vacuum pump size

Upon reflection it mightn't have been Herman - sorry Herman. But someone did tell me that you cannot infuse over plywood.

I figure I could do the infusion if the panels were done before assembly by having the vacuum bag totally encase them, that is both sides with sealing tape between the two sides of plastic, ensuring a vacuum. However, that would mean some pretty bulky seams when assembling, as the glass would be several more layers thick there.

Ideally I would like to do the infusion over the hull after it is stitched up. Then I could just overlap the glass at the seams, just like a surfboard is done - just two thicknesses at the seams. But then I would be forced to seal at the edges of the plywood panels, and that's when the questions come up can you get a seal there and is the plywood too porous to maintain vacuum?

Any thoughts, suggestions, revelations?

Barry

 

Hi Barry,
It is possible but my question is why? With the stitch and glue (S&G) method you will need to ensure all the ply edges are vacuum proof as well. Usually there is only a thin layer of glass added to the ply. The ply provieds the stiffness and the glass provides the strength. If you want to infuse over ply you will need to "paint" a layer of resin over it to seal it, perhaps two coats. Then you will neeed to use a media and peel ply. By this time and effort you would have finished it by doing it wet or perhaps even a light vacuum bag. If you wanted to infuse the boat use foam for the S&G then at least you have saved a lot of weight for your efforts.

Peter S

 

I tend to agree with Peter here. You probably could find a way to infuse over stitch-and-glue. But sealing it up would probably take as long as hand-laying the whole thing to begin with. Plywood will hold a bit of vacuum, if you can seal to it- which is not easy. And envelope bagging a hull sounds like more effort than it's worth.

I think you'd probably get similar results by spending the money that would have gone into bagging gear on some good multi-axial fabrics, instead. Even hand laid, it's possible to get some pretty good fibre/resin ratios with stitched multi-axial fabrics.

 

OK, I think you guys have me convinced. I agree with the cost and effort being excessive. It seems like the hand layup is the easier way to go. I have never done a large area of layup, so that was what was a bit scary, and the control of the infusion process was appealing.

Thanks

Barry

 

Barry
For smaller S&G ply boats normall practice is to only resin seal inside and light weight glass on outside, so the benefits of infusion are only marginal.
If you want to save weight and use infusion then build in foam. You can still use S&G by premanufacturing the panels.

 

Andrew,

I had considered premanufacturing the plywood panels (foam would add to the cost) with one side glass as you say. The problem I had with that concept was that you end up doing the layers backwards. With S&G they say to tape the seams, then cover that with a full layer of glass. With Prefabbed panels it ends up being something like 1) first layer of glass (full layer premanufactured) on the plywood, 2) second layer of tape, 3) third wider layer to taper off the tape edges. You never get the smooth effect of the full glass layer covering the taped edges, or at least I can't see how to do that. Seems like it would be better with foam because you would use more layers of glass.

Barry

BTW where are you in Oz? I used to live in Sydney, now in Arizona - miss the ocean.

 

I don't build, but I have looked at several designers of kit boats using balsa panels pre-covered with glass, precut to the patterns and joined using a female frame and taped in the inside, then before the bridge-deck are rolled over and the outsides are done with tape and then finished (including all bottom finishing to just above waterline, taped and covered with plastic apron to protect from dribbles and other splashes etc - the peel-ply stays on for the sides to protect the sides and chamfer then the return to upright for build or bridge-deck and rest of exterior remove peel-ply and bog and sand before final paint finish... I guess ply S&G would be somewhat similar - the method of finish anyway...

Not the best example but some idea and mistakes can be seen here http://www.thecoastalpassage.com/bblog.html - click on the lighthouse sketch to return to the website home page.... enjoy - - lots or reading from Queensland Whitsundays region

 

Sweet - i have a nice 6cfm vac pump I bought off of amazon. one of the robinair types for Airconditioning systems. It seems to work great.
just an FYI for those looking for a good home, low cost alternitive.

 

Barry,
I have lived in Brisbane now for 20 years, before that in Melbourne.

Although building in foam alows you to make rebates where the glass is overlaped I would not be too concerned about the tape overlaps in your S&G.
The thickness of the tape should be <1mm.
What type and weight of glass is your outer laminate? any on the inside?
Weight of tapes?
In small S&G ply boats the outer laminate is usualy only 200 - 400g/m2, and its there mostly for waterproofing rather than strength.
If this is same for your case then hand laminating is better than infusing as it will be more resin rich.
Light weight plain weave or DB glass wets out easily so you should have no problem in laminating the hull of your size in one hit on your own.
If you are having 2 tapes + laminate along the chines it does not matter in which order you place these you will still have two steps in the glass.
Personaly I would place the glass fabric down first then the wider followed by smaller tape on top. This way when you are sanding you can not acidently sand through your longest fibers, only the edge of the top tape.
Another thing to keep in mind when laminating over timber is to do it at stable or falling temperature. If you have rising temperature you will have some out gassing.

