What the differences are between 3D printer castable resins used for casting jewelry and dental applications. Specifically, does the dental resin need a high temperature during it’s burnout?
I only see that the dental resin has less shrinkage compared to the resins used specifically for jewelry. I understand there are many many options of castable resins out there, with all sorts of differences, but what are the main differences between castable dental resin and castable jewelry resin?
Hello Patrick.
3d printed models are great and I have had a great deal of success with the models - BUT NOT WITH CASTABLE RESIN.
My advice - to save you a lot of time, frustration and money, money, money- is to have your models printed in a high temp resin and make molds directly from the models.
Additionally, sprue your models in CAD! Maybe you cant do all the sprueing needed for casting but you can create enough of a gate for wax injection into the mold.
Heather
Hey Heather, thanks for the advice. Are there any resins you recommend?
Hi
I have been working with makelab in brooklyn. They have Formlab 3d printers and use
Formlab resin as far as i know.
The orices are reasonable and the quality is mostly good. These arent photocopiers so you cant expect perfection. You can clean up the models with 1200 grit sandpaper before molding. But be gentle as They are brittle.
Good luck
The 2 castable resins that formlabs sells actually perform quite well in both normal and stone-in-place casting. My favorite is the purple ‘castable wax’. The blue ‘castable wax 40’ is really waxy, and deforms easily (it’s 40% after all), so I don’t use it all that often, but it still casts well.
Formlabs has burnout schedules listed on their site for each of their castable resins.
I do second the recommendation to add sprues to the model, however depending on the complexity of the piece you’re printing, it could make removing all the support material an extra pain in the rear.
As far as spruing, gently scuffing your attachment points aids in adhesion, but the best thing to do is plan out your spruing so that you limit how much handling you have to do. Sometimes the sprues attach nice and strong, and other times they pop off with just a bump. It really just takes a bit of trial and error to discover what you can get away with. It also, annoyingly, changes with each resin.
As far as non-Formlabs resins you can use with your Elegoo, I recommend pretty much any castable resin from PowerResins. The dark has incredible accuracy (to the point where you can actually see each pixel from the lcd screen in the model), but doesn’t cast quite as well as the others. Our workhorse is currently their ‘Wax’ resin. Not quite as good at sharp detail, but prints nicely, is pretty easy to work with as far as spruing, and casts wonderfully.
I would be interested in understanding your investment and casting protocol. I consistently get porosity in my casting with castable resin models, and large areas where the investment has obviously not held up to expansion during burnout. I use Plasticast resin at 39 ratio and am casting in silver and brass. I use the formlabs proscribed burnout schedule precisely. My pieces have flat surfaces. any suggestions for better results?
I’ll try to describe my process as best I can 
First off, Investment.
Our current lineup of investments is comprised of Ransom and Randolph’s Solitaire (for stone-in-place), and Certus Prestige Optima (for everything else).
The R&R has additives that make it more safe to use for stone-in-place casting (likely just boric acid, but I’m not sure), and seems to have just enough strength to avoid the expansion forces put upon it by the resins we use. Its downsides, however, are a couple-fold: It isn’t strong enough to avoid the expansion forces from ALL resins (ex. the PowerResin Black expands too much, and causes cracking and finning, whereas the FormLabs resin and PowerResin Wax don’t expand as much, and cast fine), and it isn’t a fine enough investment to create a really clean, smooth casting. I’ve found there’s quite a bit more finish work required when working with that investment, but all-in-all, it’s pretty good. Plasticast, as far as I am aware, has the exact same base investment, minus the additives, so it should perform similarly.
We just started using the Certus Prestige Optima (recommended by FormLabs). It’s a decent investment. It’s strong enough to resist expansion forces, without being so hard that it’s impossible to get out of the flask when you’ve cast (like BlueCast X-One…holy moly I had to hammer each piece out of that stuff; it’s hard as concrete!). We’ve also been experimenting with adding boric acid to the mix to make it viable for stone-in-place casting, with some pretty good results. It produces a better cast finish that’s far closer to the finish the model had.
I follow the same mixing method for both investments.
For a single flask: 90ml of water added to my mixing bowl, and then I add investment while mixing until I get the consistency I’m looking for; in most cases, the consistency of slightly thin pancake mix). It’s by no means precise, but I’ve yet to have any problems with it, and the best part is no scale needed! 
Mix that for 3 minutes, throw it in the vacuum chamber and run it for 30 seconds after it starts to boil (for our setup, this is about a 50 second operation). Then take it out, fill the flask about 3/4 of the way (or at least above the highest point on the model, whichever is higher), and vacuum again for between 60-90 seconds. Take it out gently, top it off, and set it aside for around 2 hours.
Burnout:
We have a pretty old oven, without a lot of the fancy functions newer models have. It has 8 programmable temperatures, and a switch that lets us do 1, 2, or 4 hours per step. No ramp control or individual hold control or anything fancy like that. We set ours at 2 hours per step.
