Print quality/tuning advise.

Okay, I see that there are a bazillion topics on print quality, and I've spent some time reading and searching, but I don't want to hijack someone else's thread. my other thread on my build started as more of a rant, and not really appropriate for the business of actually getting good results.

So, I know that I have some tuning to do, but there seems to be a number of things which can have an effect, and having little practical experience, I'd like to see if I can get some advise from people who've tried things, and NOT spend many hours doing test prints to determine the effects of various things.

So, basic information, the printer kit shipped as a bit of a POS, but the basic premise should be good enough to give reasonable quality, at least until I can improve the design and print new parts.

• Printer: Prusa i3 w/1.75mm filament, 0.3mm nozzle (By seller's specifications, I suspect that the nozzle size is wrong)
• Electronics: RAMPS 1.4/Arduino Mega 2560
• Firmware: Marlin
• Control Software: Pronterface
• G-Code generator: Slic3r

I have a sample print as follows:
bottom side:


And the top side:


This piece was supposed to be 75mm by 75mm by 5mm. It came out about 74.5mm by 72.5mm by 5mm. It doesn't quite fit what it was supposed to.

Issues that I see:

There are slight gaps between the extrusion lines. Possible solutions would be to increase extrusion temperature and extrusion "steps per unit" to get more flow, which might also help with the roughness of the top layer. I could also tell slic3r that the nozzle is narrower, which would increase the print density, and possibly help both. Both have potential problems with getting too much plastic extruded, though I think that the change in slic3r settings may be the more appropriate choice, since the honeycomb fill pattern seems good for the print density chosen.

Some of my first layer border print lines did not adhere to the final print. I had a few strings come off of the edges when the part came off of the glass. This is obviously in part related to the above, but I believe it is also related to first layer thickness and/or Z homing. I see that typical settings seem to have 1st layer being somewhat thicker than subsequent layers, but that instead seems to just leave a bit of a gap between the first and subsequent layers, unless the extrusion rate is also higher to compensate, which it probably should be... I haven't looked that closely at the G-code, and it's hard to calculate because the print speed of the first layer is also slower by default.

My outer edges seem pretty good, with the exception of the first and last layers, which were a bit rough. (First because of unadhered borders, last because... Well, it looks like that top layer picture.


Other things that I'm having issues with that might be nice to change:

My Z axis steps per unit is currently at 4000. This was a number that I pulled out of my rear when trying to get the Z axis to move at all with the ridiculously low value defaulted in Marlin. I think that it should be much lower (200 steps per revolution motor at 16X microstepping, driving a 1.25mm thread pitch rod should be 2560 steps per mm, as I calculate) but for whatever reason, my 5mm piece comes out almost exactly 5mm thick, so I haven't changed it. I planned to fine-tune that by making something taller and measuring actual vs theoretical.

So first things first, I'm going to re-level the bed, and re-home the Z axis. I was thinking about reducing the step count by reducing the microstepping onthe Z axis, since it seems a little excessive that the Z axis steps are so much higher than the X/Y (About 80 each) and I can't think of a reason why I should need that kind of resolution (Unless I want for some reason to have 0.0025mm resolution layers, in which case I should probably be looking at injection moulding.)

If I change the setting for the nozzle size in slic3r, will that also change the extrusion amounts? I would like to keep the extrusion amount about the same, but I want the lines closer together, or is there a setting that I haven't seen that lets you choose how close to pack the lines?

First thing to do is calibrate the printer (search the forum) if the sizes are off then the calibration is off. Common nozzle sizes are .50mm, .40mm, .35mm & more rare is .25mm You probably have a .35mm nozzle though it could be anything that they decided to make it.

In Pronterface (or any other controller program) you can manually tell it to move an axis a certain amount, usually in increments of 1mm, 10mm & 100mm this is how you can see if it's calibrated, mark a spot it's on, tell it to move 100mm (the further you move it the more accurate the measurement) and then see if it moved exactly 100mm. Same thing for extrusion, tell it to extrude 100mm of material and see if it does (the extrusion is measured in the amount of filament used and not the length that comes out of the nozzle).

There are lots of 10mm calibration cubes out there to test print as well.

I contacted the seller, and was told that though the specs say 0.3mm nozzle, it really means 0.34. Well, I kind of thought it was smaller from the results that I got, but I'll see what changes if I set that up.

