speeds too slow?

[dgsharp 0]

I'm trying to understand how the speeds work on my UM2 with Cura. I often notice the head moving much slower than the speed that I specify.

I created a cylinder (100mm circumference for easy eyeball timing) and set it to print with a single spiralized wall, at 100 mm/s speed. The generated g-code showed no G1 moves faster than 19 mm/s, and eyeball measurements confirm this is what the machine performs.

I took the same cylinder and disabled "Spiralize", kept no infill, 0.4mm shell thickness, and it was the same, the highest feed rate it seemed to output was 19 mm/s. I then found that if I added any infill (like 5%), my outputted g-code would be full of F6000s (100 mm/s), exactly what I requested. So it appears that somehow the act of enabling infill makes it go the proper speed, but printing without infill forces it to go slower (in this case about 5x slower). Is that a bug?

What am I missing? Why am I asking for 100 mm/s and getting 19 if there is no infill? I'd like to have some understanding so I can better judge what to expect. I was printing a bunch of parts at different speeds using Spiralize to save time and couldn't understand why the parts were printing so much slower than I was asking them to (and thus making my speed / surface finish observations meaningless for use on parts with infill). Can anyone shed some light on the matter?

While we're talking about weird quirks, what is limiting the size of object I can print? In Machine Settings it says the max dimension is 230x225, but I have a large object that has a few mm surrounding it on all sides including near the clips' keep-out zones and it always shows up gray on the screen. I can't see any gray outlines from the part intersecting anything.

-Dave

 

[gr5 2,095]

In Advanced/Cool you must have minimum layer time set to 5 seconds.

This explains why it goes at 20mm/sec - so it takes 5 seconds to get around one layer.

This is a good feature because you want the PLA on the layer below to cool before the next layer reaches it. With fans on full power, this can probably be lowered to 3 or even 2 seconds. But at 1 second per layer - you will definitely have problems - the part will look crappy. It will be deformed.

 

[gr5 2,095]

The collision detection between the part and clips is not very sophisticated. the algorithm creates 2 rectangles and your part must fit in either one or the other. One rectangle reaches the left and right edges but doesn't overlap the clips. The other rectangle reaches the front and rear edges but again doesnt overlap the clips.

Someday, hopefully, Daid will come up with a more sophisticated colllision algorithm.

Also be aware that you might need to turn off brim and disable skirt by setting it to 0 loops and 0 skirt min distance. Not doing these things may extend the part on the bottom layer and give you less room for your part.

 

[dgsharp 0]

The collision detection between the part and clips is not very sophisticated. the algorithm creates 2 rectangles and your part must fit in either one or the other. One rectangle reaches the left and right edges but doesn't overlap the clips. The other rectangle reaches the front and rear edges but again doesnt overlap the clips.

Someday, hopefully, Daid will come up with a more sophisticated colllision algorithm.

Also be aware that you might need to turn off brim and disable skirt by setting it to 0 loops and 0 skirt min distance. Not doing these things may extend the part on the bottom layer and give you less room for your part.

 

Thanks! That's one thing I overlooked -- I disabled Brim and it works fine now.

 

In Advanced/Cool you must have minimum layer time set to 5 seconds.

This explains why it goes at 20mm/sec - so it takes 5 seconds to get around one layer.

This is a good feature because you want the PLA on the layer below to cool before the next layer reaches it. With fans on full power, this can probably be lowered to 3 or even 2 seconds. But at 1 second per layer - you will definitely have problems - the part will look crappy. It will be deformed.

 

Bingo! I recall I ran into this before (it was a head-scratcher that time too) but somehow forgot about it. Hopefully two times is the charm.

Here's a question: how come when I print a spiralized piece (the cylinders in question) with a single shell it has starts and stops running up the side? I expected to see a single continuous extrusion but it has clear starts and stops running up the side on all of my cylinders. Hopefully for non-spiralized parts we will one day get a feature like some other slicers have to at least scatter these starts/stops around so they don't draw as much attention and reduce strength in that region on thin parts. (I tried getting KISSlicer working and it promptly resulted in a head crash! Think I'll wait a while to try that again..)

Thanks gr5!

 

[illuminarti 18]

The collision detection in the current version is more sophisticated, but probably not perfect. However as previously noted, you also need to make sure that the skirt/brim isn't making the part too big.

[illuminarti 18]

Spiralize is a feature that has only recently been added to the new slicer engine in Cura, so it may not be perfect. You might get occasional marks as the head tries to figure out where best to start a slice of the shape, but it's shouldn't be a continuous seam like a normal z-scar on a non-Spiralized print.

Btw, note that Spiralized prints can *only* have one shell - whatever she'll thickness you specify will be used as the wall thickness, but it will be extruded in a single pass. (E.g., if you specify a 0.8mm shell on a Spiralized print, the printer will extrude twice as much plastic as usual to achieve that thickness, not make two passes.