Modelling tip: Filling resin defects

No matter how careful you are, or how much do you spend in pressure chambers or vibrating trays, it is difficult to avoid having some bubbles in your cast pieces. The same is also true with Forgewold kits.

I normally used two component putty (as A+B or Duro) to fill imperfections, but I found a product that is far more efficient for filling small bubbles and defects. It is a hard wax typically used to fill scratches in wood furniture.

The wax is soft enough to be easily worked with a modeling tool.

You just fill the hole and its done. Once painted you would not notice anything.

The same is evidently true for this Forgeworld mortar. I will later put a drop of cyaonoacrilate on top to harden the wax and glue a new rivet in place to substitute the missing one.

The wax technique is very useful for those bubbles appearing in rivets and pother ointy places.

You just rub softly the wax stick over the defect...

And it's easily filled.

You just need to remove the excess wax.

This is most convenient for all those rivets in imperial tanks (a.k.a.: "bubble magnets").

You can fill dozens of defective rivets in seconds.

Once the excess is removed, it's hard to notice it.

Generic modular Fortification Line

(versión en Español)

After many delays, I have finally finished my first modular scenery parts.

For the moment being there are just three different pieces. I plan to start selling them on eBay on a few days, using the brand name "Ultrawerke" (original, isn't it?:)). If they work, I might continue adding new scenery pieces to the range: dragon's teeth, bunkers and craters are some of the ideas I have on mind. What it is sure, anyway, is that they'll definitively have a look that would fit in any techno-gothic siege warfare gameboard...

Once I have some samples painted, I'll update the post.

Resin Casting Tutorial: Part V (and last)

(versión en Español)

PART I
PART II
PART III
PART IV
PART V

Now that we have the mold ready, we can start casting some pieces.

We'll need: Quick setting utrethane resin, plastic cups, wooden toothpicks, a tool for removing the mix, latex gloves and some polyethylene shopping bags for protecting the table below.

I cover the vibrating tray with polyethylene. The great thing about this plastic is that you can scrape the resin from it once is cured.

You can never get enough protection. This will protect you eyes or glasses in the not so very unlikely event that a resin drop gets close to your eyes.

I start measuring the same volume for components A and B. There is not an exact method to know beforehand how many resin will you use in a mold (never, NEVER, try to measure it with water. A single drop of water will ruin some some kilogrames of urethane resin by itself). So just try to get used at wasting some resin each time you make a mold...

Once the components get in contact the clock is running! You have about 120 seconds before the resin gets too viscous, more than enough. Time will vary depending on the room's temperature. Resin will set quicker at higer temps.

I normaly mix the resin during 20 seconds and then pour it, you should experiment what settings suit you better, but remember that the resing must be completely mixed for better results.

I switch on the vibration tray, put both mold's halves on it and start carefully pouring the resin.

I pour some resin on the other half to avoid bubbles when closing the mold.

Now I pick a toohpick and remove any remaining bubbles. You should be vearing eye protection when doing this. Those bubbles are very small, so you would be forcing your sight, closing to the mold while you are messing with the toothpick so an accident could happen in no time. Remember: "safety first".

The resin is starting to set. you will notice that larger volumes set faster than smaller ones.

When the resin is gooey, I close the mold in a quick motion and gently press the excess resin out. Some call it the "sandwich technique".

You should remember that your urethane resin is very sensible to humidity. It's better to recap the bottles during all those operations.

I am casting another piece here. I made a mistake in the last one. As I did not cover completely the second half with resin, I got some empty spaces to fill with putty later on.

This time I prepared too less resin... Well, this is not a problem.

I just prepare more resin, add it to the molds and repeat the "Sandwich Technique". You'll notice that gentle slope we were talking about when making the mold. Its function is to accomodate a little excess resin wich will be expelled out when pressing the "sandwich".

Here is the completed piece. Nearly perfect! Altough there are some minor bubbles that I'll fill with putty in no time.

And that's it! Hope you find this tutorial useful.

Next time, we'll talk about scratchbuilding techniques. We'll follow a step-by-step process to do a T34-like turret for Warhammer 40K games.

Resin Casting Tutorial: Part IV

(versión en Español)

PART I
PART II
PART III
PART IV
PART V

One of the main concerns when considering resin casting is how to avoid bubbles in the resulting pieces. There are different techniques to help remove bubbles, some of them involving pressure changes. Either for degassing the resin in its liquid form and/or compressing it when is inside the mold, reducing the bubbles size.

Another method, that I personally prefer as I work with open molds (as you probably noticed, I do not build pour spout or air vents, we'll see why in the next part), is to remove bubbles with vibration.

Making something to vibrate is fairly easy. Just unbalance a rotating axle adding some excentrical weight. For doing this I just took an old computer fan, removed the case and blades and glued a nut on a side. Once the motor rotates, the small nut will make it vibrate. I then play with the amplitude of the vibration adding bolts of different lengths. Finally, I glued the fan to the tray.

