Well here’s a question that I really should have thought of earlier. Now that I have a board in the bag and resin curing is a bad time, but I suddenly realized I overlooked something so here goes. First-time Vac-Bag guy here, and it shows!
The board bagged down nicely and it looks like all the other photos of bagged boards I have seen in researching this, other than some wrinkles that I wish I had smoothed more carefully before going to full vac. But I realized I don’t have any way of adjusting the vac level, or of setting the pump to maintain a certain level. I am using a Robinair, from Fiberglass Supply the smallest (1.5 CFM) one they carry. I think the 15150…? Pic included. The gauge reads -26 (pic again included). This reading holds steady while the pump runs. My vac line runs from the pump to a resin trap to the bag: nothing fancy at all.
If I turn off the pump, the vac level falls steadily: does this mean I have a leak in the system or is this just natural pulling of air through the pump? Is there a way to control the vac level, something I left out of the system? Is -26 too much vac? It seems to be conforming the skins to the contours very nicely… but is that too much? My impression from reading through vac threads was to shoot for 15-20… then as soon as I had it all going I realized there is no way to control that with my setup.
Anyway there’s no turning back on this one, so hopefully all is well… but I want to check as I have a couple other boards almost ready for vaccing too: if I need to fix something I want to fix it ASAP so I can do them right. On a hardcore glassing run for the next few days: bit of a deadline to meet to fit into my schedule!
Shortly after update: I DO have a leak, at the adapter fitting right at the vac pump inlet. I think the fitting is missing an o-ring: I teflon-taped the join but now I noticed that if I turn off the pump I can hear the hiss from there, and reduce the flow by wrapping fingers around it. I am leaving it for now as I am worried that if it weren’t for that leak it would pull lower than -26.
One other question/concern: I have a small space to work in, with a shaping section and a glassing area separated by tarps and no extra space… and the water vapour from the pump is actually becoming a bit of a haze in there!!! I have a block of EPS and the cedar I am using for skins in there: so I am not very stoked on humidifying the place! Any thoughts on whether that is a concern? I am planning on finding a hose that will fit and running a little exhaust line outside so that it doesn’t fill up the shaping/glassing room again…
Also, BIG THANKS! To Oneula and BB30 for the personal (in the case of Oneula) and great thread (BB30) support on vac bagging.
The reason for not going to low is crushing the foam core so that will depend on what eps you have and allso not sucking out too much resin from the lam. normaly 12 in/hg is enough for most thing . Some one can correct me but i belive 26 is near a full vacuum???
I have 1.8 lb EPS (true #age). The resin has cured: I took it out… it looks good. I guess with the perimeter rails and the 1.8 # EPS it was ok in terms of crushing EPS. I need a method of controlling the Vac, and also I will be trying to locally find a shutoff valve that will fit the 1/2" ID hose I have for my vac system. My thought being if I have a good shutoff I could put it between the pump and the vac gauge and turn it off at the desired level… then if there is no leak it should maintain that level of vac. Right…? heheheheh: I hope so! That is my plan for now anyway, barring more input and thoughts. As it was my vac pump ran for about 3.5 hrs straight as I waited to be sure the resin was solid and kicked all throughout. If possible I would rather run it less to go easier on the motor/pump. I will test this out if I can find a suitable shutoff. Maybe an auto supply place or something.
Anyway the board is a bit heavier than I would like so far, considering I am looking forward at adding a couple of rail strips, then glassing over top. This is with 1/4" perimeter rails, 2mm skins of cedar and 2 oz glass underneath the skins. We’ll see how it goes in the next day or so as I get the rails finished up and glass the whole thing… and add fin plugs! Ouch: weight gains!
Still hoping for more input on the original questions, as well as my proposed solution. I really am hoping to streamline and clean up my bagging system over the next few days of focussed board work.
I skip all the bells and whistles and just use a low-vacuum pump that runs constantly. In my case I converted an aquarium pump from blow to suck, and it will suck 10-11# all day long. No valves, no reservoir, no joints, just a pump, a hose and a bag connection. It’s super quiet, too. You can’t even hear it running from 6ft away. You just hook it up, turn it on, draw it down and walk away. It won’t draw too much vacuum because it can’t draw too much vacuum.
I’ve never had a problem drawing down a veneer or a wet lam with mine. It pulls just the right amount of vacuum for working with light density foam.
If you want to spend twice as much and get the industrial look with the metal housing (but the same innards) you can get this one.
Bckyle, Can’t tell from the pic, but what unit of measurement is your vacuum gauge in??
Also put a clamp on your hose that goes to your bag(attached pic you can barely see it on the left) to be able to assess leaks easier.
I don’t understand, you buy a very nice pump, nice bags, release film, breather cloth and you skimp on the vacuum switch and reservoir. A vacuum switch at ACP is around $50. I always have a new extra on hand, The resovoir is maybe $15 worth of stuff from home depot(6" pvc with caps, brass end nipple fittings and a correct size tap device to thread your nipple fittings and vac switch). Also your vac pump may have an screw to a built in vac pressure switch since it came with a vac pressure gauge???
A $15 dollar reservoir will prolong your pump life possibly for your lifetime. It keeps you and your shop safe from fire hazard. It also allows you better ability to assess leaks. If you are planning on doing a buch of boards a vac pressure switch and resevoir is well worth it.
I second bb30. Building a reservoir made a huge difference to the amount my pump cycles. Just a length of drainpipe with ends and some fittings screwed in that take tubing.
