As if we didn't have enough glue threads...
I've been building high power rockets that include 3D printed parts for some time. I've migrated from rail buttons to electronics sleds to airfoiled fin edges, and am now looking at complex centering rings. Almost all of the rocket stuff I print is with PETG filament. I've been using SCIGRIP 16 for any plastic parts that need to be permanently bonded, but I decided to try some actual experiments in order to determine what adhesive to use when gluing PETG to wood/cardboard/blue tube.
I have some 6" diameter concrete forms with the wax paper removed from the inside. I designed and printed a number of PETG test pieces that are 1.125" wide and 1.5" long. The bottom .5" is curved to match the inside diameter of the concrete form.
Each of the glues was applied to the curved portion of a test piece, which was then clipped inside the top of the form, and allowed to dry for 24 hours.
My testing rig consisted of a spring type fish scale and my mark 1 eyeball staring at the KG side of the scale. I "hooked" the scale to the top of each test piece and very slowly pulled at a 90 degree angle away from the center of the tube until the piece popped off. As you can see below, the amount of force needed was pretty consistent, but other factors were not. I've noted the amount of cardboard from the inside of the tube that was removed along with each test piece, the appearance of the test piece after removal, and results from trying to manually chip the adhesive away from the plastic.
Titebond III
3- kg
The only sample where the glue separated from the plastic during removal.
Glue easily chips from plastic.
I assumed that this wouldn't work very well, and was actually surprised with how strongly it was attached. At any rate, I wouldn't recommend wood glue when attaching plastic parts.
Bob Smith CA Extra Thick
3.5 kg
Took out the most amount of tube.
Glue is very brittle and can't be chipped off plastic.
Held up to the pull test very well. As expected, the glue itself is very brittle and I think the only reason that it can't be chipped off the plastic is because it fails so easily. Not recommended.
Bob Smith 5 Minute Epoxy
3+ kg
Took out a good amount of tube.
Slower epoxy would probably soak into the tube more.
Is possible to manually chip glue clean from plastic.
I didn't want to mix up any "real" epoxy for such a small test. I assume that my US Composites stuff would soak into the cardboard much more due to the much slower cure time. I'm not sure if it would stick to the plastic any better. That being said, I've never had one of my printed fin edges (that typically get fiberglassed over) delaminate. I think real epoxy is a "pretty good" adhesive for attaching plastic to cardboard. Maybe more testing is warranted.
Gorilla Glue polyurethane adhesive
3.5 kg
I added no moisture to either surface.
This took the longest to set before the clamps could be removed.
Visible foaming squeeze out around the edges.
Tied with CA as the strongest in the pull test.
Some chipping of glue from plastic is possible around the edges, possibly due to the adhesive foaming.
Like the wood glue, I didn't expect much from this but was very surprised with the results. It stuck very well to the cardboard and the plastic. If you've ever gotten this stuff all over your hands, this shouldn't surprise you. If the adhesive itself were a little less foamy, this would be the obvious choice for me going forward. Cheap and available everywhere.
SCIGRIP 16 Acrylic Plastic Cement
2.5 kg
Took out the least amount of tube, maybe sets too fast?
Plastic visibly deformed, impossible to chip anything off.
This is my old stand-by and works kind of like plastic model cement in that it actually softens the plastic while also acting as an adhesive. This test shows that maybe it sets too quickly to actually penetrate much into the cardboard. Not what I was hoping to discover.
3D Gloop! PET
3 kg
Took out a good amount of tube.
By far the most expensive.
Like the SCIGRIP, no post separation chipping possible.
This adhesive is a good news/bad news thing. While overall it shows the most promise, with good cardboard penetration and excellent plastic adhesion, it was also BY FAR the most expensive, at $35 for a 4oz "rubber cement" type jar. At that price, I'll gladly use it while I have it, but it will be hard to justify replacing it when it's gone. Like the SCIGRIP, it's covered in warnings about all the toxic goodies it contains, which also is a minus.
Conclusions:
My previous strategy of gluing on fin edges with SCIGRIP and then fiberglassing over them still looks OK. I'll probably switch to using the Gloop until it's gone, but it will probably not be replaced. Unless it lasts a LONG time.
As far as gluing centering rings in a big cardboard rocket, it looks like epoxy is still not a bad choice. Gorilla Glue is also very interesting, especially internally where the foam doesn't detract or lead to extra cleanup. Just don't get it on your hands.
