What materials and tooling from the site would you recommend to cast resin parts from the following objects?:
The original items are made from injection molded ABS plastic and currently coated in Plastidip (which can be removed for casting). They are not load bearing, so strength is not highly critical, however the surface finish is.
It needs to have a smooth finish, but not necessarily glossy as it will likely be painted or coated. If the finish is clean enough, I can use a black resin without any other finishing other than polishing. The inside of the larger part has two posts that will be drilled for self tapping hex screws, if that matters. Do the holes in the hollow housing and lower plate present a problem for creating a mold?
I am new to this and starting from scratch and I am ready to purchase everything needed including a vacuum degassing system, pressure system, silicone, clay, resin etc.. Thanks!
Any of the liquid type silicones will produce the exact detailing down to the same finish of the original item. Which means if the original has a smooth finish, the mold will pick that up and transfer it to the copies so I'd make sure the original item's surface is exactly how you want the copies to be. I wouldn't remove the Plastidip as that may change the surface of the original. If it needs to be smoother than the original, then I'd either add a little more to smooth it out by either or brushing on or spraying something to get the texture you want.
As for a the mold material, I'd go with either Alumilite High Strength 1 or 2 (#1 has the highest tear strength) to give you the longest lasting molds. Just be aware of the fact that those holes/openings will need to be taped on one side (or in the case of the screw holes - plugged) as you'll probably be best served making two piece molds and to remove one side you'll need a "dividing line" and I've found that tape gives just enough space between to do that without having to cut the silicone afterwards. Be aware that liquid silicone will get EVERYWHERE on an original item so plugging all holes is something you HAVE to do or you'll have a hard time removing the original. And be sure to put a release agent on the first half so that when you pour the second half it doesn't stick to the first. It won't really be needed on the original item as silicone only bonds to silicone but it is absolutely necessary between two layers of silicone when pouring a two piece mold. Alumilite has a "volume calculation" feature on their site that will help you be sure you know how much silicone you'll need. Also depending on where you put the dividing lines on the mold halves, you might need to work in some vents so that air doesn't become trapped in the castings.
Vacuum degassing is recommended but not absolutely necessary, I personally don't use it but I also don't make molds that are that big either so someone who has that system will need to chime in on whether or not it is the best thing for this application given the size of the original items. I have seen where it's recommended to vacuum the mold when making it if you chose to degassing or pressurizing the resin (or plastic whichever one you use) when making the castings.
Now as for making the two piece molds themselves, there are plenty of good videos out there about them, I just don't have any links handy. One thing I would do is to not use clay to fill up the blank spaces one half of the molds - this is just something I do, you will need to find what you prefer to do as to if you do or don't use clay. I've just always found clay to be very messy to clean off of an original item so I use Remelt as I can run warm water over the item to "wash" it off.
I hope all this information helps, let us know how things go so we can help with any problems that might crop up.