Suggestions like this are meant to go into the hopper for the next (re-)design, not a demand for implementation right now.
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Regarding the central 6 screw holes on each spool/arm:
The way these are currently placed, the arms being all the same, means that if one of these comes loose it will have a near 100% chance of falling into a slot for the arm below it and causing the two relevant arms to no longer move independently of each other.
If these holes were at a slight angle, the bottoms would no longer line up with the tops of the holes below them and a failure here would be a much smaller concern. This failure occurring mid-cut because of vibrations, etc, could be non problematic if it failed safely. It may also need a slight groove where they would sit on the lower arm if this happens to mitigate them sliding out further and getting wedged.
I only caught this because I had a loose screw I noticed when I finished my assembly in this exact spot. Lock washers arenāt a guarantee and the prospect of potentially having to replace a belt makes me not want to use them here.
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I like the idea of inserts, though I just realized now that a longer list āFirst Stepā of super glue and the existing ny-lock nuts would have a similar effect on reducing the fiddling/being pushed out during assembly.
For me, I just took the fan cover off and glued nuts into the PCB bracket. I would also do the 12 for the towers attaching to the sled, and probably anything attaching to the sled. And probably the encoder /handle assemblies.
Iām imagining gluing one screw on the end of dowel to make a tool, putting some silicone grease on the end of the screw, partially threading a nut on it, apply superglue and insert. With the sled upside down this would go pretty quickly and the tool or similar makes sure they donāt get stuck at an angle.
Then youāve effectively got inserts with the current design.
I had been thinking about some mini tapered rubber corks or pegs to hold the nuts in during assembly, but why not glueā¦
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Carson Barry wrote:
Regarding the central 6 screw holes on each spool/arm:
The way these are currently placed, the arms being all the same, means that if one of these comes loose it will have a near 100% chance of falling into a slot for the arm below it and causing the two relevant arms to no longer move independently of each other.
If these holes were at a slight angle, the bottoms would no longer line up with the tops of the holes below them and a failure here would be a much smaller concern. This failure occurring mid-cut because of vibrations, etc, could be non problematic if it failed safely. It may also need a slight groove where they would sit on the lower arm if this happens to mitigate them sliding out further and getting wedged.
right now the two halves are identical and injection molded.
I donāt think you can easily injection mold an angled hole (and it would now
require different molds for the two halves)
Then there is the problem that there just isnāt that much thickness available
for the hole.
good job in spotting a potential problem, and I think there was a post that we
really need slightly longer screws to properly engage with the lock nuts.
I just donāt see how your suggestion would work (I may be missing something)
David Lang
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Derek Graham wrote:
I had been thinking about some mini tapered rubber corks or pegs to hold the nuts in during assembly, but why not glueā¦
for the sled, I just stacked additional nylock nuts in the hole, then put a
piece of blue tape over it to keep them from falling out. It worked well there.
Iām nervous about trying to glue the nuts in place, fearful that the glue will
get into the threads and make them unusable and impossible to remove (I donāt
have much experience with superglue for this sort of thing, so my fears may be
completely unfounded)
David Lang
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I understand the issue of the molds needing redone in that instance, but I didnāt consider the slightly canted holes being an issue.
My next thought would be a ring free floating in a groove that each screw hole would be centered in, blocking the screws above from being able to reach the holes below them if they come loose. Still requires a new mold, though.
If the ringās inner diameter was just the same as the armās, it wouldnāt need the groove. Though there might need to be spacers added elsewhere to compensate.
Might also just be enough for the screws to go in from above and the nuts to be on bottom, as a nut would just fall into the hole below and be far less likely to stick out and catch on the holes above it.
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I wonder if some Kapton over the holes on the bottom side might be low profile enough and slick enough to keep the screws ācaptiveāā¦
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Carson Barry wrote:
I understand the issue of the molds needing redone in that instance, but I didnāt consider the slightly canted holes being an issue.
just about any improvement will require new molds, but thatās why weāre bring
the ideas up long before they need to make the next set.
