One Step At A Time - Need Advice On Pouring Bubbles

[Jezlad]

So every new cast improves on the first but presents another problem.

Initially I had an issue with bubbles in the resin. I remedied this with a vacuum chamber and pump rig which seems to sort the issue out nicely.

Now though I have another problem, this time the bubbles are completely gone within the resin but I'm getting bubbles at the top of the bases from trapped air as I pour. Are there any tricks or methods to stop this from happening? The air is getting trapped by the resin as I tip it into the mould holes.

Jez

[mangozac]

Hi Jez. What resin are you using? Do the areas in which the air is getting trapped have some channel for the air to escape? Any chance of showing a pic to illustrate the exact problem?

[Jezlad]

[mangozac]

Well the big thing that stands out from the datasheet is the fact that it's polyester resin. Although it's specified as low shrinkage, I wonder exactly low shrinkage is for that compound. Usual polyesters will generally exhibit too much shrinkage for modelling applications. We all use polyurethane and I'm wondering if the shrinkage of your resin in certain spots is what's causing the bubbles?

When you pour it into the moulds what would you say the viscosity is like? Water? Maple syrup? Honey?

[Lane]

One method is to make a partial pour, tilt the mold to get full coverage the finish the pour. As you tilt the mold it slowly covers the surface and uncovers the bubbles. If the resin is slow enough you can even pick out bubbles with a wire or toothpick.

[paulson games]

One trick I've seen in some of the online videos (tap plastics site) is to pour enough that it's just slightly overfull, so that the material has a very slight dome that rises above the top of the mold but doesn't flood all over. Then they use a sheet of wax paper or plexi glass which has been coated with release so that the resin won't stick, this forces the excess resin out and all the surface bubbles with it.

You can also get a simular effect by running a paint scraper across the top of the mold which will wisk off the surface layer of resin and any bubbles.

Also as Lane suggested if you use a slower curing resin with a couple minutes worklife you can use a toothpick or a small toothbrush to go over the surface bubbles and pop them.

Personally I make my bases in a two part mold that way I tend not to get any bubbles or surface distortions as all resin tends to shrink slightly as it cures and one sided molds will tend to have their face that's open to the air shrink more than the rest of the part giving it a slight concave depression mark on the underside and the outer edges will have a bit of a lip. Shrinkage in a double sided mold tends to be more evenly distributed and the underside of the base will remain flat.

[Jezlad]

Thanks for the awesome advice guys. Wheres the best place to buy Polyurethane Resin here in the UK?

[mangozac]

Drop a line to - he's in the UK and should know the best locally available products.

[Hatemonger]

There's a distributor of Smooth-On product in the UK.
http://www.smooth-on.com/pages.php?pID=105

I'm pretty sure there are ones for Alumilite, PolyTek, and other US-based companies as well. As for truly local materials, I don't know.

- H8