Mold Natches

3D design and 3D printing are enabling a rethink of almost every detail of how molds are made. The way in which natches are incorporated into working molds, what natches need to be and even if they need to be there at all, are among the changes. The precision of 3D-printing can really be leveraged to imagine and create new ways interlocking multipiece molds.

At its simplest, incorporating natches in mold parts is putting mating holes in 3D printed shells. The holes permit insertion of clips and retainers and they hold in place the embeds needed in the working molds. Natches can then be inserted (and glued) into the embeds.

More advanced options involved fitting natches to already created working mold parts. This is done by the incorporation of smooth recessed 3D printed platforms to which natch hardware can be positioned and epoxied.

While natches can be purchased the other hardware needed to embed them necessitates 3D printing anyway. So you might as well print the natches also. Making them all yourself enables the ultimate in flexibility. And you will never be caught out of stock.

Related Information

3D-printed plaster mold natches, retainers and embeds

Top left to right: The natch, the retainer, a fragment of a 0.8mm thick 3D printed mold shell and the shallow and deep receptacles that fit snuggly over it.
Lower left: The deep and shallow receptacles are embedded in a test section of plaster, the natches are ready to insert (head first or feet first). The natches have been glued in on the right.
Not shown: Cylindrical retainers that fit inside the embeds. These enable replication of an embed in a case mold to an embed in a working mold.

In some ways, these are preferable to the commercially available natches. First, the embeds enable flexibility in what will be inserted into either case or working molds (the natches, for example, are glued into the embeds). A key advantage of this, vs using commercial natches, is that working molds release from the case molds with flat matting surfaces - meaning they can be sanded to ultimate flatness for optimal fit (since a little warp can happen in the 3D printed block mold). Another advantage is that parametric drawings make it easy to change the sizes of all needed parts. This project is a testament to the accuracy of 3D printing - it is precise enough, on our Prusa MK4, that 1/10 mm is the difference between perfect fit and too tight or too loose.

A demo for using using commercial natches in 3D printed master molds

These commercially available natches are 9 mm deep (to the shoulder) inside, the inside diameter is 9.4 mm, they are 10.9 mm high at the shoulder and 18.3 mm total height. The challenge is to embed receptables (two inside this box) into plaster case molds. The embedded natches hold natches precisely in place for the plaster pour of the working mold. How can they be embedded? A simple 9.4 mm dia hole in the 3D printed block mold (which this box simulates). How are the embeds held in place? The two cylindrical flanged retainers on the outsides fit through the holes and embeds on the inside slide snuggly over them.

Imagine the plaster fill of this box creating a case mold with embeds for foot-first and head-first natches. How are the natches held in place by the embeds? The nipple fits snuggly into one. A 9.4 mm cylinder inserts into both the embed and the natch.

Three-piece vertically printed mold with natches

These 3D prints slide into slotted side rails for each pouring of plaster. Since the plaster releases easily it is possible to use these multiple times. This method is suitable for prototyping in larger quantities than prints that integrate rails. These are printed on edge so print times are drastically reduced and surface smoothness is much better. This version has a bottom piece eliminating the seam across the base. It also enables putting embossed logos on the base. The holes enable mounting flush embeds - making it possible to sand the mating surfaces flat before gluing in the natches. The three-piece mold produced is shown on the bottom.

Slotted natches make this bottle mold possible

These enable pulling apart the top halves of our ceramic beer bottle molds while the leather hard bottle is still embedded into the base. Starting upper left and clock wise:
#1 The 3D design for making a rubber case mold.
#2 It has been 3D printed in three parts (which are then glued together).
#3 PMC-746 rubber was poured in and the 3D printed parts were peeled off.
#4 Natch parts have been 3D printed.
#5 The embeds have been rubber cemented onto the rubber mold (to hold them in place during casting).
#6 Plaster was poured in.
#7 The plaster working mold has been extracted from the rubber, the embeds firmly rooted in place.
#8 The slots have been epoxied in place (lined up and positioned accurately so the natches hit the end of the slots just as the halves contact).
Centre: The mold partly assembled.

Why 3D design and printing is a better way to make slip casting molds

I dread the process, the mess, all the supplies and tools involved in the traditional mold-making process for functional ceramics - it just feels old. I am not a mold-making expert either, but 3D design and printing are enabling a rethink of every aspect of the process. This is the future. And it is much more fun!
-I spend most time on design, pouring the plaster or rubber takes minutes.
-Many fewer tools are needed, the process is less messy.
-Sanding of flat mating faces is possible (for better seams than I've ever had). This is because natches are added later.
-I can make my own natches and coupling schemes.
-No spare is needed, the 3D-printed pour spouts work better.
-The range of shapes seems limitless. Especially because designs can be split up into pieces, each printed in optimal orientation (and then glued together precisely).
-I make molds through multiple design-print iterations. 3D makes do-overs or changes in design as easy as a reprint and plaster pour. So, I can make a mold just to test an idea!

By Tony Hansen
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