Trouble Shooting Resin Casting

Jewelry Discussion
1

Looking for some help trouble shooting my lost wax/resin casting issues Any help GREATLY appreciated!

I’m using Formlabs Castable Wax 40 with Certus Optima Prestige investment.

I seem to really struggle with some surface porosity issues but mainly lots of flashing around the sprue and areas where wax is on the surface of the prints.

Im following the exact burnout as specified by Formlabs. (See attached photo) Leaving for 4-6 hours post investing before burnout. Then a 3hr at 55deg Celsius in the kiln before the burnout cycle begins.

Flasks seem to appear cracked quite often when I take them out of the kiln.

See some attached photos of this chunky belt buckle I tried to cast and a chunky heart pendant.

I’ve tried 38% water and even tried added 1% boric acid to the water for that last buckle…

Any tips on preventing flashing? Anyone out there getting great castings with Castable wax 40, I need your help!!:joy:

Thanks so much and I look forward to hopefully getting some responses :pray:

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2

I’ll be honest, I absolutely hate formlabs castable resins (along with not liking the Form Labs ecosystem in general, because they treat you like an idiot and think they are the only people who can be trusted to set up a machine or a print).

As far as your issues, there are a couple solutions I would try.
One: ditch the formlabs recommended burnout cycle. I believe Certus has their own recommended cycle, so I would go with that instead.
Two: your investment mix isn’t quite right. I know that if we add a little too much water to ours, it’ll be more likely to crack and cause flashing.
Three: maybe try out a different investment. We almost exclusively use Ransom and Randolph Solitaire (we do a lot of stone in place casting), and occasionally add about 20% R&R Plasticast to the mix as well (Plasticast is also a really good investment made for resin prints).

We used Certus for a short while, but weren’t happy enough with the casting finish we would get. Since switching to R&R, we’ve had far better luck. Granted, casting 3d printed resin is a whole can of worms to begin with.

Best of luck!
Cheers!
Scott

3

Hi Scott,

Thank you so much for the time you took to read and respond to my problem, I seriously Appreicate that!

Yes I hear lots of people hate on Formlabs… kind of regretting just buying a new form 3+ when my form 2 died… have to make it work now, otherwise I’d definitely have a go with a cheaper set up and other resins people are using!

So I’ve tried a couple other investments but certus is the one Formlabs recommend to use with boric acid so I thought I’d bite the cost and go for it.

Do you have experience mixing in boric acid? How do I get it to dissolve appropriately?

If I continue to fail I’ll have to try the R&R investment! Reason I haven’t so far is that I’ve struggle to find a UK based stockist for it.

I’ll also try the certus Recommened burnout aswell to see whether that helps.

Have you any info you can share on the temperature the flask should be when casting? I’m struggling to find a definitive answer online or a definitive way of working out what temperature it should be!

Thanks again!

Luke

4

No worries! Glad I could maybe be of help.

Yeah we bought a form 3 too, and it’s spent almost the entire time unused, collecting dust.

As far as mixing the boric acid: because we use the R&R solitaire, we don’t need to, but we did try it in the past. One trick is to treat it like when you’re adding corn-flour to a soup. You use a second bowl and whisk it with an amount of water to make a slurry that should incorporate in to the investment a bit better.

As far as casting temperature, you’re totally not wrong that you’ll get 100 different answers from 100 different people.
Again, because we do stone in place casting, we use lower temperatures for the whole process. Our casting temperature is typically around 1050 degrees fahrenheit (around 565 degrees centigrade I believe).

Hope that helps!
Cheers!
Scott

5

Hi

I hate to sound like a broken record with this comment but I don’t try to cast castable resin models any more. Too finicky for me -as I am doing everything in my small garage shop in small flasks. I have all my 3d prints done in a high temp resin (tolerate 350 Fahrenheit) and then immediately make a rubber mold. obviously you can use ‘regular’ resin and RTV molding compounds if you prefer.

My two cents,
Best,
Heather

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6

The investment is cracking because the Formlab resin is expanding a lot during burnout. You can use Invest C/P investment with ceramic flask liner to allow expansion during burnout. The ash that is not fully being eliminated during the burnout can cause porous rough castings. Use larger and/more sprues and see if this improves the elimination of the ash. Hopefully those things will get good results with the Formlab resin. As a side note, I get good burnouts using Open Grow Spectrum HD Resin with R&R Plasticast Investment and adding boric acid to my water.

1 Like
7

Hi J Raymond,

Thank you so much for your response! It’s definitely due to expansion issues of the resin I’m sure…

Couple questions, what’s a ceramic flask liner and where do I get one? :joy: can’t seem to find on Google

Also what’s your process for mixing your boric acid powder into the water?

