Taz worhorse nozzle dragging previous layers of print

Ive notied on parts that have a good bit of retraction moves, these bumps start to form on the current layers, and the nozzle begins to drag across those bumps during travel moves, and printing moves, Causing the nozzle to make a grinding noise as it moves over them. It happens on infill, walls, and top layers. First few layers go down perfectly, but the issues arise after about 15 layers, and until the print is finished. Ive tried changing the flow multiplier, down to even 80% to no avail. Ive tried raising the temperature in hopes that the nozzle will just iron and flatten it out. Still nope. Tried making sure the estep for the extruder motor was calibrated, same issue. Tried enabling z-hop, same issue. Made sure the Z steppers were calibrated, and same issue. Lowered the temperature thinking it was ooze causing it, still no. Made sure the belts were properly tensioned, and they were. Checked to make sure the gantry wasnt loose, and i could move it up and down with a little bit of resistance, and same issue. To make things clear, im trying to print gear cubes by emmet. The bumps seem to happen around the center holes in the peices, and in the infill. It causes the gantry to move up and down, causing an alarming noise as it drags across the deposited material. All the peices stay attached to the bed, but these bumps make for really crappy prints. Ive included an imgur link showing the artifacts caused by this. Keep in mind this is at 80% flowrate, and same issue persists

Material: Polylite PLA (default profile)
Layer Height: .25mm
Nozzle diameter: .5mm
Speed: 40mm/s
Z offset: -1.13
Bed temp: 55°C
Nozzle temp: 220°C
Retraction Distance: 2mm
Retraction speed: 20mm/s
Flow rate: 98.2%

If anyone with a taz workhorse, or Aleph Objects, has any ideas im open to hear them. Im at a loss at this point.

I have encountered a similar thing on my Mini and it has so far always come down to filament issues. Now when I have this happen I print of a ‘temperature tower’ and have noticed that in my case it seems to happen at a certain temperature for that particular filament.

Ill try that thank-q for the response

I too had the same problem on a Mini. I found the solution was to increase the fan speed to 100%. This is the larger of the two fans, not the one that cools the print-head, but the one that cools the freshly laid plastic - the 24volt fan, on the right as you look from the front. To do this while it is printing call up the console and enter the following: M106 S255 {Enter}
M106 is the G-code for fan speed, and S is the requested speed, zero being stopped and 255 being 100%

I have a taz workhorse. Its only got one fan.

I’m afraid I don’t believe your Workhorse has only one fan. All the toolhead pictures I’ve seen have two fans, one on the side heatsink which is always on, and the much larger fan on the front which is variable speed and cools the part.

facepalms at comment above im using 100% on the part cooling fan.

First… make sure this isn’t a bad adhesion/warping issue. The default profile for PolyLite PLA is to head the bed to 55°C for the 1st layer… then drop to 45°C for subsequent layers. For some of my parts… this 10°C of cooling allowed the corners to fractionally lift off the build plate and caused this grinding issue.

What solved that particular issue on my Workhorse… is to just leave the build plate at 55°C the entire time.

Other stuff… I’ve printed ‘retraction towers’ using PolyLite PLA as well as temperature towers with my Workhorse.

I’ve found that a retraction distance of 1.0mm seemed optimal (previously I used 1.5). Over-retraction can allow some air to pull into the nozzle. The air heats, expands, and creates an air-bubble that ‘pops’ out filament. You want to back off the filament just enough to relieve the pressure so that it doesn’t ooze… but not more.

I also found that 230°C seemed optimal for printing PolyLite PLA (although 225°C wasn’t bad). I had stringing when I used anything cooler. The hardened steel extruder nozzle on the Workhorse default extruder doesn’t conduct heat as well as a brass or copper nozzles and seems to require just a tiny bit more heat (about 5°C) then you would use with one of those other nozzle types.

I found that especially when doing z-hops that a tiny bit of filament could ooze and leave a tiny bump. Sometimes I disable Z-hops and using “combing” instead. “Combing” is in the “Travel” section in Cura. This alters the path of how Cura has the print-head travel when it is NOT extruding. Normally when it comes to the end of a “printed” (extruded) segment, the head moves directly to the next area it wants to print (with a Z-hop if that was enabled). This can leave a little tiny dot of filament (which cools and hardens as a bump). “Combing” causes the head to travel along an already printed area so that instead of getting a hardened bump in one spot, any oozed filament will get smeared along an already printed area as a very thin bit that does not result in a bump on your part. It’s basically “wiping” the ooze off the nozzle. You can also tell it to wipe it into the infill area (to avoid any possibility that it will wipe it along the surface/skin of a part if you think it might effect the quality of the surface.)

There is also an option called “coasting”. Coasting causes Cura to write the g-codes that the nozzle stops extruder just a tiny bit before it reaches the end of a printed segment (so any remaining filament just oozes naturally as the print-head comes to the end of it’s segment). You would really need to do some testing with your filament if you want to enable this (e.g. tell it to print a series of straight lines on the build-plate that are maybe 50mm long … then measure them to make sure you got 50mm worth of a good clean line segment and that it wasn’t decaying to soon (under-extrusion).

There is a an optional Marlin firmware feature called “linear advance” which is designed to deal with problem (but the printer does this in firmware… it’s not a cura setting… coasting is the nearest thing cura has that works like “linear advance” feature in firmware). I have not tried to modify the firmware to enable Linear Advance so I can’t speak to how well it works (some people swear by it).

The caveat here … is that these “coasting” or “linear advance” settings are highly material-dependent. If you switch which filament you are using… you probably need to re-run testing to come up with new settings. It’s definitely not a one-size-fits-all approach.

For me… just enabling combing helped a lot. I hope that helps. Good luck!

Thanks for the jnformation. I know its not warping, i keep the bed at 60c the whole print. I will try the combing though. If that works you are a life saver. I am already using coasting, the default value seems to do the job for me. My retraction is only at 1mm and has been since i got the machine. I appreciate the info, i will let you know if this works. Thank you