I’m building an M1780NT. The instructions include Grain Bonding Instructions and suggest using a low-foaming polyurethane-based adhesive like Elmer’s Glue-All Max. I can’t find that glue locally. I have Gorilla glue, which is polyurethane-based. Can I use that or should I wait until I can get some Elmer’s delivered? Any tips for bonding the grains to the liner without making a mess or otherwise ruining an expensive motor?
Bonding grains to liner
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Cameron Anderson
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There is debate about which is best.
Elmer's glue all is the only glue Aerotech recommends.
CTI is indifferent with regards to glue all and Gorilla - either is fine.
I'd play it safe and wait if for no other reason than to preserve your warrantee. And whatever you do, NEVER substitute epoxy for either.
For bonding, have a friend help...one person gloved up handling the gluing and another without gloves assisting. You can do it all yourself but a second set of hands makes it way easier.
Elmer's glue all is the only glue Aerotech recommends.
CTI is indifferent with regards to glue all and Gorilla - either is fine.
I'd play it safe and wait if for no other reason than to preserve your warrantee. And whatever you do, NEVER substitute epoxy for either.
For bonding, have a friend help...one person gloved up handling the gluing and another without gloves assisting. You can do it all yourself but a second set of hands makes it way easier.
heada
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I've never used a polyurethane glue to bond grains, just epoxy (Loki's method). In woodworking, I've used several polyurethane glues for various projects. I don't like the foaming you get from Gorilla glue and Elmer's just doesn't seem to bond as well. The one that I seem to always go back to when needing a polyurethane glue to Loctite PL Premium.
https://www.lowes.com/pd/LOCTITE-Pl...esive-Actual-Net-Contents-10-Fl-Oz/1000862148
I use it anytime I'm bonding something that will be exposed to the weather (picnic table and benches, garden gate, front door to a house, etc.) At $5 for a 10oz tube, its pretty cheap too. Give AT a call and ask them what options you have.
https://www.lowes.com/pd/LOCTITE-Pl...esive-Actual-Net-Contents-10-Fl-Oz/1000862148
I use it anytime I'm bonding something that will be exposed to the weather (picnic table and benches, garden gate, front door to a house, etc.) At $5 for a 10oz tube, its pretty cheap too. Give AT a call and ask them what options you have.
It looks like the downtown SLC Ace Hardware (612 E 400 S) has some in stock, if you can trust their web site.
Very confused on this- the instructions I've seen for the M1780NT do not have anything on grain bonding?
https://www.aerotech-rocketry.com/u...4805-b6c7-85cfa48ad071_75_5120nt_in_20088.pdf
I flew this motor as my L3 2 years ago, and didn't bond any grains (nor did I see anything in the instructions about it).
https://www.aerotech-rocketry.com/u...4805-b6c7-85cfa48ad071_75_5120nt_in_20088.pdf
I flew this motor as my L3 2 years ago, and didn't bond any grains (nor did I see anything in the instructions about it).
Rocketjunkie
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You can use epoxy but you must prepare the liner to remove the silicone release. Wash the inside of the liner with acetone, MEK, toluene, or similar solvent. Then sand the inside of the liner with coarse sandpaper. If you don't get the release off the inside of the tube, epoxy will not stick. Polyurethane glues will stick even if you don't remove the release compound.
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now that is one good piece of information!
quoted for importance as i would never have done this
Aerotech included a separate sheet on the bonding. Apparently it's fairly recent.
https://www.aerotech-rocketry.com/u...201d9280_Grain Bonding Instructions Small.pdf
Thanks, Clair. I'll try that on my way home from work tonight.
There is a useful You Tube video on the bonding process. He uses Gorilla Glue.
https://www.google.com/url?sa=t&rct...=c1xjJTUl-v4&usg=AOvVaw1B1ugcNJe4I-hHxWzYObK4
https://www.google.com/url?sa=t&rct...=c1xjJTUl-v4&usg=AOvVaw1B1ugcNJe4I-hHxWzYObK4
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The 10/20/16 Product Notice has a list of the motors affected by the 75 & 98mm RMS™ Reload Kit Grain Bonding Advisory:
https://www.aerotech-rocketry.com/news.aspx?y=2016
Looks like the instructions you linked above pre-date that information. But it was retroactive on several loads that we had always flown without bonding (and without incident, fortunately). But yeah, it could make a guy wonder whether you have to first scour the Web to make sure you've got all the info you need.
Rocketjunkie
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They will still work without bonding. Unless they are used in high acceleration flights such as minimum diameter rockets, sustainer or booster. It won't hurt to bond the grains in all flights but will improve reliability in high acceleration flights. It keeps the grains from sliding down and choking the core against the nozzle. (Actually, you can get the benefits by just bonding the bottom grain. Been doing this on research motors since 1995.)
What I am going to mention only applies to the two-part glues that are used on the bigger motors. You may find something useful for the smaller motors and/or those bonded with the PU style glues.