Best of luck
Andrew

 

Plywood infusion

Maybe you saw it on my website, with an attempt to infuse a plywood daggerboard case.
http://www.fram.nl/workshop/mainhull/album/Daggerboardcase/photos/photo11.html

I had to know better as Herman has told me a simular story that I had forgotten about.

By the way, I came across the perfect vacuum system at
http://www.vacmobiles.com/
and now testing the vacmobile 20/2 for my Fram project. A big step forward in comparison with my humble laboratory pump.

Henny

 

Oh, yes. plywood is a very "leaky" product. I once used it (uncoated, hurry, hurry, hurry) as a flange on the transom (only 4 ft wide!) of my mould.
When pulling a vacuum, you could clearly hear the air racin through the plywood. Luckily I was only installing honeycomb, which needed not too much vacuum, and the vacuum pump was oversized.

Another example:
A company set up an infusion, and they liberally coated the flange (MDF panels) with epoxy, to make them airtight. Perfect solution. The only detail was that they cut the peelply to size with knives ON THE FLANGE cutting through the epoxy layer... Man, that was something...

The vacmobile indeed is a very nice unit, and we have been tempted to import them. However, to be honest they did not really add to the line of materials we already have...

----
To come back to the core of the thread:

Basicly, any pump can do the job, as long as the pump is larger in capacity then the air leaking into the bag. A careful applied bag will save on pump capacity.
Overcapacity is needed with a leaky bag, leaky seams or when trying plywood...
With infusion, air leaks are highly undesired, so the utmost must be done to prevent leaks. So you can conclude that a large pump is not needed then.

To pull the majority of the air from the bag, use a vacuum cleaner, put the hose in the last bit of seam that still needs to be put down, and turn it on. A vacuum cleaner has a larger capacity, but hardly pulls a vacuum. Besides, it is dependant on air passing for cooling the engine, so it is not usable for the real deal. But it is very useful for getting the first 90% of the air from the bag. (very useful with large bags, largest I have witnessed was over 30 meters (100ft). Took a while to get the bag down...

 

Sailfish25:

I too got a Robinair pump off the Internet thinking "what a deal!"

Worked great for small test projects.

My first attempt at resin infusing a 13 foot male canoe mold failed yesterday due to the pump overheating.

I had actually connected two Robinair pumps together and they bold failed after less than 2 hours. So much for having a backup.

Lesson learned, spend the bucks and get a descent pump -- a "continuous use" pump.

My e-mail to Robinair, and their response, "the pump is not recommended for non-HVAC purposes."

One would think a vacuum is a vacuum regardless of what is being vacuumed.

Apparently not.

alan

 

Hey Alan

I've run my Robinair continuously for 8 hrs or more and it's never overheated. Were the oil reservoirs full?

I don't normally like leaving equipment running continuously for extended periods of time and you can see how I addressed that issue earlier in this thread...

http://www.boatdesign.net/forums/fi...ding/vacuum-pump-size-20419-4.html#post172840

If you've got a good bag with no leaks there's no need to have your pumps running continuously.

Rick

 

The oil was topped off in each pump.

My pump has less than 2 hours on it.

A similar pump I borrowed was an older model.

The older pump quit, then my pump quit about 30 minutes later.

Using a thermal gun, the housing on both units was in the upper 140s.

The ambient temp was 70 degrees (in my basement).

I was pulling about 21 inches.

There were some leaks I could not seal properly.

alan

 

70 F above ambient is running kinda hot there, Alan....

I had to rebuild a 40-something year old Welch two-stage rotary vane pump a few years ago after someone (not me) ran it with no oil for eight hours or so. Welch were amazingly good about getting parts, seals, etc. for this thing even though it had been out of production for two decades. I had to have two vane guide pins custom machined though.

Think about it- that was a pump from the 1950s, it saw heavy continuous use in laboratories for 30 years, then had the s*** beaten out of it in a composites shop (running continuously for 10 hours plus, sometimes running on a generator in the back of a moving trailer) for another 20 years. And only when someone ran it dry, did a seal finally fail.

Good pumps do not spontaneously fail in a matter of hours for no apparent reason. But something not meant to pull vacuum for hours on end.... well, it might not have the cooling capability needed to survive in a shop. It's not a terribly demanding task for a decent pump (nowhere near as demanding as pulling down a cyclotron or an ion chamber), but modern cheap stuff from ebay just might be a little underbuilt.