I've re-calibrated the moving axes, and the belt holder for the Y axis completely broke, so I've jury rigged it with hot glue and zip ties. (There are a LOT of zip ties holding my printer together, far more than the ones that are supposed to be.) At this point, the question is really if I'm going to be able to get this thing working well enough to be able to print parts to make it work correctly.

With that said, I can't get exact dimensions from the seller. I'd rather have good dimensions to work with in order to make better parts, but as it sits, I don't have them. I can put my callipers onto the existing parts and get an idea, but having actual hole centers and diameters would be a good thing, even better if I don't have to disassemble the printer, measure the parts, and then reassemble the printer, print the replacement parts, and then disassemble and reassemble the printer. (At present, I don't think that the current parts will survive the disassembly/reassembly process.)

Since it is really difficult to get really accurate dimensions from an STL file (Or so it seems, though I'd think that since the STL file has very accurate dimensions in it, it ought to be relatively easy to get accurate dimensions from, though apparently that is not the case. Nothing is ever easy. )

I realize that marking where the printer is usually done to calibrate the printer, but my problem is getting accurate measurements of where the extruder is. I'm not really satisfied with the measurements that I've got, because they don't seem to translate into accurate measurements for my projects.

Well, there are 2 things that I feel that I need to fix first and foremost at this point, which are the feet and the Y axis belt holder. I'd also like to change the Y axis bearing holder for something more stable.

For the feet, I've got a set of files that will help enforce square of the X to Y axis (Provided that I print them with a square X/Y to Z axis printer in the first place.) They have a longer arm for the nuts and bolts which should reduce any possible warping of the axis. Of course it's more print time, therefore greater chance of something going wrong, but the total print is about 60mm tall. there are also a set of spacers in there to change the configuration for the long rods on the Y axis, so instead of:
nut-washer-foot-washer-nut-space-nut-washer-X/Z carriage-washer-nut-space-nut-washer-foot-washer-nut
It will be:
nut-washer-foot-spacer-X/Z carriage-washer-nut-space-nut-washer-foot-washer-nut
My hope is that by eliminating the space for the X/Z carriage, I can be more assured of an even relationship between the Y and X axis as well as improve the capability of the Z axis to remain square without excessive pressure from the nut on the acrylic frame. Of course it might not work either...

Okay, I've got things calibrated, but print quality is still kind of ... well, crappy.

I've got my X, Y and Z axis settings very close to exact, parts up to 90mm across have less than 0.5mm variance from expected dimensions in either X or Y sizes. I have not yet tried printing anything higher than about 25mm high, but this is also well within expectations.

Last time I tightened some of the frame nuts, I seem to have managed to twist my X axis to not quite be square to the Y axis. This seems to be about 1mm over a run of 90mm out of square. I can fix that easily enough, but it's definitely something that I want to make impossible when I can get sufficient quality printing to replace the plastic parts in this kit. I have the parts designed, but printing them to acceptable standards hasn't happened yet.

I printed a small stand for the top of my TV to hold the sensor for my XBox. The top of my TV is very rounded, so it was difficult to make the sensor stay. I printed the stand as 3 parts, 3mm thick with a tab/slot setup to make it the overall shape I wanted. The first attempt really sucked. My 3mm wide "slots" were nowhere near able to fit the tabs. Though the overall size of the print was okay, the holes were way too narrow because the sides are inconsistent. It does not appear to be missed steps, and should not be belt slop. It just looks like inconsistent extrusion. (Maybe not surprising, as this seems to be an all around issue with this printer.) How do I fix this?!

Currently, I am using PLA, though I want to be able to use other materials as well, I want to get reasonable results from this before complicating matters. I'm currently heating the bed to 75 deg C for the first layer, 70 deg C for subsequent layers. Extrusion is at 175 deg C for the first layer, 170 deg C for subsequent ones. At this setting, there is some visible sagging for the top layer over the infill when that is at 30% (About as low as I've used) or 40% (More typical) it doesn't matter if I use rectilinear or honeycomb infill patterns.

Software wise, I'm using Slic3r as a gcode generator, Marlin as firmware on a Mega 2560/RAMPS 1.4 combo, and Pronterface to run the thing. Printing is going at about 30mm/s for outlines, 60mm/s for fill.

