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The story behind the #PIRANHACLAMP

Kunststoffschmiede kunststoffschmiede

The story behind the #PIRANHACLAMP

22/05/2018 at 22:37


I (@carlf from the Kunststoffschmiede) will share with you the process of how we got to our final mould. It took us nearly 9 months and a team of mainly 4 people.

Don’t even think that we were full time on this clamp, but be sure: Product development takes some time…

So here it is:

The way from an idea to a functioning mould.

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22/05/2018 at 22:39

In summer of 2017 we finished building the injection machine, and made the first tests. One of these first test was the clothes peg.

We tried an old design from DDR. We replaced the metal spring with a plastic spring, but it didn’t worked out very well. The spring fractured quite often:( So sad…

Nevertheless it was a success, because we learned a lot about plastic, made an undercut injection mould and presented the first try with many other fancy community creations at the DDW’17.

22/05/2018 at 22:42

So our main advise in product development: Failure is essential.

We made the spring thicker, thinner, shapeless and even, but it did not help. She was still breaking. So we came to the realization that we need a completely different design.

Anna made a research about clamps. There’re so many way’s of clamping your laundry. We never would have thought that:)

We wanted to have a clothes peg with just one part and Anna found a design on thingiverse:) https://www.thingiverse.com/thing:339768

22/05/2018 at 22:46

As well as the first clothes peg, we made our first prototypes in plexiglas/acrylic glas (You want to know how it works? Watch the turorial on youtube: https://www.youtube.com/watch?v=24ECE3VL13k)

We tested it and it worked. Yes it worked:) Such a good feeling!

But we also had to notice that plexiglas isn’t the right material for the mould. Not in the long run. Because in the current design of the #piranhaclamp we have this tiny bridge from the inner circle to the outside. This bridge is too weak, so it easy breaks when you demould your clamp.

At first we had a working mould and a bad design. Now we had a bad mould and a good design. It did not feel like failure, but we still had not achieved our goal…

22/05/2018 at 22:48

In the meantime, we have been able to establish contact with an injection molding company. The Schicktanz GmbH: 70km away from our workspace and very supportive.

They have their own workshop to build high-end moulds.

It ended up that they made the mould for the #piranhaclamp for free. Thank you!

Even if the mould was for free, it was a huge charge on our team to supply the right files. It is quite different if you make a testmould with plexiglas or give something in order, which is worth several thousand euros.

We made the last prototypes with the 3D printer.
And after a few hours of discussion we decided us for one design and made all files ready for Schicktanz GmbH.

Here some specs:

parting line: central

draft angle: 3%

engraving depth: about 0,5mm

curves: 0,5mm radius

22/05/2018 at 22:50

First they milled a positiv of the clamp out of copper. This copper electrode was used to burn (EDM technique) the form of the clamp into the metal mould. Here are some pictures of the production.

22/05/2018 at 22:52

The last steps we have to make is the engraving of the plastic type (we purposely left it out to test if PP is the right plastic) and to find the fastest way to open and close the mould


I hope I could explain it to you well! Feel free to write every question or remark in this topic;-)

Besides we are testing all use cases we can imagine;-)

#champagnerclamp: Check!
What comes next?

22/05/2018 at 23:47

Awesome, thanks for sharing!

23/05/2018 at 07:37

Hey @kunststoffschmiede !
Thanks for the sharing of tall that work; very interesting to follow the “walls” you encountered in the whole process !

So if I am correct; you decided to use PP for your Piranhaclamp?


Is there any reason why the molding may not be able with other types ?

Also; i am curious how you operate the cooling on the molded product; do you let it cool naturally or do you force it with fresh water cooling?

Does your product warp much after cooling ?


Looking forward to read more about this project;
Peace !!

23/05/2018 at 09:17

Hey @carlf this is a fantastic topic. Thanks for sharing. So much knowledge ❤️.

I think this topic needs the space it deserves. Would you like to write (copy and paste 😀) a guest post for our news section?

Also, this needs to be on our Bazar, yes or yes 😇

Keep up the great work.
Great news coming soon

23/05/2018 at 09:35

@imhu thanks!
well yes, we didn’t test other types:) but for all we know, pp is one of the most flexible types of plastic.
maybe we will use an external tool to brand. currently we are testing the dremel versa tip. in this case we would be free to try other types. but for every clamp it’s another step.

we don’t cool or preheat the mould. all natural:)
in the beginning the clamp shrinks a lot and it’s a little bit difficult to demould it. after some injections the mould is a little bit cozy, then it’s very easy to demould the clamp.
as a generel rule you can work with 2-3% of shrinking. it also depends on how much pressure you give.


23/05/2018 at 10:26

@mattia-io hehe thanks man!

ahhhh! copy&paste would be to easy;) i’ll send you an email!

there wil be a limited edition for the bazar, soon;-)

23/05/2018 at 12:53


Very nice! Is the mould made from hardened steel? Can you share CAD files for the clamp itself?

