Weird distortions internal holes

Okay, I thought I had things pretty well sorted out, but I'm getting some weird results here.

trying to print the gears from a Wade's extruder (Thingiverse, thing # 5111: [www.thingiverse.com] )

The outside gear pattern is good, and meshes well with the small gear, but I'm getting some reall weaird effects in the holes in the middle.

This is the bottom side of the print:


The 4 big holes are supposed to be teardrop shaped, and the other 13 are supposed to be round, but they've all deformed.

The bolt hole (highlighted with pencil some) is similarly distorted



The edges aren't even parallel.

Yet, the outside of the gear is pretty good. The gear teeth are the size that they're supposed to be, the outer ring is very circular. If I roll the gear on the table, or floor, it rolls well at low speed, |The gear teeth are well formed and regular, certainly within acceptable tolerances.



So... The outside of the print is coming out reasonable, but the inside is weirdly distorted.

Printing material: 1.75mm transparent ABS
extrusion temperature: 240 deg C
bed temp 110 deg C
Ambient temp: 25 deg C
Printing on clean glass

Print characteristics:

Overall diameter of print (Measured along 4 axis, 0 deg, 45 deg, 90 deg, 135 deg) 63mm, +/- 0.25mm

Size of internal bolt hexagon (Nominally 13mm) measured across each of 3 pair surfaces: 12.6mm, 13mm, 11mm tapering to 10mm.

Centre hole (nominally 8mm) 5mm by 7.5mm

Other features that I notice:

All of the holes appear to be distorted in a similar manner, that is to say that they are compressed neither along the X not Y axis directly, but along a positive X/Y slope, that is to say that it appears that the print head is not moving far enough if both the X and Y axis of the printer is moving in the same relative direction. if they are moving opposite directions, they seem to be better. Distortion is not uniform, however, and does not appear to be a fixed amount, since round holes appear to be the same shape regardless of size. Related is the fact that this does not appear to be a distortion happening over time, as the walls of the holes appear to be uniform and vertical, which I would not expect to be the case if the printer were putting a circle on top of an oval.


My initial suspicion was that there was something with G Code communications, say too low a baud rate to keep up with the arcs of the circles, but if that were the case, I would have expected more problems with the gear teeth, and also less problems with the larger holes than the smaller ones. This does not appear to be the case. I also checked belt tension on the X/Y axis, but ruled this out, since overall dimensions appear to be correct, belt tension seems fine, and again, the gear teeth look good.

So... Anyone have any ideas as to what's wrong with this thing?

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Have you calibrated the X and Y axes and made sure they are orthogonal? Have you measured the outer diameter of the gear at different points to check for roundness?

X and Y axis are calibrated and are perpendicular to each other. I've done prints up to 18cm by 16cm, and checked with my framing square that they are of the size expected, and they are, +/- 0.1mm -- that is to say as accurately as I can measure. I measured the outer teeth of the gear at 0, 45, 90 and 135 degrees. I could measure more, but without a good idea of where the centre of the piece is, since I don't trust the hole to be centered, but using the other holes on the gear as landmarks, I was able to expand to 8 measurement points, and they all check out within reason. There isn't much deviation in the outer diameter, nor is there in the size and spacing of the gear's teeth.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Well, I tried again. I had heard somewhere that a different slicer might generate better Gcode which could alleviate that problem, so I tried slicing with Cura instead of Slic3r. I got very similar results.

Taking both gears and comparing them, the overall diameter is identical, and it is as close to perfectly round as a gear like that is likely to be. The one done with slic3r has somewhat better gear teeth, the one with cura has a more regular fill pattern. both were done with a similar print speed, hotend and bed temperature, and in the same ABS material.

I'm wondering if it's too hot or something and the material is distorting as it extrudes, say the fill pattern is pushing the walls of the material somehow, Maybe I'll try a fill pattern that isn't rectilinear and see if that resolves the problem, or at least changes the outcome. (The hexagonal fill pattern would seem to make sense, but seems to be pretty hard on things, and makes the whole printer shake like crazy, but if it works...)

Printing ABS at a cooler temperature seems to make it want to curl, which I don't like at all. The bed temperature is probably a bit high, as the plastic is still relatively soft at the end of the print, but it doesn't deform if I don't do anything to it.

