Vacuum Switch setting for cut-out

I’ve got a question for the Vacuum Baggers out there. I’m adding an adjustable cut-out switch and relay to my system for my next steps in bagging. When I was bagging the bulkheads I had a problem of sucking them to dry. The pieces where bagged to a table a combination of to good of a seal and a strong pump. I had to use an alternative method that works well enough for the bulkhead pieces.

So here is my question if you use a cut-out on your systems what PSI do you set it at? I’ll be using West System Epoxy on basically 2 layers of 200 gram uni carbon cloth / 1 layer of 6 oz Eglass uni - so a thin layup.

My reading so far on this topic has indicated a setting of 14.7 PSI and I’m looking for some real world input on the setting. I’ll run some test panels, but I’m looking to see what others have found --- Jake?

When I did the inside of the hulls I was not able to achieve the “perfect” seal on the bag when it was in the jig so it was not an issue. But doing the outside of the hulls I am afraid I will get a much better seal.

Looking forward to your input……

Mike

Personally, I feel that the more vacuum, the better. You get a higher fiber to resin ratio and better strength. I go for max vacuum I can achieve without my pump running 100% of the time. When I need a good finish, I usually brush in a layer of epoxy (or polyester) on the mold first and let it gel in the open to "pretty stiff but still a little tacky". then I lay in the fiber and resin, then vacuum bag. I get a really nice finish that way. You might also try to use some carbon or glass "veil" fabric - it's an extremely fine random woven fabric to help relieve the fabric print-through you get with all these advanced processes and it keeps the pinholes from showing through so bad on the exterior (but you don't get a clean carbon weave pattern).

Even the resin infusion process, where the amount of resin is dictated by the amount of fibers, will leave voids between the fibers and the mold surface (or gelcoat). I infused a 1 meter R/C sailboat and it had pinholes in the glass from the voids (I had to paint it to make it water tight). My Nacra infusion has voids between the gelcoat and the woven glass fabric from that process...but it had an outer layer of gelcoat sprayed and gelled to the mold before the fibers were laid in and vacuum infused so the exterior looks fine (other than the crappy mold surface).

I don't know that the voids take away much strength from the lamination - so i don't worry about them unless I need a really nice exterior finish.

Mike,
I'm building an F85SR with all possible work done using a vacuum. I've put some info and pics in another forum on this sie.
Farrier suggests no greater than 22 inches of mercury, That would be around 10.8psi.

I've used a lot of west system in the past in non vacuum jobs but due to an ever worsening allergy to West I'm using Gurit (SP Systems) Resin for the F85SR.
They provide data sheets that clearly specify the earliest and latest turn on time as well as the earliest turn off time and even earliest demould time for a given hardener (fast, standard, slow and extra slow) and ambient temperature. By keeping to the appropriate Vacuum window I can pull as much vacuum as I like without starving the laminate of resin. So I aim at a the max. It may pay to see is West publish similar data sheets.

Otherwise if I were you I'd do a test run at 10.8psi and see how that goes. Farrier is unbelievably thorough I think you will find that spot on.

Regards,
Phill

Your problem probably is not too much vacuum. It more likely has much more to do with your bagging schedule (peel/bleed/barrier/breathe, etc). You mostly have to figure out where the resin that you want in the part is going - then stop it from going there.

I build skis and snowboards. I made a similar mistake once by confusing the roles of the bleed ply and the breathe ply. Many of the books out there blur these definitions, and many use them interchangeably. On that fateful day I laid up a board covered it with peel ply, Breathe ply, and bagged it. The breathe ply ended up good and rigid. The board was really light as the resin all ended up in the breathe. Doh. Board broke immediately.

Questions. Did you use a barrier ply and a breathe? Where did the resin end up? In the hose?

More information will help.

Good luck, Carl

The resin ended up in the Breather ply.

Guys
When I had the problem my gauge was pegged out at 30 inches of vacuum, no telling what the real vacuum was, and the pump did not have a cut-out so it was a constant pull before I caught the problem. The epoxy had already kicked so damage done. The panels well they were light but looked starved. Kind of what Jake said but very extreme (it had the appearance of a fiber glass cast). The next day after it was dry I grabbed the lay-up and peeled it right off the foam.

Good Input Thanks!

First I will actually answer your question.

For West slow cure epoxy at 70-85F

For small projects using thin layups, roughly 120 gram/m2 of carbon and glass. I set the cutoff on my Gast pump at 20-24 in of Hg as marked on my gauge.

For large layups, I normally adjust the pump to give me 10-15 in of Hg at the mold.

If it really important or I have the time, I pump the setup down with dry cloth as a test. This gives my some practice, checks for screw-ups and lets me see how the cloth lays. A couple of times I found big wrinkles.

