Metal to Metal glue? Will it hold? That is the question!

So my 18 yr old and his friends built an electric car out of a little tykes car for a senior prank. Well, they tried at least, hit a bunch of snags, didn’t have the right parts, time delays and other things lead to them completing the car with steering, but couldn’t get the electrical motors to work properly so they pushed each other around the halls. Pretty amusing and funny - good to see them putting in so much time and effort on something so trivial that taught them a bunch of skills like construction, woodworking, mechanical engineering, electrical engineering and fabrication. My son has now decided to major in electrical engineering in college mostly because of this project and his friends who are also doing some kind of engineering. Cool!

They’re finally in the home stretch after figuring out the electrical setup between the monster battery and multiple motors along with the switching and throttle (pretty fun to watch them do this, although playing with capacitors and big batteries freaked me out - they were extremely cautious and employed various friends with backgrounds in this kind of stuff - I learned a lot from them!) and now they’re doing power transfer from the motor to the gearing on the wheels.

They want to mount the final gear onto the wheel and are stuck with how to do it. A VERY simple way and probably the strongest way is to simply weld the metal gear onto the housing of the wheel and subsequent shaft to spin the wheel with the gearing off of the motor. But of course we don’t have a welder (I’m a woodworker, not a metal worker) I can’t justify buying a small welder (Harbor Freight has decent ones for $200) and even though I keep coaching them to find someone or a shop with a welder that they can have someone lay down a bead of weld which would probably take 30 seconds per wheel, they think they can use some other methodology to attach.

Far be it for me to say “that won’t work” even though I’ve said that a lot, I have to hand it to them in that they are REALLY trying all manner of things to get a gear to bond to a metal shaft. They asked me about gluing it and I said no way would a glue bond hold up to the torque of the motor on the shaft - but then again it might? We’re not talking a drag racer here, it’s a little tykes car with a relatively small motor (the 2 motors are about the side of soda cans).

So the question, after all of this back story, is would something like a JB Weld or a metal epoxy hold? I’m sure it would hold the piece in place, what I’m curious about is would it actually hold under torque. I tell them to just try it and see - why not. They want to drill out things in metal on my beautiful drill press that’s built for WW’ing, not metal work (all of that lubricant on my fancy jigs and drill press table!?!?!). So would it hold? Anyone ever try something like this?

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Not my own experience, but from folks who play it seems that J-B Weld Steel Reinforced Epoxy might totally be up to the job:

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That JB weld epoxy will work, just clean the surfaces thoroughly with something like acetone before you apply it.

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Ok - trying the JB Weld Epoxy - will let you know how it goes!

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Oh and like any glue, roughing up the surface tends to help.

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Not an engineer so take this next idea with a grain of salt.

Can they add something mechanical to take the force of the torque. Like a key slot? That way the force is not all on the epoxy.

https://i0.wp.com/www.engineeringchoice.com/wp-content/uploads/2021/01/Shaft-key-and-keyway.png?fit=450%2C221&ssl=1

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I saw a video a while back, where a guy tested different Epoxies by gluing the head down on a small 1 cylinder gas engine (like lawn mower sized). He use the head’s bolts to clamp it together while the epoxy set, and then he removed the bolts and started the engine. Unsurprisingly, Epoxy did not do well in this evaluation. Though it’d last a few cycles before coming unstuck.

I wouldn’t expect Epoxy to do that well in this Kart use case. But if you are going to try, slather it on. The more the merrier.

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Ultimately the metal surface will be the key weakness, but matching holes with metal screw threads breaking the split plain would go a long way to breaking that up. The mechanical equivalent is freezing a couple of hamburgers together, though the goal is letting it break along the line rather than making it not do so. The more breaks to the plane perpendicular to the forces the more it will resist, so a grinder mark perpendicular to the forces should have the strongest hold even before the bond or strength of the epoxy is figured in.
:slightly_smiling_face:

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That was my suggestion as well. Unfortunetly the way the hub of the wheel meets where the motor will be there’s no way to pin it.

And honestly, I could solve this pretty easily if I wanted to by stepping in and fabricating something myself, but I want them to solve. They had the idea for the JB Weld, so I’ll “encourage” them in that direction.

Thanks all!!

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Just make sure that when the Epoxy bond fails, parts won’t fly off and injure anyone…

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I think max speed for this will be 5-8 MPH although torque might be an issue. I’ll suggest a shrowd over the drive train.

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JB is just epoxy with color/particles to make it look solid.

If the parts are a good fit, loctite is the solution. Green is pretty much permanent. It is used to attach gears to shafts.

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Check out

This to That

Please do post images or a video of the project.

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I love that page - that’s where I got the answer to search in YouTube for!

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there may be a welder who could do it for them for a small fee. check out craigslist in your area.

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Will do if the boys let me!

If you can heat it, Phos-copper melts quite low, and with further heating the phosphorus leaves and there is only copper. There is also some weird stuff that can braze Aluminum to other metals though it is hard to work with.

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