I got tired of changing the temperatures back and forth between stone-in-place (which requires a lower temperature as to not burn the stones) and normal casting, so the following temp schedule will definitely seem lower than anything else you may find, but it still works for us.
(all temps in Fahrenheit)
Step 1: 350 degrees
Step 2: 500 degrees
Step 3: 750 degrees
Step 4: 900
Steps 5 and 6: 1000
Step 7: 1100
Step 8: 950-1000
This allows about 8 hours at the highest temperature to ensure the plastic melts out and the ash burns away. Previously, if we weren’t doing stone-in-place, the only change would be that step 6 would go up to 1150, and step 7 would go up 1350.
Casting:
I use centrifugal casting, but have had success with vacuum casting as well (granted, I’ve done very little as our setup isn’t really laid out well for it). One thing I have found with vacuum casting though, is that it works far better if you use the wax web that Rio sells.
Otherwise it’s just heat the crucible, toss in the metal, once it melts take the flask out of the oven, little pinch of flux in the crucible, and let 'er spin.
One note on sprues: I’ve found that you have to use far larger sprues for resin casting than for normal wax casting. The stuff likes to have a nice big channel to flow through as it melts. For example, on just a standard solitaire, my sprue at the bottom of the shank will be typically 5mm or more wide (but still only as thick as the width of the ring, if that makes any sense). Also, orientation matters. You want to give a good path for the melted wax to just kind of pour out, instead of relying on it to burn out. So that means something things get put at an angle, and sprues go to anything that may hook back on itself (I don’t know how to describe that better 
)
So that’s my process. Hopefully it helps you get some better castings, or at the very least, gives you a base-line to go off of.
As far as the stuff you’re casting: I personally haven’t ever had much luck casting flat pieces without porosity no matter what material I use (wax or resin). It seems to be in the hands of the jewelry gods every time. We don’t cast a lot of flat pieces, however, so my ability to experiment with it has been limited.
One thing I’ve yet to try, that you could definitely experiment with, is something I learned when I worked at a titanium casting house that made aircraft engine parts. If there was an area that was flat and/or thin, we attached a kind of feeder bulb to those areas. Think of it like tear drops attached with the thin part contacting the piece. This allowed the thin areas to pull hot, molten metal from them as they cooled, preventing stretching and porosity from forming. I just wish I could remember what the heck we called them.
My experience casting silver isn’t vast (and I’ve never cast in brass), but I have found that I have to get it way hotter than I expect. It seems as though silver will appear molten, but still have a chunk within it that hasn’t reached the appropriate temperature for casting.
So, there’s a very long read for you
Let me know if you have any other questions!
I’m contemplating just making a thread about resin printing and casting so we can have all the questions and answers in one place as well.
Cheers!
-Scott
So a little update. We went ahead and casted the model printed from the dental resin. We used Ultra-Vest from R&R. We held it at our top temp of 1350F for an hour longer than we typically do hoping it would burn the resin out. Our casting setup is a Jz-P Autocast and the grain we use is the 57NA from United PMR. Unfortunately, (and honestly somewhat expectedly) the castings turned out horrible.
Even before we casted, I dove deeper into the different resins as well as specific resin casting procedures and materials. We landed on using Open Grow Spectrum HD from Stuller. The instructions from the website say to use ProCad barrier liquid as a pretreatment coating before investing. However, I also heard from someone who knows that you can use Rustoleum gloss clear coat spray and use that to apply a barrier between the resin and investment. Instead of our typical Ultra-Vest, we’re going to use R&R’s Plasticast instead, should help prevent any unwanted reactions with the resin.
We were in a time crunch, so we just made a cold mold of the print and shot waxes from that. Those castings turned out alright, but we’re going to repsrue them a different way because we were getting porosity on the surface (see below for more pics). So we’re going to print and cast sometime next week just to experiment and see if this procedure I discussed above is successful. Whenever we cast the new resin, I’ll post an update. It’s getting close to the holidays so we wont have much time for experimenting soon…
Also, if anyone has any spruing ideas for this particular pendant, let me know. Below is the printed sprue placement, along with the new sprues we’re thinking of going with. Pendant is 2mm thick, and approx 15mm x 15mm. Sprue gauge is 10 (2.6mm). Hoping the larger gauge going directly into the surface will stay molten long enough to prevent shrinkage porosity. Included are also magnified pics of the porosity we saw after polishing one of the castings. Shrinkage? Gas? Combination of the two? Casting temp is a bit high, but we’re going to resprue first and alter our casting temp if we’re still seeing porosity. Spruing flat thick pieces gives me a headache…
3D Printed Sprue
Micro images of the porosity we saw on the polished piece.
Sorry for derailing the thread a little bit.
If I were putting a sprue on that, I would place a single, somewhat wider/tapering out sprue at the far entrance of the ‘boot’. Or, I suppose, the NorthWest corner of the state. I’ve found that the castable resins really need to have a good big path to drain out of (also provides a good path for the degassing that happens as it melts/burns). In the first picture, it looks to me like an amount of resin got kind of stuck there at the bottom and didn’t really have a good path to go. Edit: I think I would actually put it on the ‘heel’ (SW corner instead)
The castable resins really just barely act like wax, so we have to give them all the help they can get.
