You can print that as one piece if you change the shape a tiny bit, if you really wanted to keep it multiple pieces you can make the connection like the primo corners and leg clamps.
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Unfortunately if it’s printed as one piece, it would lose modularity. That’s not a big end-user problem, but it is an issue for stocking parts.
I think with the primo you’re referring to how the clamps work like a bike seat-post tube? https://docs.v1engineering.com/mpcnc/Pbase/#legs-and-feet
On a hunch, I tried inserting a piece of notebook paper between those two planes. It worked great! I suspect that PLA-PLA is slippery and it’s too hard to mold into an interference fit. The paper seems to be soft enough and grabby enough to work. The joint now only slips under great load, which is probably comparable to the load at which a bolted joint would slip.
I’m going to print up the other side with my fixes, as well as some material reduction changes, and then maybe it’ll be ready for assembly. The true test is whether it works with the new bearing blocks, but all of the other original LowRider2 printed parts.
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In what way, lots of center pieces and different end caps vs just different complete brackets? Do you plan on selling these? If you do keeping track of one piece vs three is always easier.
No the printed shape of the corner bottoms and leg locks, careful geometry that interlocks and is printed in two different orientations.
I’m just looking at your project. Regarding the long hardware, an alternative approach would be 4 hex coupling nuts at the midpoint of the sandwich with short tension bolts from both ends.
If the nuts are press fitted you basically have the single center piece that was suggested earlier in the thread.
Going back to when I started this design, I figured it would a useful contribution if you wanted to do a LowRider3. I recall that you were having trouble finding a way to consistently source inexpensive and good quality tubing worldwide. So the driving goal is to allow any tube size between 1/2" EMT and 1.25" OD tube, and at the same time not to require specialized parts or industrial-grade printers.
In addition to meeting the main goal, the result was a structure which:
- is many times stiffer in torsion about the long x-axis (but less stiff in the short z-)
- uses less plastic (I think?)
- is lighter and has lower inertia
- clamps an order of magnitude tighter, which means less chance of slipping or chattering at the joints.
- all parts are printed in their optimally strongest and stiffest orientation
The parts are all generic, and the modularity allows for field upgrades in case someone wants to try a weirdly-sized steel tube along one axis. Heck, you don’t even need the same tube size from side to side (although I don’t honestly see the use case for having two differently-sized x-tubes)
Whether this is, in fact, useful to v3 will be your call. But it was a fun trip and I’m very pleased with the outcome.
This, right? https://www.v1engineering.com/wp-content/uploads/2020/06/corner-bottom-scaled.jpg
Intriguing! The challenging difference is that the x-cradle and the z-outer clamp both have two precision faces. I think if the x-cradle and z-cradle are turned on their sides during printing, that could allow easy high-accuracy printing.
The downside of turning them on their side is, IIUC, a higher chance of warping, since these objects will be tall but thin.
I’ll keep that in mind in case I notice any kind of slipping problem. It would be nice to lock things in place, but thanks to the clamps I have less slippage than I would if I had used bolts. Time and experience will tell if trapezoidal slipping is a problem which needs addressing or not, but my hunch is that this problem is solved.
That’s a good idea. I think the hose clamps give a better result, though. The downside of bolts is that the head of the bolt rides on plastic, greatly limiting the amount of pressure. Plus, I would have 16 screws to adjust down (right now I only have two). Definitely something to keep in mind, though.
With the hose clamps, it’s awesome just how much you can tighten down. All the plastic is in compression in all axes, and so based on what I’m seeing here it’s entirely possible that the hose clamp would break before the plastic cracks. If that’s the case, there’s room for further optimization in plastic usage.
Is threadlock needed on the hose clamp adjustment? There is a LOT of vibration while milling…
I would suggest safety-wiring them because it’s easier to undo and redo. I safety-wire the clamps on my airplane, it has a high-power single-cylinder engine which vibrates the crap out of everything.
Here’s how to safety wire hose clamps:
It’s also wise to cut off excess hose clamp tail. According to my airplane mechanic, anything longer than 2-3cm can flap around and cause a fatigue failure inside the worm screw.
But once you do those two things, hose clamps are incredibly reliable and will work in high-vibration environments for decades.
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