I have been laying up both CF and FG parts and trying many variations in my process in an attempt to produce a flawless part. I have been using Fibre Glast Series 2000 and Series 4500 resins and have similar problems with both. Regardless of how long I let the mold sit under clamped off vacuum and test the seal (I usually do 20 to 30 minutes) I still find pinhole leaks as the resin advances across the part as indicated by branching paths of bubbles.

How much of a problem do you think various trimmed pieces of infusion mesh, jacketed bleeder cloth, and sharp corners on a part are (90 degree corners). What can I do to improve my layup process?

Do a longer vac drop test. 20 minutes to half a  hour is ok when you have the experience to pick up on those smaller leaks, but when you are just starting out then you should do a minimum of an hour.

In my experience, actual punctures in the bag are quite rare, and these tend to be the leaks that you can actually hear. And they are normally quite big leaks, ie. you will lose half your vacuum in 5 minutes. But this is my experience with the type of vacuum bag and mesh I use, etc. so it doesnt completely rule it out. I know some bag materials are more prone to punctures than others.

My number one piece of advice for people suffering with leaks, especially very slow ones, is to make your vacuum bag bigger. Even if you aren't getting bridging or anything like that and your bag seems big enough... make it a little bit bigger. As soon as I changed this, I virtually stopped getting any leaks, ever. It is very rare that I have to look for leaks after pulling vac the first time, and if I do then a quick press around the bagging tape normally takes care of it.

Which is the other key point. A lot of people dont realise how much effort it actually takes to get a good seal on the bagging tape. Your thumbs should be quite sore when you're finished. 99% of the time when you have a very slow leak that only drops vacuum by a fraction over half an hour, then this is a leak at the bagging tape.

Wow thanks for all of that. That's really helpful. So when I infused my last part like this, it looked great as the resin front moved across the part. But I demolded it today and I have hundreds of tiny bubbles in the part as if the resin didn't penetrate deep enough into the reinforcement.

Are they actually bubbles, or are they voids at the intersections between fibres? If it is the latter, then it is dry laminate. Try making the next part a little bit more resin rich.

Just clamp the vacuum outlet when the resin reaches it, then leave the resin feed hose for another 30 seconds (depending on how big/thick this particular part is; for parts bigger than 0.5sqm or 3mm thick then you might want to leave it open for up to a minute or so) before clamping.