Resin Casting Guidance

It's a tall order to answer your question without writing reams. Every resin casting job offers a different challenge. But it can be done reasonable easily with a minimum of equipment.
If you were here in the UK I could suggest several supplier for professional quality rubber and resins but looking on Micromarks website I found the following, which are very similar to the stuff I use at work, only we buy ours 20 kgs at a time.

Item # 81544 CR-300 QUICK CURE CASTING RESIN

Item #: 83027 SEMI-TRANSPARENT SILICONE MOLD RUBBER

The resin is a 2 part Polyurethane resin that sets quickly and has a low environmental impact.

The rubber is semi clear so you can see that the mould fills completely and it gives you a chance to eliminate air bubbles in the rubber.

As for how you go about your casting jobs... you'd have to tell us what you want to cast to get advice on the best way of going about it. Micromark's website has simple guides to casting with resin and there must be plenty of stuff online.


HTH

Without doing lots of research, I would start with Bragdon. He has the right stuff for starters. After learning the tricks, you can order
different density silicones and various viscosity, even clear resins. There are many dealers with very good selection of materials, also some sites even have tutorial pages too. Here is one: www.moldmakingsilicone.com/index.htm

Lajos

zthek wrote:

Without doing lots of research, I would start with Bragdon. He has the right stuff for starters. After learning the tricks, you can order
different density silicones and various viscosity, even clear resins. There are many dealers with very good selection of materials, also some sites even have tutorial pages too. Here is one: www.moldmakingsilicone.com/index.htm

Lajos

I've just had a quick scan of this site and it looks good. The starter pack looks like excellent value for money. In Z that 2Lbs of resin will go a helluve long way. You American guys are really lucky, I can't think of a comparable site serving the UK.

This is a favorite subject of mine. I am no expert, but I do have experience in making RTV Molds and Casting!!! If I had a $1 Dollar for every time I have mixed a batch of resin I'd be rich.

Mold Making and Casting is an art and requires lots of practice. If you get it right every time, you are a natural. That link Lajos posted above is an excellent place to start. You can watch mold making and casting videos for hours on Youtube if you want too, but till you put a pair of gloves on and mix your first batch, you just haven't lived!!!

Let this message thread be the place for Z scalers to come with questions and also tips on this subject!!!

Great Topic!!!

Hobo Tim

Tim,

I'd be interested to know what things you've casted. TIA

Ask and you shall receive.

Gathered below are several links to a photo gallery I have on Trainboard. I started dabbling in mold making, resin casting and home etching in late 2004. A guy named Harold Grady put a notion in my head that the one PS2 3bay rib side covered hopper I made needed to be mass produced so that one thing is what got me started. Needless to say the project never got as big as it should have. Knowing what I know now, would have been a breeze. Robert Ray is the owner of all the PS2 castings that are shown in one of the photos.

Note, most of these photos combine castings and home etched brass to complete the projects!

Enjoy!!!


www.trainboard.com/railimages/data/506/ST1.jpg
Sanding Tower

www.trainboard.com/railimages/data/506/14.jpg
Mi-Jack Translift Crane

www.trainboard.com/railimages/data/500/DSCN3243a.jpg
Several Mi-Jacks

www.trainboard.com/railimages/data/506/6a1.JPG
Molds to cast the pieces for the Mi-Jack

www.trainboard.com/railimages/data/506/Rural_Grain_Elevator_002_edited.jpg
One of the two grain elevators I use to cast, 2005

www.trainboard.com/railimages/data/506/DSCN14421.JPG
First Casting Project, 3 bay rib side covered hopper, 2004

www.trainboard.com/railimages/data/506/TrainZ_015.jpg
First Roadrailers in Z scale, 2005

www.trainboard.com/railimages/data/506/Corn_Combine_3.jpg
First Ever Combine and Grain Truck in Z, 2005

www.trainboard.com/railimages/data/506/DSCN2084.JPG
An Army of Ottawa Yard Mules for Intermodal container work, 2005

www.trainboard.com/railimages/data/506/DSCN2088.JPG
Tractors, hay bailers and stacks of hay, 2005

www.trainboard.com/railimages/data/506/DSCN14211.JPG
53' Smooth side containers, 2005

www.trainboard.com/railimages/data/506/TrainZ_005.jpg
53' Rib side containers, 2005

www.trainboard.com/railimages/data/506/DSCN1959.JPG
Intermodal Entrance building, shed and guard shacks, 2006