I've printed other parts with holes, even ones where one printed part has to fit inside the hole in another printed part, and it seems to work fine, but round holes have been problems since day 1 with this printer.

Just one stupid question: Are you sure that that's ABS? Does it's smells like ABS? I have printed so much with nylon and that part just look nylon to me. Do you heard any popping noise as you extrude the filament?

Your printer might be calibrated, but something is either loose or catching, or one of your motors is underpowered.

When you slide by hand both X and Y axis, do they move smooth or there is any stiff place?

I would not trust any files coming from thingiverse, I have seen some really bad ones, have you run it with netfabb cloud?

If as you mentioned your printer have shown problems with circles from day 1, then most likely something it's out of square in your printer. There is a feature in either marlin or the slicer (can't remember where) that help you deal with out of square settings you might have to play with it and see if it helps.

I'm reasonably sure that it's ABS. It's supposed to be transparent, but comes out looking white. it dissolves as expected in acetone, no popping noises or weirdness from the hotend. Nylon will not dissolve in acetone, nor will PLA, so that's not it.

The X and Y axis slide smoothly and without any issues when I disconnect the belts from the motors. I've checked and double checked that they are perpendicular to each other, though there may still be a slight (<0.5degree) skew to the Z axis, though that's not significant for a print that's only 12mm high. I've done a print that is 180mm by 160mm, and checked it with a square, and the corners are exactly 90 degrees, no weirdness.

The model may or may not be crap, but the G code certainly LOOKS like circles, and I am seeing the same results in parts that I have modeled myself, though only with openings, not with exterior dimensions. If I make a part solid, it is much better. I would think that if it were catching, or the motors are too weak, there would be missed steps, and that should translate to problems on the outside circumference as well, but there is no evidence of that.

I haven't printed it yet, but I've also got some test objects to do which will try holes at varying diameters to see if it's just a small diameter thing, I'm also going to see if changing the fill pattern helps.

Oh, and most of the problems that I had initially with circular holes was that they were undersize, though they may have also been out of round, all I know for sure is that I had to drill them out if I wanted the things to fit inside that I wanted to, I did not check them for roundness other than trying to fit whatever it was that I needed inside of it. I believe, however that the problem isn't as apparent when I print with PLA. I'll have to check that, too.

Well, it look like you have checked all possibilities, since I'm running out of ideas to help you, there is one last thing I can think off but not sure if will help: micro stepping. Settings and or the jumpers in the board, if some differences in the firmware (I doubt) or one of the jumpers are missing or not connecting right (possible).

I appreciate the help.

for the time being, I've got a couple of tests to run.

1. Print hte part in PLA. If this resolves it, then it's probably temperature related, since the motion of the printer will be the same regardless of medium. I don't know why temperature would do this, but if it does, then it's probably the rectilinear fill material forcing things to go weird. too bad, since printing cooler and I get problems with ABS warping/peeling as it prints.

2. See if the problem is related to the diameter of the circles. It may be that larger circles work okay, and smaller ones have the problem. Annoying if so, but then it's a clue as to what's wrong. Maybe that the print head speed can't adjust that quickly, and a slower print speed would fix it. I hope this isn't it, since prints are already kind of slow, particularly with small layer heights. I should also check interior circles (holes) with exterior ones. If it is all circles of diameter X then that's an easier problem to solve.

I'd check with a thermo couple if the temperature is correct in steps of 10 degrees. If it's off you could try a differerent lookup table for the ntc in firmware.
It looks like the temperature is too high. Maybe finding a better way to prevent warping at lower temperatures is also helpful, try improving bed adhesion with glue, hair spray, abs slurry etc.

Edited 1 time(s). Last edit at 03/11/2015 09:45AM by imqqmi.

I've checked temperatures with an IR thermometer, and they seem reasonably close to what they're supposed to be, si I'm thinking that the thermistor lookup is oka. It's probably right for where the thermistor is actually located versus where I can test. Bed temps are spot on.

Hairspray is a fail with ABS, works fine with PLA.

ABS slurry is good, though I don't like the film it leaves on the part, and it doesn't always prevent warping with prints of uneven layers, I often use it for smaller prints as it's definitely an improvement over clean glass.I didn't manage to get to printing the part in PLA last night.

