Newbie with a Prusa i3, Z endstop woes, 1st layer alignment, loose hotend

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04-21-2015, 03:18 PM
fitzy89

Newbie with a Prusa i3, Z endstop woes, 1st layer alignment, loose hotend

Hello all

I'm a new owner of a Prusa i3 and new to 3D printing as well but very technically and mechanically minded so hopefully I've got the skills to get this working. After extensive research I decided this would be the most fun and suitable printer to play with. I got it from Greg Colbourne on eMaker. I believe it to be a fairly high end version of the i3 if I've done my research right. The build went well, had it all up and running within about 7 hours, quite impressed how simple it is.

I am however having some teething problems with it. Sorry to dump it all in one post which will likely be a long one, I've been doing a bit of searching online but haven't found anything so far that has helped.

Probably the most annoying one seems to be the Z endstop doesn't seem to stay accurate. I've run through the calibration process on this page and the first print following calibration seems to be pretty good but by the end of it the Z endstop is out of alignment again causing the nozzle to hit the bed on the next print. I've done a handful of prints on the machine now and I've only once been able to do 2 prints in a row without the Z endstop causing issues. It's mounted on tight, calibrated using the thickness of two sheets of standard A4 paper. I'm at a loss now what could be causing these issues, the machine is also on a flat level desk and all nuts/bolts are tight. The endstop is the type with a small microswitch (with lever) mounted on a PCB which is mounted to the vertical smooth rod on a 'candy cane' shaped plastic bracket with a bolt to make it grip on the rod, I'd assume it's standard for these although if I can print a better one I likely will.

The next issue is that with every print, the first layer is misaligned by about 1.5mm on the X axis and just under 0.5mm on the Y axis. The only thing I can think of is a slack belt or loose pulley grub screws but neither of them seem to be the issue, the belts are fairly tight, I've tried loosening them (made all layers sloppy) and making them even tighter (no noticeable difference), grub screws as well are tight. Strangely it's only the first layer though, after that all remaining layers are very straight and aligned well. This seems to happen on all prints no matter what the item is. Out of interest, does anyone recommend those spring tensioners available on ebay, the ones that look like clothes peg springs that clip on the belt? If so, where on the belt could it be mounted? As far as I can tell, wherever along the belt it could be put would cause it to catch on the frame or pulleys during printing.

Also another thing, not sure if it's a design flaw or if it's meant to be this way but the hot end does have some movement where it slots into the extruder, by hand the nozzle end can be moved a good 3-4mm in all directions. The bolts holding the extruder to the bearing plate/X axis are fairly tight to the point where it's deforming/denting the front surface of the extruder when tight. It has been like this since new and slackening/tightening the bolts makes no difference, is this normal? I can't visibly see it moving during prints but it had me a little worried that it shouldn't be like this and may be contributing to other issues.

Another thing that has only happened once, but may be worth a mention. I was printing a 20mm hollow test cube and right at the top just before it did the bridging, all the axis motors went spaz and vibrated at the same time and the extruder pumped out a good amount of filament on the edge of the cube, moved 5mm along the Y axis, and continued to print (so there was a lot of excess filament, and the bridged lid of the cube was hanging over the edge of the cube by 5mm). Not sure what could have caused it, sounded like a motor current issue but that's all been calibrated fine so I'm not sure, either way it's only happened once so far so I'm not too worried.

Any help would be much appreciated. If it matters, I'm printing with 3mm white PLA with hotend at 180C and bed at 60C.
04-26-2015, 08:20 AM
zx81

How is your Z endstop atached ? .. I just use a tie-wrap with a couple of rubber washers (sold as anti vibration dampers for pc-fans) and it holds the endstop without any movment.

as for misalignment that's a difficult one to say, if your belts and pulleys are ok then you might not have enough current or to much current going to your motors, could be skipping steps or your steps may need calibrating.

there's a couple of ways your hot-end can attach to the extruder body assuming its a Greg's wade Extruder, two bolts through at the top of the extruder shaft or a metal plate which bolts on from the bottom of the extruder which is what I ended up doing as I replaced my chepo hotend with a hexagon fairly early on.
05-05-2015, 04:26 PM
fitzy89

