I know that topic was already extensively discussed but I can not find on our forum.
Question is : What is the vacuum level required for fiber glassing bag ( to avoid squashing polystyrene core ) ?
I did my vacuum pump from old fridge and now trying to attempt first fiberglass.
Still few more questions: how to regulate the vacuum? Maybe by creating water level in vertical pipe 1 m or 2 meter?
How to connect hose to the bag and where to buy fitting ?
Select to expand quoteMacroscien said..
I know that topic was already extensively discussed but I can not find on our forum.
Question is : What is the vacuum level required for fiber glassing bag ( to avoid squashing polystyrene core ) ?
I did my vacuum pump from old fridge and now trying to attempt first fiberglass.
Still few more questions: how to regulate the vacuum? Maybe by creating water level in vertical pipe 1 m or 2 meter?
How to connect hose to the bag and where to buy fitting ?
sorry macro, can answer your Q, but can you post some pics of your setup when you get running?
I'd like to play with vacuum bagging as well, and would be starting from scratch.
Also, have you used carbon fibre before?
I'd be interested to know if there's much difference from using epoxy and normal gf cloth.
Select to expand quoteMacroscien said..
I know that topic was already extensively discussed but I can not find on our forum.
Question is : What is the vacuum level required for fiber glassing bag ( to avoid squashing polystyrene core ) ?
I did my vacuum pump from old fridge and now trying to attempt first fiberglass.
Still few more questions: how to regulate the vacuum? Maybe by creating water level in vertical pipe 1 m or 2 meter?
How to connect hose to the bag and where to buy fitting ?
here you go, all you could possibly need. Cut and paste this into google and away you go:
vacuum bagging site:seabreeze.com.au
If you built the vac pump yourse;f I think you will want a vacuum gauge on it - and a screw-on gauge is way easier then measuring in inches of water 
Any place that sells fibreglass supplies will have bags, breather cloth and peel ply, the fitting attachment etc.
Crusty - carbon = same as fibreglass. Unless you are moulding and want the carbon glossy gee whizz look that is. But for laminating on a board etc, same same.
I ended up using a car vacuum gauge, just because it was easy to source, and it was a decent size and price. The vacuum gauge that came with my pump is meant for vacuuming down air conditioning lines, so it was not really a good range for vacuum bagging.
Vacuum pumps on ebay are a decent price, so that's what I ended up with after trying a few fridge compressors. The guy I bought it from also gave me a fitting that I tapped into some PVC, so that I could use the air-con vacuum hoses. I also tapped an airline fitting, plus a ball valve to dump the moisture, into the same high pressure PVC pipe.
I should really check, but I think I have my setup set for 15 to 20 inches of mercury. Without a reservoir, it will cycle quickly, with some decent reservoirs it cycles much less frequently. This is important as if you run it at night, it only cuts in for a minute or so every 30 minutes or better, and it doesn't matter. If it cycles every minute, it gets annoying.
Surprisingly, normal air-line fittings work fine with vacuum and to my surprise seem to seal themselves under vacuum. I can plug in two reservoirs, a few pickups, as well as the pump and gauge. Its a nice way to be able to connect everything together.
I believe compression moulding is far More superior although your limited to the shape you can build. I have loads of experience with this method If you would like to look into it!
What sort of negative pressure we could expect for the standard board vacuum bagging ?
If "0" is our atmospheric pressure and 10 is the max negative (10 meters of water equalize our atmospheric pressure).
Alternatively we could express in pulling water in meters.
If that will be 1 or 2 meters or rather 5 to 8 meters ?
I use 1/4 atmosphere so that's about 2.5 meters of water.
I agree with FormulaNova, you also need a reservoir, and like him I use an old automotive vacuum gauge.
The problem with fridge compressors is the motor is designed to be cooled by the incoming refrigerant gas. If you run it for too long under vacuum it will burn out. (I know from experience, one of my mates used it and couldn't get a good seal on the bag).
Also electric motors draw maximum current on start up, so a very quick cycle time isn't good. FormulaNova's 1min every hour is close to ideal I think.
My reservoir is one of those big residential gas bottles, it's a bit bulky but I wouldn't like to go more than half that size.
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?
Just a thought.
Select to expand quoteMark _australia said..
