Jump to content

Recommended Posts

I`ve been toying with this idea for a long time but it`s still just a daydream. I really want to try it out but i can`t seem to find a "way in" if you like. Is there anyone out there who has gone through the paces and sat down and learned the ABCs of casting your own resin parts? Maybe a clever "way in" would be to cast some spare parts for your project just to get started? I can see a lot of uses for this type of work. I have no idea what to buy but i know there are several good quality products out there.    

Link to post
Share on other sites

My short answer would be to obtain the following:

 

- a simple rotary vane vacuum pump (100-200 euros)
- a laboratory-style plastic vacuum desiccator (75 euros)
- 10-15 shore-A addition-type silicone rubber (aka platinum cure)
- a 7-10 minute pot life polyurethane resin

 

For all four components it will take you some effort to find a Norwegian supplier. It was the same for me in the Netherlands. Here's one example of a Dutch supplier:

 

https://polyestershoppen.nl/vacuummaterialen

 

I developed my methods over a long period, trying lots of different materials, and with lots of failures. But the above combination has worked very well for me for the last 15 years. I helped two club members developing their methods, and they ended up using exactly the same. Here are photos of a recent project, based on a scratch-built master of a 1/48 ALE-2 chaff pod:

 

forsale-36.jpg

 

forsale-35.jpg

 

Since you're posting on a mostly US / Canadian forum, you will probably get the advice to do pressure casting. It seems Europeans (including the big names in resin, like Eduard, Aires etc) do vacuum casting, and Americans do pressure casting. If you want to go that route, take a look at this video channel by Robert Tolone:

 

https://www.youtube.com/channel/UCPA1NCFqYebL6RBW5-bnOrg/videos?view=0&sort=dd&flow=grid

 

Rob

Edited by Rob de Bie
Link to post
Share on other sites

Those are some pro cast parts, Rob!  Very nice!   Hi breadneck, I've cast a few basic parts myself and this video might help you understand the basics: 

Making a two-part mold

 

The main things I bought were some Easymold molding rubber, Alumilite casting resin (cures in 15 min) and some clay.   Other things you need are measuring cups, masks, rubber gloves, popsicle sticks for stirring, protective glasses.  I used some talcum powder instead of mold release.   Someday I want to pick up one of those vacuum chambers for bubble-free casts but the ones I've cast so far turned out pretty smooth.    There are some basic kits such as this to help you get started quickly. 

Alumilite Casting Kit

 

Just a question, Rob -- were those cast using two-part molds as well?   I don't see any mold lines and I'm thinking if they were cast in two halves that opening in the back would be a problem, so this must have been done using a more advanced method.   I always scratch my head at how you guys do stuff.  Like those Aires or Eduard cockpits with impossible multi-tier details - I can't wrap my head around how those are made.

Link to post
Share on other sites
1 hour ago, crackerjazz said:

Just a question, Rob -- were those cast using two-part molds as well?   I don't see any mold lines and I'm thinking if they were cast in two halves that opening in the back would be a problem, so this must have been done using a more advanced method.   I always scratch my head at how you guys do stuff.  Like those Aires or Eduard cockpits with impossible multi-tier details - I can't wrap my head around how those are made.

 

I cast *everything* in single piece molds. The trick is soft rubber, and 10 Shore-A is perfect for me. I can cast cockpit tubs and seat like you describe without any problem. The undercuts are sometimes amazing, but the rubber can take it.

 

Two-part molds would not work with my method of vacuum casting. The slit would allow air into the mold cavity, instead of resin, resulting in incompletely formed parts. Maybe you could clamp them together, closing the slit, but it sounds like a band-aid method to me. Hence my choice to work with single-piece molds only.

 

I'm not sure whether pressure casting would work here, since it would be really hard to fill most of the mold before pressurization.

 

Here's another nice example of undercuts that are possible:

 

csm-16.jpg

 

Rob

 

 

Edited by Rob de Bie
Link to post
Share on other sites

That’s pretty impressive. If those are one piece, what purpose does the Swiss cheese looking part next to the pattern serve? It’s not touching the pattern, and as a negative in the mold wouldn’t it be the same  as a slit? I assume you use a slower setting resin to fully degas in the pressure chamber? 
 