To build the tray, I bought a cheap wooden frame and fixed the tray with four springs. This is to allow the tray to vibrate freely. I also built a box with polistyrene (I didn't had any wood at hand) and added a switch.

Here it is the final result. It can vibrate big molds like the one in the pic and get rid of more than 90% of the bubbles, although you'll need to remove some of them manually (this is why open molds are so convenient).

You can see below the mechanism working:

I suppose that I will someday build another table, with a more powerful motor and frequency and amplitude controls. But, for the moment being, this small tray does the job.

Next time, we'll see finaly how to cast. See you then!

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Resin Casting Tutorial: Part III

(versión en Español)

PART I
PART II
PART III
PART IV
PART V

Well, 24 hours have passed and we have now a solid white surface again.

It is time to remove the casting frame and see if the demoulding agent has worked...

Everything works fine:

I remove carefully the rest of the lid:

And that's it, the mold is ready to use:

Those are all the molds needed to do one of my Soviet-themed tanks. About 2500 grames of silicone rubber!

We'll see next about the vibrating tray.

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Resin Casting Tutorial: Part II

(versión en Español)

PART I
PART II
PART III
PART IV
PART V

Hi again:

We saw yesterday how to make the first half of our two-part mold.

Once 24 hours have passed, it is time to put the mold upside down and remove its bottom.

This is how it looks. Now I remove the excess of silicone (you can save it for later recycling) and the casting frame.

Now it looks cleaner.

I remove the plastecine used to mask the parts we did not want to include in this half (Don't use for this anything with a cutting edge or you could damage the mold).

I clean any plasticine rests with rubbing alcohol and a tissue.

Now I put the piece back to the mold and rebuild the casting frame.

I add a demolding agent to the silicone. This is to avoid that the silicone that I am about to pour reacts to the first mold half, forming a solid block with you model in the middle!.

I use 5% vaseline disolved in 95% white spirit, so I let it dry before pouring the rest of the silicone. You can also put a little blob of vaseline, heat it with a hairdrier and spread it with a brush (pay attention to not damage your model with the heat). In any case, you don't need to apply vaseline to the model, just to the mold, as it can obscure detail.

The rest goes exactly as in the other half. "Paint" the silicone.

And pour the rest.

Now we must wait for further 24 hours to let the mold cure.

In the meantime, we'll learn how to do a vibrating tray to avoid bubbles during resin casting.

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Resin Casting Tutorial: Part I

(versión en Español)

PART I
PART II
PART III
PART IV
PART V

Well... Yesterday you saw a custom resin tank. But, the original model has to come from somewhere, isn't it?

The model used to make the silicone molds is called a Master Model. I did it using scratchbuilding techniques (that will be discussed here later on), divided in some basic parts and cast them separately.

Now I going to show you how to cast one of those parts, in particullar the hull piece of my KV-II like futuristic tank.

First, we must be completely sure that the piece we are going to cast is completely airtight. That mean that you must close all little gaps or cracks before starting. Once everything is ready we'll start making a mold from our original piece.

I am going to do a two-part mold, so I start making some masking with plasticine (modelling clay). I use rubbing alcohol (isopropilic alcohol) and a soft brush to clean and seal the joint betwen the model and the plasticine.

I put the plasticine covering the lower hull and making a gentle slope (you'll see why later). The mold line will be at the same level of the plasticine, so be careful when where you put it.

I also add four small stumps using more plastecine, this will serve to make the two halves fit once the molds is ready.

Then I build a box around the model and seal it with more plasticine (those are casting blocks that I got from www.hlj.com, but you could use Lego blocks, plasticard, wood, etc...).

This is the Room Temperature Vulcanizing (RTV) that I use. I get it hera, at Spain, from www.feroca.com, but you can buy similar products locally. RTV means that the silicone cures without need of heat (wich would be fatal for our litte plastic model). The small flask is the catalizer, you add it at 5% of the silicone weight (that means, you add 5 g of catalizer for each 95 g of silicone). I recommend you to have a spare bottle of catalizer around, as you normally use more than you really needed.

You can also see that there are some silicone chunks lying around. those are old molds that I am going to recycle. I will use also a handy disposable brush (those little thingies are very useful, come in great quantities and are dead cheap. What can I say?)

I weight the silicone and mix the catalizer.

Now I do some evil things to the brush. I bend the point and cut the bristles. This is to fix the bristles in place and make it easier to access to difficult places.

Then I add a little silicone to the mold and reserve the rest.

I use the brush to force the silicone into difficult places and remove superficial bubbles.

It's a bit like painting...

Now I start recycling all those old silicone chunks.

I simply push them carefully in the mold, to be later covered with more silicone. Once the silicone vulcanizes it will become a solid piece... So, just don't throw away old molds. Recicle them!

You can see all the bubbles raising to the top. Now, it's time to put it in an even surface and let it cure during 24 hours.

As this is real-time, we'll have to wait until tomorrow (or later, as I simply run out of silicone) to continue our little tutorial. Next day we'll learn some things about demolding agents and how to produce the second half.

See you...

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