Hi TheWolfOfWalmart:
At the risk of sounding negative about this, do you have any idea what you're getting into here?
As others have pointed out, there is much to know and the "what to know" varies quite a bit depending on what the tool is supposed to make.
The best advice I've seen so far is to have experienced mold makers looking over your shoulder and an experienced and talented mold designer making your design for you if there is any complexity to your build.
If you are convinced your tightest tolerance is going to be +/- 0.002" you will have a nasty surprise.
You will need to do way way better than that in some areas and you can be much much sloppier in others without compromising the quality of the tool, but if you don't know where it matters and where it does not, you'll have a very hard time indeed.
Mold designers commonly do not make toleranced drawings; they assume the moldmaker knows what to care about and what not to care about, so they make a CAD mold model with no clearances and no interferences and the toolmaker is expected to make a workable tool from that primitive design.
It's true that some of the more sophisticated shops will design and build to print, but not with a Minimill and a couple of mikes in the garage.
These are heavily capitalized operations with millions invested in equipment and metrology.
Those of us who don't have the benefit of that technology need to fit the mold as they build it, and there is a workflow you need to know about to do that successfully, even for quite simple molds.
None of it is rocket science, but....
So there will definitely be handholding in your future in one form or another.
So I gotta ask: how did you even quote the tool knowing so little about molds and molding?
Do you expect to make money on this project or are you willing to eat it in order to learn something new?
Who designed the part?
Who (if anyone) designed the mold?
Do you know the plastic it will run, do you know the shrinkage factor you need to work to, do you know if it even matters?
Is it a simple core-cavity mold in your opinion or is it a mechanical mold with special features to release and eject the part?
It sounds as though your customer can support you to some extent, but why is he offering you this project when there are specialist mold shops out the wazoo in Utah and everywhere else in the USA?
Does he hope to get it for cheap?
Does he have expectations about the required performance of the mold before he pays you?
Is he perhaps a buddy, and will he still remain a buddy if you fuck it up?
My gut tells me this is probably a simple core-cavity or cavity-cavity mold...if that is so, are you sure at this point that you can mill all the features?
What will you do if you can't?
I know you specifically asked about milled finishes, and they are important, but that is such a trivial concern next to everything else that it's not the thing to get too focused on.
Polishing stones and elbow grease have solved many sins for a very long time in the moldmaking world.
So I encourage you to post as much as you can...there are lots of very knowledgeable people on this forum.
Once we see what you're up against, we can give more useful advice.
Cheers
Marcus
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