Z Axis to Mount Threaded Rod Issue

I’m having a difficult time getting my z axis put together with the middle assembly tonight. The first issue I had was that I didn’t know that my 5/16" threaded rod wouldn’t hold in the pineapple coupler. Turns out there were 2, and the one I had printed was too big. I finally printed the right one, and the new one is tighter.

The 2nd issue now, is that I’m trying to put together the z axis with the middle assembly, to make the gantry. I don’t see where the instruction pages say how to connect/attach these 2 together, only to insert all 4 rails, check for tightness before the z axis is together in the middle assembly portion, and then later in the gantry portion, it says to set the middle assembly on the rollers. Does the threaded rod screw down into and through the coupling nut at the bottom of the middle assembly? How far should the threaded rod be sticking out the bottom. Should a lock nut be put on the bottom of the threaded rod or something? I am having a hard time finding this portion of the assembly. Also a note, The thread rod I have won’t easily screw into the coupling nut, meaning it won’t screw into it. The ends look a bit odd. A regular 5/16" bolt will though. I need to hacksaw off the end of the threaded rod a bit and clean it up somehow?

Also, the calculator I use for 30 x 37 x 4.75 Z says to use 7.75" minimum length allthread/screw length. I have one that is 12" long. Do I need to shorten this? I’m using this calculator https://jscalc.io/calc/Y1Db347ni9eckSKc


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The motor turns the threaded rod, and the nut doesn’t rotate. Thats what moves the z axis parts up and down. You should be able to just thread it in, turning the coupler with your fingers.

The coupling nut needs to move freely on the threaded rod, or you’ll get a bunch of problems later. Your z will lose steps, it will plunge into your work. It doesn’t have to spin like a fidget spinner, but you should be able to move the z up and down with your fingers.

I’m not sure what you’re saying is on the end. Maybe post a pic? Are you sure it’s 5/16" threaded rod?

When I cut threaded rods or bolts, I like to put a nut on first, then cut it, clean it up a bit and the act of removing the nut will finish any clean up.

I can’t really speak to the length. I personally would either trust the calculator (threaded rod is cheap) or do a dry fit and see where I would cut it. I might even Mark 7.75" and she how that looks.


Well, after jacking with this the last 2 days(buying a file, hacksaw, angle grinder, etc to try and get a nice clean cut on this threaded rod, I figured something out. I bought a foot long stick of this 5/16 threaded rod at Lowe’s, but finally looked at it closely, and discovered that the threads are not “angled”. I can stick my fingernail down an inch from the end in the groove, spin it around, and it never moves up or down. Not sure the technical term, but this piece of krap isn’t angled. So that would be a good reason that this won’t fit onto either a regular nut or coupling nut. Has anybody ever heard of something like this? The grooves are basically flat across it. I will try and find another piece tomorrow, but super frustrating. Been stuck on this since Saturday.

What? I have not seen that. I hope that is some crazy bad batch, not an actual product.

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Here’s what I’m talking about, 5/16" bolt on the right, “threaded rod” on left. You can see this krap doesn’t angle like the bolt does.

That is crazy, I have bought so many sticks of that and had some crazy threads but never, NO threads. Shoot how frustrating.

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Hahahahaha! That usually doesn’t make it past qa! Have you ever seen how this stuff gets made? It’s not run through a cutting die, like if you made a bolt yourself at home. It’s standard smooth rod run between two ribbed roller dies that press the grooves in. Sometimes the bar will get caught and cause weirdness.

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