Estimated Printing Time Difference between Cura and Actual Printing

[hassanfarouk 0]

Hi Community,

I've recently got Ultimaker 2+ Extended version for some functional prototyping. I designed a model in Google Sketchup and loaded the STL file in Cura. After doing the necessary settings in Cura, the estimated time to print that Cura was showing was around 2 hours. I created the GCode and loaded that in the Printer's SD Card. The job completed in 6.5 hours.

Can someone explain me the reason for this?

Regards,

Hassan Farouk

[00D00B 58]

Well, that's pretty strange.

Normally printing time is shorter than the estimated one in Cura, around 15% perhaps.

Is it the only prototype you had to print ? Or maybe you tried other models and it was the same ?

[ahoeben 1,948]

Calculating the print time is not trivial. There are a lot of physical aspects to take into account, such as the actual speed and acceleration (and "jerk", the rate at which acceleration changes) of the print-head. With actual physical mass, and things like a bowden-tube pulling on the head, things are a lot more complicated than position = speed * time (or rather, it is complicated to calculate that velocity over time).

Having said that we have recently discovered some inaccuracies with the algorithms that simulate these physical aspects in the Cura engine, and future versions of Cura will likely have a better print-time prediction.

[Statler 1]

Print time prediction with Cura seems quite weird. Cura tells me 14 hours and then the Ultimaker 2+ eventually tells me it is 19 hours. At the end of the print, the time left drops faster than the printing advances. It tells me 1 minute left and still prints 2 minutes later. I really don´t get it....

[avogra 68]

I think, the printer divides total print time from cura by total number of layers. Then it extrapolates from the number of layers it already printed to the layers still to print. As the first layers are usually printed slower, it expects extra time for the rest of the time. At least this is my guess It would explain, why in the beginning for me it always shows too long print times.

I think the whole print time estimation is quite rudimentary and I usually take it only as an rough estimate. Maybe they improved it with Cura 2.3?

[Statler 1]

Avgora,

Thanks for your reply. Your guess goes with what I am seeing here. The first layers tend to be solid and therefore take a lot longer while the layers after that are infill are printed faster. So once I reach the infill layer, the Ultimaker 2+ time prediction drops again.

[00D00B 58]

Avgora,

Thanks for your reply. Your guess goes with what I am seeing here. The first layers tend to be solid and therefore take a lot longer while the layers after that are infill are printed faster. So once I reach the infill layer, the Ultimaker 2+ time prediction drops again.

 

This is due to the buffer system. When you print something, the machine takes a little part of the gcode instruction in buffer, it helps to be faster and more secure. (Only one SD read each buffer size instead of one read for each gcode line).

But time estimation shown at screen it made by calculating how much longer would it last to print all the gcode lines if the printer continues to print at the speed it's it when it's doing this estimation.

So when you print the first layer, you do it slower and time is estimated very much more longer. And then, when you print your infill and stuff like that, it's faster and estimations goes (almost) right until the next slow phase of the print