Workhorse heating issue, Material printing, and Z offset

Recently purchased two Taz Workhorse printers. I thought it would be ready to print right of the box, plug and play but I am having issues right away with printing. The primary issue is that I am having difficulty with “spider webbing” with my prints. The filament is leaving not only things strands of filaments between print objects but also actual string of filament. I have used varying degrees of temperatures and can’t seem to find the correct temperature. This is a heating issue with both the printers I bought.

Also, I am trying to determine the right nozzle height for these particular printers. Currently they are both at -1.23 z offset. This seems to help with the first initial layer, just with my heating issue with these printers it is affecting my prints.

Questions that need answers:

  1. What is the correct nozzle height? Is there a method to measure the correct nozzle height?

  2. Materials that are being used are Matterhacker PLA, Amazon basics PLA and Ninjatek Armadillo–What are the right temperatures ideally for these? Despite what they say on the reels it seems with these Workhorse printers, it is too hot for the material.

  3. What is the ideal retraction mm/sec for these printers?

  4. What is the ideal speed for these printers and for the material used?

Any tips would be appreciated!

I’m not trying to dodge your questions but all four can be self answered by printing various calibration prints. A temperature tower, etc. Try a Google search for “best 3d printer calibration prints”.

The reasoning is that every printer / environment is different even for the same model printer. Filaments will vary by lot even within the same brand. Filament profiles are a “starting point” and not necessarily the “best point”.

For the most part, settings are based on the material. Even within the same material… behavior can change based on filament color or just spool-to-spool variation. As you get into 3D printing, you’ll definitely start to notice that filament quality counts and most people have their favorite brands.

The Workhorse has a hardened steel nozzle. Most 3D printers use brass nozzles. Brass is softer and wears more easily and, for this reason, it’s not well-suited to printing some types of filaments. The hardened steel nozzle lets you print a greater variety of materials without worrying about nozzle damage. BUT… because it doesn’t transfer heat as efficiently as brass, you’ll find that you usually need to run the printer a little hotter than most.

For example, I use PolyLite PLA. PLA is usually printed somewhere around 180-200… but on the Workhorse, I find that 230°C works best for this particular PLA. But I worked this out by printing something called a “temperature tower”. This is a part that has many identical sections… each section is printed at a different temperature. You compare the quality of each section to determine which one had the best result. There is a post-processing extension built into Cura LulzBot Edition that lets you change settings either at a layer number of a height (in mm). You use that extension to control when it’s time to change temperatures.

Nozzle Height

The correct nozzle height depends on the material being printed.

The bed leveling washers are 1.5mm thick. This is the 0 point that the printer detects when it levels the bed. The nozzle offset needs to be a negative value because the print surface is 1.5mm lower than the top of these washers. HOWEVER… you do not want to set it to -1.5mm because that would put the nozzle directly on the glass. Not only could this damage the glass… it will seal the nozzle so that it can’t even extrude. The nozzle needs to be a little higher.

With PLA, the first layer will bond better if it gets a little “squish”. If the squish is so much that the PLA is flattened out and the edges are frayed… that’s too much. But if it doesn’t squish at all, then there’s very little surface area of the extruded PLA touching the surface and that could break free in mid print – ruining the job. Values of around -1.2 … are probably not a bad starting point for PLA.

Another popular filament is PETG. PETG is in the “intermediate” category because it’s just a little fussier than PLA. It turns out that PETG loves to stick to EVERYTHING. It can bond to glass so tightly that the glass is damaged when you try to remove the part. For this reason, the note on PETG will tell you to use some type of release agent… such as the PVA glue-stick (e.g. Elmer’s Glue Stick). The “glue” isn’t used so much to help the stuff stick… it’s really so the PETG will stick to the glue and the glue and the glue is actually easier to release. (BTW, PVA dissolves in water … which is why Elmer’s is good for school projects where young children will probably manage to get it on everything… a quick soak in water and the PVA is gone. PVA is that plastic-like substance that is used in things like Tide Packs or Cascade Dishwasher Packs… they hit the water and dissolve into nothing.)