Charlie

Link to post
Share on other sites
8 hours ago, Charlie D. said:

That’s pretty impressive. If those are one piece, what purpose does the Swiss cheese looking part next to the pattern serve? It’s not touching the pattern, and as a negative in the mold wouldn’t it be the same  as a slit? I assume you use a slower setting resin to fully degas in the pressure chamber?

 

 

Indeed the 'Swiss cheese' parts serve as 'slits' but they don't run all the way out to the sides of the mold block. Otherwise they (again) would allow air in, instead of resin. They did not touch the parts during mold production, but I cut open the connection with a sharp blade. The slits allow more room for the part to come out. Without that, the part would be stuck.

 

And yes, I use a relatively slow resin, Smooth Cast 305, that has a 7 minute pot life. I mix for 30 second, pour the resin, load the mold in the vacuum chamber (1 minute total time), the pump takes 1 minute to achieve deep vacuum, then I de-air for 3 minutes, and lastly air is let in again. By then ~5 1/2 minutes have past, and usually I can see the resin getting thicker.

 

I thought of one more example of extreme undercuts. Long time ago I used a 5 Shore-A rubber, really soft. It allowed me to cast these NASCAR wheels in one piece, and they came out of the small opening that you can see inside the resin chamber. I'm not sure I could repeat that with the 10 Shore-A that I'm using now. But I would probably find a way to make it work 🙂

 

tbird-18.jpg

 

But maybe we're drifting away from the original question, which was about the basics of resin casting.


Rob

 

Edited by Rob de Bie
Link to post
Share on other sites
On 3/6/2021 at 6:51 AM, Rob de Bie said:

My short answer would be to obtain the following:

 

- a simple rotary vane vacuum pump (100-200 euros)
- a laboratory-style plastic vacuum desiccator (75 euros)
- 10-15 shore-A addition-type silicone rubber (aka platinum cure)
- a 7-10 minute pot life polyurethane resin

 

...

 

Rob

 

Link to post
Share on other sites

Beautiful work Rob, but you left out two important things: a reliable compressor (edit: not needed with a vacuum pump) and a well-ventilated workshop, preferable a garage, because of the toxic resin fumes.

Edited by sierrascale
Link to post
Share on other sites
1 hour ago, sierrascale said:

Beautiful work Rob, but you left out two important things: a reliable compressor (edit: not needed with a vacuum pump) and a well-ventilated workshop, preferable a garage, because of the toxic resin fumes.

 

I totally agree on having good ventilation, but I'm not so sure were talking about 'toxic fumes'. Polyurethanes are nasty because of the isocyanate component, but as long the resin is a liquid (and solid later), I don't think a mask is required. And a mask probably would not stop the isocyanate anyway.

 

If you're *spraying* polyurethane, like in a car paint shop, it becomes a whole different game.

 

Rob

Edited by Rob de Bie
Link to post
Share on other sites

Hi Rob, single part molding seems like witchcraft  : )     Looking at the those rims, I imagine the rubber would flow and solidify in between the spokes, essentially locking the object in place and making it impossible to pull out after.   Sorry for all these questions.  I just find it so interesting and your work so inspiring.  Hi breadneck, what kind of parts are you planning to cast?  What I find nice about two-part molds is everything is visible.    You take the mold halves apart and you get to see the hollowed-out shape inside and makes it easier to imagine how the liquid resin would flow and understand the whole process if you're starting out.   Easier to pull the cast out as well and the molds last longer, I think.   Also, two-part molds have the advantage of allowing some air in so that no vacuum chambers are required to force resin into the passageways -- is that a correct assumption, Rob?  I for one don't have a vacuum pot but my casts have turned out pretty well so far.  Or could it be type of resin?   I use Alumilite but I haven't used anything else.

Edited by crackerjazz
Link to post
Share on other sites
15 minutes ago, crackerjazz said:

Hi Rob, single part molding seems like witchcraft  : )     Looking at the those rims, I imagine the rubber would flow and solidify in between the spokes, essentially locking the object in place and making it impossible to pull out after.

 

That's easily solved: before casting the mold, all openings in the master are treated with Kristal Klear, creating very thin clear 'windows'.

 

Rob

Link to post
Share on other sites
On 3/6/2021 at 9:58 PM, crackerjazz said:

Those are some pro cast parts, Rob!  Very nice!   Hi breadneck, I've cast a few basic parts myself and this video might help you understand the basics: 

Making a two-part mold

 

I just reread this thread and took a look at the video. The clay method is easy enough, but also messy and a ton of work!

