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Sep 20, 2001, 06:41 PM
York Electronics
Gary Warner's Avatar

What type of gule for foam blocks and sanding?


I used Sorgum contact cement for my latest white foam (1.5 pound per sq. ft.) fuselage. Sanding across the glue lines has resulted in "bumps" that are hard to get rid of. Too late for this plane, so I was wanting to know what works best. Assembly was very fast using the contact glue and I thought I was onto something - not. White glue? Epoxy? Nothing?
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Sep 20, 2001, 08:17 PM
Scott Black, Montreal
sblack's Avatar

Re: What type of gule for foam blocks and sanding?


Sorgum is a rubbery glue. There are other contact cements available and some are water based. Years ago I used 3M 30-Bond. The local hardware store should have something.

If you can figure out where the outer surface of the finished fuse will be and can keep glue away from it then that is your best bet. Then you can use anything. Is this for a lost-foam fuselage? Or some other method where the foam in the middle is removed making glue weight a non-issue? If so then the fastest method is 5 minute epoxy.

But if you aren't removing the foam in the middle you have to be careful. It gets heavy so you have to go easy on it. And you certainly don't want to be sanding it so you have to keep it away from the surface.

If the glue joint is very near the surface so that air can get to it then you can use white glue. If air can't get to it it will never cure.

sb
Sep 20, 2001, 09:25 PM
Registered User

Foam and glue


I think a very suitable, very sandable glue that doesn't need air to set is polyurethane glue, from various sources. It seems expensive, but it goes a long way, and if handled appropriately, i.e., follow the instructions on the bottle, it would work very well indeed, and it is extremely sandable. I have used it in vacuumbagging balsa skins onto white foam cores, and for a variety of construction involving foam like setting landing gear blocks in a foam wing. I think using it to join blocks would be a wonderful use for the stuff. One warning, its foaming/expanding feature, highly desirable in joining rough foam block ends to each other, is relentless. I have seen it shove landing gear blocks completely out of their slots in a wing. so a little goes a long way, and anything joined needs to be jigged/clamped until the glue sets overnight. And it does set, not dry, so that blind areas like between foam blocks get to completely cure without the assistance of air.
Sep 20, 2001, 10:05 PM
Registered User
I have not tried this yet, but I have heard of using light weight spackle,as a bonding glue for foam.
Sep 20, 2001, 11:26 PM
York Electronics
Gary Warner's Avatar
Thanks for the good ideas guys.

Peter, do you know what trade name that poly gule is sold under and where I might find some?

The light weight spackling sounds good too. The spackling I'm using would be good for this and sands easy.

It does sound as though all of this could have been avoided if I'd just use some forethought and didn't use the glue where I'd be sanding - but heck, I'd have to actualy "plan out" these models. Where's the fun in that

Here's some pix's taken in the last week. Started the plane a week ago and hope to fly it at the DEAF event next month. It's a stand-way-off scale of a Lear/Gulfstream/what-ever. Will use two Grop 600 fans, 14 cells, 5.5 pounds and Spring Air 600 retracts. Testing of fans shows 3 pounds total of thrust at 35 amps. Heck, it might even fly well!!!



Gary
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Last edited by Gary Warner; Sep 21, 2001 at 01:28 PM.
Sep 20, 2001, 11:27 PM
dusty bible = dirty life
Majortomski's Avatar
Ironically I did a search earlier tonight over on the foamies list and came up witn elmers PROBOND or something called Gorilla glue as the preferred stickem over there

Tom S
Sep 20, 2001, 11:56 PM
Registered User

peeper


Gary, the polyurethane glue that I have been using is Elmer's Probond POLYURETHANE glue. Emphasis intentional. The manufacturer also sells a 'Probond' aliphatic resin glue in very similar bottles, it is very easy to confuse the two. Just because it comes out of a bottle, do not mistake this stuff for air-drying aliphatics or white glues. Its properties are substantially different, and the techniques to take advantage of those properties are quite different from those for the water-based glues. I think it's quite magical stuff. So far I've been using it to put on wing skins and to set hidden bits (l/g arrays) into foam wings. I originally used it to build a new bookcase for some of my wife's books, and it made a strong and immediate impression on me. What's really unusual is its tendency to foam up, easily controlled with the vacuum bag, but that characteristic gets it to attain completely-wetted glue ares between two irregular surfaces. And it sands like spackle.....(anything I sand is in the open, so its foaming habits are uncontrolled at that location). Experiment with it a bit before committing it to your project. Good luck.
Sep 21, 2001, 02:39 PM
Lithium Member
Herb's Avatar
I agree about the magic qualities of Probond Polyurethane glue. By now it has become a major fraction of the glue joints in my recent projects, due to its superior adhesive abilities (even to hands!!) and it's lightness compared to epoxy . It is a very good epoxy replacement when the joints aren't perfect - and it's a lot lighter. For high stress joints - like formers to fuse - I have mixed it with chopped carbon fibers, like in my <A href=http://aeneas.ps.uci.edu/edf/mig15/p8300053.jpg> MiG </A>

One drawback is that it takes about 4 hrs to cure, so you need to hold the parts in place for a while - and prevent any foaming into unwanted areas, using for ex transparent tape - so you can see what's happening underneath! At the same time the slow cure allows the parts to be placed/arranged precisely.

I have used it for skinning wings as well, since its tendency to fill any gaps again is quite desirable.

Probond Polyurethane sands a lot better than epoxy, but of course not quite as well as a lightweight filler. So it's best to prevent it from spilling into unwanted areas.

For gluing foam together, it's perfect. But it has to be used very sparingly if you are joining well matches smooth surfaces... This <A href=http://aeneas.ps.uci.edu/edf/su31/p1200005.jpg> little foam toy </A> was glued together with probond only, and it's still going strong after a lot of flights.

This <A href=http://aeneas.ps.uci.edu/edf/fa18/p9180014.jpg> latest project </A> was put together almost exclusively using Probond polyurethane - almost no CA and no epoxy, just a bit of elmer's alipahtic here and there. The airframe is light and yet quite strong due to the gap filling properties of Probond...
Last edited by Herb; Sep 21, 2001 at 08:05 PM.
Sep 21, 2001, 03:09 PM
p471701
p471701
Guest
herb: the hornet looks great! flying it this weekend?...........gregg
Sep 21, 2001, 03:35 PM
Lithium Member
Herb's Avatar
Flying? Who mentioned anything about flying it ? My wife said "make sure you take a pic of it from every angle before you commit it to the bungee"...
Sep 21, 2001, 03:52 PM
p471701
p471701
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it will go smoothly with a 2wire landing!......................gregg


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