Also what temperature do you have your flask at to cast and how would you recommend working out the right temperature for your flask?

Thanks,

Luke Brient

8

I use this for the liner. High-Temperature Ceramic Fiber Pipe Insulation, Alumina Oxide, 50 Feet Long x [Flask Height"] x 1/16" Thick.. Ebay may have cheaper prices. I use petroleum jelly to get it to stick to the inside of the flask and waterproof it.

Add 150 grams of boric acid powder to 1 gallon of distilled or deionized water (recommended), and let it dissolve overnight at room temperature. I use this boric acid.

While there are specific recommendations given by the investment and alloy manufacturers as to casting temps, generally you can cast sterling silver or 10, 14, and 18k gold at 1075 to 1350F, and get good results. Nevertheless, experience thru experimentation with the kinds of pieces you’re casting will give you your best answer.

9

To get a 1% w/v (weight by volume) boric acid solution, I pre-mix 37 grams of boric acid crystals to 1 gallon of deionized water and shake the gallon container for about a minute. As long as you are using quality boric acid, it dissolves pretty quickly and stays in solution.

When I mix my investment, I grab the gallon jug, give it a good shake to mix it up and dispense the volume of water I need based on the flask I am using.

10

Luke,

You haven’t described your setup enough to help narrow down your problems.

One, what type of kiln/oven do you use? How much control do you have in setting temperatures, how much air gets inside your kiln/oven to help with combustion? This can cause negative defects in the surface due to ash against the outer surfaces. If you have positive defects (erosion of the investment walls), that is a completely different problem like curing and cleaning of the resin prints needs to be revisited.

Two, how long do you let your investment set before you put it in the kiln/oven? Does the flask have the right amount of moisture in it to allow the investment to transition through the chemical changes that occur during the heating process?

Three, how accurate is your kiln/oven? Being off by 20-30 degrees can cause problems, especially if your kiln/oven reads lower in temperature.

Resin casting is nothing like wax casting, so the traditional rules that work with wax don’t always apply to resins. It might make sense to use smaller flasks with less items or a single item to ensure that you aren’t biasing the flask temperatures with uneven heat distribution, etc. You may need to do some experiments to figure out how to make everything work in your casting ecosystem.

Regards,
Ron

11

Hi Luke,
I had many of the same problems as you’re describing. I use Zero from Power Resins and R&R Plasticast and it has worked out really really well.
I followed the mixing directions that R&R has posted for Plasticast, including the ratio of deionized water to investment, mixing steps and times. The deionized water and temp is essential or the investment sets up way too past to pour. I also created my own burnout schedule based on Power Resins, Legor, and what R&R suggests for Plasticast.
Please bear in mind that castable resin is much more temperamental than wax. So success is in the details. See my notes below on two burn out schedules:

  1. Best instructions, combo from Legor and Power Resins:

Let Plasticast cure undisturbed for exactly 3hrs after pouring, then place in a 300 degree F preheated kiln, sprue down. Be sure there is at least 1” space all around the flask, including from the kiln floor.

Hold 300 for 3hrs

Remove tray of melted wax, and flip flask so sprue is facing up. This allows fumes to escape.

200/hr to 700, hold 2hrs

789/hr to 1292, hold 30 mins

270/hr to 1427, hold 3hrs

FULL/hr to 1076, hold min 2hrs

Total Time Takes around 14-15hrs. End temp depends on metal to be cast, size and detail of the model.

Then cast

Sample of past casting:

-poured investment at 5:45pm

-burnout began at 9:05pm

-flip flask and pulled tray on at 11pm.

-end temp at 1005 F. Cast reg sterling silver at 1775 F at 12noon. (min 1762-1940 max)

(Would be 1800 if I used a argentium)

  1. Below are notes on another casting that went well:

2/5/23 Used exact Power Resins burnout schedule today:

Let investment set up for 3 hrs exactly, then place in preheated kiln.

115C hold 5 hrs, 239,rate full

700C reach n 1:20, hold :30, 1292, rate full

750C reach n :30, hold 3:00, 1382, rate 180

600C reach n 1:00, hold 1:00+, 1112, rate full

10:05 AM started burn out

Arg 935

<.5mm, 1184,1904. Koki Beads

1.2mm,1070,1800. Ring

8pm 1184 w/10 hrs, hold time yet to go

Results:

-The beads casted perfectly! The prong/pegs fully casted

The notes will take a bit of deciphering, but I don’t think it will be difficult.

Best,
Sam