Resin casting large parts and rubber tires?

[Oldmopars]

I am looking into doing some casting of large parts, mostly 1/8th scale that can not be had anywhere but EBay in old issue kits. 

Some of the parts are engines. Should I cast them as 2 solid chunks, or try to make a buck for the back to allow them to be hollow like the kit parts?

Also, Fireball, and a few other companies are casting tires in a rubber like material. They are wonderful and I have bought several sets in 1/24-1/25 scale. However they do not offer anything in the scale I need. 

Does anyone know what material they are using? I would like to cast some 1/8th scale tires as none can be had at any price without buying a vintage kit. So, I will not be stepping on anyone's toes by making them, as nobody currently is casting them. 

[Mark]

I'd start out casting parts (not tires) and move on to tires later.  I have cast (and sold) thousands of parts over the years (though not recently) but never did get the hang of doing tires.

Don't start out experimenting.  Start with a set of matched supplies from one source, that way you will know everything is created as a system and will work together.  For example, some mold making involves the use of clay to block off an area.  Some clays contain trace amounts of materials that are not compatible with certain mold materials, and using the wrong combination will result in a mold not curing.  You want compatible materials that you know will work together until you get enough confidence to start experimenting.

If you are making large parts like engine blocks, you definitely do not want a 1/8 scale one to be solid.  It's not so much the weight of the part or the amount of resin used, it's that a large solid part will generate a lot of heat while curing.  That heat is what dries out the surfaces of your molds, wearing them out quickly.  "Hollow" parts cast in two-piece molds look more professional anyway.  I would start with small parts and work up to larger/more complicated ones with the experience you accumulate over time.

[Ace-Garageguy]

^^^ Heed Mark's words.

Pretty much exactly what I would have advised, and I also have decades of working with various casting and other composite materials.

There are many good and CORRECT sources of information from the manufacturers of casting products, including excellent videos.

Here are some:

https://www.smooth-on.com/tutorials/

https://www.freemansupply.com/library/video

https://www.polytek.com/how-to/tutorials-videos

[Deuces ll]

What 1/8 scale tires are you looking for????......

[Mark]

One more thing.

If you are making or modifying parts to use as masters for casting (as opposed to making copies of existing parts) then put the time in, and make that part the best that you are capable of.  Any sandpaper scratches, assymetry, poor fit, or other flaws will be reproduced in the as-cast parts.  You will then have to fix every part that comes out of the mold.  Why not just fix one part as opposed to a couple dozen of them?

Do NOT rely on primer to smooth over deep sanding scratches.  The curing of the RTV mold material will shrink the primer and reveal sanding scratches.

[Ace-Garageguy]

1 hour ago, Mark said:

...If you are making or modifying parts to use as masters for casting (as opposed to making copies of existing parts) then put the time in, and make that part the best that you are capable of.  Any sandpaper scratches, assymetry, poor fit, or other flaws will be reproduced in the as-cast parts.  You will then have to fix every part that comes out of the mold.  Why not just fix one part as opposed to a couple dozen of them?

Do NOT rely on primer to smooth over deep sanding scratches.  The curing of the RTV mold material will shrink the primer and reveal sanding scratches.

This is also excellent advice. 

The molding process will duplicate EXACTLY anything that's on your master. ANYTHING. EXACTLY.

If your surface finish is, say, 400 grit sanding scratches, that is what every part pulled from the molds will have too.

I've seen countless "experts" and "professionals" who, for some unfathomable reason couldn't grasp this fact, and wasted untold hours correcting parts that were halfassed as masters...a stupid waste of time that's entirely avoidable if you get your masters PERFECT.

[Oldmopars]

5 hours ago, Deuces ll said:

What 1/8 scale tires are you looking for????......

Any tires. I have 3 of the Lindberg T kits and the tires are hard 2 part junk. I would love some from the 32 Ford kit or the Big T Monogram series.

I ordered a set or tires off E-Bay, but they are slicks, no tread. I am waiting for them to arrive, but they are not here yet. I want to be able to customize the 1/8th scale kits beyond what the kit has in it. 

I now have a fair collections of 1/8th scale kits. 7 in total. 

[Mark]

If you only want a couple of sets of tires, and they are ones included in kits, you'll be cheaper off just buying or trading for them.  Look for started or even built kits.  The plastic parts in any poorly built kit can be ruined with paint or cement, but tires usually escape serious damage.  Paint slobbed onto tires can be cleaned off.  The only real damage you can encounter will exist if they came attached to sprues, and were torn off or trimmed poorly.

[mikemodeler]

You might want to check with Joseph at Fireball, he may be able to scale a tire to 1/8 for you to have 3D printed. From there you might be able to either have a bunch made or use one of them for a resin master.

[Oldmopars]

Thank you all for the advice. It sounds like I may be better off just buying used kits and being patient to wait for them to show up. I am not great at that, I tend to get fixated and want to find it all right now. But, in reality I have more kits than I can finish in several years as is and I may end up spending more time and money casting the parts than I would just waiting and buying them used.  

[Casey]

2 hours ago, Mark said:

If you only want a couple of sets of tires, and they are ones included in kits, you'll be cheaper off just buying or trading for them. 

^This.

The issue is there are a very limited number of 1/8 scale tires available. There hasn't been a new 1/8 Monogram automotive kit since 1985 or so, which means Goodyear Gatorback VR50 tires are the newest tires from those kits. They do seem to hold up well over the year, though, and can be found on eBay for a reasonable cost.

Pocher has released newer 1/8 scale kits, and the tire set I have from one Ferrari(?) kit is excellent, but not exactly common, nor easy to source.

Look at large scale R/C cars, too, as they have modern, low-profile tires which sometimes have a realistic tread pattern...not always, but they are out there of you regularly shop thrift stores. I found these on an Dodge Challenger(?) R/C car at Goodwill:

 

Edited December 31, 2020 by Casey

[Oldmopars]

I have been looking at E-Bay for RC car tires and I have found a few that may work, but it seems the 1/8 are too big 100mm+ and the 10th are too small 65mm=/-. I really need something around 80mm overall to fit. There are some out there, but the options are few. 

[Casey]

The 1/8 Monogram Goodyear VR50 tires I mentioned, found in the '85 Corvette and Camaro IROC-Z kits, measure 3-3/16" in diameter, so pretty close to your needs, as 80mm = 3.15"

[Erik Smith]

Have you looked at 3dScaleparts? 
He has a few 1/8 items. They aren’t cheap, but neither is casting your own resin - especially if you factor in time away from building a model. 
https://www.3dscaleparts.com/1-8-wheels