![]() |
If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
![]()
Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small strips (1/4" or so) seem to want to seperate. Is this common or did I mix the epoxy wrong? The big parts are staying together, the fiberglass itself is staying to gether but the small parts are seperating from the foam. Lou |
#2
|
|||
|
|||
![]()
Could be a number of things. The smaller the part, the less bonding
area there is to hold everything together and the easier it might be for separation to occur. If the small parts and large parts are bonded the same, the strength shouldn't change. Looks like the mechanical application AFTER the bonding has occurred is causing the separtation, not the bonding technique specifically. Using a wrong bandsaw blade could also aggravate the problem, and using this technique might not be the best route anyway. For flight structures, I always used a dremel with a cutoff disc or saw blade to make the final cuts needed. Makes a much cleaner cut than a bandsaw blade and no separation between the foam and fiberglass. Hope this helps Neal Lou wrote: Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on both sides. When I cut the pieces to shape with my band saw, small strips (1/4" or so) seem to want to seperate. Is this common or did I mix the epoxy wrong? The big parts are staying together, the fiberglass itself is staying to gether but the small parts are seperating from the foam. Lou |
#3
|
|||
|
|||
![]()
It sounds like you didn't prime the foam with resin before aplying the
fabric in the layup process. A common failure in Boats when corners are cut on the layup process. Lou wrote: Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on both sides. When I cut the pieces to shape with my band saw, small strips (1/4" or so) seem to want to seperate. Is this common or did I mix the epoxy wrong? The big parts are staying together, the fiberglass itself is staying to gether but the small parts are seperating from the foam. Lou |
#4
|
|||
|
|||
![]()
Actually I did prime the foam first.
Lou |
#5
|
|||
|
|||
![]()
On 24 Sep 2006 02:28:05 -0700, "Lou" wrote:
Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on both sides. When I cut the pieces to shape with my band saw, small strips (1/4" or so) seem to want to seperate. Is this common or did I mix the epoxy wrong? The big parts are staying together, the fiberglass itself is staying to gether but the small parts are seperating from the foam. Lou I'm going to need to make some assumptions, so I'll start by assuming that you are using epoxy such as the West System and that the foam is the blue building material trade named Styrofoam. I'd suggest staying away from the white foam or bead board which isn't nearly as strong. Another assumption is substituting the word seal for prime. Typically the foam is "sealed' with either a layer of epoxy, resin, or microsphere or Q-cell mix (microspheres are mixed with the epoxy or resin to reduce the weight, fill voids, and still give a good bond.) Usually the microsphere mix works better than straight epoxy for sealing the foam, but follow the directions for what ever you are working on. So... based on the above... I'll start out by saying I believe what you are seeing is normal. I'll also note that small sandwiches of fiberglass and foam are no where near as strong as pieces with larger areas. I rarely see a sandwich made smaller than one inch and then there are flanges of 3/4" to nearly 3" depending on the use. The only pieces I've seen that didn't have a flange when they were created were control surface ribs and bulkheads. As far as cutting sandwiches, I cut oversize and sand to shape. As Neal said, using the Dremel cut off rather than a band saw is a good idea as are patience and a good dust mask. (not one of the little fiber ones either) NOTE the pages pointed to by the links below are relatively large with lots of relatively small photos. A few of the photos in the builder's diary link to larger versions. I'm using Vinyl Ester Resin, but other than viscosity and cure time epoxy is going to work much the same. Control surface rib construction shown a bit over half way down on the following page http://www.rogerhalstead.com/G3_file.../glasair12.htm Bulk head construction is shown about half way down the following page with the bonding in place a bit farther down. http://www.rogerhalstead.com/G3_file.../glasair10.htm I'm guessing this problem is pretty much a function of size. Small sandwiches with open edges are not strong until they have been bonded into place. Both the ribs and bulkheads shown above are very fragile until bonded into place and this foam is much stronger than the blue Styrofoam (TM) Follow the instructions on what ever you are building and good luck. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
#6
|
|||
|
|||
![]() Lou wrote: Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on both sides. When I cut the pieces to shape with my band saw, small strips (1/4" or so) seem to want to seperate. Is this common or did I mix the epoxy wrong? The big parts are staying together, the fiberglass itself is staying to gether but the small parts are seperating from the foam. Lou I have made a substantial number of parts using 1/4 inch foam as the core material and have never experienced any problems with peeling. I have cut the parts with a band saw as well as the dremel and never had any problems with separation. I believe the key issue is use of the right foam core material and preparation. The foam must contain openings for the microepoxy to penetrate. I spread on the microepoxy mix and pressed it into the foam followed by the wet glass. That was covered by pealply and where possible a layer of plastic and weight. So far, I have never had any problems with this method. |
#7
|
|||
|
|||
![]()
Is it separating on both sides or just the bottom? If just the bottom
Maybe you just need a smaller insert in your table or a sacraficial backer board and maybe a fine toothed blade |
#8
|
|||
|
|||
![]()
Roger (K8RI) wrote:
Both the ribs and bulkheads shown above are very fragile until bonded into place and this foam is much stronger than the blue Styrofoam (TM) Follow the instructions on what ever you are building and good luck. If you're using the blue stryrofoam, rough it up good with sandpaper before priming it. It comes with a very smooth finish from the factory, and there's nothing for the epoxy to grab hold of. It holds much better if you sand off all the shiny until the surface has the texture of good suede leather. If you're building a smaller part that needs just a little more stiffness, try getting a bundle of the fan folded 1/4" foam. It will split down the middle and has a paper like film between the front and back halves. Get it to splitting in the corner and you can slide your hand through it in karate chop fashion to split them apart. Hold one half up to the light, and you'll notice hundreds of pinholes. Keep the expoxy/micro mix thin, and it will run through the holes. When you do your layup, the two sides will be locked together with hundreds of epoxy pins going through the foam. I did some tests of a sample of this vs straight layups of various thickness and compositions. Overall, the 1/8" foam sample came out at only 60% of the weight and 50% stiffer. Trying to tear it apart around a headlight portal, where I needed to remove the foam layer, had me convinced that this was solid stuff (I also got to create a few new words...but children might be reading). You won't be able to do it with out a pair of pliers. |
Thread Tools | |
Display Modes | |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Fiberglass vs. Fabric | Lou | Home Built | 35 | July 6th 06 05:08 PM |
Fiberglass / Mold release advice requested | Mark Zivley | Home Built | 10 | April 2nd 04 11:15 PM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart Hull | Home Built | 1 | November 24th 03 02:46 PM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart Hull | Home Built | 0 | November 24th 03 03:52 AM |
Fiberglass Tip Tanks Question | Jay Honeck | Owning | 7 | September 26th 03 04:23 AM |