Going to grind resin scrap and reuse it

Yes, I will start grinding the used support base and support scrap into a powder that will be used in our resin castings as a filler. Better than throwing it in the trash. If I had an extruder I’d make it into filament for others.

Here is a photo of just 3 days support base and supports from one Form 2 and a second Form 2 is planned to be added in July.

I purchase a large coffee grinder that can grind the scrap down for this use. Here’s a photo of that.

One way to deal with plastic scrap and another to extend the use of liquid resin in mold casting.


have you run a test to determine that the resin powder won’t inhibit or alter the materials you’re casting in?

Would be interested to hear what resins you are casting with this as filler and your impressions on resultant part quality.

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I’ll find out soon enough but don’t expect any issues. First I need to get the grinder here. Just got an email it’s been shipped.

I’ve used similar fillers in the past with no issues and I’ve been resin casting for 15 years.

I use Smooth-On urethane resin.

curious to find out if the resin scrap absorbs moisture from the air- which would cause urethanes to foam.

Many less than fond memories of hygroscopic fillers causing bad castings because some apprentice left the top off the can of filler.

Please post your results… also keen to know if the urethanes bond well to the filler, or if the urethane is weakened by the fill.

just to avoid any confusion : SLA resins aren’t thermoplastics, you can’t melt them into shape once the polymerization has occurred. Grinding them really is the only thing that will work to get some king of re-usability out of the left over materials.

Regarding grinding, be cautious with coffee grinders as these might not make a fine enough powder for detailed work.


Moisture has not been an issue in 15 years of doing the mold casting resin. I have a couple of additives to use. One will make the hardent resin very light and like wood in texture. The other is a metal additive and can be polish to make the finish resin look like shiny steel and magnetic.

I don’t seen any issues using this method of the ground ALW resin scraps. I’ll color the casting resin the same color. The pieces are large and the reason I don’t 3D print them. They get quite hot when curing and can burn your fingers if you arent’ careful.

U cast in silicone molds with either two part or one part open molds. The one part get a clear plexiglass cover and are cured under 60 lbs air pressure in a pressure pot for 1 hour curing time. This drives the resin into very fine detail points and also reduces the chance for bubbles.


I will Enjoy following this I swell have many scraps that I don’t want to toss right into the landfill.

I used to have an old autoclave- the kind with a big submarine door on them with a wheel in the middle to engage the door clamps. We would slam 80 PSI on urethane all the time- only not the 1 hour cure stuff- but the 3 minute cure.

It works by squeezing air bubbles to microscopic size - or into solution… but it has to cure under pressure.

Also used to run a large vaccum tank for casting filled polyester. Its the same basic idea- except you drop the air pressure, allowing air bubbles to expand to the point that they mostly boil out- but with vacuum casting you have to release the vacuum while the resin is still liquid… Any air still left in the mold is at nearly zero pressure and when you release the vacuum, you are slamming 14 lbs/sqin on it to, again, squeeze the air bubbles microscopic, or into solution.

we used a similar rig for demolding glove molded parts… the silicone mold had an apron/gasket that got clamped between two steel plates with the mold hanging in the vacuum cabinet. Pulling a vacuum caused the mold to stretch out away from the casting like a big bucket… and we just lifted the casting out of it.
The molds were uniform in thickness and the vacuum demolding spread the stresses so evenly that the molds would last 200 or more seamless castings- which is pretty good for polyester…

for folks who don’t have pressure cast or vacuum systems, the thing to do about bubbles is to pounce the interior of the mold with a light dusting of talcum powder. The talc on the mold surface prevents bubbles from adhering to the mold surface detail and acts like a wicking agent… giving results almost as good as pressure casting.

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I use vacuum for the silicone molds. Gets the silicone into the fine details real well.

I use pressure on the castings as that doesn’t distort the molds. The reason for one hour is the resin I use is a 15 minute pot life and a 1 hour cure. I cast four to ten molds at a time this way and not rushed to get the work done. Castings come out great when you take your time at it.:smiley:

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yeah- back then no one made a 1 hour cure urethane… 10 minutes was about the longest you could get- but we were running a production shop… the idea was to cycle the molds as a fast as possible… the autoclave had two pull out drawers that each held a removable rack of molds ( two sets of racks for each autoclave ) - and a timer set up with a big button… Fill the molds, slide the racks in and close and dog the door… hit the button… boom- 80 PSI from the reserve tank slammed on top… the timer would auto- release the pressure after 5 minutes and turn on a yellow flashing light that would not go off until the operator opened the door. Operator pulled the two cured racks out, and slid in the two racks he had filled just before the yellow light went on. Close the door and hit the button, and while the autoclave was under pressure he demolded and set up to mix the next batch of resin.

We filled the resin almost to the point of porridge… this reduced resin costs, made the castings a little heavier, and most importantly acted as a heat sink for the exotherm- so the urethane would not burn the molds out too fast.

When we were running refrigerator magnets the autoclave held 96 cavities… cycling every 15 minutes for an 8 hour day. 3,000 castings per day for a single operator.

Sorry, I’ve been otherwise detained… Heart hospital for 2 days having a couple more stents inserted to open back up a clogged artery on my heart. Doing great and will be back at it soon.

On the pressure curing of the resin molds. I use a 2.5 gallon painting pressure pot and made up a shelf unit to slip down into the pot. has two shelves that hold acrylic trays I made up. The trays generally can hold to molds as I make them long and narrow with each holding anywhere from 6 to 10 cavities of the same item. Because it takes time to pour these molds and cap with a sheet of acrylic and small weights I need the longer curing resin.


glad you are bouncing back!

Yeah- since I sold those autoclaves, I too have to rely on longer cure resins…
for anyone else considering pressure cure- just be aware that you need to be able to have the liquid resin under high pressure while it is still liquid- and to fully solidify under pressure.

So figure out how fast you can get fill the mold and get it under pressure and pick a resin formulation that will give more time than that takes.

Exactly but the results are the best. I get comments all the time from customers about the fine detail I achieve in my castings.
I’ll use the Form 2 to make large masters for casting as it’s far more cost efficient but the smaller Items will be still 3D printed only. I will also tint the casting resin to the same color as the Form 2 resin so it will be almost impossible to tell them apart.

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