analyze retractions and Z hop

[curasurf 4]

Because I often see retractions spending as high as 30% of print time, I try to understand why retractions happen.

 

In the example below, A/B/C/D are 4  major travel moves (in the order of A >>> B >>> C >>> D) on layer 5. But only C is retracted. Why are A/B/D not retracted?

 

Some clues, even very brief ones, are appreciated!

ttt.3mf

Edited February 24, 2021 by curasurf

[curasurf 4]

I just figure it out. It's due to "Max Comb Distance With No Retract = 30mm". C is over 30mm and so retracted.

[nallath 1,120]

Might it not be the "Max Comb Distance With No Retract"?

 

 

*edit* Lol, our posts crossed.

Edited February 23, 2021 by nallath

[curasurf 4]

@nallath   Can you have a look at why there is no Z Hop at the start of C? You can see "Z Hop When Retracted" is enabled and  travel C is over the printed part. Thank you!

Edited February 23, 2021 by curasurf

[curasurf 4]

Could you help look at why there is no Z Hop at the start of C? Thank you!

[nallath 1,120]

I don't really see a reason why it shouldn't be hopping on first glance. Could be a bug.

[curasurf 4]

Hi @nallath   There seems to be no Z hoppig throughout the model. Thank you for your comment! 

 

I just tested a simple cylinder, and also no Z hopping. It seems that Z hop does not work.

 

@fvrmr Could you have a look at this issue? You can simply slice a simple cylinder to see whether it's possible to observe Z hopping. Thank you!

Edited February 24, 2021 by curasurf

[curasurf 4]

Could you slice a simple geometry and observe Z hopping? If yes, could you share the project file? Thank you!

Edited February 24, 2021 by curasurf

[GregValiant 1,245]

If combing is enabled there only 2 z-hops for this cylinder.  One at the start and 1 at the end of the skirt.  In this 3mf I disabled combing.  When you slice it there should be Z-hops of 10mm (easier to find in the gcode).  Whether moving up or moving down, the Z-hops occur on their own line Ex.: "G1 F2400 Z12.4".

cylinder.3mf

[curasurf 4]

@GregValiant   I was never aware that combing would suppress Z-hops. Thank you for your help!

 

It's odd that Z-hops can't be observed in Cura preview mode. I opened the g-code file in S3D and did observed those Z-hopps.

[GregValiant 1,245]

A part like this needs Z-hops because when the 55mm hole starts to come together its large radius creates feathered edges that want to curl up as they cool.  I've printed this part a couple of times and I compromised at .5 for the hop height.  That's too much for the bottom and not quite enough for the top.

I added a utility to my printing app (modestly called Greg's Toolbox) and I can adjust the Z-hop height in a file.  So in the case of this particular part I slice the file with Z-hops at 1.0 and then have the utility open the G-code file and adjust the Z-hop height for layers 0 to 430 to "0" and then layers 455 to the end to 0.  The lines of code remain in place but the head doesn't move up and down until it gets to layer 430 and then it stops bouncing at 456.  On parts with horizontal holes but that will require z-hops I don't get the under-extrusion I was seeing between two hole features as I just kill the Z-hops for the layers I see as being problem children.

[curasurf 4]

2 hours ago, GregValiant said:

I added a utility to my printing app (modestly called Greg's Toolbox) and I can adjust the Z-hop height in a file.  

 

@GregValiant   Thank you! Very interesting work for manipulating Z hops. But I can't find it in the market place. Is it a script?

[GregValiant 1,245]

Not in the marketplace and not a script.  I wrote my own Application for controlling the printer from a PC.  It's "Windows only" as VB doesn't port to anything else.

 

HERE is the download link if you want to give it a shot.  There are instructions and a readme.  At the lower right on the Recovery Page is the command for fiddling with Z hops.  You can alter one section of layers at a time.

 

The app is unsigned (that costs money) so you may have to talk your anti-virus into allowing the setup file to run.  If you do install it, let me know how it goes.

Edited February 27, 2021 by GregValiant

[gr5 2,167]

I recommend not using z-hop - it depends on the printer but I recommend it mostly only for delta printers.  It can give your print lots of ugly horizontal lines in "random" places because the Z axis in most printers has at least 0.05mm of play (that's a half of a tenth of a millimeter!) and that's plenty to make it over or underextrude a layer because the nozzle distance to the part varies and gives you layers that stick out (or inward).

 

On a delta printer, all 3 servos are moving all the time anyway.

 

Some printers just have a rock solid Z movement so it's fine.

[GregValiant 1,245]

My dial indicator died so I never checked.  I know the z stop switch varies but it isn't really part of the Z system once a print starts.  Now I'm curious.  I won't be getting a new one but I might start hitting garage sales.

 

@gr5, similar posts of yours are the reason I wrote the utility to alter the z-hops in a gcode file.  Now I put them in when I know there may be a chance of catching on a lip and pushing a print.  I remove the ones from the layers where there isn't any chance of that.  It works for me.

[curasurf 4]

@GregValiant  @gr5   Thank you both!