Patching/preventing air bubbles in resin knife cast?

[Cursed]

I’ve casted up a bunch of these buck 120 knives and I’m struggling to patch these holes. Does anyone have any recommendations? I plan to use a pressure pot in the future but I’d like to save these.

These were casted with smooth cast 300. Also, will this resin work in a pressure pot? The work time is 3 min, is that enough time to get the bubbles out?

 

[Duncanator]

I use Smooth Cast 300 all the time. It cures fast so you need to work fast, but if your compressor is up to the task, you can do it.

One misconception about pressure casting is that the pressure draws out the bubbles. It actually does the opposite. It squeezes them down so they are tiny. The bubbles are still there, they are just little. Then the resin is allowed to cure while under pressure. It works very well.

A vacuum chamber is what you would use to suck bubbles out of resin. I have done this too for some clients. You would need to use a slower setting resin tho, because the whole process takes longer. You mix your resin, vacuum de-gas it, then put it in the pressure pot to cure.
This makes for really nice castings.

 

[Duncanator]

As for filling the holes in your existing castings - Bondo! (or Evercoat, or your favorite...)
make sure you scuff up the inside of the holes so the condo has some roughness to grab on to. The inside of those bubbles are shiny smooth, and I've had fillers just pop out of those clean smooth holes if they are not scuffed up a bit.

 

[Riceball]

I personally recommend and use model putty, like the stuff from Tamiya, Miliput, and others. This is what model makers use all of the time to fill in the gaps of seams in model kits. It's easy to use and pretty inexpensive, once dry you can sand it smooth and can be painted over.

 

[shpider]

Mix CA glue with baby powder to make a paste... Make it in tiny batches as your working time is short...

 

[PHArchivist]

Elmer's Wood Putty

 

[lmgill]

There are a lot of "patch materials" suggested here, and they all will work, although automotive spot putty for tiny holes and Bondo for larger ones would be my first choice, but the biggest issue you need to be aware of is; any filler you add, will likely trap air below the material as you try to squeeze into the hole or cavity.
This air will get trapped, and limit the amount of filler you can get in the hole. This is because to mouth of the hole will generally be smaller than the cavity below, and once you cover the opening, the air will keep you from completely filling said hole.
To help avoid this, grind out the upper edges of the hole with an X-Acto knife or a dremel, so that the opening is wider than the original void.
Now when you add your filler of choice, the air has a way to escape, and the filler material will more fully fill the hole. Also, as stated above, before adding the patch material, scar up the inside of the hole (or Bubble as you call it) with the point of the knife or dremel. This will give the filler something to bite into and help keep it from popping out. Now sand and finish the surface.

 

[Cursed]

There are a lot of "patch materials" suggested here, and they all will work, although automotive spot putty for tiny holes and Bondo for larger ones would be my first choice, but the biggest issue you need to be aware of is; any filler you add, will likely trap air below the material as you try to squeeze into the hole or cavity.
This air will get trapped, and limit the amount of filler you can get in the hole. This is because to mouth of the hole will generally be smaller than the cavity below, and once you cover the opening, the air will keep you from completely filling said hole.
To help avoid this, grind out the upper edges of the hole with an X-Acto knife or a dremel, so that the opening is wider than the original void.
Now when you add your filler of choice, the air has a way to escape, and the filler material will more fully fill the hole. Also, as stated above, before adding the patch material, scar up the inside of the hole (or Bubble as you call it) with the point of the knife or dremel. This will give the filler something to bite into and help keep it from popping out. Now sand and finish the surface.

Thanks for the explanation and info!

 

[Cursed]

Thanks everyone! I’ve picked up some materials and will be patching these soon!

 

[Gerard2567]

Coat the mold with baby powder next time when casting; it stops bubbles sticking the surface of the mold resulting in less visible air bubbles.

 

[JPH]

degass!

I resisted getting one and regret not having purchased one sooner.I degas the parts A and B individually, then degas again. If you have a quick setting resin, get a slower setting resin instead.

Also, make sure you do all of this in low humidity. Even if it says, "self degassing", degassing will still help. When you mix, mix gently, SSlllloooowwwlllyyy. If you mix fast, you are folding in air. When mixing, I feel when the resin starts to react, it heats up in your hand.

When you pour, try pouring from up high with a thin stream of resin. That helps get rid of bubbles.

When all else fails, you can use a heat gun to pop bubble.