Modified TAZ5 for 1.7mm filament, have 'bulging' corners

Got a TAZ5 a few months back, and having a huge number of spools of 1.7mm filament left from my Makerbot nightmare, I wanted to modify my TAZ5 to run the 1.7mm. Purchased and swapped out a .4mm nozzle/1.75mm filament hexagon hot end. Tweaked some settings and found that setting Cura to 92% flow rate, .4mm nozzle and 1.75mm filament gave me the best prints.

But even after optimizing that, I still get corners that are bumped out, as well as some parts printing ‘fatter’ than they should be - as in I’ll print an item with a hole, and a peg that should fit that hole, and after printing the hole diameter is too small and the peg diameter is too wide, and it does not fit.

Thinking that I’m still pushing out too much filament I lowered the flow rate some more - but then I had layer adhesion issues. I don’t think the flow rate can safely go any lower.

What else could be causing this? Some images below to show what corners look like. These were printed with PLA (I hate ABS, no matter what I do large prints curl off the print bed, not worth the tinker time. PLA just WORKS for me). All corners shown in these pics should be hard 90 degree corners.

Part of the bad adhesion shown in this pic is due to a try at less than 92% flow rate. The more important part is seen from the side, as opposed to above, how far out the corners are bulging.

Quick question, related. Googling this issue I saw mention about retraction being an issue. Does the TAZ retract when making a 90 degree turn? I can’t imagine it would, only when stopping a path and moving elsewhere? I dont want to waste the time messing with retraction settings if it’s impossible that it’s a retraction issue.

First, you are heavily under extruding. Have a look at your top surfaces, it looks like a fly screen :wink: Don’t try to achive good dimension with flow rate, the first may not be related to the other one. Tune your flow rate with the 100mm extrusion method and fine tune until your top layers have no gaps in it.

Second, the corners have nothing to do with retraction. As you mentioned, no slicer will retract while it’s changing direction. I guess you print at quite high speeds, in this case the corners are an artefact due to low acceleration and jerk of the TAZ. The nozzle pressure stays high during the slow down in the corners, which means it extrudes more filament as expected. As the Marlin FW has no working pressure control features at the moment, you can only slow down the print speed or try to increase jerk and/or acceleration. But last one will lead to increased corner ringing…

I actually never touched print speed - thats the default for the TAZ5 Cura settings. I do see what you mean about the screen door and it makes sense that its under extruding.

I lowered the extrusion % in part because it felt like it was flowing too much. I know 3d printing isn’t like a high precision CNC mill so some sizes may be off a tad, but I feel like when I have an 8mm hole and a 7mm peg it should fit, but they wouldnt, always too ‘fat’.

When printing with the stock nozzle and 3mm filament I didn’t have this issue. It feels like using a smaller nozzle and thinner filament shouldnt be effected by acceleration or jerk? Dunno. No expert though.

Best way to gauge your extrusion speed is to print an object that can be fitted over a control shape like a screw head. With that said, here are a M3 and M5 thumbscrew cap that fits over the respective socket caps.

I think you’re on the right track adjusting the flow to help parts fit. If they don’t fit you’re probably over-extruding… causing both parts to be “bloated”. Adjust the flow rate % lower… usually 95-97% is good. Its probably worthwhile to check your esteps and sample the filament diameter to ensure everything is accurate.

To cure the bulging in the coners, try slowing the print down a bit. This will increase the accuracy of the head movement. I’m thinking lowering the flow rate will help the corners also.

Looking at your part, I can’t tell if the screen is to be textured like that. If its supposed to be solid, I would agree with Sebastian that it looks a bit under-extruded. But that seems to contradict the holes being too small.

I think you’ll be surprised how precise you can get parts when the printer is dialed in… I attached another STL which is a print in place rotating swivel. You won’t be able to make that off a CNC machine.
TAZ5-Cam Swivel Mount-GoPro.stl (439 KB)
M5 Thumbscrew.v7.stl (276 KB)
M3 Thumbscew cap SingleColor.stl (278 KB)

Lots of terms in there I’ve heard but am not 100% sure of (esteps, for one). Is there a good central place that defines all these terms? Of course I’ll be googling them once I get some free time to read up, but if there is a place here, or a central wiki somewhere that is a solid source of good info, I’d rather start somewhere that someone can recommend, rather than doing the google-and-hope method.

Good call with the printing something to fit over a known object. I’ll give that a shot tomorrow. I’ve a bunch of M5 stuff laying about from a build I did a few years ago that I never got around to finishing.

How is it that printing too fast would cause a corner bulge? Because of the deceleration and acceleration coming into and going out of the corner and that not being matched with a change in the flow rate? I can see how a slower overall speed would result in a smoother decel and accel, thus leading to a better corner. Am I understanding that correctly?

How would I adjust acceleration to attempt to fix that?

Googling the terms or searching this forum will yield good information. E-steps relates to the stepper motors accuracy to feed the requested amount of filament… so if you request to extrude 100mm of filament, the motor should accurately perform. The calibration steps can be found here.

Yep, you’re on the right track why slowing things down will produce more accurate prints. The stepper motor is a lot of mass to move around and creates a lot of momentum. So slowing things down will allow the toolhead to keep up with the requested movements.

With that said, I guess I’m a bit impatient. :slight_smile: I regularly print at 90mm/s. The real key is to ensure the printhead slows down where it counts the most, the exterior finish. So print the infill fast, but slow it down to 50-40mm/s for the exterior layer. The speed settings can be found on the “Advanced” tab.

I’ve had my print speeds at 50mm/s since I unboxed and installed it, so I’m hoping I dont need to slow it down more. I’m running some box calibration tests now and trying to get my extrusion amount right so that I dont have screen door prints. I lowered the extrusion % because I thought it was over extruding causing the issue, but it’s clearly not extruding enough.

Am I right in this assumption that Cura takes the input filament diameter, extrusion %, nozzle size, and print speed to calculate a correct extrusion speed? They all seem like they would effect that. Reason I ask is I know it’s a bad idea to change two things when doing a test. I wouldnt want to adjust both extrusion % AND speed at the same time, because then I don’t know which one had more effect.

Am I correct in all those effect it? Is there anything else I’m missing that does?

Yes, Cura takes all of those things into account, as well as print acceleration which becomes critical in corners. Your nozzle diameter is essentially a constant. Filliament diameter should be exactly whatever you measure on your filliament with calipers. if it varies a bunch, throw that filliament away and get good filliament. Trying to dial in a printer on bad filliament is worse than not trying to improve it at all. Infil % determines the density of the parts. For troubleshooting and calibration I would reccommend starting near 85%. Print speed won’t affect final quality unless you go over a certain speed rate past the Taz abaility to print precisely. You aren’t anywhere near that point though.

The other variables are idler spring tension, hobbed bolt teeth being full of uncleared plastic shavings and bearing movement. If the idler arm bearing is siezed, you get underextrusion. If the idler arm tension is too low (start with 8mm between the two washers on the idler arm on either side of the springs and tighten from there) you get underextrusion.

The filliamentextrusion amount extruder steps or esteps is also critical. Look up extruder calibration when you get a moment to see the proceedure to check that.