Hey Dmat,
I don't usually give machining advise since I'm not that all-'round knowledgeable, but the difference between drawing (Where anything is possible) and practical manufacture depends on the equipment, mostly. I have a 3-axis- left/right, forward/backward, & up/down known as the X,Y, and Z axis. Soon I'll have a 4th axis, which is like a lathe attachment sorta, but is for, say, engraving around a horizontal cylider and similar.
The subject is difficult to fully explain to anyone who has not seen machining done, but a couple limitations. One is, no 'organic' forms or curves from the top of the part, generally. This requires 3D machining, and needs programming for that which is not a huge deal, but the machine time is: It takes a LONG time to cut, and this is reflected in the price (As is anything that eats time.)
The big one is Ops, or operations required. Say you want to cut all sides- This may mean making several setups, most on a vise w/Al. jaws, which each jaw is another program. So, say you're doing a part that needs holes drilled/milled, etc. on several sides- This may mean 3-5 different setups, so 6-10 different programs: Things get pricey fast doing this.
Try to stay so the part can be done mostly from the top and the bottom if possible to avoid setups and ops. I must 'Stage' my ops- Take the trannys, for instance. Machined the outer features, all at once, then tore down that setup and did another for all the inner ops. Them programmed & cut a Delrin holder to be able to drill & tap the top & bottom holes. Now, if I already had the 1st op done (The outer features) and someone wanted to get a few after that, it's too late- I've already torn that down and am working on the next step, so can't practically go back & do a few more outers. I always do a few extra as some inevitably get chewed up locating & de-bugging later ops, so I may have some extras at the end or not, depending.
It would be much easier to see a drawing, and focus on what's not ideal specifically. In industry, they're trying to bring CAD guys, programmers, and machinists together more to avoid the drawings that can't be machined practically, if at all, to save time and problems. I wish I had a nickel for every kid that learned some CAD & said on a forum "I've done the hard part, now I just need someone to cut it."
You are wise to check into this first!
All I know is, I've seen a million threads with guys that post their pretty 3D renderings of a part, and talk about how this will will be available soon etc.: 99+% of the time, this never happens as they find out just how much one needs to know to make an actual part.....
If you like, you can Email me an example, and I can 'splain why something may be undoable, or simply done differently, or?? Again, this will be within my perspective, and not generally true of every machinist: But a lot of things, while technically possible, are abandoned as soon as price enters the picture. I get asked all the time if I can do such-and-such: The answer is usually Yes, but it is not practical price-wise. This is why I no longer do 1-off custom work, all the time invested in understanding someone's part only to have them choke on the price (Not that I blame them.) Chris REC