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Can't print below x=5 ish - print truncated  

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JoanTabb
(@joantabb)
Moderator
RE: Can't print below x=5 ish - print truncated

has anybody had a chat with prusa, on this matter?, perhaps linking to his thread!

 

regards Joan

 

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 29/01/2020 9:27 am
JoanTabb
(@joantabb)
Moderator
RE: Can't print below x=5 ish - print truncated

has anybody had a chat with prusa, on this matter?, perhaps linking to his thread!

 

regards Joan

 

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 29/01/2020 9:27 am
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

There are several comments about this on the manual for the extruder assembly at https://manual.prusa3d.com/Guide/3.+E-axis+assembly/1073?lang=en.   Go down to the section on the end-stop and read them.  Replies from Prusa indicate that it is correct as is, but people are still reporting problems.

Posted : 29/01/2020 10:04 pm
Ian
 Ian
(@ian-3)
Eminent Member
Topic starter answered:
RE: Can't print below x=5 ish - print truncated

I think it's reasonably clear that the lost 4mm is "corrects as is" in so far as it is what Prusa intend.  Prusa do intend the endstop to trigger where it does (i.e. the endstop is the size they intend), and do intend that the print nozzle doesn't reach below about 4mm, having used as the definition of the axis that the far end should be at 250mm (detected by the PINDA calibration probing) rather than that the near end should be at 0mm (detected by the microswitch).

The only thing wrong in those comments, I think, is the reply from Prusa saying they haven't reduced print volume, when it is very apparent that they have done so - my guess is that they haven't told all their support people that they've done it.

 

...
Posted : 29/01/2020 10:31 pm
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

Agree with ian-s3. 

The problem seems to be the cables interfering with the printer frame.  Only a redesign of the extruder cable routing to make the bundle come out slightly to the right, and significantly thinner in the X direction, would allow the full X travel.  

Messing with the endstop in the existing design may give you an extra couple of mm, but is barely worth it.

Posted : 30/01/2020 1:34 am
BillC
(@billc)
Reputable Member
RE: Can't print below x=5 ish - print truncated

In this thread https://forum.prusaprinters.org/forum/original-prusa-i3-mk2.5s-mk2.5-hardware-firmware-and-software-help/not-getting-full-x-axis-travel-mk2-5s/ OP @kenny-b2 says he was able to resolve the issue by meticulously eliminating the slight skew in his frame. I would love to try this, but am currently away from home. 

Anyone else want to try it and report progress?

Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor...
Posted : 31/01/2020 11:49 am
Ian
 Ian
(@ian-3)
Eminent Member
Topic starter answered:
RE: Can't print below x=5 ish - print truncated
Posted by: @billcampbell

In this thread https://forum.prusaprinters.org/forum/original-prusa-i3-mk2.5s-mk2.5-hardware-firmware-and-software-help/not-getting-full-x-axis-travel-mk2-5s/ OP @kenny-b2 says he was able to resolve the issue by meticulously eliminating the slight skew in his frame. I would love to try this, but am currently away from home. 

Anyone else want to try it and report progress?

I don't believe it's attributable to skew - you can get a report of skew from the calibration menu.  I have less than 'slight' skew, and the wizard tells me the axes are perpendicular and says congratulations, but I still lose 4mm-ish x travel.  Furthermore, 0.12 degrees across 250mm is only 0.5mm offset, so I can't see how it accounts for the loss of travel people are finding - it's literally an order of magnitude different.

I probably could 'fix' it by moving the bed to the right.  My cables from the back of the x-carriage are very close to the frame edge at full left, but my print bed plate has a gap of just over 4mm at the right side.  However, I don't see any means to shift it over - there isn't that much play where the threaded rods go through the frame plate, and there is much less where the rods connect to the feet blocks, where the smooth rods fit into the feet blocks, or where the bearings connect to the bed frame.  I think I'd need new feet blocks with offset holes.

I don't consider the 4mm to be worth the effort.

...
Posted : 31/01/2020 3:13 pm
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

@ian-s3

While the bed may be 4mm from the right edge of the frame, have you noticed there are two protruding lugs on the lower side of the power supply, allowing only about 2.6 mm space ?  You would have to remove either them, or the whole supply, to gain the 4mm space. 

I too dont think its worth the effort.

Posted : 31/01/2020 11:22 pm
kenny.b2
(@kenny-b2)
Trusted Member
RE: Can't print below x=5 ish - print truncated

@ian-s3

On the printer, go to support -> XYZ cal. details then go to the third screen by clicking in the wheel till you reach it.  It will be titled: [0;0] point offset.  The value for X should correspond to how much X travel you lost from your x-axis  

To fix it, there are two options.  The one I recommend (and what I did) was to keep adjusting my frame till I got the skew low enough and the X offset got to nearly zero.  That completely resolved my issue.  The second option is to modify and re-compile the firmware to give yourself more X-axis travel.  If the X-offset from your frame is negative, this doesn't work.  You need it to be positive and then you can extend the max x travel variable in the firmware to 250 + that offset.  I did this for a different reason to trigger a purge mechanism off the bed and realized it also could have fixed this issue.  

