Creating Tool Handles by 3D Printing and Casting

As part of a personal project, I developed a method for creating custom tool handles for people with hand related medical issues. The process consists of creating a silicone casting mold with a rotatable and interchangeable end unit (for fitting different tool heads) using a "positive" printed on a simple open source 3D printer. The reusable silicone mold is then used to cast thermosetting plastic handles.

This process has many advantages over simply 3D printing the handles:

• The cast plastic (I used G-26) has significantly greater mechanical strength.

• The material is non-toxic.

• The material is resistant to high temperatures (dishwasher safe).

• FDM printed objects have internal cavities which can enable accumulation of filth and bacteria if used for cutlery handles, but cast handles are completely solid.

• Minimum 3D printer machine time - parts are printed only once.

Step 1: Creating the Molds

After designing the CAD model for the handle I created models for the 3D-printed molds (the yellow ones). the small third mold is for the rotatable insert which allows to fit different tools to the same handle mold. The molds include thin ridges that will become (in the RTV mold) air ducts for prevention of air bubbles in the finished product.

Once I printed (and post-processed) the molds I added the mold walls. The walls are not part of the print because the fact that they are removable makes the seperation of the RTV from the printed mold much easier. The next step is to spray it all with mold release and pour the RTV silicone (I used Mold Max 30) and let it cure. Notice that both sides of the RTV mold end up with positioning holes, the pins are separate pieces.

Step 2: Casting the Handles

Although not necessary for a good end result, I created a jig for the casting process for better repeatability.

I used G26 for the final casting because it cures quickly, doesn't stink while doing so and the end result is strong yet easy to rework.

Comments

[haraldhorn008]

Great idea - a pity that I found it only now.
One question on the molds: I have never tried it out yet, but will the texture of the PLA negative be smooth enough? Or did you smoothen the PLA in one way or another before creating the final molds? Thanks for any insights. BR, Harald

[moshe.boruhin]

the mold duplicates the original texture very well, which in this case means you'll have to smoothen the original.
if geometrical accuracy is important to you think of using a harder silicone (higher Shore value).
if you have access to a vacume chamber, use it!
and don't forget mold release :)

[haraldhorn008]

Thanks a lot Moshe for getting back - very much appreciated.
Creating the form using PLA (even when printing with 0.1mm layer size) will most likely create an uneven surface.
How do you treat such a surface? Do you postprocess it with aceton or similar?

BR, Harald

[moshe.boruhin]

I used PLA so aceton won't help. sanding down and using filler is the best way.
I tried XTC-3D on a few prints (in combination with sanding), with good (not great) results.

[LilithC3]

I did something similar for single part silicone candy molds. But rather than than build a box around the part I just made it part of the printed positive. I made the walls thin enough to rip off easily so as to pull the silicone off the main body.

[Firedrake26]

that's a great effort - I've been casting using silicone for years but I never thought of using the 3d printer to make such beautifully straight moulds! You've made my night!

[spawninggrounds]

I want to get into molding. What kind of 3d printer did you use? I want one and have a reasonable budget but I need detail. And what did you do to clean up the casting? Did you have to smooth out lines in the 3d prints or anything?

[moshe.boruhin]

I used an UP printer and sanded down the result with standard sandpaper.

[GabrielleGera]

Well Done!

[moshe.boruhin]

Thanks :)

[Funky Diver]

How is the rotatable insert removed from the mold?

Very nice instructable!

[moshe.boruhin]

the insert mold is shallow and the RTV is flexible enough for it to be easily pried out using a flat and thin tool.

[Jobar007]

That is a very practical application of a combination of techniques. I like it a lot!

[acaig]

Wow I wish I was able to access a printer or someone to help me with this I have had to use special cutlery for ages but is never right and must of it is blunt which makes life harder if I could change the handle on a set of good stuff id be set
You are a genius

[cpurola]

Excellent! How do you secure the metal end in the handle?

[moshe.boruhin]

Thanks!

as long as the metal is clean (no oils or mold release spray) and has some notches it will sit firmly in the G26.

[tysonvw]

This is awesome well done!!!!

[LynxSys]

This is an excellent method for creating something with a 3D printer without being limited to the materials that your particular printer can print! I also imagine that if you had a printer with a lower resolution than you needed that this method would allow you to correct defects before casting the final product. This is a great idea all around!

[gravityisweak]

Yeah, this is a great idea. 3d print a prototype and if its bad, refine, print again, repeat. Once you like it, make a mold and cast to reproduce, instead of repeatedly 3d printing.

[GabrielleGera]

I'm going to try this!