3 Attachment(s)

Quote:

Originally Posted by zx81

How is your Z endstop atached ? .. I just use a tie-wrap with a couple of rubber washers (sold as anti vibration dampers for pc-fans) and it holds the endstop without any movment.

as for misalignment that's a difficult one to say, if your belts and pulleys are ok then you might not have enough current or to much current going to your motors, could be skipping steps or your steps may need calibrating.

there's a couple of ways your hot-end can attach to the extruder body assuming its a Greg's wade Extruder, two bolts through at the top of the extruder shaft or a metal plate which bolts on from the bottom of the extruder which is what I ended up doing as I replaced my chepo hotend with a hexagon fairly early on.

Thanks for your response and sorry for the delayed reply on my part, haven't had much time to play with it recently due to work.

I'm using the all metal E3D v6 hot end which I gather is fairly good from what I've read about them, it's got two bolts that go through the extruder body to hold it in place but there's still a good amount of play in it. I can't see it moving when printing but by hand it moves probably 4mm or so in total in all directions, the bolts don't really grip it they just seem to sit either side of the top of the hotend heatsink.

My Z endstop mount is a plastic printed 'J' shape bracket that clips onto the Z smooth rod and is clamped in place with an M3 bolt, the micro switch PCB is then attached to that with a zip tie, very tightly and it doesn't move at all by hand, I'm just unsure what is causing it to be inaccurate, whether it's the endstop itself moving that is causing it or something else. I've been suspicious about the silicone tube couplers that join the Z motors to the threaded rod, some say to leave a small gap between the end of the motor shaft and the rod to allow it to flex, some say have them butted tight together, at the moment there's about a 1mm gap, although actually I've just noticed it does move more than expected when pushed by hand, also the motor shaft seems to have some slight play as well when downward pressure is put on it - slides within the motor body by I'd guess 0.5mm but takes moderate weight in the Z axis to make it do this so I don't think it would normally happen when printing.

Attachment 5949 Attachment 5950 Attachment 5951
05-05-2015, 08:29 PM
fitzy89

1 Attachment(s)

Hi again. Something else I wasn't quite sure on is the Z motor calibration, I've tried adjusting it and as far as I can tell it's right but when starting a print it makes the noise as shown in the video (only when starting a print, not at any other time).

https://www.youtube.com/watch?v=JuTEbjLSgRI

Should it be doing this or have I got too much or too little current set on the potentiometer? I wasn't sure if it needed to be set higher than the other axis as it's driving two motors.

Edit: As in my last reply I have now tightened the silicone couplers so the motor shaft and threaded rod are tight together now, no noticable difference in print quality. The one thing that's really bugging me is the first layer being offset, most of the other things I can live with if I have to but the first layer being offset does cause some issues. I do occasionally get a layer further up a print be slightly out as well, very rarely though. I tried printing this: http://www.thingiverse.com/thing:76898 and it happened must be a good 20-30 layers up and it skipped nearly 2mm on the Y axis, almost as though it had slipped a tooth on the GT2 belt but I can't see how it could have, the gears are good, grub screws tightened and it's tensioned well. On some smaller prints it will go out of alignment by a very small amount, a fraction of a millimeter in both X and Y so it looks like a sort of diagonal misalignment but again it's very rare. Hopefully you can see in the attached picture (10mm solid cube), also shows the first layer offset issue..
Attachment 5952

Edit 2: I also appear to have a blocked nozzle now too after printing the 'Holy Dice' from the thingyverse link above, happened half way through the print, shouldn't be too hard to sort out, will take it apart hopefully tomorrow. Not sure what could have got in there as I've got the filament cleaner (sponge in a small box, filament goes through it) installed on the extruder that came with my Prusa kit. Got some welding nozzle cleaners (hopefully they are small enough for this) on the way from ebay, a feeler gauge for levelling the bed accurately and some of those spring belt tensioners, should be here by Friday.