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?
Just a thought.
I can see the same, although I can't criticize. I often have a go at re-inventing the wheel. Sometimes the results are better than something you can buy, but often its not. I enjoy the making of things as much as anything else.
Select to expand quoteFormulaNova said..
Mark _australia said..
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?
Just a thought.
I can see the same, although I can't criticize. I often have a go at re-inventing the wheel. Sometimes the results are better than something you can buy, but often its not. I enjoy the making of things as much as anything else.
That could be the easiest if you could just find complete vacuum pump with pressure switch on eBay. But we can not.
Beside now I know now thank to decrepit that we need negative pressure 2.5 meters on average.
One more: How do to seal the hose entering bag ?
Select to expand quoteMacroscien said..FormulaNova said..
Mark _australia said..
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?
Just a thought.
I can see the same, although I can't criticize. I often have a go at re-inventing the wheel. Sometimes the results are better than something you can buy, but often its not. I enjoy the making of things as much as anything else.
That could be the easiest if you could just find complete vacuum pump with pressure switch on eBay. But we can not.
Beside now I know now thank to decrepit that we need negative pressure 2.5 meters on average.
One more: How do to seal the hose entering bag ?
Use bluTack.
Control vacuum by putting a hole in the hose.
Select to expand quoteFormulaNova said..
I ended up using a car vacuum gauge, just because it was easy to source, and it was a decent size and price. The vacuum gauge that came with my pump is meant for vacuuming down air conditioning lines, so it was not really a good range for vacuum bagging.
Vacuum pumps on ebay are a decent price, so that's what I ended up with after trying a few fridge compressors. The guy I bought it from also gave me a fitting that I tapped into some PVC, so that I could use the air-con vacuum hoses. I also tapped an airline fitting, plus a ball valve to dump the moisture, into the same high pressure PVC pipe.
I should really check, but I think I have my setup set for 15 to 20 inches of mercury. Without a reservoir, it will cycle quickly, with some decent reservoirs it cycles much less frequently. This is important as if you run it at night, it only cuts in for a minute or so every 30 minutes or better, and it doesn't matter. If it cycles every minute, it gets annoying.
Surprisingly, normal air-line fittings work fine with vacuum and to my surprise seem to seal themselves under vacuum. I can plug in two reservoirs, a few pickups, as well as the pump and gauge. Its a nice way to be able to connect everything together.
I know of others who have used old fire extinguishers as a reservoir. They are made so cheaply in China that it is more economical to replace them rather than pressure test them (at 5 years old), hence your local fire service company may be able to give you an old one.
Select to expand quoteSkid said..FormulaNova said..
I ended up using a car vacuum gauge, just because it was easy to source, and it was a decent size and price. The vacuum gauge that came with my pump is meant for vacuuming down air conditioning lines, so it was not really a good range for vacuum bagging.
Vacuum pumps on ebay are a decent price, so that's what I ended up with after trying a few fridge compressors. The guy I bought it from also gave me a fitting that I tapped into some PVC, so that I could use the air-con vacuum hoses. I also tapped an airline fitting, plus a ball valve to dump the moisture, into the same high pressure PVC pipe.
I should really check, but I think I have my setup set for 15 to 20 inches of mercury. Without a reservoir, it will cycle quickly, with some decent reservoirs it cycles much less frequently. This is important as if you run it at night, it only cuts in for a minute or so every 30 minutes or better, and it doesn't matter. If it cycles every minute, it gets annoying.
Surprisingly, normal air-line fittings work fine with vacuum and to my surprise seem to seal themselves under vacuum. I can plug in two reservoirs, a few pickups, as well as the pump and gauge. Its a nice way to be able to connect everything together.
I know of others who have used old fire extinguishers as a reservoir. They are made so cheaply in China that it is more economical to replace them rather than pressure test them (at 5 years old), hence your local fire service company may be able to give you an old one.
I think this is where volume matters. What sort of volume would the extinguishers be?
I worked out that my reservoir worked out to be about the same volume as in a 9kg propane bottle.
My first reservoir is about 4 metres of 100mm pipe. The sort that they use for underground electrical. It has pretty heavy wall thickness. For the second I used normal 100mm dwv pipe, and it works just as well.
