Bit of an engineering question: Working with a threaded metal rod as an axle?

[DR4296]

Greetings All!

So, as a part of this year's Halloween costume, I've been working on a sort of "hand-held gatling gun". (Actually, it's basically the character's HAND / an extension of his arm.)

I'd been using a couple of Youtube vids as my guide. As of last week, I had built this:

Of course, even as I was putting this together, I was telling myself it was way too long. And rather heavy too.
As you can see, I was using a metal L-bracket to support it. Now, it turns out, the motor I was going to used to drive this was way under-powered / not enough torque.

So I changed plans and decided to circle back around to using a cordless screwdriver to power this. I'd been avoiding it, because I'd tried researching how to get a cordless screwdriver to attach to a threaded metal rod and had come up empty. However, this time around, I got an idea: I bought a hexagonal "coupler nut" that would fit the rod...and then I bought a socket for the drill that would fit the coupler nut nicely.

However, what I'm struggling with is this: On the one hand, I need that L-bracket (or something similar) to support the entire gun barrel assembly. So, it seems like that means I need to tighten my nuts and washers on both sides of that L-bracket. But on the other hand, if I tighten them TOO much, the metal rod won't spin!!

I'm not sure what people do in situations like this. The Youtube vids don't seem to apply. And I certainly am not a workshop / tool kind of guy, in terms of my upbringing, training and experience.

Here's a photo I just took a few minutes ago, with the coupler nut on there, as I was thinking about how I might shrink down this assembly. (I'd shorten the barrels that you see here. I'd probably totally overhaul this "skateboard base" in order to slim it down and support my cordless screwdriver.):

Maybe I just need to position the nuts on either side of the L-bracket just as I want them... and then lock them into place somehow? Do the same thing for the coupling nut?


Thanks!

-= Dave =-

 

[Karstein]

Either 2 nuts tightened against each other or superglue. Loctite blue thread lock would be better but if you don’t already have it I wouldn’t worry.

 

[JPH]

you would benefit using bearings. The center shaft that everything rotates around should go into a housing with bearings. Bearings are cheap, use a few to hold the center shaft and you can spin the barrels. The thin "L" will waste your time as you try and reinvent the wheel. Put a second L further away from the gattling housing.

 

[Duncanator]

I would agree with JPH, that bearings would help you a great deal.
Also, I would recommend that you support the shaft with 2 L brackets rather than just the one. You are asking a lot of that one bearing surface to support everything AND keep it aligned. Two shaft supports (even just an inch or two apart) would make the whole assembly much stronger.

 

[TazMan2000]

Personally, I would have used an aluminum pipe with bearings and mounts on either end. You don't need to drive the barrel assembly directly on the axis of spin. The cordless screwdriver can either drive the barrel assembly geared from the side or be belt driven. The speed of the spin could modified with the diameter of the gears or pulleys.

In order to make something convincing, the business end of the barrels have to spin without a wobble. Having a very solid axle can make that happen.

TazMan2000

 

[DR4296]

Thanks everyone!

I can't extend that axle back much further as I'm going to have to have somewhere to shove my hand.
What I ended up doing...and I think this is going to work... is I re-thought what I was doing with my original design and that skateboard wheel, which has bearings inside it. Now, that original design, based on the Youtube video I saw, used ANOTHER wheel to rub against and turn the central wheel. So, in that case, the actual bearings were locked into place with a bolt, washers, and nuts. The bearings held still while the wheel, which was attached to the gun housing, did the spinning.

I have now reversed this. I attached the wheel to that L-bracket, so that the wheel doesn't spin, but the bearings will. So, the thick skateboard wheel butted against that L-bracket actually provides horizontal support to the shaft. I've tested it with the screwdriver-coupler rig and it seems to work.

So, thanks for pointing me to bearings!