Here was the original ticket I opened regarding this issue last year: https://github.com/prusa3d/Prusa-Firmware/issues/2007

I suspect somewhere back in time (maybe around when the 2.5s kit came out) they modified the firmware a bit to enforce the [0;0] offset to prevent you from having the extruder collide with something if your bed was super square.  

This post was modified 2 years ago by kenny.b2
...
Posted : 01/02/2020 6:46 am
Ian
 Ian
(@ian-3)
Eminent Member
Topic starter answered:
RE: Can't print below x=5 ish - print truncated
Posted by: @ajisis

@ian-s3

While the bed may be 4mm from the right edge of the frame, have you noticed there are two protruding lugs on the lower side of the power supply, allowing only about 2.6 mm space ?  You would have to remove either them, or the whole supply, to gain the 4mm space. 

I too dont think its worth the effort.

My power supply is elsewhere already - I have a remote power supply that's switched by an Octopi, so I don't have that clash.

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Posted : 01/02/2020 2:03 pm
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

@kenny-b2

Ok, thanks for that.  Printer reports the 0,0 offset as X=-4.28, Y =1.05.  From the fact that others report slightly different values, it seems to me this cant be firmware, but is just differences in the location of the bed within the frame, and the exact length of the X endstop on the extruder.  And it cant be 'skew' ie X and Y axes not perpendicular.  That would be a huge angle.  The reported skew after XYZ calibration is 0.04 degrees.  And even visually, the X smooth rods are well within 1mm of parallel to the bed alignment lines.   What exactly did you adjust to get this X number smaller ?  I cant see that you can move anything by that much without clashing with something else ?

I am inclined to leave mine as is - I dont desperately need that 4mm extra travel in any case.

Posted : 01/02/2020 11:32 pm
kenny.b2
(@kenny-b2)
Trusted Member
RE: Can't print below x=5 ish - print truncated

@ajisis

I'm using the skew term generically in that your bed isn't quite where it should be translationally or rotationally.  That is probably bad nomenclature on my part.  I have a bear frame so I just made some jigs and moved the rail mounts around till I got it right.  On the original frame, I think there is a little slop (not 4mm of slop) in the slots where the big z plate interfaces to the threaded rods.  You could slide it over a little there.

Just reading a little more on this today: https://help.prusa3d.com/article/PBlnvMN6pt-xyz-calibration-details   it doesn't seem like the offsets it is giving is corresponding to that explanation on the article regarding skew.  I took a quick peek in the mesh_bed_calibration.cpp file of the source code which is where I think the offset gets calculated.  It's doing a bunch of matrices math and I'm lazy so I didn't really try figure out exactly where the problem is.  Maybe doing a diff of this file against one of the really old firmware files would give some hint as to if its just calculating the offset incorrectly on the newer firmware. 

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Posted : 02/02/2020 1:05 am
Ian
 Ian
(@ian-3)
Eminent Member
Topic starter answered:
RE: Can't print below x=5 ish - print truncated
Posted by: @kenny-b2

@ajisis

I'm using the skew term generically in that your bed isn't quite where it should be translationally or rotationally.  That is probably bad nomenclature on my part.  I have a bear frame so I just made some jigs and moved the rail mounts around till I got it right.  On the original frame, I think there is a little slop (not 4mm of slop) in the slots where the big z plate interfaces to the threaded rods.  You could slide it over a little there.

Thanks for the clarification - yes the nomenclature was what was causing confusion (on my part at least).  Shifting the whole bed sideways is not what I would term skew.

Effectively (functionally) this is what I already contemplated up the thread - displacing the bed frame sideways.  Up the thread I suggested that the easiest options would require creating and printing new foot blocks that offset the smooth rods from the threaded rods, but you could alternatively enlarge the slots in the vertical frame plate - since it's only 4mm it wouldn't take much filing, and I suspect that's actually less effort than new blocks, mainly because it requires a less intrusive dismantling of the printer.  However, I think it's still more effort than it's worth.

...
Posted : 02/02/2020 10:02 am
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

@kenny-b2

I think the offset is generated from the fact that the X endstop is not correct.  Other users have reported shortening the endstop by about 4 mm, and then the physical switch trigger agrees with the targets in the bed used during the XYZ calibration.  This diff is what causes the X offset. 

While that fixes the diff, it does not fix the problem of the extruder cable bundle being too wide, and in the wrong place.  Modifying the X carriage back plate would allow this.

But yes, I agree that its hardly worth it.

