Feeling frustration over the huge mountain of low value plastic JUNQUE I have printed has moved me back to my previous passion of wax carving and lost wax casting durable silver items.
I have made a very serious attempt to use 3D printing to create masters for use with silver casting. Much of that effort is shown here is this "lost wax" category. The inherent layering and complex chemical reactions in the casting and burn out proved to be far too complex for the results obtained. Some success, but several magnitudes of effort over the pure lost wax carvng process. The variable results were far from dependable or as consistant as wax.
The use of wax is also a complex process but provides extremely dependable results every time. The movie shows the CNC milling of the wax.
I developed some good CAD skills in designing 3D printed items. The very popular Autodesk Fusion 360 (F360) was the starting point for this project. But not the only software tool used. Vectric Aspire provides a very comfortable, easy to use, double side and 4th axis milling CAM. Aspire was used in this project as well as F360.
Not used here but I should mention another CAM that is good for CNC milling 3 and 4 axis. a product from the Netherlands called DeskProto. I own the hobbyist multi-axis version 7. Not an intense CAD as F360 or Rhino, but a get-the-job-done for CAM
This is about milling wax and silver casting a KAUTZ key fob with an owl design.
I originated the design using Fusion360. Creating the tag shape and size. The KAUTZ lettering was done in F360.
I used Aspire to create the owl, then imported the owl into F360 as a .dxf file. The complete CAD design was finished in F360.
Finally, I exported the key fob file as a stereolithographic (.stl) file and made a single 3D print in black plastic.
I returned to Aspire and imported the key fob as a 3D model (the .stl file) and used the Aspire double sided CAM to locate the key fob model in the middle of my wax carving block. Then I exported two CNC gcode files, one for each side of the wax block. The carving would be accomplished using a tiny 0.005 inch tapered end mill in my Taig milling machine, to which I have installed a 25,000 RPM water cooled spindle.
Three key fobs were carved from the wax requiring six milling operations. Two per key fob, once on each side. Run times were about 90 minutes per side.
The wax carvings were then cleaned up manually and sprued together for a single, all at once, casting.
The wax masters were invested (surrounded) with a plaster like material in a steel sleeve called a flask. Investment set-up was about 3 to 4 hours. Then the flask was placed into a kiln for firing.
Firing is a staged process. 300 degrees to let the wax melt out, then slow rise to 1350 degrees and held for the three hours burn out. Next the temperature is permitted to drop to 900 degrees where it remains until casting. It is a 12 hour process of firing.
The silver is melted by torch while the flask has a vacuum pulling on the investment from the bottom side opposite the pouring side. The actual cast (pouring) is just a second or two long. This cast required about 86 grams of silver, about $52.00 at my cost. Some silver will be recovered from the cut off sprue and used in the next cast.
After quenching the very hot flask in cold water, the cast silver is freed from the investment. The hot quench literally blows the investment into a fine slurry, freeing the cast. It makes a very exciting rumbling boiling sound. An exciting part of the process.
The silver is almost black from fire scale (oxidation) coming straight from the quench. Remaining investment is cleaned off the casting by hand (toothbrush) and by ultrasonic cleaning.
Then the casting is put in a hot water/acid “pickling” bath for about 30 minutes. The black fire scale turns to bright white which is the natural color of pure silver.
The sprue is cut off and hand finishing progresses from here. Filing, then polishing the silver to a mirror like shine or multiple other finish options. One of my favorites is blackening the background with a sulfer based acid. I have also used fired glass enamel which is another complex process of its own. These tags are polished up shiny and will develop an aged silver patina from use.
Final step was a couple of hours in the steel shot tumbler which burnishes and creates a hardened surface.
This is an example of my custom work. As I think I have shown, it is a very complex multistep process.
The value of silver is an easily priced commodity. There are many other consumable materials that add to the cost and value. Such as the wax and investment and electrical power needed to run the kiln. Tools wear out and require replacement. I try to make more than a single item at a time to share consumable costs.