 

With my one-piece molds all that is not needed: I simply superglue my master part on a small block, superglue the block to an aluminum plate, put a casing around the parts, tape the seams against leaks, and pour the rubber. Literally minutes of work!

 

The above is not meant as boasting about my methods, but the claying method might put off some modelers, who want to start casting.

Rob

 

Link to post
Share on other sites
On 3/7/2021 at 12:19 PM, Rob de Bie said:

 

That's easily solved: before casting the mold, all openings in the master are treated with Kristal Klear, creating very thin clear 'windows'.

 

Very cool trick, Rob, thanks! : )

 

16 minutes ago, Rob de Bie said:

The above is not meant as boasting about my methods, but the claying method might put off some modelers, who want to start casting.

 

No, that's really great info.  I hate claying myself and thought that was the only method until you opened our eyes.   Your last post about the entire process is golden.   Just another question, do you create tubes as well (where the resin should drip somehow) to fill the voids completely?  I understand that once the mold is created, the pour point will  be where you superglued the part to the plate.  Should there be another tube on top (which will be underneath when pouring resin.

Link to post
Share on other sites

No, there are no extra parts, no tubes, no vents. I wish I could show some photos of mold making, but I never made any photos. However, the photo below show the basics - just image the master part instead of the casting, plus the block. That's the way I developed my methods: by looking at commercial parts.

You *do* have to study closely how to cast the part. You have to imagine it inverted, and study whether bubbles can be trapped. That study can take a few minutes, and sometimes you need to employ tricks, like the thin pieces of  plastic card that I placed in line with the bomb fins.

f84f-58.jpg

 

f84f-57.jpg

 

Rob

Edited by Rob de Bie
Link to post
Share on other sites

The way vacuum casting works is also a bit strange, and it can take a bit of time to get your head around it. If I put it a bit extreme: during the build-up of the vacuum, both air and resin are sucked out of the mold cavity. The resin, foaming by this time, de-airs while in the 'resin chamber', the little casting block. Therefore the block needs to be large enough. Only when you let the air in again, the mold is filled with bubble-free resin. It's pushed in by the incoming air. This description is not totally accurate, but it serves its purpose. I made a drawing of the steps of the process:

 

Edited by Rob de Bie
Link to post
Share on other sites

This was part of the above reply, but the database won't accept it!

 

castingprocess.jpg

 

With the above understanding, it becomes clear you need a deep vacuum. If your pump would achieve 10 mbar (absolute) coming from the average 1013 mbar ambient pressure, there's still 1% air in the mold cavity (10/1013 = 0.01 = 1%). Therefore 1% of your product would be an air bubble after the mold is filled. Thus you need a deep vacuum, say 0.5 mbar (abs), and therefore  a rotary vane pump, and leak-free setup. The added advantage is that the resin de-airs really well at this vacuum level. It seems to boil, and maybe it does. I've been told this is mainly absorbed water cooking off.

 

Rob

Edited by Rob de Bie
Link to post
Share on other sites

A most informative thread! :thumbsup:

 

Edit:

Rob, when pouring the rubber mould, do you also pull a vaccuum on that before the rubber solidifies? 

Edited by ChernayaAkula
Link to post
Share on other sites
1 hour ago, ChernayaAkula said:

A most informative thread! :thumbsup:

 

Edit:

Rob, when pouring the rubber mould, do you also pull a vaccuum on that before the rubber solidifies? 

 

Ah, yes, good that you mention it. I vacuum the mixed rubber briefly in its own container, basically until it foams and then collapses. Then I pour it into the mold box, and vacuum the rubber again again. I can see small bubbles popping up to the surface almost continuously, but I have to stop at one point, before the rubber starts to cure.

 

You might wonder why do it twice. In the first de-airing, the foam roughly triples it volume - you need an oversize container! The second de-airing is the 'real' one I would say: you de-air the rubber much better, and also remove air around the master (undercuts etc).

 

BTW: I wonder whether the original poster reads his own thread. So far no sign of life  from 'breadneck' ..