Have you tried with a different STL just incase your's is bad you could try looking at Gears I would try the one with 6 plain round holes and see what happens?

Doug

Edited 1 time(s). Last edit at 03/11/2015 11:37AM by dougal1957.

It isn't unique to this print, it also happens with other things. In this case, it's a very clear example.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

One last thought from me: what kind of hotend you have? A makerbot style or a J head one? If it's loose, that could explain deformities on the print, they will show all over but definitely more prone in circles.

It's a J head style, and when I got the kit it was definitely not as tight as I thought that it should be. I've tightened it up, so it doesn't move much relative to the extruder, but I will check this again, in case it is moving again. Thanks for the suggestion.

Okay, I double checked everything.

The Y axis belt wasn't as tight as I thought that it should be, so I tightened it. The J head is tightly attatched to the carriage. I lowered the extrusion temperature from 230 to 195, re-printed the part.

There is some lifting at the gear teeth at the lower temperature, which I kind of expected, as that was a big part of the reason for increasing the temperature in the first place. Tightening the belt seems to have made no difference, lowering temperature, no difference. Well, there seems to be a slight reduction in the amount that some of the walls have been pushed in, but it's tiny.

So things that I know it isn't:

X axis belt. (This is tight. The axis moves smoothly and with little to no effort when the motor is powered down.)
Y axis belt. (Just re-tightened, and again, moves smoothly when the motor is powered down.)
Z anything. There is no noticeable distortion in the Z axis direction.
J head flex. The J head is remaining stationary relative to the carriage.

So at this point, I'm suspecting that it has something to do with the control electronics, since the very first outlines seem to exhibit the distortion problem. It seems as though there is a lack of coordination between the X and Y axis in changing speeds. I am going to try playing with the max accelleration settings in Marlin. It seems to affect the circles and not the rectilinear infill, which also suggests that it may be the timing of updating the print head's direction. I still have the baud rate for printer communications at 115200, I will first try to bump it up to 250000 and see if that makes a difference. I do know that I want to put the temperature settings back where they were, since that made no improvement at all, and in fact brought back problems that I really want to be rid of.

I had thought that maybe slowing down the print would help, but I'm not at all certain that it will, seeing as how the first layer prints at 75% speed, and still shows the same issues as the rest of the layers. Well, maybe I'll try it this weekend anyway, though as is, that gear is a 3.5 hour print at 12mm high with 0.1mm layer heights. (Total 119 layers, since the first layer is 0.2mm) Slowing that down isn't really a desireable action for me.

I'm wondering if there are also integer conversion errors taking place. There must be some, since it's just not possible to move a decimal of a step, but I would think that it should not come to whole millimeters, even if the capacity of the motors to microstep isn't as good as the RAMPS board thinks that it is. Also the accuracy of the outer dimensions of the print seems to indicate that things should be able to be closer than that...

I was thinking that it could be arcs that it doesn't do well, but one of the distorted holes is hexagonal, which are just straight lines.

I gather that other people aren't seeing this problem, so I will assume that it isn't an issue with the Arduino or RAMPS boards. I don't THINK that it's my stepper motors having some sort of weird timing issue, as they seem to move properly otherwise.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Well, I know you have already replaced 2 drivers, but might be a good idea to try new ones. Don't think so, but check the steppers wiring, a flipped coil wire could be the problem. Test your motors before you discard them as the cause slowly turn them and feel if missing steps.

On the software, things will be a lot harder to find. Save your current marlin and flash a new one or a different type. I can just imagine how frustrating this might be for you but don't give up, the light it's always on the other side of the tunnel, once you get to it clarity and knowledge will stay with you forever.

Good luck.

It's running a new print right now.

I've replaced all of the drivers. I've checked that the hotend mount is securely fastened to the carriage and the carriage to the bearings, tightened the belts. Nothing changed there, so I went ahead and upped the baud rate to 250000.

It's distinctly better. I will have to let it get to the hexagonal hole to be sure, but so far the round holes look promising. They're still a tad flattened on one side, so I'll have to check things for flex and bend, but at least they don't look football shaped.