I am trying to vacuum bag my new hull and I can’t pull a good vacuum. I have a small leak somewhere. I’m using a female mold made from 2 or 3 lays of 1 1/2 oz matt not cloth. I’ve tried 3 and 6 mil plastic sealed with window laying tape. It will come up to about 20" of vacuum,the pump shuts of and then starts again in about 5 seconds. Is it possible that the mold itself is porous? The glass is about 1/8" thick. Any other things I may be doing wrong?
Thanks
Don
make sure you have a good vac pump, and the right vac-bagging supplies.
alternatives work, but not as good as the propper materials.
check this thread for other info.
Don,
Actually I think 20 " should be adequate for the task, but I’m puzzled why the pump is shutting down. Are you sure there’s not a pressure switch in the system? The other possibility would be a defect in the pump itself, causing a thermal overload switch to shut it down when it overheats. What kind of plastic are you using? I found that the readily available poly used as a vapor retarder in buildings actually has alot of small leaks. Bagging film sold for the purpose will be much more effective.
BTW, there’s alot of good info at this subforum at rcgroups.com :
http://www.rcgroups.com/composites-fabrication-210/
Regards,
Bill K
I guess I didn’t phrase that right. It does have a pressure switch and it’s doing what it should. It’s just cycling to quickly because there is a leak somewhere. The epoxy I’m going to use takes 12-14 hours to stiffen enough to turn of the pump. I’m using an old frig compressor and if it runs continuously for 12 hours it will overheat. If I plug the hose and run it it works fine. It will hold a vacuum for for a couple of minutes and then run for 10 seconds or so. It doesn’t overheat then. Since my first post I have spayed the back of the mold with auto undercoating. I will see tomorrow if that helps. I used “Glad” storage bags for doing the fin and they worked well. Maybe I’ll cut one of them open to try and get around the porous plastic.
I’ll report back
Thanks
Don
Don,
You could try placing the whole mould etc in a bag. Get a large garbage bag or similar (I buy a long length of wide plastic tube and cut it up as required, seal one end, glass boat in mould and place in “bag” and then seal other end - I have stopped using one layer of plastic and placing seal on my moulds).
I also use the large re-sealable bags intended to vacuum pack clothes - no sealing tape used at all, and re-usable about 5 times.
A stethoscope or similar ( I just use a length of plastic tube stuck in one ear) can be used to pinpoint leaks.
Otherwise it could be a machine problem (try vacuuming an empty garbage bag to see if symptoms repeat?).
Goodluck, Jon
I just couldn’t get a seal so I took Jon’s advise. I bought one of those bags for storing bedding(with the vacuum cleaner nozzle for sucking the air out), smoothed out the back of the mold and TA! DA! success. These bag have a Ziplock type closure so it’s easy to pull a vacuum and then open it up to make sure nothing slipped (I’m paranoid)and then close it up and suck it up.
Thanks for the input
Don
I just pulled a hull from my mold and it turned out pretty good. I ended up with a few resin wrinkles on the inside of the hull. I assume they are from the perforated plastic wrinkling. How can I avoid this? I am surprised that the vacuum (22 inches) didn’t flatten them out. At the very least it should have sucked the resin through the holes and left a very thin wrinkle line. Any suggestions? Should I suck it down and then take it all apart to inspect for wrinkles and then put it all back together? How do I stop the plastic at the bow from wrinkleing up and glueing itself into the resin?
Thanks
Don
Don,
What size are the wrinkles approximately? (a few lines of triangular 1/32 x 1/32 or smaller are getting hard to avoid inside our small compound curves using a plastic layer).
What do you have behind the perforated plastic? (a fine nylon layer, absorption cloth etc)
Jon