Oddly shaped holes?
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@mrehorstdmd They're 12mm rods. I don't think that's the issue. As soon as this part is done, I'll show it to you, but after loosening the belts up a bit I don't see the carriage wobbling anymore, but the artifacts are still pronounced, even on large circles (3" diameter)
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@Surgikill, picture ?
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@mrehorstdmd I might be able to use something like this. https://www.igus.com/product/1185
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@Surgikill, I was looking for a picture of a round thing of 3" like you mentioned. Surely the first picture doesn't show a round object ... is it ? Sorry for not being clearer.
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How fast do you print with that machine?
Maybe you should use the Igus rails that match the bushings.
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Carbon fiber rods aren´t precision ground sliding surfaces,
I don´t know who came up with that idea but it´s terrible. This will not last for any significant amount of time.
You may temporarily get less ringing, but so will upgrading the steel rods to a bigger size.
I would personally never use igus bushings or bushings in general because by design, they require a bit of slop / play that causes backlash.
An added negative is that the carbon fiber dust that will accumulate over time is REALLY bad for your lungs. -
@mrehorstdmd I was considering just grabbing some cheap steel rods to see if that fixes it. I don't print that fast right now, but the goal was to have a light carriage so I could up the speed. I was looking at Igus aluminum rods. Not sure if I should get those or the steel rods.
@NitroFreak said in Oddly shaped holes?:
Carbon fiber rods aren´t precision ground sliding surfaces,
I don´t know who came up with that idea but it´s terrible. This will not last for any significant amount of time.
You may temporarily get less ringing, but so will upgrading the steel rods to a bigger size.
I would personally never use igus bushings or bushings in general because by design, they require a bit of slop / play that causes backlash.
An added negative is that the carbon fiber dust that will accumulate over time is REALLY bad for your lungs.Not really sure how I'm going to get carbon fiber dust. The bushings are designed to wear. Not the rod.
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@Surgikill said in Oddly shaped holes?:
Not really sure how I'm going to get carbon fiber dust. The bushings are designed to wear. Not the rod.
The bushings are designed to wear on STEEL rods, or their anodized aluminum rods. IGUS never stated a compatibility with carbon fiber rods
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@NitroFreak Igus sells carbon fiber rods.......
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You can see there is this weird flat area where it' not a smooth curve, kind of like the other holes.
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Thanks for posting the pictures!
This is certainly a puzzle. It seems pretty clear that either x or y is not stepping in those flat areas but what is the other stuff going on in these areas. It seems like a combination of issues.
Did you post your config.g? I looked over the thread but couldn't find it .... -
@jens55 Here's the config.g
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@Surgikill I have a 24 x 8 mm linear guide for the X axis, 608 bearings for pulleys with 8mm bolts as axles, and a direct drive extruder with a 36 mm motor- a bunch of pretty heavy stuff. The X axis weighs about 1.5 kg. I drive the mechanism with two little 64 oz-in NEMA-17 steppers and it can print with acceleration set to 10k and speed at 200 mm/sec.. Of course, I don't ever print at that speed/accel combo, but it demonstrates that you don't need a particularly light assembly to keep the speed up. Extrusion and the behavior of molten plastic will become the limiting factors before the mass of the assembly will if you're using "normal" size steppers to move the mechanism.
If you were building a really big machine to make really big prints, speed might be more of an issue. On a small machine, printing relatively small objects, printing faster doesn't mean the print will finish sooner. Let's say you have a print running at 400 mm/sec with high acceleration so you can actually hit that speed. Even if you manage to get the extruder to work properly at that speed, each layer will finish so fast that you'll have to allow some time for the plastic to cool before depositing the next layer or the print quality will suffer. That means you have to print a sacrificial object, or multiple copies of the print, or just move the extruder away from the print and sit and wait for a while upon completion of each layer. Even at speeds like 80-100 mm/sec, you often have to use those techniques to slow things down a bit to maintain print quality. Print speed is overrated.
Reliability is the thing to shoot for, so you don't have to babysit the printer or restart failed prints. Then you can start up prints when you go to bed at night and they're done when you wake up in the morning. It doesn't matter if they take 1 hour or 6.
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@mrehorstdmd Makes sense. I might just order some 12mm steel rods. However, I don't think that's the issue. I'm noticing that the 16mm steel rods I have in there right now for the Y axis are sticking? It's kind of weird, like when you drag your finger over a piece of glass or glossy plastic. It kind of sticks, then moves. I can try to take a video of it. Not really sure what is causing it. Any suggestions?
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@Surgikill There are a few possibilities, but I think you're using bushings on those rails too, no? It may simply be stiction- static friction is always higher than dynamic friction that you get when the bodies are moving relative to each other. It may also be an issue with the angle that the bushing makes with the rail. See: https://www.machinedesign.com/mechanical-motion-systems/article/21836017/linear-bearings-understanding-the-21-ratio-and-how-to-overcome-the-stickslip-phenomenon
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@mrehorstdmd said in Oddly shaped holes?:
@Surgikill There are a few possibilities, but I think you're using bushings on those rails too, no? It may simply be stiction- static friction is always higher than dynamic friction that you get when the bodies are moving relative to each other. It may also be an issue with the angle that the bushing makes with the rail. See: https://www.machinedesign.com/mechanical-motion-systems/article/21836017/linear-bearings-understanding-the-21-ratio-and-how-to-overcome-the-stickslip-phenomenon
I re-tensioned the belts and slit the bushings like you suggested. With the zip ties, if I tighten them too tight, the bushings lock up around the carbon rod, so the zip ties are just snug. Everything moves freely by hand. This was the test print afterwards (it's TPU filament). I really have no idea what the problem is. Now the curve has shifted around the circle. There's supposed to be a circle, an ellipse, a square, and a hexagon. The dimensions on the X axis are also wrong. They're all supposed to be 12mm. The square is 10.5 wide (X axis) by 11.75 tall (Y axis). Now I'm really confused.
Maybe it's the slicer? I'm using Prusa Slic3r 2.2
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I just printed this piece out. It looks like a layer shift, but only on one side. I can't really wiggle the hotend/mount. I'm really baffled by this.
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I had a look at your config file and my hunch did not pan out BUT
Now that you are talking 'sticktion' this points in a similar direction.The signal going to the stepper motors is micro-stepped. Micro steps inherently have limited power. I think what you are seeing is a situation where the stepper has been asked to go to a particular place but there are insufficient micro steps to overcome the sticktion.
Eventually the number of accumulated microsteps get big enough that the stepper overcomes the sticktion and snaps into place. -
@jens55 Can I just up the amperage to the motors a tad? After messing around with the gantry, the sticktion is greatly reduced.
