Part Wobble (Formerly: [need] Gates GT2 Belt[?])
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@edgars-batna I'm hoping the (slightly) loose wheel on the x carriage may have cause the worst of it. Machine is warming up. I'm likely to order the GT2 20t genuine pulleys as I know mine are off centre, but that would be a ~40mm ripple not 1.5-0.75mm ish ripple. I'll order the dampeners at the same time. I've been dubious of them but I am getting a lot of stepper vibration and noise now with the v0.8.5 16x microstepping so will try it.
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This was the change when I changed stepper motor on the x axis to a salvaged: 17HS19-2004S1
This is the better surface, rather than the original issue pictured before. Original on the left, new motor on the right. No pressure advance steps on the right.
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Definate progress.
As always I think this was a multi faceted issue and I've been slowly fixing the issues as I've worked through this. I've ordered some longer bolts and nylocks for my x-carriage and will use them on the next carriage rebuild.
Picture on the left is the original, on the right is the part after rebuilding the x-axis carriage. You can still see the ripple, but it is far less pronounced. There is a little of the higher frequency / shorter wavelength ripple that I originally saw on the best side now beginning to show through on this side. I think this is ripple being driven by the major step size of the motor. I'll look at this test piece again when I've got the dampeners in, but until then I am happy to continue with the setup of this machine at long last!
Couldn't tell you why the shineyness has gone on the part on the left. Loss of a shiny finish tends to happen when the extrusion rate increases, but I haven't changed that much, if any.
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@doctrucker From my observations, shininess goes away if the layers don't have time to fuse properly and basically get frozen as "pancakes with gaps between layers" instead of forming a continuous wall. This is either too low temperature or too low pressure / too little material. It might seem like the prints get better, but I'd test strength to make sure the layers have proper bonding.
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That's a fair observation, I'll bare it in mind. I've been wondering about an open source tensile test rig. Not even done initial searcjes to see if it has been done.
When I do open air non linear extrusion tests I see the finish of the bead going from shiney at low speeds to dull/matt at higher. In industrial extrusion the effect is called sharkskin. I think it happens when the melt slips past the nozzle bore walls/surface rather than flow. As temperature increases the polymer would tend to flow with less resistance.
I often find my models are half and half, particularly where I'm not printing enough per layer and the slicer decides to slow down the layer. Obviously a situation to avoid in a proper print but often great at showing up uglies on your printer during test!
Edit: I realise you can swing a weight of a hook or similar for a strength test, I was just interested in a more capable machine.
Running 3 P3Steel with Duet 2. Duet 3 on the shelf looking for a suitable machine. One first generation Duet in a Logo/Turtle style robot!
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@doctrucker Never heard of the "sharkskin effect" so I just learned something new. I do observe the shininess going away at high flowrate and increasing the temperature usually brings the shininess back. I'd think the skin is less likely to form if there's enough temperature, but it's a whole, huge other topic.
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@doctrucker said in Part Wobble (Formerly: [need] Gates GT2 Belt[?]):
I've been wondering about an open source tensile test rig.
Here you go: https://www.youtube.com/watch?v=uvn-J8CbtzM
Links all necessary info to build one are in the video's description. -
Direct over head lihhting makes these look worse than they are in the flesh, this wobble is hard to photograph!
Right to left we have:
Control with previous mods,
Stepper motor dampeners,
E3D Pulleys.Dampers made a big difference to noise, with a small difference in part quality. Pulleys are no longer visually off centre and the axis feels much better, but made no difference to the part.
Acceleration for the perimeter is currently 500 and Instant speed is 400 which I thought was already conservative even for a cantilever.
I think I may still have a mechanical/frame issue somewhere...
Extruder mods not expected to improve the situation because the surface 90 degrees to the pictured is much better. That said I had a Titan knockoff (came with a bundle of second hand E3D parts) to try at some point.
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I sped things up to avoid a resonance on the bed and there was a noticeable improvement but still not fixed.
I'm now convinced the way I've joined the z-axis extrusion to the y-axis has resulted in excessive spring. I need to return to the drawing board.
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Would be interesting to see how the pattern changes by printing perimeters at 75%, 100% and 125% of nozzle width. I'm trying to figure out a much lesser, but similar issue and found that 75% works best and I have yet to figure out why exactly. The axes are reasonably stiff on my printer, but I don't use linear rails.
