+x+x+xAs for the 2 layers of s-glass, I should have been more clear. These are the bottom layers. I will then add a core and two more layers of glass. My goal is a canoe less than 20 pounds. This includes the gunwales. It will be close.
I see, this should be fine then! I thought it may be the case, but figured I'd ask.
And yes, you want the resin to be very close to the secondary feed point before you unclamp it - but not past it. If you open the feed line after resin has passed, then you will introduce air into that resin that will struggle to escape again. In theory theres a chance that air could happily travel along with the resin and then end up on the outside of the laminate and not cause any issues. However in my experience, it will likely get trapped in the laminate. How big an issue this is depends on how much air is let in and how critical you are of void content. But considering it is not hard to avoid, and 0% void content is desirable (if not realistically achievable), it is best to just try to avoid it.
Really it is ok and probably better to unclamp a little bit early. The closer the resin is to the feed line, the less disrupting the flow front vacuum will matter. If you unclamp too early, the two flow fronts won't want to flow towards each other. But resin will happily penetrate an inch or two without the high vacuum flow front. So I would start unclamping when the resin is about an inch away from the secondary feeds.
It also isn't completely necessary to clamp the primary feed - I would use your intuition here. If the resin has reached or nearly reached the perimeter of the layup, then I would probably clamp it for a bit simply not to waste resin. If it still has a way to go before reaching the perimeter, then leave it open. Or close it for a bit to let the secondary feeds somewhat catch up, and then open it again to complete the infusion. There's lots of ways to do it. Likely none of them are very critical. You won't ruin the infusion because you clamped or didn't clamp the primary feed. But you may speed things up or saves a fraction of weight if you get it all correct. So do what you feel is right based on how your infusion is going.
Thank you again. I have asked in different forums the importance of where the resin bucket is in relation to the part being infused. I would say the majority opinion is to have the bucket below the resin infusion inlet. The opinion is having it higher will lead to resin pooling in the part. I had much prefer to have the bucket next to the inlet to reduce waste. My question is how does resin pool in a part under a complete vacuum when the resin inlet area is already saturated?
Also, in one Easy Composite document I read it states the resin line should be clamped off when the resin front in 2/3 of the way across the part. Others say clamp off when the resin is a few inches from the end of the part. What would be your recommendation?
Alan
Because as soon as you open that inlet line, the part isn't under complete vacuum anymore, it is under partial vacuum. And due to the mechanics of infusion, you have something of a 'wave' of resin moving through the part, where the laminate will be under less compaction closer to the resin inlet and more compaction closer to the vacuum outlet, leading to an uneven laminate thickness and an uneven resin content. This
should balance out again as the infusion nears completion and the vacuum equalises. But sometimes, depending on your layup, it doesn't, and you end up with resin pooling around the inlet. That is because while the pressure differential is the driving force behind infusion, you still have other physics in play as well - namely friction.
Both of your above questions are actually related to solutions for the same problem. By clamping early when the resin is 2/3 of the way through the part, you allow the excess resin near the inlet a chance to move through the laminate and even out. Or, by having the resin pot below the inlet, you use gravity to reduce some of the pressure on the resin to help slow how quickly the resin flows into the chamber. If you have the resin pot above the inlet then you have the opposite effect, and you increase the pressure on the resin and how quickly it can flow into the chamber.
The reason you get so many varying opinions and methods is because there is no hard and fast rule - these are all things you can do to influence the mechanics of infusion, but whether you want/need to depends on what you are doing and your specific layup. Personally, I will often clamp and unclamp the feed line throughout an infusion if I notice the area close to the entry is slacking off. This is easy to monitor because you can see and feel it. If the bag is loose or you can see excess resin, clamp it off for a few minutes or until the flow front really starts to slow (DD Compound have actually invented the MTI Valve to do this for you, though I prefer to just do it as I see fit). I never clamp for the final time until the part is fully infused - you dont know how much excess resin is in the part, nor how much resin the unsaturated part of the laminate needs to fully wet out. It's all well and good to say 2/3 of the way across - what if your laminate is 2 layers for the first half of the part but 10 layers for the second half? It depends on what you are doing. So better to just regulate the flow, but always finish the infusion before shutting it off.
As for pot height - I don't worry about it 99% of the time. Place it next to the resin inlet, it just works. Occasionally I have a complex infusion that I know will need to flow faster or slower and so I'll move the feed pot appropriately, but its very rare.