I made a pressure control from a car vaccuum switch (that was fitted to the carburetter in older cars). Cost was minimal. Here’s a pic of a similar one: http://www.glide.net.au/flyingwing/vacbag/
If you want to do it the “right” way and want a professional set up then listen to the voices of experience, and adhere to what has been stated above…
However if you find yourself in a bind and need to control your vaccum on the fly… it can also be accomplished by installing a tee near your vaccum source with a short piece of hose attached, then you use a pair of vice grips to partially clamp off the hose (a controlled leak) until you get your desired vac( is that similar to the plan you had to use a shutoff valve?) …
I have a question though, is this not a resevior?
If it is, making one from pvc is definately cheaper than that …
and I’m not sure weather anyone mentioned yet but that wasn’t water vapor you had hanging in the air… it was oil vapor…
Also ,Venturi vacuum systems do work, but I’ve found that they use a LOT of scfms so if you only have a small compresor it isn’t practical…
We’ve used a vac compressor from harbor freight and have routinely left it running overnight pulling about 12" and surprisingly it just keeps going, as long as you keep oil in it (not that I recommend it).
charlie has a nice setup with pvc reservoirs on his racks and on the wall where he has wall racks to hold boards while they are curing.
I wanted something more mobile so he helped helped me make mine out of this 10 gallon compressor can used for filling tires. The little blue pump is also from Charlie and has been in use since 2004 when I started making these things. Its not an oil pump because it came from a hospital ventilator tray.
I run two hoses from that little pump and reservoir and can pull two bags at the same time.
I recently(4-5 years ago) bought the joe woodworker kit which my brother has but we haven’t got it to stop leaking at the fittings yet to use it. Its way more potable than this set up.
below the pump is a crazy pull of woven bamboo mat 10 mil thick over a 1" deep nose concave of a beegboy gemini I haven’t finished (4" thick)
About as complex a pull as you can get since the skin is so thick and hard…
Thanks to everybody for chipping in… Oneula, that looks like a nice setup and it must work pretty well to get a nice clean contour into that concave: what a crazy pull, especially with 10 mil thick bamboo!!
BB30, thanks for the extra info: your vac bag threads gave me most of the ideas and process information to base my system around. I used your system almost exactly only I can’t figure how to clamp the hose without damaging the poly tubing as it seems too rigid to be happy about crimping… I certainly didn’t intend to skimp on a vac switch or reservoir: on a shopping run to FiberGlass Supply I got delayed so was running out of time before they closed. I said: “I need everything to vac bag with this pump”. Heheheh I guess they didn’t think of a pressure switch, and I honestly hadn’t even thought of it since I kept seeing threads where the pump was running all the time so… live and learn.
Redboards, cheers for the link. I am going to have to bag the skins onto one other board before I have time to work out a better switch system, but after shopping around here I haven’t found anything that seems like it would work. A part that is a fairly common automotive thing might be easier to find.
Where I’m at now: Pulled the skins onto another board yesterday. They went on nicely… but with the leak I had and no switch it was a quick run out to the shop every 5 min. to cycle the pump manually for about 15 seconds. This kept it swinging from -20 to -10 in/Hg (BB30: that’s the unit my gauge reads in). This was a real pain… but it got the skins on.
Now I have a 3’ piece of 4" ABS with end caps. I still have to find hardware that will fit but I am going to drill holes in one end cap and attach thread-to-barb fittings so I can hook it in as a reservoir. Wish I had stumbled across this idea before, as it is a LOT cheaper than the $100 resin trap that FG Supply sells. (which IS indeed a reservoir, wooddave: I just don’t think it is big enough to make a significant difference. Maybe I’m wrong on this… it has a 1.5 litre capacity, maaaaaybe…?)
For the next board it’s going to be whatever I can get with the reservoir and manual on/off. Hopefully the reservoir buys me a bit more time between manual cycles. Then I have to source out a proper switch, preferably a canadian source. Everything I have found online seems really complex and expensive so far. Maybe I’m just using the wrong terms or something.
It’s starting to come together though, thanks to swaylocks and you guys. I’ll post up a couple of other pics when I get a bit more done.
my one extra concern right now is the vapour from the first bagging effort… Info I had seen online at that point said it was water vapour, but you’re right: there is an oily-ness to the shop towel that I put over the exhaust as an extra layer of filtration, and I found other sources online talking about oil vapour coming from these pumps too… the issue here being that my whole shop was a little hazy from this stuff. Including my wood storage area. So I am dreading the exterior lamination and fill coat steps right now out of fear that oil has coated everything very finely and that I will be experiencing the worst fisheyes imaginable as a result… also possibly bad adhesion in general… just another stress component to add to the mix I guess.
I was using an old fridge compressor to pull. It started spitting oil. I attached a tube to the outlet and into a jar of oil. The level of oil in the jar would go up and down as the pump spit and sucked oil but the oil bath limited oil vapour excretion.
From my experience if you have a hole in your bag you can’t really trust the pumps gauge because the pressure is so different in parts of the bag. I use stuff I got from ebay, the pump was 35 + 25 shipping, the tank was the same, the controllers (I got from Joe mentioned above) turn the pump on and off with the power cord. Some pumps don’t like to be turned on under vacuum so it’s best to have a system that has the ability to let it draw from a small reservoir first then conect to the main tank. See the small piece of PVC pipe on top. Watch out for those pumps you have it will pull plenty to crush your foam if the bag has no holes and you use breather material and that is oil vapor coming out. I use one like that to take down the air in the bag then use the smaller pump to maintain the vacuum. I would keep the oil pump out of you lamination room just to be safe from oil slicks.
