Casting resin and air bubbles

[Hawk312]

I am using a simple 1 piece mold cast from a kit wheel. The mold itself looks perfect. When I cast the wheels though, there is always air bubbles right around the rim or around the wheel lugs/center cap area. I have tried both the 3 minute white and 7 minute tan alumilite casting resin. I tried pouring very slowly immediately after mixing and "flexing" the mold immediately after pouring which seems to help alot, but I still always have an air bubble somewhere. I have also tried using baby powder without much success. Poking holes through the bottom of the mold doesn`t seem to help either. Is there something else I need to do? Or what other options does one have if they are on a tight budget? Is switching resins my only choice?

Thanks.

[guitarsam326]

im no expert, I haven't tried this myself yet, but I have talked to someone on this forum on multiple occasions about casting because they do it themselves. but you need to research using a pressure pot to cast resin.

[Mike Kucaba]

Hands down on the pressure pot. If you can't go that route, some way of vibrating the mold would help. I used a pad sander that vibrated pretty good and helped.

[Mark]

Apply some talcum powder (dollar store baby powder works fine) to the mold; it will allow the resin to flow more quickly. I apply it by putting the powder into a small container with a snap-on lid, putting a few molds in with it, then shaking everything around to give the molds a light dusting. The powder won't affect the ability of the resin to be painted or plated, and you won't have to clean the molds or the parts. Of course, you want to mix the resin without whipping air bubbles into it also. For small parts, pressure is nice but not absolutely necessary. I've done thousands of parts, bodies included, without it.

[kitbash1]

Try heating the mould in a microwave oven for 1 and a half min. and then pour your resin. Once poured, gently tap the mould on the table and let set for 10 mins more then you normally would. This should help with the pin-hole problem.

[Hawk312]

Thanks for the tips guys. I`ll give them a try!

[shucky]

David do yourself a favor and pick up a thin metal pick from hobby lobby. Not sure what exactly they're used for perhaps sculpting, etc but I've picked up two of them from hobby lobby in the past. Heating and powdering your mold is all nice and good but sometimes some molds especially wheels with lug details will still hold a bubble that needs to be released. I use the metal pick for this purpose. Pour your resin, locate the bubble and "release" if from where its stuck with the tip of the pick. The purpose is not to pop the bubble but to release it from where its stuck. Now use the pick and slide the bubble away from the cavity of the 1 piece old. In addition, you'll need to stir your resin slower and more carefully trying to minimize introducing or causing bubbles to occur. This will also help. Lastly, place a flat piece of glass on top of your mold with a light coat of mold release. This will generally move those bubbles away that you freed up with the pick and give your resin piece a nice flat backing. After each use, just wipe the tip of the pick clean with paper towel. Works like a charm every time.

Edited September 2, 2014 by shucky

[GasPunkAlley]

I agree with the talc. The talc is used to releave surface tension and cut done on static. The rubber can pick up static electricity and cause the resin to repel from the rubber causing a very rough texture. Using some sort of metal pick or in a pinch a tooth pick you can poke out air bubbles. Vibration is a second step to remove air bubbles. Best bet is a presume pot if you can afford it. Heating a mold just burns it out quicker. It also causes the resin to kick quicker. If you are just using a pokey stick to get the bubbles out you want the longest pot life resin you can get. Then you can take your time to poke out the bubbles.

[Aaronw]

If you pour the resin with some height (12-24") so that it is a very thin stream, you can reduce the air bubbles. You want the stream about the size of the tip of a ball point pen. This will help keep bubbles that formed during mixing from getting into the mold (it will pop all but the smallest bubbles). For very small parts you might dip a popsicle stick into the resin and dribble it instead of pouring from the cup, since that would be hard to control such a small quantity.

Poking the bubbles as suggested (I use a tooth pick) can be effective for shallow molds, I have less luck with deeper molds.

A pressure pot is very nice, but if you are careful and are only doing a small amount of casting for personal use, it isn't absolutely necessary.

[IceMan Collections]

A lot of great suggestions.

I think the resin being poured from high is for the silicone when creating the mold. A pressure pot seems like a big expense if you're casting small parts.

Not an expert but this works for me every time. Microwave mold for 1 minute per pound. Powder it right after. Stir slower, don't "whip it" per say. The metal pick is a good idea if you have slower, clear setting resin. If you can't see the bubble you can't push it out.