www.trainboard.com/railimages/data/506/DSCN2181a.jpg
48' Trailers to ride on my Spine cars

www.trainboard.com/railimages/data/506/177.JPG
53' Trailers to ride on my 89' flat cars

www.trainboard.com/railimages/data/506/Picture_092_edited.jpg
Second of the two grain elevators, 2005

www.trainboard.com/railimages/data/500/Handcar_2.jpg
Handcar and Pushcar, 2005

www.trainboard.com/railimages/data/506/DSCN5743.JPG
SD70ACe shell, cab and walkway

www.trainboard.com/railimages/data/500/DSCN5484a.JPG
various cast parts to make 20' Tank-tainers and pieces to make tank cars

www.trainboard.com/railimages/data/500/DSCN5326.JPG
Dash 9 shell and cab, 1 piece

www.trainboard.com/railimages/data/506/Car_Shop_Pieces.JPG
Concrete base for embedded rails and the roof vents

www.trainboard.com/railimages/data/506/DSCN6400.JPG
Turbine Load for the 195ton HD Flat car


Those are alot of examples of things I have cast in the past. I have two projects where I took many photos while making the molds too.

Hobo Tim

Tim,
Is that all you have made in all this time? Gee whiz, not much to show for your efforts.....

Seriously, if each one of us had produced as many items as you have, Z would be a lot richer for the efforts.

You are a shining example of creativity and excellence. Those you own your creations own some very special objects the rest of us can only admire.

Well done my man.

To follow in your footsteps is a worthy goal for all of us garage inventors.

Salute !!!

Loren

About 5+ years back I tried Alumalite to make castings. I was totally unsucessful in my many attempts. It chewed up a whole lot of time for no results. Thus said, I would still like to be able to make castings sucessfully. I'll look into these threads. Thanks.

Also I got lucky. Marklin made a steel mill bottle car so I no longer had to try to cast one.
bh

Tim, I hope you'll be able to give me lots of verbal help. I am just getting started, using the micro-mark kit. I think their "quick" resin is not so great for think stuff but when I run out, I suppose I shall try their "strong" stuff and it will be a bit better.

Tim,

I'm in awe of your work Thanks for posting the links

Though Karin doesn't cast her work, she's also prolific

Beverly56 wrote:

Tim,

I'm in awe of your work Thanks for posting the links

Though Karin doesn't cast her work, she's also prolific

Bev, the only thing that seems to be prolific around here is Karin's four cats.
And last night one of them did a no no and I seriously considered ending about half its lives. The thing that saved the lives was the fact that Karin did the clean up. Still I was what is considered a "unhappy camper"

I'll live,
Loren

andyjbj wrote:

Tim, I hope you'll be able to give me lots of verbal help. I am just getting started, using the micro-mark kit. I think their "quick" resin is not so great for think stuff but when I run out, I suppose I shall try their "strong" stuff and it will be a bit better.

Micro-Mark resins and RTV rubber are a main portion of what I use to make my castings.

You mentioned one word that does not sit well with me and that is "quick". Without asking I presume you are talking about the CR300 resin. Suppose to have 3-4 minutes work time, 10 minutes set up and within 30 minutes demold the casting.

I tried it once!!!ONCE!!!! I hate the stuff!!! When I ready molds for casting, I have several and to mix one batch of the CR300 I would only have time to fill one, maybe two molds(even small molds) before the resin starts to gel. Nope, need a watery consistancy for at least 8-10 minutes as I fill usually 4-7 molds and need the time to ensure no bubble activity too. I use the CR600. I wait on average of 54 minutes to de-mold. Sometimes the casting is still plyable, sometimes not, but all in all the casting will eventually harden completely. 54 minutes is a norm for my casting, be it with or without the pressure pot.

Looking at the above mentioned website I see that WD40 makes several mold releases. I will definitely try the top one listed as it sounds like just what will work to prolong the Micro-Mark RTV rubber so I can get perhaps double or more castings from it. Average for me, depending on mass of detail, 10 to 30 castings per mold, if I am lucky and designed the mold right.

What I need to find is someone who is basically giving away a vacuum pump that pulls in or near the 30s to remove the bubbles from resins and especially rubbers, then I could use the expensive rubbers to make molds that will last years and hundreds of castings!! $300+ is still too much for me to purchase one of these cheaper vacuum pumps, and most that cheap still won't pull the vacuum needed.

