2 questions: Print time and slicing

[Johncoffee]

I'm using Mattercontrol V1.4 and have two questions:

1. estimated printing time seems often longer than the real printing time. See the attached picture: 1hr 9min real printing vs. 1hr 44min estimated. Why is this so much different?
2. I printed two different shape: one has a lower height the other. interestingly when looking at the print speed, the speed of the larger piece changes according the 'need' of the first piece. When the first part has finished its layers, the speed seems a little reduced for the rest of the piece. whats more is that I can even recognise the different print speeds on the final printout. Why isn't the larger piece printed with speeds unrelated to the smaller?

Thanks for any answer !

*John*

[geneb]

I've yet to see any slicing package give even a remotely accurate time estimate of print time. Slicers only know how fast you want the part to be printed, not how fast it actually is printed. The issue is that while the slicer knows that it's commanding a movement between point a and point b, it doesn't know how fast the printer accelerates up to the commanded move speed from point a, or how slow it decelerates before arriving at point b.

g.

[Xenocrates]

As for why one relates to the other, there's a minimum layer time setting. The more time a layer takes, the faster it will print as far as movement.

[Johncoffee]

Xenocrates - sorry I can't follow your explanation... (Maybe because I'm not a native english speaking person)....

[Xenocrates]

I went for brief over a good explanation I suppose.

The slicer has a setting which determines the least allowable time (in seconds) for any given layer of a print. When the time would be under this threshold, the slicer slows print speeds to maintain this minimum time. Thus larger, more complicated layers will print at the set maximum speed, while smaller layers will print at slower speeds, with the speed decreasing as layer size does. There's also a minimum speed setting. When the print has reached this minimum speed setting and still is under the layer time, the hotend will move away from the print and wait.

If you want to even out speeds, you have a few options.

1) Decrease set maximum speed, and bring all speeds down to be more equal.

2) Increase minimum print speed when layer time is under the threshold. This will cause the hotend to park more often, and will result in more ooze on the side of the part (Unless you add an ooze shield or wipe tower)

3) Decrease the minimum layer time setting. This has the fewest potential drawbacks if done carefully, but will ruin parts if set carelessly, as softened plastic will buckle, bend, and slump as you add more plastic on top.

[cope413]

MatterSlice has some default values set for acceleration and jerk. If those match your firmware values, the estimates will be closer. I don't know what those defaults are, but they're likely lower than what your machine settings are - it's better to say it'll take 2 hours and finish in 90 minutes than the other way around.

If your printer had instantaneous infinite acceleration, and the computing/planning power to process all received commands in real time, then the estimates would be dead-on.

If you decide to go to an ARM board like the Smoothie or Azteeg x5, you'll notice that your estimates get much closer to actual

[Johncoffee]

Awesome - thanks Xenocrates and cope413 for your replies - very much appreciated!