glue sets too fast

[DJ Delorie]

I just screwed up three glue joints in a row (body tube to coupler) because either the glue was setting WAY too fast, or the tubes were swelling and sticking. EIther way, that technique just isn't going to be usable when the replacement parts show up. Any suggestions for getting more working time, without seriously weakening the glue joint?

FYI it was yellow wood glue, which is what I usually use for this purpose.

 

[astrowolf67]

You could use some two part epoxy instead. Good strong joint, choice of working time, and doesn't shrink when it dries.

 

[Stymye]

been there , yellow glue will really grab under those cicumstances..once it squeezes thin it grabs like crazy....

white glue seems to be a little more forgiving in such cases
or even a little epoxy..annother trick is to apply the glue inside the tube(not the coupler) where it does not contact the coupler right away but rather once the coupler is mabey halfway in than just continue pushing(don't stop) till you hit the mark..the bond should still be plenty strong

I've gone to white glue or epoxy on these type of joints for this exact reason

 

[DJ Delorie]

Will epoxy swell the tube like water-based glues do?

 

[rbeckey]

Try polyurethane glue. It does not swell tubes and will never fail.
A little goes a very long way. I dampen a paper towel and wipe both parts, put a lilttle glue in the BT and slide the coupler in to the mark. It is completely cured in a humid environment in about 6 or 8 hours.

 

[DJ Delorie]

I dampen a paper towel and wipe both parts,

I think that alone would cause the tubes to stick. They're a tight fit even when dry.

 

[rbeckey]

I mean just the slightest trace of moisture. This helps poly glue set, and is not totally necessary if you can put the part outside in high humidity. The glue itself is the thickness of honey and very slippery. It will actually act as a lube during assembly.

 

[flying_silverad]

Originally posted by rbeckey
Try polyurethane glue. It does not swell tubes and will never fail.
A little goes a very long way. I dampen a paper towel and wipe both parts, put a lilttle glue in the BT and slide the coupler in to the mark. It is completely cured in a humid environment in about 6 or 8 hours.

Yep...I second this. Makes for real easy sliding and positioning.

 

[teflonrocketry1]

That's a sticky problem that can be solved with laundry detergent or soap!!!

Apply a solution of laundry detergent (Tide TM) in water over the bead of white or yellow glue placed on the inside of the tubing the coupler fits into. I use a cotton swab and just run the soapy water over the surface of the glue. This causes the glue to form a non-stick skin that makes it take longer to grab. Alternatively, you can rub the end of the coupler with bar soap or soft soap. The soft soap paints on nicely with a cotton swab; use a very thin coat, blot most of it off with a paper towel. You will have to test out this technique with the glue and soap or detergent you choose, I find some glues require more soap than others.

If you pour white glue into a detergent solution it will form globules of glue that you can actully pick up with your hands and you will see how little adhesion or grab remains after the glue has been treated this way.

I have no idea if this weakens the glue joint or not, once the two parts are in place the glue seems to soak into the materials and give a strong bond.

Bruce S. Levison, NAR #69055

 

[DynaSoar]

Originally posted by DJ Delorie
I just screwed up three glue joints in a row (body tube to coupler) because either the glue was setting WAY too fast, or the tubes were swelling and sticking. EIther way, that technique just isn't going to be usable when the replacement parts show up. Any suggestions for getting more working time, without seriously weakening the glue joint?

FYI it was yellow wood glue, which is what I usually use for this purpose.

I have that problem when I don't use enough (read: too much) glue. If it's got enough, it slides in slowly, but it slides in. Then I have to hold the tube horizontal and turn it around to keep the glue coating evenly, and rock it back and forth to run it down the tube a bit, and up onto the coupler a little, but that just makes for better structural stuff. Twisting while inserting keeps it moving. Oh, and I never coat the coupler -- just put it in the tube. Of course this only holds if it already fits dry. If it's too tight before glue, no amount will help.