 

Rob

 

 

Link to post
Share on other sites
9 hours ago, Rob de Bie said:

Here's an updated version of the image that shows all steps:

 

castingprocess2.jpg

 

Rob

Great pic! Thanks for posting. Question, on molds where you do need to put in a slit to facilitate removal of the castings, do you use backing plates or rubber bands to hold the mold tightly together? Wouldn’t resin otherwise escape from such slits while under vacuum?

Link to post
Share on other sites
20 minutes ago, Charlie D. said:

Great pic! Thanks for posting. Question, on molds where you do need to put in a slit to facilitate removal of the castings, do you use backing plates or rubber bands to hold the mold tightly together? Wouldn’t resin otherwise escape from such slits while under vacuum?

 

The slits in my molds *never* run all the way to the exterior of the molds, *only* to the 'resin chamber' or the 'flller opening' for lack of a better description. Slits that go the mold exterior would create air paths that would allow air instead of resin in. And I don't want to trust on clamping with rubber bands or other methods - there's always the possibility that some resin flash creates an air path.

 

Since my silicone rubber is soft (10 Shore-A), the molds are quite floppy. During the final cure of the resin, I like to set them next to each other, touching, so they support each other and are held in their original shape . I sometimes use empty molds for this purpose.

 

Rob

Edited by Rob de Bie
Link to post
Share on other sites

Hi Rob, fantastic tutorial. The key seems to be the vacuum pump. Can you post a picture of it or describe where you got it. Is it one used for automotive repair or air conditioning service? Thanks, I've been looking on Amazon, but there are many different types.

And what about the vacuum chamber - what does that look like? Something like this?:
https://www.amazon.com/Chamber-Pressure-Stainless-Chamber-Shipping/dp/B08NVXDJ2C/ref=sr_1_3?crid=3C95YL8HFRIHO&dchild=1&keywords=vacuum+chamber+with+pump&qid=1616328415&sprefix=vacuum+chamber%2Caps%2C190&sr=8-3

 

The reason I'm interested, is that I need fourteen 1/48 Snake Eye bombs to hang on a Marine A-4E in Vietnam - buying enough Hasegawa weapons sets is a going to be expensive.

Edited by sierrascale
Link to post
Share on other sites
30 minutes ago, sierrascale said:

Hi Rob, fantastic tutorial. The key seems to be the vacuum pump. Can you post a picture of it or describe where you got it. Is it one used for automotive repair or air conditioning service? Thanks, I've been looking on Amazon, but there are many different types.

And what about the vacuum chamber - what does that look like? Something like this?:
https://www.amazon.com/Chamber-Pressure-Stainless-Chamber-Shipping/dp/B08NVXDJ2C/ref=sr_1_3?crid=3C95YL8HFRIHO&dchild=1&keywords=vacuum+chamber+with+pump&qid=1616328415&sprefix=vacuum+chamber%2Caps%2C190&sr=8-3

 

The reason I'm interested, is that I need fourteen 1/48 Snake Eye bombs to hang on a Marine A-4E in Vietnam - buying enough Hasegawa weapons sets is a going to be expensive.

 

That set on Amazon looks fine to my eye. It has the right type of vacuum pump: a single-stage rotary vane vacuum pump. Mine is a single-stage rotary vane vacuum pump too, a typical Chinese product that is (was) sold under many, many brand names. It was sold as a pump for air conditioning service. According to the specs, it can achieve 0.02 mbar (abs), and it does 1.1 liter/sec or 2.3 CFM.

 

The two key pump performance parameters are vacuum level and CFM. A low CFM with a large vacuum chamber means it will take longer to achieve deep vacuum. With my set-up it takes 1 minute. The vacuum level is where things become complicated, since there are so many units for vacuum. I'm used to SI units, so I like to use millibars. Average ambient pressure is 1013 mbar (absolute), and you need (say) 0.5 mbar (abs) vacuum to achieve full de-airing.

 

Note that the 0.5 mbar (abs) is not a scientific value. But I noticed that things start happening when your're down to 2-3 mbar, and a lot more is happening when you're going  deeper. I do not know exactly how deep my set-up goes, I don't have a vacuum gage that can measure this accurately.

 

Two remarks:

- it's quite possible that you boil off components of the chemicals at these low vacuum levels. Therefore it is advisable to have the pump's exhaust air evacuated

- another exhaust problem is that the pump will create a fine white oil mist. It's best to buy a pump with an oil mist filter. But you could skip it if you follow the remark above

 

Rob

 

 

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...