I've been building high power rockets that include 3D printed parts for some time. I've migrated from rail buttons to electronics sleds to airfoiled fin edges, and am now looking at complex centering rings. Almost all of the rocket stuff I print is with PETG filament. I've been using SCIGRIP 16 for any plastic parts that need to be permanently bonded, but I decided to try some actual experiments in order to determine what adhesive to use when gluing PETG to wood/cardboard/blue tube.
I have some 6" diameter concrete forms with the wax paper removed from the inside. I designed and printed a number of PETG test pieces that are 1.125" wide and 1.5" long. The bottom .5" is curved to match the inside diameter of the concrete form.
Each of the glues was applied to the curved portion of a test piece, which was then clipped inside the top of the form, and allowed to dry for 24 hours.
My testing rig consisted of a spring type fish scale and my mark 1 eyeball staring at the KG side of the scale. I "hooked" the scale to the top of each test piece and very slowly pulled at a 90 degree angle away from the center of the tube until the piece popped off. As you can see below, the amount of force needed was pretty consistent, but other factors were not. I've noted the amount of cardboard from the inside of the tube that was removed along with each test piece, the appearance of the test piece after removal, and results from trying to manually chip the adhesive away from the plastic.
Titebond III
3- kg
The only sample where the glue separated from the plastic during removal.
Glue easily chips from plastic.
I assumed that this wouldn't work very well, and was actually surprised with how strongly it was attached. At any rate, I wouldn't recommend wood glue when attaching plastic parts.
Bob Smith CA Extra Thick
3.5 kg
Took out the most amount of tube.
Glue is very brittle and can't be chipped off plastic.
Held up to the pull test very well. As expected, the glue itself is very brittle and I think the only reason that it can't be chipped off the plastic is because it fails so easily. Not recommended.
Bob Smith 5 Minute Epoxy
3+ kg
Took out a good amount of tube.
Slower epoxy would probably soak into the tube more.
Is possible to manually chip glue clean from plastic.
I didn't want to mix up any "real" epoxy for such a small test. I assume that my US Composites stuff would soak into the cardboard much more due to the much slower cure time. I'm not sure if it would stick to the plastic any better. That being said, I've never had one of my printed fin edges (that typically get fiberglassed over) delaminate. I think real epoxy is a "pretty good" adhesive for attaching plastic to cardboard. Maybe more testing is warranted.
Gorilla Glue polyurethane adhesive
3.5 kg
I added no moisture to either surface.
This took the longest to set before the clamps could be removed.
Visible foaming squeeze out around the edges.
Tied with CA as the strongest in the pull test.
Some chipping of glue from plastic is possible around the edges, possibly due to the adhesive foaming.
Like the wood glue, I didn't expect much from this but was very surprised with the results. It stuck very well to the cardboard and the plastic. If you've ever gotten this stuff all over your hands, this shouldn't surprise you. If the adhesive itself were a little less foamy, this would be the obvious choice for me going forward. Cheap and available everywhere.
SCIGRIP 16 Acrylic Plastic Cement
2.5 kg
Took out the least amount of tube, maybe sets too fast?
Plastic visibly deformed, impossible to chip anything off.
This is my old stand-by and works kind of like plastic model cement in that it actually softens the plastic while also acting as an adhesive. This test shows that maybe it sets too quickly to actually penetrate much into the cardboard. Not what I was hoping to discover.
3D Gloop! PET
3 kg
Took out a good amount of tube.
By far the most expensive.
Like the SCIGRIP, no post separation chipping possible.
This adhesive is a good news/bad news thing. While overall it shows the most promise, with good cardboard penetration and excellent plastic adhesion, it was also BY FAR the most expensive, at $35 for a 4oz "rubber cement" type jar. At that price, I'll gladly use it while I have it, but it will be hard to justify replacing it when it's gone. Like the SCIGRIP, it's covered in warnings about all the toxic goodies it contains, which also is a minus.
Conclusions:
My previous strategy of gluing on fin edges with SCIGRIP and then fiberglassing over them still looks OK. I'll probably switch to using the Gloop until it's gone, but it will probably not be replaced. Unless it lasts a LONG time.
As far as gluing centering rings in a big cardboard rocket, it looks like epoxy is still not a bad choice. Gorilla Glue is also very interesting, especially internally where the foam doesn't detract or lead to extra cleanup. Just don't get it on your hands.