Be very cautious in hot weather. I tried to glue an O3400 a few years back and made a few mistakes. Only got three of the six grains in before the glue went off
. I was able to recover the motor, but the flight (my L3 cert) was scrubbed for that weekend.
My recommendations:
Have at least one helper available.
Have a nice piece of broom handle, or similar dowel, on hand to help push the grains home.
Work quickly.
Mix only half of the glue at a time, and bond as many grains with each batch as you can. Don't skimp on the glue though!
You can chill your grains in the fridge beforehand if it is very hot.
Working in a nice cool environment rather than in the sun on the field helps greatly with stress levels.
I just grab a handful of the glue and smear it on the grains as quickly as possible and then insert and push the grain home. Step and repeat. Keep careful note of which grain end surfaces do or don't need glue.
The glue goes off very quickly in the heat. Mixing only half a batch reduces heat buildup from the exothermic mix of glue components and buys you some extra time. Having a second batch (since we halved it earlier on) is invaluable if it does go off. Quite often only half the glue is needed for the job, leaving the other half to help someone else if they stuff up!
I guess these hints become more necessary as the motor size goes up. The smaller motors should be a lot easier.
Be very cautious in hot weather. I tried to glue an O3400 a few years back and made a few mistakes. Only got three of the six grains in before the glue went off
. I was able to recover the motor, but the flight (my L3 cert) was scrubbed for that weekend.My recommendations:
Have at least one helper available.
Have a nice piece of broom handle, or similar dowel, on hand to help push the grains home.
Work quickly.
Mix only half of the glue at a time, and bond as many grains with each batch as you can. Don't skimp on the glue though!
You can chill your grains in the fridge beforehand if it is very hot.
Working in a nice cool environment rather than in the sun on the field helps greatly with stress levels
.I just grab a handful of the glue and smear it on the grains as quickly as possible and then insert and push the grain home. Step and repeat. Keep careful note of which grain end surfaces do or don't need glue.
The glue goes off very quickly in the heat. Mixing only half a batch reduces heat buildup from the exothermic mix of glue components and buys you some extra time. Having a second batch (since we halved it earlier on) is invaluable if it does go off. Quite often only half the glue is needed for the job, leaving the other half to help someone else if they stuff up!
I guess these hints become more necessary as the motor size goes up. The smaller motors should be a lot easier.
Interesting. I've helped/used epoxy on many motors, from the Loki's up to 6" P motors going past Mach 2, and we've never cleaned the liner tube other than a cursory wipedown. Never had an issue with grains not bonding to the liner. I don't think I've ever heard that from anyone else either. I'm sure it can't hurt but at least in my experience I haven't found it necessary. I only mention it because I try to limit my exposure to solvents, especially something as nasty as toluene, as much as possible.
Tony
gldknght
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Using hot solvents like MEK or toluene absolutely require the use of gloves and a very well ventilated space. Doing the cleaning outside in the shade is a good idea.
Also, test your gloves with a few drops of whatever solvent you use, before putting them on your hands, to make sure the glove doesn't melt in the solvent.
JDcluster
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I usually take a flap wheel with an extension and buzz the inside to rough up the surface. I use BSI 30 min. It works on everything I've flown: 38 mm x 8 grain J's to 98 mm M's
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I just ordered another Almer's Glue-All Max just for that explicit purpose.
Gary Rosenfield covered this very subject in his talk at about 22 minute mark:
Please be careful with, and avoid Epoxy for, bonding certain AT grains. 1780NT is one of those.
Please refer to the above video, 23 minute 25 second mark, for reasons why.
Unfortunately, that is not the failure mode to guard against.
The issue with epoxy is that it does not expand and fails to fill in all the air pockets. Please see Gary's talk above.
Almer's Glue-All Max can be had for under $10.
Substituting for it with some other glue is a false economy.
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I prefer to put the glue where I want it and NOT use glues that expand and move to places I don't want it.....
I'd be curious: What air pockets are you filling? How are NOT filling the "air pocket" between grains?
JimJarvis50
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Gluing motors with spacers is difficult because you have to move all of the grains each time you insert a grain. If they start to tighten up, you can lose the motor. One thing that I do is to glue the spacer to the grain in advance. I use a thin bead of epoxy - just enough to keep the spacer from coming off when the grain gets pushed in. Then, I wrap the grain in mylar so that the spacer is entirely within the perimeter of the grain. Then, each grain can be pushed to the end of the tube. It makes the gluing process a snap.
Jim
Jim
rharshberger
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Neat trick Jim!
JimJarvis50
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Thanks.
Back when I started making these motors, the CTI instructions said to dampen the grains. If you did that, and used the Gorilla glue, it became impossible to assemble the motor fast enough to beat the glue. That step has since been removed from the instructions. But, I highly recommend my little trick because it makes it much less stressful to put a motor together.
Jim