Theory and FYI

From what I know on the subject, the resin supplier gives you minimum pressures for a temperature range. If you go below that you can have problems. It has been years but I remember the experts talking about wicking, wetting, boiling and viscosity.

The pressures the resin suppliers give you are normally at the mold.

A lot of what you see and hear on the internet is what someone knows works for them. It is specific to their methods and setups

Thanks for all the information!

I just spoke to West System to find out what they recommend and do in their shop. They recommend maximum vacuum up to 24 inches to make sure all the air is out and control the resin by the size and amount of holes in the bleeder cloth. The technical person went on to tell me of the $40 dollar clip board exercise they do in the boat building school that demonstrated the effectiveness of the types of bleeder cloth.

So what I’ve learned so far seems to be a formula that takes into account the size/type of lay-up, ambient conditions, mix of epoxy, amount of vacuum, and the size of the bleeder holes.

Good info! I guess I need to keep reminding myself that even 24 inches of mercury of vacuum results is still over 1,500lbs of pressure on a 1 square foot surface.

Average sea level pressure is 29.6 inches of mercury...which is the most vacuum you could achieve. I don't know how much that varies with weather systems (probably not much).

I also want to experiment with a set formula by weight of the amount of resin vs. the weight of fibers so I could possibly do away with the bleeder ply (for the most part). At least for small parts, I think you can still extract the vapors from the laminate with vacuum contact around the edge perimeter.

Last thought, when bonding to foam, I first squeegie in a thickened layer of epoxy and filler (microballoons) to fill in all the little pockets of the foam. I then lay the glass and resin on that. You get a much better bond that way and the thickened resin doesn't pull through with the vacuum (much).

Jake let us know how the experiment works out. I was not using bleeder cloth on the larger lay-up, but it looks like on a smaller lay-up you need to play with pressure or use bleeder cloth. I use thickened epoxy in my lay-up on the direction of my NA by adding a slight amount of filler to my epoxy and buttering up the foam first also.

I guess it is always good to step back and re-think our process especially when there are large amounts of time and cash involved.

Time to make test panels after I build my new vacuum pump system.

Just to share my feeling of being outdated:

A couple of years ago I had a chance to ask an expert why the new composites were so much lighter and stronger than what was being produced in the past. She said "in the old days they talked about vacuum in terms of in of Hg". She said a lot of other things but I lost a lot of interest after the in of Hg comment.

Well, yeah...the in of Hg now is just what you put on the laminate before it goes into the heated and pressurized autoclave where those inches of Hg multiply significantly....but...I'm probably not investing in an autoclave anytime soon.

Can't you just make one? You can make anything else.

Joking aside I actually saw a homemade one!
I should have grabbed it - it was junked when he finished his mast and boat. I got the hull mold. It was made to do a carbon fiber mast.

In Maryland maybe?

Kevin Cooke had one in his backyard that he used to make carbon masts with.

Just takes a steel pipe, a way to heat the interior, a way to connect the vacuum tubes through the exterior, an internal heater, and a door (can be threaded). Believe me, I've tossed around a few ideas...but I'm reaching the point in my life where something things are simply worth paying someone else for.

welcome to middle aged, married life.

Add kids and/or high-maintenance pets (like Timbo's horses) to that equation and you've got the "I have to pay someone to do it because I don't have the time"

Oh...I have that syndrome. A heavy daytime sales job, a home business on the up, and garage (and new 2nd story office space) under construction combined with a little too much of "do it myself" syndrome....

Time and no money.
Money and no time.
Hard to have both.

Interesting discussion. I always bag to the limit of my system, which is 17 in of Hg. I don't use real breather cloth any more; for the layups I am doing, paper towels generally get the job done. The key is in how you apply the epoxy. Typically my layup schedule is so dry to begin with-I wet-out cloth, bag with paper towels to remove excess, then proceed with the rest of the layup, place peel ply and 2 layers of paper towels down. The key is not removing too much epoxy from carbon, which is tough as carbon looks nearly the same wet or dry. Another issue is saturating the foam/plywood in the layup, which you really don't want as that is just adding weight without adding strength. Higher density foams (I'm using Rohacell IGF31, for boat work IG 71 is the ticket) aide in this.

Of course, I'm working on such razor thin margins that West Systems is useless to me, as the viscosity is too high. I prefer Resin Research Composite Pro Systems, as it is less expensive, has equal or better material properties, and has lower viscosity. For really weight critical applications, I'm using Pro-Set or MGS. http://www.rcgroups.com/forums/showthread.php?t=1546707

I've been layed up for a few days. Along with the house, bills, jobs, kids are gone now, dog and horse are old - but now you got the old body to deal with - in my case too many of the I treated my body like a tent while acting like superman years.

Yep it was Kevin that had the oven.

Paper towels may work for a RC size job but not a 20 footer.

Truer words were never spoken.

Yes, in general I agree, but for smaller items like bulkheads, give the paper towel method a shot.