What questions do you have about casting of mold making?

Here are some photos of my making the molds for the SD70ACe shell, cab, and walkway(which needs revising).
Prep the mold and build a reverse mold;
www.trainboard.com/railimages/data/500/DSCN5677.JPG
www.trainboard.com/railimages/data/500/DSCN5682.JPG
www.trainboard.com/railimages/data/500/DSCN5686.JPG

I will brush on thin coats of RTV to ensure no bubbles are touching the masters.
www.trainboard.com/railimages/data/500/DSCN5689.JPG

I then build the mold sides using styrene .040" sheet plastic, mix RTV and pour carefully into the molds. I vibrate the molds by tapping fingers under the the molds after pouring or slowly tilt the molds in all points on the compass to make bubbles rise to the top.
www.trainboard.com/railimages/data/500/DSCN5690.JPG

Remove the styrene sides
www.trainboard.com/railimages/data/500/DSCN5707.JPG

Carefully remove the RTV from the molds once it's cured 3-4 hours. Carefully remove any clay used to create the contour.
www.trainboard.com/railimages/data/500/DSCN5708.JPG

Once the clay is removed, remove any areas of RTV where it might have seeped into cracks or tiny nooks-n-crannies. Areas where it does not need to be.
www.trainboard.com/railimages/data/500/DSCN5709.JPG
www.trainboard.com/railimages/data/500/DSCN5710.JPG
www.trainboard.com/railimages/data/500/DSCN5712.JPG

Next, secure styrene round or square rod to raised areas or the master or areas where you might get bubbles.
www.trainboard.com/railimages/data/500/DSCN5713.JPG

Then take the styrene sides you used to build up the first mold and attach them around the molds as shown. This time the sides ARE NOT glued to the bottom styrene sheet. Raise them so you can pour the RTV as high as you need to cover the master.
www.trainboard.com/railimages/data/500/DSCN5714.JPG

Next, Very Important to coat the exposed RTV with a rubber-to-rubber release agent so that the top we are about to pour DOES NOT stick to the bottom mold already poured. IF YOU FORGET THIS PART, you will be cutting your master out of the mold with a hobby knife.
www.trainboard.com/railimages/data/500/DSCN5715.JPG

Next mix up more RTV and pour. Use the brush on thin layers first if you have exposed detail on this side too that needs to remain bubble free.
www.trainboard.com/railimages/data/500/DSCN5716.JPG

Once the RTV has set and dried, remove styrene sides and carefully seperate the top from the bottom mold.
www.trainboard.com/railimages/data/500/DSCN5717.JPG

This is the end result before I remove the masters.
www.trainboard.com/railimages/data/500/DSCN5719.JPG

Here are the 3 masters for this project, crafted by the one and only David Freehling!!!
www.trainboard.com/railimages/data/500/DSCN5720.JPG

And this is what the molds look like with the masters removed.
www.trainboard.com/railimages/data/500/DSCN5721.JPG


Please note, there are many different ways to make molds for casting in resins or metals. Both are different and similar in design and creation but it depends on the persons preferences. I make the majority of my molds like described above. I find I can get more bubble free castings by using the "Squish" mold method as opposed to the pour in the canal slowly and hope the detail is bubble free. Nope, not for me. Micro-Mark send a mold making instruction sheet with every set of RTV and resin and this way of doing it is not my prefered way. Nope! You have to do what works best for you. What I do, have done, and will do in the future depends on what I am wanting to cast in multiples. For this fact, when you hear me say Experience has taught me what I know about casting and mold making believe you me I have wasted many many many bottles of resin and RTV in gaining what I know today!!

Now, ask away!!!!! I know you have questions!!!!

Hobo Tim

Hi Hobo Tim,
I'm thrilled to see this thread. I've been fascinated by resin casting and have wanted to give it a try. Your photos and descriptions have already answered several of my questions. But, what do you mean by the "squish" method instead of the resin pour that's in the manufacturer's instructions?
Thanks,
Rainer

I have had such terrible luck with resin casting, that every time I get ready to mix tome up, I mix a like size test batch first, and make sure it sets before using mixing another batch to pour into my molds. I have ruined more than my fair share of molds because the resin did not set and stayed sticky or made tiny bubbles.

rayzz wrote:

Hi Hobo Tim,
I'm thrilled to see this thread. I've been fascinated by resin casting and have wanted to give it a try. Your photos and descriptions have already answered several of my questions. But, what do you mean by the "squish" method instead of the resin pour that's in the manufacturer's instructions?
Thanks,
Rainer

The "SQUISH" method of casting is nothing more than designing the mold so that the top can be easily pushed into the bottom mold.