The three tags are worth at least $150 retail, $50 each. They are one of a kind (well, three of a kind) and are custom made. Solid Sterling silver makes them much more intrinsically valuable than the single copy 3D printed in plastic. At least I think so…
My wife, Gloria has her hobbies. The main one is certainly her quilting avocation. We could probably sleep every night of the year under a different quilt. Well, that might be an exaggeration, as I have never counted them, but she does have a passion for making lots of them. It's also a social gathering for her and her quilting buddies. They are all female, but there is no reason a male couldn't enjoy this sewing art as well.
The ladies gather in "retreats" where they spend a few days in secret hide-outs doing their sewing thing. As far as I know there are no men invited. :)
Gloria likes to give away some of my three dimensional printed objects as little gifts at these gatherings. The last item was a drink coaster with a quilting design called a square in a square in a square. Evey quilter knows that basic design pattern in their quilting work. I thought it was a good idea for a design quilters would recognize.
I designed a suitable coaster in Fusion 360 and was soon busy making a big pile of them (see pictures).
After the retreat, I was searching for ideas for creating a lost wax cast silver pendant design. There was an obvious conclusion. A pendant with the three nested squares is a perfect jewelry accessory for a quilter. It's a simple design and a recognizable symbol to them. It is also a good conversation topic starter to explain to a non-quilter what it represents.
Back to Fusion 360 and a new square drawing. The pendant needed to be small. I chose a one inch square as quilts are produced to inch measurement. The CAD drawing is metric though, because I intended to three dimensional print the master model. 3D printers almost exclusively use the metric measuring system for the materials as well as the print designs.
Being well practiced in both measurement systems, it is no issue to use either or both. It is the way it is today.
The bars in the design are designed to be 2 MM wide and the pendant is 3 MM thick (and 25.4 MM or 1 inch square).
I try very hard to use three dimensional printing with my silver work. It should be a natural fit, but there have been issues with the castable resin used to create the model. It has to burn out of the mold as clean as the standard wax model. That has been a very long learning path. It does work when all the production methods and secrets are known, and a rigorous process strictly followed. That's a story told in previous posts.
I will continue with both wax carving and 3D prints for my silver work. Each has it place.
I produced the green plastic example as a proof of concept to show my "boss" (Gloria). It was quickly produced on a FDM fllament type printer. It is a low resolution prototype.
Resin DLP 3D printing (by UV light) requires a lot of design effort in supporting the model for printing. Not necessary for FDM printing and the reason for doing the FDM print first.
AS it turned out, the first DLP print was what I can only call a disaster. My supports were inadequate and only one resin pendant survived. As I said above, resin printing is a bit of a challenge to get right. A re-think and a re-design of my supports and I was able to produce three high quality resin master models on the next try.
The printing is the first step. It is working well now that I have the correct resin and I don't make poor support designs. The really big issue has been getting clean cast silver from the burnout. Many of the resins tried and the process variables (trade secrets) are incorrect for the low cost equipment used by me and most other low volume craftspeople. But as you can see, it can be done. Much learning by failure is required as what doesn't work becomes a learning experience.
Happy days are here and the silver pendants are examples that printing master models will continue at KautzCraft.The pictures tell the story.
I have succeeded in producing a fairly good cast ring from a 3D print master model. This came after many failed and unsatisfactory attempts. There have been numerous issues but the hardest one to overcome has been the failure of the investment during the model burnout. The resin from the model apparently doesn't totally cure. Especially in a thick section model. The uncured resin combines with or attacks the gypsum in the investment during the investment cure and subsequent burn-out.
I found a written article published over two years ago that confirmed every one of my suspicions. A jeweler in Bellingham, Washington, Jim Binnion (https://mokume-gane.com/about/jim-binnion/) offered a solution. It involves high vacuum curing the model in a heated oven, after ultrasonically cleaning it in water, fresh off the printer. No alcohol is used on the model and a UV cure isn't necessary either.
Jim is a professional jeweler and has professional grade equipment. I assembled a hobbyist grade equivalent, seen in the following pictures. I can't get or measure the 10 micron vacuum Jim recommends. I did notice the vacuum stop at one level, then about an hour later it dropped anotherl .5 inch WC. An indication there was gassing off of the tiny model, which created the drop in negative chamber pressure. I was heating the chamber to 180 degrees Fahrenheit. There was also some condensation (resin?) on the clear and cool lid of the chamber during the vacuum operation.
