Resin casting an entire sprue

Ok, before any of you start flaming me by telling me to read the FAQs, it's not there.

What I'm curious about is how one goes about resin casting an entire sprue of parts? How do you cut the mold? I'm just at a loss. I'm sure some of you have done this before and could give me a clue, as I need one desperately...

Thanks!

Daniel

unless you already have the materials, to cast anything is going to have a roughly £40 (or whatever it is in US$) start up.
with that in mind, it is often easier and cheaper to just buy another kit, especially if it is a whole sprue you want because a home silicon/resin job is never 100%.

Also take into account the option of sprues and parts from HLJ's replacement parts service if the kit is still available.

For me, making your own casts is a last resort.


If you still want to go ahead with it this is the general gist of it.
You'll figure out the problems depending on the sprue/parts.
The trick is to pour a layer of silicone then position the sprue so that it sits halfway in the silicone. You'd probably need a little rig of some sort to suspend the sprue in the silicone layer.

Wait for this layer to cure.

Spray a good layer of mold release agent, pour on another layer of the rubber.

Wait for this to cure.

Instant two part mold.

You will get mold lines.

unless you already have the materials, to cast anything is going to have a roughly £40 (or whatever it is in US$) start up.
with that in mind, it is often easier and cheaper to just buy another kit, especially if it is a whole sprue you want because a home silicon/resin job is never 100%.

Also take into account the option of sprues and parts from HLJ's replacement parts service if the kit is still available.

For me, making your own casts is a last resort.


If you still want to go ahead with it this is the general gist of it.
You'll figure out the problems depending on the sprue/parts.
The trick is to pour a layer of silicone then position the sprue so that it sits halfway in the silicone. You'd probably need a little rig of some sort to suspend the sprue in the silicone layer.

Wait for this layer to cure.

Spray a good layer of mold release agent, pour on another layer of the rubber.

Wait for this to cure.

Instant two part mold.

You will get mold lines.

Thanks, Monkey. This is the process I was thinking of doing. Mold lines shouldn't be too big of a problem, as I'm used to having to clean parts up.

With this type of two part mold, I take it you have two choices in how things proceed--1) pour resin in both sides and then mate, or 2) make vent holes. Am I right, or is there a better way?

that's the hard bit; the pouring.

that is also why for whole sprues, it is easier to just spend the cash.
With single parts you can usually lead a "pour hole" from an inconspicuous place like the top of a damper or make a "solid" mold of half an engine and cast quite easily.

when you're dealing with a complete sprue, there are too many little nooks and crannies for the resin to flow into properly and consistantly. And yes, you will need a vent hole on the sort of opposite position from your pour hole. Usually, your rig to support the sprue/part will end up being your pour hole because it will lead to the surface of the mold.

You will also end up pouring lots of resin and maybe never getting all the parts you need cast well.


Once again, seriously not worth the effort.

Well, I found a way, I believe, to do this and have good success.

I saw a video that says to use clay as a first step, pour the silicone on top, then remove the clay and replace it with more silicone, making the second half of the mold. (VS what was suggested before--guesstimating half.)

I think what will be important, since this is a sprue and not a single piece is to make small tubules that air and resin can flow out and in, respectively. Otherwise, I think there would be some massive bubbles left over.

Does this sound right? Or somewhat close?

you can do the clay half first.
I've mainly cast single parts and for me, pressing a part (that has suitable backing) into poured silicone has gotten me better results than trying pour silicone around the part.

It makes sense to me to use clay for a sprue but bare in mind that using clay to block off half of a sprue isn't a simple task either. Of course this does depend on (parts on) the sprue in question.

And yes venting is important as it allows the resin to flow.
From experience, with complex parts, giving the mold a good squeeze/twist/shake helps move the resin around the mold in the absense of a centrifuge or pressure pot.

I agree that generally it wouldn't be worth it. However, I just bought something that has been out of production for many, many years and will not be in production any time soon.

If I get 50-75% success each time I do it, it would be great. I'm not going to get rid of or use the originals. I'd rather make and use copies if I can.

What about filling th mold (while on it's side) and then sandwiching them back together, thereby having the resin flow into the edges of the sprue? It sounds like the best course of action to me...