Here is a photo of the Ottawa Yard Mule Squish Mold that has just been cast.
www.trainboard.com/railimages/data/506/Ottawa_Mold.jpg

You mix up slightly more resin than you need to fill the mold. I pour to the top of the mold to ensure all detail on the side of the bottom mold is bubble free. Then I use the mixing stick to put resin on the bottom area of what will be the inside of the casting,of the top mold, and then push the top mold down onto the bottom mold thereby squishing all of the unwanted resin out of the mold. It is kind of messy, but that is why I use big styrene sheets or plastic under the molds and also wear the rubber or vinyl gloves.

Basically you pour more resin than needed and then squish out the unwanted portion. The last mold I made is for signal sunbonnets. I actually made the mold where the top part will lock into the bottom mold holding it in place. I did this to try a theory. I make my molds where I do not need to place a weight on top of the mold except in the pressure pot, so I tried an experimental mold. Still to damp and cold to cast right now so I can't comment further yet, soon.

I wish I had video/sound capabilities for I'd post How-To videos on Youtube on how I make molds and casting, heck even etching at home. Gives me an idea, as I have never searched Youtube for home etching. Gotta go!!!! Youtube bound!!!

Ask questions!!!! I'll answer all, except what has been cast lately!!!

Hobo Tim

pray59 wrote:

I have had such terrible luck with resin casting, that every time I get ready to mix tome up, I mix a like size test batch first, and make sure it sets before using mixing another batch to pour into my molds. I have ruined more than my fair share of molds because the resin did not set and stayed sticky or made tiny bubbles.

Here is a great question I have never thought about responding to.

Sticky resin!!!

First of all, damp, humid air will make resin bubble something fierce!!! If you have a tiny drop of water in a mold, then your casting will be all messed up!!!! Water and resin don't mix!!!

Sticky Resin!!! Mixing resin in small amounts is a norm for me. I can fill 4 molds with 1/4 to 1/2 ounce of resin. Mixing an equal part "A" and "B" together is very, Very, VERY important. Now, how do you mix 1/8 and 1/8 perfectly!!!! I use clear plastic medicine cups with the gradient marks on them.

The norm for mixing resin is to pour part "A" in this cup, then pour part "B" in that cup, then pour both parts into another cup together and then mix. BUT, what do you do with the first two initial cups? Throw them away? I'd waste hundreds of dollars in little plastic cups if I did that. No, I get to eye level with the cup and pour part "A" till I get 1/8th ounce mark EXACTLY and then part "B" to the 1/4th ounce mark EXACTLY, set my timer for 54 minutes and then start mixing for 60 seconds to ensure it's mixed thoroughly. Then I pour the resin in the molds and SQUISH!!!!!

After I finish pouring the resin I will slightly tilt the plastic cup and rest the stir stick to the lower side and in 54 minutes, when the molds are ready to separate so is the resin that is in the stir cup. I just pull on the stir stick and the dried resin pops out of the cup and it is ready for another mixture of resin. I recycle everything except the rubber gloves and stir sticks. The mixing cups will eventually dry out but not before they have mixed near 100 times.


To eliminate Sticky Resin you need to pour the exact amount of part "A" and part "B" resin, mix thoroughly and make sure no water, or damp humid air is present. Oh, and it helps if your resin is FRESH. Check the expiration date. Even Micro-Mark sells resin that is within the expiration date yet performs poorly. Once you open a set of resin you need to use it quickly. 5, 10, 20, 100 castings, whatever you need, cast, cast, cast!!!!!

Hope this helps!!!

Hobo Tim

Casting in a Pressure Pot

Them confounded bubbles!!!!! Even one measely tiny bubble, in the wrong place can destroy days of eventual mold making and casting!!!!

One way to eliminate this is by shrinking that tiny bubble, or bubbles, where it cannot be seen!!!

