Tee nuts, rotation and bkm’s (best known methods)

As we assemble our FarmBot, we are noticing that the tee nuts do not always rotate the full 90 degrees when being tightened.
Sometimes they rotate about 45 degrees or maybe a bit more.
The questions we have are:
1). Is this expected?
2). Is a rotation of ~45 degrees adequate to hold the structure together?
3). I have read a lot of posts on tee nuts, and it seems this is a common frustration. I have tried many ways of getting the nuts to fully rotate, but my results are about one in every three will rotate 90 degrees; the others will rotate ~45 degrees.


@Gabriel & @roryaronson
The forum seems quiet on this one…
Any input?
(Only if you have time)

I am wondering if I can use standard style (slide in):

Instead of the FarmBot kit supplied “drop-in” style:

I would like to hear from the FarmBot team why they choose drop-in over the slide in style.
I suspect there are a few assemblies that do not lend to using the slide-in style, and adding two different tee nuts types would add to complexity and confusion.

Tickling the forum…
Anyone have any input, thoughts, experiences, etc…

A tee nut that has only rotated 45 degrees is usually fine, as long as it is sufficiently engaging the faces of the extrusion slot. Usually the tee nut will either sufficiently engage or it will not engage at all, requiring you to loosen the screw and try again.

While this can be annoying in some cases, our experience with slide-in style tee nuts in versions of FarmBot v0.8 and below is worse. With slide-in style tee nuts, you must pre-meditate exactly how many tee nuts you will need along any extrusion slot before tightening components to those nuts. Otherwise, you may need to undo substantial amounts of assembly if you need to later add more tee nuts (that aren’t on the ends of the slot). You also need to undo parts of the assembly if you need to remove parts and wish to not have loose tee nuts left in the slot which can rattle. Furthermore, slide-in style tee nuts are very difficult/impossible to work with in a vertical extrusion slot because there is no way to hold them in position while you add the part and screws. In some cases, you could slide the part+screws+nuts in from the end, but in many other cases that won’t work due to the order of assembly steps.

In a nutshell, using drop-in tee nuts affords a lot more flexibility in the assembly process and avoids the need for time consuming disassembly/reassembly when a mistake is made or a modification is desired.

That being said, there are some locations in the assembly that could benefit from slide-in tee nuts, which may make an appearance in future versions. In the meantime, you are welcome to use slide-in tee nuts with your current version FarmBot, just make sure they are stainless steel if your bot is going to be exposed to water. (The ones from OpenBuilds are not stainless steel)


Thank you for yet another well-formed, complete and thorough response.
I suspected that the partial rotation (~45 degrees) was adequate to hold, so very good to get confirmation. I have noticed that when they hold, they hold and when they don’t hold they don’t. :slight_smile:
Your explanation of your choice of drop-in vs. slide in makes total sense. I had not considered having to remove parts post-build, and I can see how this would suck. :smile:
Also, I did not think about the vertical aspect.
Of course we (the FarmBot community) can change and mod as we see fit, but I think on this one I will side with the experts (you!)
I noticed the the slide in style that I linked from OpenBuilds were just nickel-plated steel. I was concerened they were not stainless, and I think, had I chose to go this route, I would have looked for the same in stainless. Thank you for noticing and pointing this out. I should have been more clear, as I would not want anyone using these on an outside structure (FarmBot)
Big thanks, as always, for your thoughts and input. Always sage, always aprechiated.

Btw - I have been at the school all this week and last slowly building the XL. I have had lots of interested students (1st through 8th graders, and some kindergartners (so cute)), teachers, parents, community members, school district administration and other drop in to observe and help. Such a STEM-rich endeavor!

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