Anyway… turns out it’s better to gently lay the PETG onto the bed rather than “squish”. When I use PETG … I set the Z-offset to something closer to -1.1

Ideal Retraction

This printer uses a “Direct Drive Extruder”. More commonly, 3D printers use something called a “Bowden Extruder”. With a “Direct Drive”, the extruder motor and hobb gear are located directly on the print head. As soon as the filament passes through the extruder, it travels through an extremely short “filament guide path” and into the hot-end. This leaves the filament with very little wiggle room and that’s a good thing. It’s easier to control the filament. In a “Bowden Drive”, the extruder motor and hobb gear are not on the print-head… they are typically bolted onto the frame. There’s a teflon tube (the “Bowden Tube”) and the filament has to travel through this tube into the hot-end. While it’s a moderately snug fit … obviously it can’t be so snug that it creates excessive friction. So there’s wiggle room in that tube. That means when the filament retracts, it relaxes the pressure in the tube … but doesn’t really back the filament out of the extruder … unless it has a higher retraction amount.

For this reason, Bowden Drive printers need higher retraction values than Direct Drive printers.

I find my retraction settings really only need to be about 1mm … maybe 1.5 (but I almost always use 1mm).

Some materials are exceptions to this… TPU is very stretchy (it’s a rubbery flexible filament). It doesn’t respond as well to retractions and for this reason it tends to need higher retraction amounts. The Workhorse actually does qutie well printing TPU (a Bowden Drive printer usually does a miserable job trying to print TPU).

Print Speed

In general… slower is better if what you are after is a high quality finish. Some people who 3D print are making parts for some utility need where the cosmetic quality of the part is less important and they want the parts to print faster. So they’ll dial up the print speed.

First layers benefit tremendously from a slow speed to help the filament get a good bond to the build plate. Typically the first layer is half the normal speed (or less).

For PLA, I generally print at 40mm/sec … but I’m also usually not in a hurry. If I am in a hurry I might go up to 45, 50 … or even 60. But that’s rare. Also it takes the printhead time to come up to speed or to slow down for a turn or the end of a printing move. This means that it’s really only traveling at max speed for a tiny amount of time on long printing moves. In other words printing at 60mm sec isn’t actually 50% faster than printing at 40mm sec (even though 40 x 1.5 = 60) because that increased speed is only reached on long printing moves and only for a brief amount of time… most of the time the print head is moving more slowly (the printer firmware automatically has acceleration calculations to deal with inertia).

Some filaments need to print slowly. TPU prints slowly and the softer the TPU, the slower it needs to print.

Don’t be afraid to run test parts and to learn how changing settings affects the print. It’s a bit of a learning process but starts to make sense as you learn how each setting affects the print.

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I’m curious about something you said. You mentioned that the bed leveling washers are 1.5mm thick, so a z-offset of -1.5 would make the nozzle touch the bed, so it should not be set to that. With my Taz 5 that is how I level it (set the thumbscrew so that the nozzle is just enough off of the bed so that I can slide a piece of paper between the nozzle and the bed). I thought that this would be the same with the printers that auto level (the z-offset should technically be the thickness of the washer), and then the first layer height setting would raise the nozzle above that point. Is this not the case?

@markgm you bring up a good point. When I got my first printer, I thought … if the bed level washers are 1.5mm thick then the z-offset should cancel that out (e.g. use -1.5mm) and set the first-layer height in Cura – which does have a 1st layer height that can be different from the layer heights on the rest of the print.

But I noticed that if I didn’t set it higher (e.g. somewhere around -1.2 or -1.25) then the filament squished out far too flat … even with a first-layer height set to 0.4mm. Ideally, you should be able to lay down the skirt around the print, let that cool, pull it off and measure the thickness with calipers to see if it matches the requested 1st layer height and adjust from there. I think the factory default was -1.23mm (but that might vary by printer).

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