I use a modified 2 gallon paint pot I purchased from Harbor Freight
www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66839
Of course they now only have a 2 1/2 gallon pot

Also picked up a small 1 gallon air compressor from there too. Since then I have replaced it since I cast and airbrush so much I wore the 1 gallon compressor plum out!!! Here's a few small and compact. I now use the one in the first link;
www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=97080
www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93796
www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95275

I modified the paint pot by removing the tube from under the lid. I added a valve to the gauge on top so I could plug the airhose to it, male/female connection, and use the valve to hold the pressure in the pot and also release the pressure once the castings are ready to be removed. I wish I had photos of my set-up, but words will have to do for now. The paint pot is rated for about 80psi, but casting requires no more than 40psi. I usually pressure up to 25psi everytime I use the pot. If the bubble is big, then not even 80 psi will eliminate it. That is why mold design and pouring technique is so vital a part of bubble free casting. Trial and error is speaking here!!

One note of Extreme Caution!! The pot has 4 clamps placed every 90 degrees to hold down the lid. I suggest you tighten the two opposite each other equally. Tighten them to seal the lid and prevent a catastrophy!!!! Safety has got to be First and Foremost on your mind when you use a pressure pot in casting!!!

Now, mold design is another issue I have come across. If I make a mold that will no doubt be cast using my pressure pot I will add resin resevoirs inside the mold so when pressure is applied and the resin is compressed, there is extra resin to fill the void that the bubble created when shrunk. Sometimes the vent holes in the top mold don't hold enough extra resin so I add the extra. An example will be the molds I made for the Mi-Jack crane. I made about 5 set of this mold in order to cast more than 50 Mi-Jack's, some molds being made twice as many times being I needed two of that part for one Mi-Jack.

Here is a photo of the molds and then a photo showing the highlighted lime green areas for extra resin!
www.trainboard.com/railimages/data/506/65.jpg
www.trainboard.com/railimages/data/506/6a1.JPG

Here is a detail of how I made these molds;

Prepping the masters for the Squish Mold method
www.trainboard.com/railimages/data/506/216.jpg
www.trainboard.com/railimages/data/506/119.jpg

Build up the styrene sides
www.trainboard.com/railimages/data/506/316.jpg

Brush on top thin layers to eliminate bubbles in RTV touching the masters, then pour RTV to fill the area!
www.trainboard.com/railimages/data/506/413.jpg

And the rest of the mold making is as described in the above message for the second pour. The only difference is the fact that some of the clay is left in the second pour. It will become the area for extra resin.

Hope this helps anyone wanting to eliminate the problem with a few unwanted bubbles in their castings. Remember, this works on small bubbles, not the big ones!!! Small bubbles are tiny bubbles!!

"TINY BUBBLES!" [echo "Tiny Bubbles!"]
"IN MY BEER!" [echo "In My Beer!"]
"MAKES ME HAPPY!" [echo "Makes Me Happy!"]
"AND FULL OF CHEER!" [echo "And Full Of Cheer!"]

In this case, just the opposite, unless you are drink a beer right now!

If you have any questions on casting, that I may be able to help you with, please ask!!!!

Hobo Tim

p.s. A good Timer is needed if you are set on doing lots of castings!!! A digital kitchen timer is great for this as it is small and portable!!!

"TINY BUBBLES!" [echo "Tiny Bubbles!"]
"IN MY BEER!" [echo "In My Beer!"]
"MAKES ME HAPPY!" [echo "Makes Me Happy!"]
"AND FULL OF CHEER!" [echo "And Full Of Cheer!"]
...
"NOW I DON'T KNOW!" [echo "Now I don't know!]
"BUT I'VE BEEN TOLD! [echo "Now I've been told!"]
"HOBO TIM!" [echo "Hobo Tim!]
"MAKES A MIGHTY FINE MOLD!" [echo "Makes a mighty fine mold!"
On the way to ANCOC in 2 weeks!

Kelley wrote:

"TINY BUBBLES!" [echo "Tiny Bubbles!"]
"IN MY BEER!" [echo "In My Beer!"]
"MAKES ME HAPPY!" [echo "Makes Me Happy!"]
"AND FULL OF CHEER!" [echo "And Full Of Cheer!"]
...
"NOW I DON'T KNOW!" [echo "Now I don't know!]
"BUT I'VE BEEN TOLD! [echo "Now I've been told!"]
"HOBO TIM!" [echo "Hobo Tim!]
"MAKES A MIGHTY FINE MOLD!" [echo "Makes a mighty fine mold!"
On the way to ANCOC in 2 weeks !

It's about darn time!!!!!!

You gonna sneak a Z loco in with you to play with while you are there?? Don't be skeered, you can tell us!! We are all adults here, well, some of us are!!!

Hobo Tim