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Waxes vs Resin Models

I’m not casting at present, but I just lack a couple of small pieces of equipment and I would be in business for vac casting, so I’m following the discussions regarding printed models with interest and considering learning some kind of jewelry CAD program. The latest posts about burnout problems and surface difficulties with resin models make me wonder whether anyone is still carving waxes via CNC lathes for casting. Or is this new resin with 20% wax in it the magic trick to this stuff? I’m capable of wax buildup and carving for one off models and wonder whether it is worth it to get up to speed with the CAD programs or whether it might be just as effective for me to carve waxes and later make molds of my successful casts. Anyone gone down this road already and have some insights to share? Thx, -royjohn

There are factors, depending on part configuration, that favor building models over carving them with CNC (usually using mills, not lathes), but there are also reasons to do the opposite. You can make more complex models with 3D resin printers, but they’re harder to cast. The CNC process can work with wax that casts easier than resins, and also is easier to pull molds from, since the process doesn’t yield as many undercuts. People are still doing it.

Whether to go with CAD modeling rather than a hand-carving process really depends on the sort of things you want to produce. It does make some things easier; for instance if you have an asymetrical model for an earring and want to make a mirror-image duplicate, that’s really simple in CAD, as is coming up with the same design in multiple different sizes. On the other hand, if you’re happy with the results and production rates you’re getting by hand-carving waxes, it might take a while for your CAD modeling skills to catch up to the ones you’ve already mastered. You have to be ready to cope with a learning curve that can be steep, depending on the program you choose. But it does offer the ability to do some things that you couldn’t do before. Whether it’s worth all the time (and money) you’d have to invest is up to you.

Got to the library for and search on resin curing. Free access.
Judy H

Hi JudyH,
I did take a look. Resin curing didn’t bring up anything, but curing did…I read an Italian paper from 2011 on casting defects and another from 2018. Unfortunately neither showed comparisons with wax models even though there were superb magnified pictures of rough castings. The paper from 2018 discussed ash elimination. His conclusion was once you have the ash, there are going to be surface defects. Ash elimination is accomplished by a fast burnout. In his experiment if the model was too close to the center of the flask, if the investment was too wet, so that the temp stayed low too long, or even if the flask was shaded in the kiln by other flasks and took longer to get hot enough, bingo, ash. Also, the kiln needed to have air flow through it. None of this filled me with confidence about these resin models.

What concerns me is that I couldn’t find any comparison photos of wax cast items, so I can’t say that their surfaces are better conclusively, altho’ AFAIK, there isn’t a problem with ash with normal burnout of wax models. It would certainly be interesting to hear from someone who once cast with wax who now uses resin models.

One other comment I would make is that, unlike the paper on soldering I criticized here, which I thought wasn’t very scientific, these studies were excruciating in their detail and densely written. Reading them was like pulling teeth…but the data was there. Anybody out there got practical experience with both methods? Anyone use the “new” resins which have some wax in them?
Thanks, Judy, for reminding me about this treasure trove of metal stuff! -royjohn

royjohn - this is the paper to which i referred - 2016 - A New Method for Preparing 3D-Printed Acrylic Photopolymers for Investment Casting. James Binnion presented it.

Rhino is a great CAD program and easy to learn, however it is expensive. A powerful free program is Blender 3D. But it is difficult to learn and I’ve no great books to help. Most books on Blender deal with character design.

Hi Judy and All,
Well, I read the paper you reference and it seems the upshot is that, in order to prevent casting surface roughness, the resin model is best treated by vacuum heat curing, but it didn’t look like a rig I would have or easily procure…so is this what the makers of resin models do now before they send out models? Judging by the questions here about resin models and casting flaws, I’m guessing the answer is no. I’m still a bit puzzled.-royjohn

I don’t think very many people are using vacuum heat curing on their resin models; that would be expensive to set up and difficult to manage. One simple alternative is to set the model in a cup of water and boil it in a microwave oven for 5 minutes or so; this seems to heat-cure the resin without scorching it.

We sell a 3D CAD program called MOI (Moment of Inspiration), which was written by Michael Gibson, the original author of Rhino. It doesn’t have all Rhino’s myriad features, but it’s even easier to learn and a lot less expensive.