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joshuaSmith2021

Estimated Time Algorithm

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I have noticed that print times are often way off of actual print times. I use ~v3.0.0 with a Printrbot Simple Pro w/heated bed, if it matters. Almost all of my prints take about 30-40% longer than the estimated print time. I understand that estimating the print time is difficult because of lots of factors involved in printing.

 

What is the algorithm that calculates this print time?

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The algorithm works incredibly well for Ultimaker printers.   It is making assumptions about the accleration and jerk settings on your particular printer.  These are pretty high on (for example) the UM2 printer - 5000mm/sec/sec is the default acceleration.  "jerk" is 20mm/sec (not true jerk - this is a weird marlin terminology).

 

I think there *might* be a way to tell Cura what the acceleration is for your particular printer so that it calculates these print times more accurately.  I guess you have to know how long a typical retraction takes as well?  I suspect cura cheats and just has a certain amount of seconds for each retraction (versus knowing the E axis acceleration, max speed, retraction distance.

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It doesn't make assumptions; It uses the exact values the machine definition provides. In the case of Ultimaker, we set those to the correct values. The quality of contributed definitions can vary, so they quite often have (blatantly) wrong acceleration rates.

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I'm having this problem too with my Anet A8, I've only printed a few things so far (I've only had it 2 weeks), but print times have been up to 40% longer than the estimate, but oddly enough, material use has been as much as 25% less than the estimate...

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On 6/6/2018 at 11:41 PM, joshuaSmith2021 said:

Great. So... What is the algorithm?

 

It simply tots up how long it takes to carry out each extrusion and travel move based on the values for speed/acceleration(/jerk?) that Cura believes are right the printer. As is mentioned above, you can specify those values for the various types of move. I think Cura assumes linear acceleration (speed ramps up, constant speed, speed ramps down) for each move and so if your printer implements some fancy acceleration scheme (s-curves, or whatever) then it's not going to be right. Also, I don't think that Cura knows about extruder acceleration and so if you are using low acceleration values for your extruder that's going to make the print take longer than estimated. I find for my Kossel deltas that the estimate is very good, maybe a couple of minutes per hour optimistic but really OK.

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