Your new sprue design looks good, but I would add a little feeder/drain to the bail portion as well.
As far as coatings, I’ve tried some of the non-commercial methods, and they have all yielded worse results than adding nothing.
I’ve also not had good results with any resin that requires post-curing. The 3 resins we use the most just need cleaning, then they’re good to go. Those are PowerResin’s Wax and Dark, and FormLabs castable resin (although I haven’t used that in a non FormLabs printer, so I’m not sure how it would perform on anything else).
As a setter I am seeing more and more CAD CAM “castings”, and every one of them has what I call a “fingerprint”, raised texture pattern that has to be removed to get a good finish.
This texture is on every surface, and requires a great deal of labor to remove… Castings from carved waxes do not have this texture.
My question is: is there a reason why CAD CAM has to come out this way, or are there ways to produce a pattern without such a texture?
What you’re seeing is, for lack of a better term, growth lines. When 3D printing, and to some extent milling (although there are extra milling processes that can be done to produce a smooth finish, they just take a lot more time), a 3D model is ‘sliced’ into a series of layers. The printer will print one layer at a time, until the full model is produced. Those lines are from the fact that each layer can’t really be absolutely perfectly aligned with the layer before it. This is especially apparent when printing anything curved, or anything that isn’t perpendicular to the printer.
Some types of printers do a better job with smoothing than others, but when you think about it, everything is being produced from individual pixels, and it’s hard to make a smooth slope or rounded surface from a bunch of squares.
What layer height do you print at?
I switch back and forth between .05mm and .03mm, depending on the piece and how quickly I need it. On the Form3 I print at .025mm
I am not doing the designs, the printing, or the casting for this customer.
These models are being handed to me in Gold, to completed and set, and I am finding that they are extremely rough, and I am wasting way too much time ( and customer’s Gold) trying to produce a product I can be satisfied with, and deliver with some pride in my work.
The details are fantastic, but often far too delicate to smooth in the wax, and extremely wasteful to finish in metal.
That sounds about right. I occasionally get repairs in where it was clear they were 3D printed and not fully cleaned up.
As far as what we 3D print, we try to file down the layer lines as best as possible in the wax before we cast. We’ve also put a lot of work in to fine tuning our printer to minimize the appearance of those lines and roughness (still a work in progress). Still ends up with a fair amount of cleanup, but we factor that in to our labor costs.
My guess is that the print/casting house you’re getting those pieces from isn’t too concerned about that.
It is, unfortunately for now, just the way 3D printed stuff tends to look.
Ringdoctor,
Depending on the type of resin they use, if it’s heavily wax based as some of them are, they could probably use lighter fluid or some other mellow solvent to smooth them up a bit before casting. And perhaps if it’s less wax based, they could potentially soak it in denatured alcohol for a little longer than they typically do and that could help smooth the surface a bit as well. I don’t have as much experience with the castable resins as AurumArcanum does, but it may be worth a shot.
I believe at least part of the problem that I am dealing with is that the artist who works for my friend is pushing the limits of CAD.
He is a fantastic jeweler in his own right, but CAD is a new toy.
He has never actually seen the results of his designs after they have been created in CAM.
Many sections and elements of his designs are coming out with areas only 0.5mm thick, with design elements even thinner than that.
Casters are also having difficulty getting complete castings due to how thin some of these designs are.
When you then add this printing “chatter” to deal with, I am having issues producing a good finish. I was trained to finish the hidden areas on jewelry nearly as well as the viewable areas, but this is nearly impossible on these castings.
Maybe I am being too rigid and picky.
I stopped at the jeweler who is contracting this work, and the one wax extra model that I touched, crumbled instantly when I attempted to clean it up.
Just because you can create a wax only 0.5mm thick with this technique, in my opinion does not mean that you should. This jeweler’s customers can, and would pay a bit more for their exclusive designs, so going 25-75% thicker on design elements would leave the customer, the jeweler and I with a far better product, that I can do a better job of finishing.
I was careful to share an image of a less exclusive casting than much of what I am seeing, to avoid trampling on copyrighted designs.
I’ve found over the years that this is a common issue with some designers.
Once they get their hands on a CAD program, they feel like they can pretty much print and cast a finished piece, and don’t put any consideration in to how much metal may need to be moved/removed in the finishing process.
CAD is both a blessing and a curse in that regard.
My feelings exactly when I first began to see CAD CAM appearing.
My thoughts then, and continue to be now, that this process could be a great tool in the hands of skilled craftspeople , but unless one is experienced in casting, setting and finishing the end product, it can also be just a dangerous plaything, creating nightmares for those asked to complete some “artist’s” creations.
Like any media, you design to take advantage of the process (and modify for its nuances).