24/05/2018 at 00:07

inspiring topic! Going to use this one as an example for proper documentation 🙏well done

24/05/2018 at 07:34

@davehakkens thanks!

i’ll try to upload a step file from the clamp itself.

that didn’t work. any suggestions how i can upload it in the forum.
furthermore i can send you the file via mail.

24/05/2018 at 09:08

Awesome work, thanks for sharing

24/05/2018 at 10:34

You need to make a zip-folder with the step file in it. Zip-files are possible to upload here.

24/05/2018 at 12:37

Or upload it somewhere else and post a link.

19/07/2018 at 20:28

@kunststoffschmiede I would love the clamp files as well! Can I send you my e-mail? Maybe I can figure out a link for us?

19/07/2018 at 20:30

@kunststoffschmiede also does The Schicktanz GmbH serve customers in the US? I am probably going to start with a 3D printed mold but will want to eventually mill an aluminum version.

26/07/2018 at 13:44

@kunststoffschmiede : same here, we’d like to have the CAD files, could you please put them in github repo, so everyone can find it ?


27/07/2018 at 13:21



Are you actually happy to share the design for the clamp, or for people to copy your idea/produce it themselves? Precious Plastics is based on the open source model and most people here assume that other peoples designs are presented as free to use, even disagreeing with the idea of intellectual property and patents/copyright.


However you have obviously put a lot of time and money into designing and perfecting this and it’s understandable you might not want somebody else to take all the results of that and just use it for their own purposes, possibly making a profit from it or competing with you/ taking credit without acknowledging or even appreciating what’s gone into it.

So if you’d rather other people didn’t use your designs I think we ought to respect that, it doesn’t diminish in any what what you’ve achieved, and it’s still appropriate for you to post here to showcase what you’e created, I find the story behind the evolution of the design particularly interesting.

27/07/2018 at 15:31

Hey, sorry to all of you! The past month I was travalling through Kenya without internet…
I have just arrived… for these two points i need some time 😉

1. I’ll have to check what I can share with you. I’m sure we will upload the files. But Kunststoffschmiede is a group of a few people and I have to check if the majority agrees with it.
2. Translate the technical drawings into english

peace carl

27/07/2018 at 15:41

@adyn, I have just contacted them yesterday on Facebook. I am sure they are happy to share as much they can. The problem is rather that the guy who made the mold (external) has all the rights first, and so they are trying to contacting him right now. But I fully agree with the general direction of your question. I asked myself recently too: so now we have the machines but quite some people here don’t seem keen to share their molds or even the needed details for others to reproduce and get us actually going somewhere. That can have as said many reasons but at the end it’s quite sad ending for all of us.

however, i am more the guy who just does, ignoring and leaving all that copyright/patent crap aside and so I started a PP mold directory, stay tuned! I think I have something to share in the next 2 weeks (v-clip, piranha clip and some other things :-). I have to create first some more infrastructure: new forum, and some other goodies to make proper development in this mold/pp story because unfortunately the PP team is too slow to adapt to user needs here. lets see in Sept. for v4, i hope it’s addressing finally R&D

31/07/2018 at 19:11

any news ? otherwise i just do the thing from scratch and publish it here myself, with changes if needed.

if you need a mold for this clamp, let me know, i will have the first ready next friday, bug me in here.

31/07/2018 at 22:32

Yes we will share the drawings. Licensed under a CC BY-SA 4.0

These are the files we used. pick what you need.


01/08/2018 at 09:46

Good morning
thanks a million kunststoffschmiede for sharing and caring !

I placed the files for further processing in our mold directory (updates/github there). There is also a preview to the Fusion-360 file here.

I’ve modeled the CAM operations so far and from what i see now :
– 25 Euro for 6600 Aluminium
– around 14 hours (+/-5h) machining time (because of the narrow slots with a 2 mm ball end-mill) = 140 Euro (incl. electricity, end-mills, labor)
– 20 Euro Shipping

not sure where to place channel for the plastic entry yet, nor i don’t know this can be done actually with Dave’s default injection/extrusion machine but i will try my best to get it working for both. I know there is a tool to simulate injection molding…. anyone has suggestions ?


ps: finally pp got it’s first nice open-source mold

02/08/2018 at 13:32



Thanks for sharing the design! I’m going to make a mould based your cad files, if it turns out well I might even offer it in the Bazaar so people can make their own Piranhaclamps locally (makes more sense than shipping the actual clamps around the world).  If I do, I will of course give you the proper attribution you deserve for coming up with this.



02/08/2018 at 16:59

Ok, here’s my first go at making this mould. Made one small Ooops, set the machine origin in the wrong place on the first half! But not a disaster, was able to recover it. I moved the injection point to where I prefer it, added a gate, and threaded it M10. I haven’t used the toggle clamp system before, I’ll see how it works out. I made the whole mould a bit smaller to save material (kept the same dimensions of the Piranhaclamp obviously).

Now to test it!

02/08/2018 at 17:02

02/08/2018 at 17:03


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