 

[Fore Check]

Originally posted by DJ Delorie
Will epoxy swell the tube like water-based glues do?

No.

I really nice thing about epoxy is the fact that it doesn't. Now, if you coat the inside of a tube with epoxy, you will notice that it's "tighter" on the inside after the epoxy sets, but this is from the dried build up of epoxy, rather than a swollen tube

Have you ever installed a motor mount using white glue or wood glue and noticed a "ring" on the exterior of the body tube where the centering rings reside within? I'd call it more of a "shrink" than swelling effect - but it's definitely noticeable.

You won't see these rings if you use epoxy.

I've not tried using polyurethane glue (although I have a bottle of Gorrilla Glue on my build table, unopened.) I prefer using epoxy for couplers and motor mounts because it's nicely workable before it sets and the finished joint is "inivisible" from the outside after it sets.

 

[wwattles]

Call me ignorant, but I was under the impression that the water-based glues (white and yellow alike) both shrink as they dry, due to the fact that water is coming out of the adhesive. Polyurethanes (gorilla glue, Ultimate glue, etc) expand. Epoxies remain the same thickness, but just harden. Some epoxies may appear to shrink slightly, but that is due to a tiny amount of adhesive wicking into the surface to form the bond. CA's absorb moisture from the surfaces they bond, or from the air itself, and so don't change size much.

Am I right in my observations, or have I been looking at this all wrong?

 

[DJ Delorie]

My problem isn't shrinking when the glue dries, my problem is swelling when the wet glue hits the paper tubes. I have noticed the ring around the CRs in my models, though. Sounds like I'll try epoxy on this project, as I have eight CRs to deal with.

 

[lalligood]

Call me ignorant, but I was under the impression that the water-based glues (white and yellow alike) both shrink as they dry, due to the fact that water is coming out of the adhesive.

Correct.

Polyurethanes (gorilla glue, Ultimate glue, etc) expand.

Correct.

Epoxies remain the same thickness, but just harden. Some epoxies may appear to shrink slightly, but that is due to a tiny amount of adhesive wicking into the surface to form the bond.

Correct.

CA's absorb moisture from the surfaces they bond, or from the air itself, and so don't change size much.

Sounds good but I'm sure someone else will chime in with a more substantial answer.

HTH,

 

[rbeckey]

I would add for those who have not used both, that while white or yellow glue may shrink enough to dimple a BT, polyurethane glue does not do the opposite when it expands. For instance, used on a coupler it does not create an unsightly bulge in the BT over the glued area. Such a small amount of adhesive is trapped between the parts that it doesn't cause swelling, but does wedge things very tightly in addition to the adhesion caused by the glue itself. The expansion can cause a mess in external areas, making poly glues unsuitable for fin fillets and such. I have found it useful working with Crayon rockets for placing bulkheads into the NCs. In that situation the expansion is exactly what the doctor ordered.

 

[DJ Delorie]

Follow up...

I got the replacement BTs, and this morning glued them with West Systems 105/205 epoxy. Lots of time to work, went together smoothly, no rush...

I should have started doing that a long time ago. Thanks for the help!

 

[powderburner]

If you want to use water-based glues in the future, and you have a tight joint/assembly where you don't want to gamble on the glue 'grabbing' at the wrong time, try this:
Assemble the joint dry. Tack it in place with a few DROPS of glue. Check to make sure that everything is located where you want after the glue drops are dry. Make a small batch of watered-down glue (I mix glue:water at 1:1 or 2:1) and apply to the joint with a small brush, or an eyedropper, and let the thinned glue wick into the joint. Do not apply too much at once because the thin glue can penetrate the joint and puddle inside (where you probably don't want it).
If the joint is not quite so tight you can pre-coat the mating surfaces with glue and let dry. Assemble, position, verify, then wick a small amount of water into the joint to re-activate the glue. Finish off by applying a small amount of thin glue to wick into the joint.
Or, if you're in a hurry, skip all the water-based glue and just use epoxy.