -> STEP files πŸ˜€

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