Also if your mold has imperfections in the spots where your bubble are appearing, then they're actually not bubbles. The smallest imperfection will show when you pull the resin from the mold.

Maybe some pics of your finished product may also help us help you identify the issue.

[Art Anderson]

Over the years, I've cast literally thousands of wheels, from mags to open steelies, and this is a trick I used:

I took ordinary toothpicks, and dipped an end of each into freshly mixed resin (only takes a little bit. getting a smooth surface at the tip with just a tiny "ball point" to them.

Then, when pouring wheels, I took one of those toothpicks, and very quickly "wiped" it around down in the lip of the rim, with about 95% success in getting wheel rims with no air bubbles in the rim. I also used the same toothpicks to quickly push resin down into the little cavities which formed the lug nuts, for the same reason and with even better results.

Art

[Steven Zimmerman]

I pour a lot of resin wheels, and use the Alumalite 'white' resin, offered under the label 'AMAZING resin' , it has a longer working time before solidifying, and have had better results then their tan resin. I spray my molds with a mold release called STONER, and after pouring, I use cheap paintbrushes, with the bristles trimmed to about a quarter inch, and quickly run it around the wheel mold, spending extra attention to the recesses where the wheel 'lip' is. I buy these brushes at Hobby Lobby or Walmart, cost about a buck for 30 brushes. If you clean the brush immediately, you can use it several times. Also, I don't lay anything across the top of the mold, but slowly swipe a credit card size piece of plastic slowly across the top of the mold, removing excessive resin. Walmart offers , in the kitchen utensils dept, a set of 4 'counter top' protectors, size of a placemat, and is flexible - and CHEAP.... I cut them to business card size. Resin will stick, but peels off easily...........I also place my filled molds in a food dehydrator immediately, as small pieces like wheels don't create enough heat to harden alone - I leave mine for a half hour, using a 2 dollar kitchen wind up timer and let the molds cool for 5 minutes after removing, or they will still be soft.....'Z'

[goodguyinar416]

I have been casting for many years and I always pre-wet the mold with a small amount of resin from a dipped Q Tip in resin first and rub it around mold and then pour the resin, but I never really pour it unless it is a large mold. I use Pop cycle sticks that you can buy a 1000 at hobby lobby, Michaels, or other places.

I dip the sticks into the resin and drop a few drops into wheel mold and then use a toothpick to finish. I have used the same companies for my casting materials for over 10 years now. I buy my rubber from a company in Kansas and my resin from a company in Chicago..

Good Luck.

Art

ABC Specialties

Resin Casting

[Skip]

How much vacuum do you need to pull to help pull the bubbles from the resin then the poured part? I am wondering what about using a Foodsaver vacuum sealer's vacuum port to pull the bubbles? Think it would work or help?

The one I have we picked up for like five bucks at a garage sale, it works great, still in the original packaging. Looked like it was never used or outside the packaging other than to look at.

[Joeys Models]

I never have problems with bubbles. I always pressure cast. I mostly do two part molds. Some cheaper resins have a tendency to naturally produce bubbles. Careful, Some resins will foam up when you vacuum. I use Smooth-On products for all my casting needs.

[Greg Wann]

You can refrigerate your resin. This will give you a little more time to pick bubbles out. Try this simple exercise: Take a toothpick. Hold it steadily in your fingers comfortably. Place the tip in the area that will create the outer rim. move the tip in a circular motion around the perimiter of the rim. Practice this motion a bit. Then add some resin. This motion with the toothpick will help break up bubbles in this part of the wheel mold. Despite my casting at about 62 PSI in a two piece mold, air pockets can still exist. According to my local SMOOTH - ON rep, 60 PSI is the magic number to crush bubbles in resin and especially silicone molds. Stay away from tin silicone, it will shrink. I switched to Mold Star 30 recently also, this is a platinum silicone. The Mold Star15 was too mushy for my taste. I do not heat molds. The resin will reach a temp of about 140 degrees.

Edited September 25, 2014 by Greg Wann

[Hawk312]

Thanks to everyone who contributed to this thread. I think I am taking each suggestion and applying it, and my castings are coming out much better. Hopefully you will see them on one of my projects soon.

Thanks!

[Plankwing]

Before I got pressure and vac pots, I used a 6' cable, one end looped around a bolt, hung a tin can on the other end, placed the mold inside with 10-minute cure resin and gave it a good twirl for a couple minutes. No bubbles. A friend now has my pots and does all my casting for me: www.amsresin.com.