Posted : 02/02/2020 9:36 pm
kenny.b2
(@kenny-b2)
Trusted Member
RE: Can't print below x=5 ish - print truncated

@ajisis

That doesn't make sense though (coming from someone who has tried shortening the endstop block).  It would point to a firmware issue then as clearly the design of the endstop can't be wrong (as you said the cable bundle hits if you shorten it).  There is plenty of space for the extruder to travel beyond the bed on the near and far end of the x travel so we aren't travel limited on either end.  

That only leaves two things, your bed is offset or the firmware doesn't calculate the offset correctly.  For me, the former fixed it but I have the unfair advantage of a bear frame.  It's quite possible the firmware is at fault.

...
Posted : 02/02/2020 10:41 pm
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

@kenny-b2

Hmm, thats interesting.  On mine, the frame measures 260, and the bed measures 254, so 6mm total clearance  ( the right clearance to the frame is about 4mm, but there are lugs on the power supply that stick out about 2mm of that.  So moving the bed is not really an option, or at least not to regain 4mm of travel.

Posted : 02/02/2020 11:52 pm
BillC
(@billc)
Reputable Member
RE: Can't print below x=5 ish - print truncated

Would be interesting to get the measurement from z-frame edge to the leftmost line on the bed with

a) bed fully forward

b) bed fully backward

i.e. Y min and Y max.

theoretically if the missing travel can be recovered, the difference in those measurements should equal the experienced offset.

Wish I was home to do these checks myself. I am suffering Prusa withdrawal symptoms.

Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor...
Posted : 03/02/2020 8:42 am
Ian
 Ian
(@ian-3)
Eminent Member
Topic starter answered:
RE: Can't print below x=5 ish - print truncated
Posted by: @billcampbell

Would be interesting to get the measurement from z-frame edge to the leftmost line on the bed with

a) bed fully forward

b) bed fully backward

I think you are still assuming the offset is due to skew, and I think it clearly isn't, because the stated skew is not enough to give rise to 4mm, which is the typical figure reported.

Notwithstanding that, on my machine (which has a stated 0,0 offset of -4.48mm) full back the offset from frame to near edge of the printed line on the heatbed (not the removable printbed steel sheet) is 3.0mm and with the bed as far forward as the printed line is still alongside the frame (which is not fully forward), 3.3mm (by slightly magnified eye, and probably only good enough for +/- 0.2mm).

That's 0.3mm over about 170mm of travel, which is 0.101 degrees, which ties up with the stated skew in the 'support' menu item, and the wizard saying the axes are perpendicular.

Skewed bed does not account for the offset.  Even perfectly eliminating skew will not get 4mm back - at best, it's going to get that 0.3mm back, which (as noted up the thread) is an order of magnitude less than the 'missing' dimension.

In my opinion:

  • The stop is the right size (i.e. the intended size for the carriage and printhead) because if it was smaller the cable bundle would strike the frame (in my case, I think I could get about 0.5 to 1mm by tweaking the endstop).
  • Prusa intend the x-travel to be a bit less than 250mm, but rather than have the x-axis active over a range of (say) 0 to 245.52 they have it set the axis travel from the far end not the near end and you get (say) 4.48 to 250.00.
  • The slicer is oblivious of this and will generate GCODE over 0.00 to 250.00.
  • There is enough space to get 250mm (or much closer to it) travel for a 2.5s head within the frame, though you need to change a few things - offset the smooth rods from the threaded rods, or enlarge the slot for the threaded rods, and possibly relocate the power supply (I've relocated mine already, so can't confirm the latter).

I don't know that this limited travel was introduced with 2.5s, but I didn't notice it before 2.5s.  Maybe it has always been the case, or maybe the carriage / printhead assembly on previous versions was a few millimetres slimmer so you really did get a full 250mm.

...
Posted : 03/02/2020 9:59 am
adrianj
(@adrianj-2)
Eminent Member
RE: Can't print below x=5 ish - print truncated

@ian-s3

I did bills suggestion too, and got zframe to bed left line 3.49 at Ymin and 3.31 Ymax. Possible error about 0.05, mostly the thickness of the line on the bed.

In an earlier post I had already commented that my printer when it was a MK2 gave the full 0 to 250 mm travel.

My impression is that someone noticed that the extruder cable bundle was now too thick to allow the full travel, and rather than making more changes to the extruder, they just silently 'fixed' it by adding more to the endstop, and tweaking the firmware to notice the difference.

Posted : 03/02/2020 10:57 pm
BillC
(@billc)
Reputable Member
RE: Can't print below x=5 ish - print truncated

@ian-s3, @ajisis,

Thanks for trying that. Colour me disappointed, but not surprised.

I guess the answer - for me at least - is to change the bed dimension in PrusaSlicer. I already run my printers on a personalised copy of the original printer settings so changing that profile is a no-brainer.

More difficult will be remembering, when I am cutting oversized pieces to multiple plates, not to exceed the 245mm limit if I am going to print on the 2.5S.

 

Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor...
Posted : 03/02/2020 11:20 pm
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