Daniel

ahh since its out of production, then I guess casting is the only option. How big are the parts that you want to cast? doing an entire sprue is going to be a very complicated mold. it might be worthwhile to cast the parts individually. I tried casting an entire engine parts sprue before and it was a disaster since I wasted so much materials. In the end, I had to cast the individual parts.

Doing a whole a sprue tree is going to be impossible to do in only a 2 piece mold. Youll have to do a three to four piece mold. Take a pic of tthe tree your trying to replicate, so we get a btter picture.

I would make a two-part mold, then pour resin on both sides. Wait until the resin begins to cure, then put two halves together, and squeeze out the excess resin. (I've done this method myself.) If you are lucky, all parts will come out fine, but that will probably not gonna happen. But once you have a partially good tree, you can just concentrate on the failed section, and do another round of casting to make good parts. If two stage doesn't work, do three or even four stages, casting pieces by pieces on one large mold.

In any case, I don't think you can cast an entire tree in one go, unless you use a spinning table. But if you do it in several stages, you should be able to make usable parts with a conventional two-part mold.

The parts and sprues are quite small. This is a set of Modeler's hose ends that are really cool, but have been OOP for quite a while. What I was thinking is that if I were to make keys so that the mould fits accurately, use wood or plexiglass to compress it using rubber bands. (And in the meantime turning it to make sure the resin has sufficiently spread throughout the mould.)

If you google image Modeler's Hose End Set, you'll see what I'm talking about.

Daniel

oh right.
them 1/12 resin hex/circular pieces again.

just buy these (https://www.hiroboy.com/catalog/images/T2M-fittings.jpg) or these (http://www.hiroboy.com/catalog/product_info.php?manufacturers_id=44&products_id=558) and save yourself a hell of a lot of hassle.

Ah, the hose end set shouldn't be a problem for a two piece mold. Everything is quite "flat". A sprue with bodywork parts or the likes would be tricky:-)

So you can proceed by either pushing the sprue halfway into clay, pouring silicone over it, after curing remove the clay and then pour the other side. Make sure your clay is sulfur free or the silicone will not cure properly!
To avoid that you can also suspend the sprue for the first half of the mould and pour the silicone besides it until the sprue is "half drowned" from underneath :-)

You will very likely have trouble however when pouring the resin and not get out "perfect sprues". With the small parts and thin sprue that are not good for the flow of the resin you will get many air bubbles. In an injection molding machine the plastic is inserted with serious pressure....
To work around that problem i don't "pour" the resin from the top but the bottom of the mold. I make a hole in the mould ( after taking the original part out ) at the lowest point that is just big enough to insert a plastic syringe ( without injection needle ) and one or more vent holes of the same size around the top. Then i mix the resin inside the syringe and slowly press it in through the bottom hole until the resin comes pouring out at the top.
That needs some trying, but for me it has improved the results :-)

You might also consider to make a mould for only half of the sprue. Like others already said....the more parts, the more complicated :-)

oh right.
them 1/12 resin hex/circular pieces again.

just buy these (https://www.hiroboy.com/catalog/images/T2M-fittings.jpg) or these (http://www.hiroboy.com/catalog/product_info.php?manufacturers_id=44&products_id=558) and save yourself a hell of a lot of hassle.

Not what I am talking about.

Why the sarcasm? I could certainly buy turned metal pieces, but they're expensive. Why not try something like this? If it works, great! I've saved myself quite a bit of money by having a nearly endless supply of them for a one-time cost. If not, I can certainly sell them and go your course. I'm just a bit adventurous and not afraid to try something new. I just don't understand your (monkey) negativism. And no, it's not just this thread. :uhoh:

I appreciate JayKay's response and help. I truly appreciate it.

The parts yout talking about reproducing are blue and red? I think i know what your talking about. A Two part mold should work.

not what you're talking about? No idea. I did a google and couldn't see a good/clear example of what you we're talking about.

And excuse me but what sarcasm?
Just trying to give a realistic response. Yes it is a nice idea to replicate things for yourself but it is a lot of work and there may be better ways to get the same result.
Besides, a lot about making molds and casting you learn by doing it yourself and seeing where it/if it goes wrong.

Show me a clear photo of what you want to replicate and i can better judge what is the best method i know of.
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The parts yout talking about reproducing are blue and red? I think i know what your talking about. A Two part mold should work.

Yep, that's it! :sunglasse

racer93,

care to PM me what it is? :biggrin: