Mold Natches

We have been promoting natchless molds because of not yet having developed a good way to make them via 3D printing. And because we have been doing testing. But now that focus is on production it seems that the precision of 3D-printing can really be leveraged to create a good way of interlocking molds.

Now we have! It is just a matter of provisioning a hole in the 3D-printed block mold. This enables inserting an embed into the case mold and propagating it into working molds. And it is all done by 3D-printed natches, embeds and retainers.

This method of printing in a hole also enables the use of commercial natches. By adjusting the size of my own the same block mold can be used to deploy either my own or the commercial natches.

Related Information

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.

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.

Version 4 Ball Pitcher 3D printed block mold

3D-printing v4 of Medalta ball pitcher mold

This project continues to demonstrate that multiple redesign, test cycles are a fact of life when making a new shape. 3D printing makes this so much easier. Here are the changes from v3:
-This time I am not going to back fill with plaster. I have heftier side rails that should hold things firmly in place.
-The rim is now cast in into final shape.
-The includes a distinct footring, this will enable easier cleanup of glaze on the foot and a cleaner edge line.
-The handle is thicker and looks a little further from the body (to enable getting my fingers in there).
-I am using natches this time, the two 9mm holes will mount embeds (the retainer and embed are shown beside the holes) - they will position flush in the case mold (I will propagate the embeds into the working mold also).
-I am casting it upside down, positioning the spout between the lower handle join and the foot ring. We will drain for ten seconds then plug the hole using a plaster insert made to fit snug. Remaining slip inside will refill the hole and even build the wall a little thicker there (increasing wall strength by the lower handle join).

Ball pitcher v.4 case molds cast

3D printed PLA mold to plaster case mold

We are just using pottery plaster for now. Notice the embeds for the natches. This time I did not backfill the 3D prints, that is better - because they are flexible they were much easier to remove from the set plaster. The side rails help keep them firmly in place and scotch tape on the backs was sufficient to keep them lined up at the join (these prints have a wall thickness of only 0.8mm). I did not need to use a parting agent nor did I do any smoothing on the 3D prints (although some cleanup on the plaster case mold will be done). Next step: A working mold, version 4.

By Tony Hansen
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