Oh, and when starting a print, there is a code to raise the Z axis to 5mm. This and the command to lower it back down for the first layer seem to cause problems. The Z axis motors buzz and don't seem to move the correct amount. I usually pause the print and re-home the Z axis while it's printing the skirt. moving the Z axis using any of the home/move commands in Pronterface never gives a problem, it is only the part where the gcode moves it before heating the hot end, and after the hot end has come up to temperature that cause problems. I do not want to set the bias current higher on the Z axis motors. I'd like to just slow down the speed that the Z axis is adjusted so that the motors can keep up.

When designing engineered pieces remember you need tolerances to fit parts together eg shafts or bolts into holes.

also current technology on the slicing software tends not to have any smart recognition for thru-holes for shafts/bolts/connection holes, so tends to add 0.5x extrusion width to the solid outline (ie the holes end up narrower) than the CAD design shows.

Also, some slicing software and printer designs are worse than others for doing overhangs, and CAD designed round holes often come out a little distorted ("teardrop" / "egg") shaped, although this might be counter-able with speed (to allow work area to cool and set), extrusion speed (being certain of no narrowing effects), or most likely a carefully placed work-point fan.

0.3mm nozzles exists. I own 5 of them, with +-10% at the output. Nothing close to 0.34mm. Supraguy, there's nothing more different than two Prusa i3 kits. A Prusa kit means nothing at all. Especialy when talking about extruders/hotends, the most important parts of any printer. Some kits have great ones, some have rubbish ones. I did not managed to print someting decent with my original Folger's extruder. I had to replace it.

With the measurement you give, I guess you own a digital caliper, that's a good point. Do you own a good square too ? Did you check your rods are strictly parallel and perpendicular from Y to X ? How do you "calibrate" your axis ? Does the printer stands on a thick flat surface ? What type of extruder/hotend do you own ?

Edited 1 time(s). Last edit at 01/06/2015 10:49AM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Thanks for replies.

Yes, I own a decent set of calipers and a good square. The rods for my Y axis are indeed exactly parallel, and the X axis was exactly perpendicular at the point where I initially built it. I've had to tighten nuts a couple of times, and the X axis has subsequently drifted by about a mm or so, which I intend to rectify asap. (It is of course that I tend to tighten the nut on the left and hold the one on the right, so that pushes the axis to the front on one side and to the back on the other.) This is one of the things that I want to change with new parts.

I did actually leave 1mm+ allowance all around for fitment, as I suspected as much with the slicer settings. The tabs on my parts were 3mm by 20mm, and the holes were supposed to be 4mm by 21.5mm. I had thought that should leave enough tolerance for fitment, but I actually needed to make them 5mm by 23mm in order to get the desired fitment, and at that, one was tight and the other kind of sloppy. (Well, nothing a little hot glue couldn't fix, but I have other things that I want to do that will require better fitment. I don't mind doing a small amount of machining (Drill press, planing or the like) for some of the more precisely fit parts, but some things (Cams, levers, clips) are difficult to do that, which is why I'd use 3d printing to make them in the first place.)

The kit that I bought was the one from a2aprinter.com (And I'd be hard pressed to recommend it, though at least shipping was prompt and reasonable cost.)

I'm reasonably convinced that at least some of my print quality issues are with the hotend. The shaft flexes a little, and does not always remain vertical. It's worst of course when the Z axis gets screwed up and it starts to drag the hotend on the print bed. (The Z axis endstop switch likes to move a bit, plus the errors when the Z axis gets adjusted at the start of the print job.)

I absolutely do not mind the idea of buying a replacement hotend. I'm not sure what size I should get as a nozzle, but I'm also not averse to the idea of buying multiple nozzles for different purposes. Say 0.5mm for large builds with larger tolerances or 0;3mm for finer precision detail or smaller parts. At this point, I think I'm that plus a couple of 8mm rods and LM8UU bearings away from having the parts to build another complete printer... Well, maybe the Z axis gantry, though I'd do it differently anyway, and I've been giving thought to V groove construction as well.

[mixshop.com] I believe that this is the extruder/hotend that I have, seeing as how Mixshop and A2A seem to have very close ties

So recommendations for a hotend/extruder setup would be most welcome.

I suspect that if I can achieve a more rigid hotend, I should get better side printing results. I still need to determine how to get a better top surface though.