This ring is one of my best 3D printed casts so far. So, it looks like Jim's information about using a vacuum was good and I am on the right track to good casting. I will continue using this method. I have also resigned myself to keep the model section as thin as possible. The thicker the model the harder it is to properly cure.
That’s Three Dimensional Printing. My first attempt with resin material was not satisfactory. I posted the sad results HERE. However, one attempt does not qualify as a final result. Successful people keep trying what they want to do until they get it right. In this case, find the combination that works. Thomas Edison once said he discovered hundreds of ways not to make a light bulb.oweverH
Luckily, I didn’t have to go that far. There are people other than myself already doing it correctly. The materials for a successful 3D print casting exist. It just a case of sorting out all the variables and putting them together in a production stream that works for my conditions and situation. That’s what I enjoy. Working out the details of a very complex process.
The 3D plastic still doesn’t burn out as well as wax. I continue to see evidence of ash or debris on the resin castings. Not as bad as my first test. The PLA burned out quite well. The results are useable but not as good as I can cast with wax masters. Next run I will extend the 1350F hold from two to three hours.
The "wiggly" thingy was hand carved wax. The Fleuer-de-cross is resin DLP and the ring is PLA via FDM printing.
The new Plasticast investment powder is a wonderful product. It will be my new preferred investment powder for use with wax as well as plastic. The vacuum de-airing was a bit frightening. It rises over twice the height of my previous powder. I mentioned this in my previous post. Mold release (water quench) is outstanding. I love when a plan comes together, and things start working the way intended. It opens the door to making 3D printing a part of the LWC process and I have a new ability to design and create.
I am not at the point where 3D printing is going to be the only way I create models. Wax carving by CNC milling and hand is not going to go away. I enjoy the manual carving. The “squiggly” pendant is an example. It was completely hand carved. I enjoyed making every curve with files and wax carving knives.
The investment process brings out EVERY minute detail in the model. It hides NOTHING. The 3D prints, especially the FDM with PLA shows every layer line in the model. My first instructor warned me, it is far easier to smooth and detail flaws on the model, than to remove those flaws from the silver casting. How true that is!
I was able to grind and polish out the slight “evidence” of the FDM layers, but that’s doing it the hard way. Resin 3D prints are much smoother, but not perfect. Wax is still the best material for masters but can be fragile to handle. Everything has a compromise to understand and consider.
I may have a use for FDM 3D prints now that I know the PLA can be burned out. I may want that look. I am now feeling better about doing design with my DLP (Wanhao D7) printer.
Full STEAM ahead. (I like model steam engines, too) I am already getting requests for jewelry that can be designed in CAD, 3D printed, and cast is silver!
I just filled three LWC casting flasks using my new investment powder. It’s Plasticast Investment made by Ransom & Randolph, Maumee, Ohio (My birth state.) It is supposed to be a superior investment powder for when waxes and plastic are used in investment casting.
I have been using a R&R investment called Ultra-Vest since day one of my silver casting. It’s been a wonderful investment powder for my work. Always produces good results with wax masters.
My first impression with Plasticast is that it is definitely different material. It LOOKS the same but the mixing and especially the vacuum de-airing is totally different. The mix is extremely smooth when mixing and the rise when under vacuum is MORE than twice as high! The air bubbles stick together very well and just keep rising. Almost frightening compared to what I have become accustomed.
No problem, I was aware of the extreme rise and was prepared. I was also grateful when the second vacuum (in the flask) did not rise, but just came to a boil as it should.
In about 15 hours, I will know how the material works coming out of the kiln and silver casting is attempted. I have a slightly modified schedule for the burn out. It now includes a hold stage for two hours at 700 degrees F. for the better transition of the plastic materials. It was a part of the R&R burn-out recommendation
This first try has one flask with the usual wax master. The second has the resin master made with my Wanhao D7 3D printer. The third flask has a finger ring made from FDM 3D printed PLA plastic.
I love to experiment (a little, not forever) so I am excited to see how this will all virtually come out.
I can work forever, er… the rest of my life, using wax for casting silver, but I really want to do highly detailed work with 3D printing of the masters. Next post will show the results.