After many years vac-bagging and avoiding infusion I was tempted to try it after some gentle persuasion.  Freakin' awesome!  Not hard and great results.  Yay!

However, I recently made a booboo.  Infusing a 1.2m x 0.2m part; 4x200g with 6x200g in places; peel ply, mesh, bag.  I opened the inlet clamp and it seemed to stick.  A little jiggle and the resin shot through, not all the way but a good chunk was done in about 20 sec.  Bugger!  Let it flow at a more sensible rate to finish up.  I let a little more flow in on completion but as expected its pinhole-tastic on the fast bit.  Is there any contingency for things like this, ie should I have let more resin flow through or is it a once the damage is done thats it?

If there's a fix it would be good to have a list of problems and solutions.

I have really never had a problem with infusing fast. I infused a 1sqm bonnet the other day in under 30 seconds, no pin holes. I guess it probably varies depending on resin and infusion mesh, though I would be tempted to say your issue is probably more from slowing it down again. If it infuses fast then let it, just let a touch more resin in at the end. If you are calculating the resin requirements correctly then you know the part won't be resin rich anyway. By slowing it down, you increase the effect of the vacuum on the flow front, causing any air in the resin to expand and when it gets trapped you get voids. 

That's interesting.  I've always controlled the flow to keep it slow.  That comes from some of my early experiences where slow was better.  I did calculate the resin requirements but I guess I could have been in a bit of a panic when it infused so quickly and shut off the resin supply too early.  I should weigh the left over resin and see how much there is.

Yeh I used to do the same. These days it is my opinion that infusion does not need to be as complicated as you often read about. Things like degassing and reducing the vacuum and slowing the flow, it isn't necessarily the best way to do things. Mix your resin and let it sit for 10 minutes, full vac with no leaks, and infuse. Simple. Less to go wrong, less chance to make mistakes. 

Awesome, thanks. 

For me one of the main attractions of infusion is the ability to control and fine tune the process. I always start my infusions off slowly, just opening the clamp enough to allow a steady flow of resin. Once the resin has traveled the entire length of the spiral I begin to open the clamp a little at a time. The flow rate will decrease naturally the further the infusion advances. On smaller parts I may never open the clamp fully.
On laminates that vary in thickness or have strategic areas of reinforcement a slow infusion is necessary to allow these areas time to fully wet through. The resin will always take the path of least resistance and thicker areas can be left starved of resin if the infusion is too fast.  On hard points for example I try and decrease the size of the reinforcement slightly on each subsequent layer. This produces a tapered edge for the resin to feed into rather than suddenly hitting a wall of reinforcement which it will try and go around rather than through. Doubling up on flow mesh in these areas can help also.
Also with a slow infusion if some drier areas appear you can massage these areas to manipulate the resin into the reinforcement. With a fast infusion the resin has reached the outlet before you have even noticed them. 
I don't feel there is any greater chance of air bubbles in the resin being trapped in the laminate in fact I think the opposite is true. Its just with a fast infusion you don't have time to notice the air as much.
Rather than stopping the flow mesh short of the vac outlet I prefer to place a small piece of breather cloth under the vac outlet to act as a resin choke.
Stopping the flow mesh short reduces the air path to the laminate which can lead to air being left in the reinforcement when vac is pulled.
I don't degas but in the colder months I stand the resin pot in a bath of hot water whilst mixing. The heat not only makes dispersion of the hardener easier/quicker but will cause any air to rise to the surface, self degassing if you like.

As with many things individual set up will determine what works best for you.

Warren
  

Carbon Copies Ltd

A lot of it will depend on the resin and consumables each of us are using. I've tried several techniques, and the way I described above is what works best for me and yields the best results with what I'm using. As with anything composites, you should always try different combinations and then stick with what works for you. 

Ahh, now this is interesting as I do have some thicker areas (7 x 200g) and it is these where its a bit pin-holey.  I'm getting the impression that there's an element of 'feel' to infusion that can only come with experience.  I shouldn't have shunned it for so long!

What happened for me is that I too had warmed the resin in hot water and when I opened the clamp it seemed to stick a bit and then release on the next turn.  The resin shot through the moulding fairly quickly.  My previous experience suggested a slow rate was better.  The original question still stands though, if this were to happen again what is the best course of action to deal with it, flow more resin for a bit, warm the mould to try and get the resin to soak through better etc.

Luckily this is a panel for painting so I got lucky.

I don't think there is any part of the composites world that doesn't have an element of feel. I'm sure I'm going to go through it all again when I start producing pre-preg parts more critically. 

Some good advice from Hanaldo there