My next thought would be a ring free floating in a groove that each screw hole would be centered in, blocking the screws above from being able to reach the holes below them if they come loose. Still requires a new mold, though.
If the ringās inner diameter was just the same as the armās, it wouldnāt need the groove. Though there might need to be spacers added elsewhere to compensate.
Might also just be enough for the screws to go in from above and the nuts to be on bottom, as a nut would just fall into the hole below and be far less likely to stick out and catch on the holes above it.
Iāve been thinking of getting a thin ptfe or uhmw plastic to stack between the
arms
David Lang
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Derek Graham wrote:
I wonder if some Kapton over the holes on the bottom side might be low profile
enough and slick enough to keep the screws ācaptiveāā¦
There is ~3mm of slack in the stack.
David Lang
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I just read that Kapton at least is poorly rated for mechanical wear. maybe your ptfe / uhmw - I was thinking of the super-thin flexible cutting boards, or adhesive window security filmā¦
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Got my 4 yesterday, so have been putting it together. Thereās quite a few places where the bolts donāt actually have enough length to reach the lock nut locking plastic! Which seems like a waste, for want of 2mm more bolt.
The strain and wear relief on the steppers for the z are rather poor.
(And the next post)
Iāve already added a bit of tape.
The last thing is, of course, the reliance on the Dewalt 611 router, which seems to be almost unknown in the UK - Iāll likely have to mod it to use something else. (Iām actually thinking of trying the Ryobi 18V āpalm routerā for a battery solution throughoutā¦)
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Can you post a photo how you added strain relief? That could be helpful for others. Cheers
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NKT wrote:
Got my 4 yesterday, so have been putting it together. Thereās quite a few
places where the bolts donāt actually have enough length to reach the lock nut
locking plastic! Which seems like a waste, for want of 2mm more bolt.
most of it was designed for the non-locking nuts
David Lang
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Iām not sure if this is the correct place to suggest this, but I think it would help if the Serial Messages were timestamped, even if the timestamp is just seconds or seconds and milliseconds since startup.
For example, I changed my frame this afternoon and did a new calibration. I uploaded a fresh maslow.yaml file from the .70.2 firmware, used the GUI to enter my frame dimensions and calibration info, then did a retract all, extend all, apply tension, calibrate. Looking at the Serial Messages, I see this:
[MSG:INFO: Retracting all belts]
[MSG:INFO: Top Right pulled tight with offset -0.011]
[MSG:INFO: Top Left pulled tight with offset -0.011]
[MSG:INFO: Bottom Right pulled tight with offset -0.021]
[MSG:INFO: Bottom Left pulled tight with offset -0.021]
[MSG:INFO: Extending all belts]
[MSG:INFO: All belts extended to center position]
[MSG:ERR: Motor current on Top Right axis exceeded threshold of 4000]
[MSG:ERR: PANIC! Stopping all motors]
[MSG:INFO: Measured waypoint 0]
But without timestamps, I canāt really tell if the motor current error was when I did the Apply Tension, or if it was when I started the calibration.
Thanks,
Russ
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I literally just put the last of a roll of insulation tape round it. Itās more to stop the abrasion that the sleeve should have, but wonāt becuase itās a few inches down the lead!.
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An alternative approach from offsetting the holes would be to include 3 thin plastic āspacerā disks that would fit in between each spool (like a very big, thin plastic washer).
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That was also my next thought (you can see the reply above).
At that point, the only potential thing I see going wrong is the chance for the head of the screw to become wedged while it is sticking out of the bottom of the upper arm.
If the ālarge plastic washersā had raised nubs that fit into the holes for each of the screws, it would keep them (the screws) fully captive and only the bottom surface of it would need to worry about friction.
I still feel like bolt-on-top, nut-on-bottom, is worth recommending to people in the meantime so they are mitigating the potential for this to be an issue for them without changes to their hardware.
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