UM2 extruder carrier collides with right-side pulley rods

[eldrick 65]

There appears to be a goof in what I'm guessing is either the Marlin or the Cura definition of the printbed size.

I was trying to get a maximum-size print by scaling it in Cura, and discovered that because of the off-center extruder position in the head, one cannot print in the inch or so at the right edge of the printbed - not at all, no matter what you do. If there were a second extruder installed one could use it to print there, but not with a single-extruder U2.

In doing this I created a piece that was nearly the width of the printbed, and when printed, the extruder carrier collided hard with the rod at the top of the right side of the machine. This stresses everything a lot and makes a horrible noise when it happens, and could conceivably even cause a belt to skip.

This sure seems like a bug...

 

[gr5 2,167]

extruder carrier

 

Let's call this the "head".

 

and could conceivably even cause a belt to skip.

 

Yes, maybe, but definitely will cause steppers to lose steps. Many steps. Causing the rest of the layer and subsequent layers to print in the wrong place.

The head is probably hitting the black block on the rod and not the rod directly, right? Is it possible the fan shroud is hitting the right wall?

I believe the spec is either 225 or 235mm in X travel before it hits the "software limit switch" in Marlin.

1) I had a similar problem where I hadn't noticed but there are 2 linear bearings near the top of the print head that the two rods pass through - one of my linear bearings was sticking out the side of the head a bit - I think I bumped it when I had taken the head apart and didn't line it back up when I tightened it again. Could that be it? If so you can see the metal cylinder that houses the bearing sticking out the side of the head a few mm.

2) Some people have had their fan shrould miss bent such that it hits one or both sides of the UM.

I recommend you donwload pronterface (it's free and easy to use):

http://koti.kapsi.fi/~kliment/printrun/

Connect your computer with pronterface up to the printer with USB cable, then command it to go to various X positions. For example

G1 X0

goes to postion 0 (left side)

G1 X200

goes to position 200

Then see how far it goes before hitting something (or hitting software end stop). Will it go to X225? X235? X240?

Repeat this with Y axis - one of the axes is 10mm longer than the other. Not sure which.

 

[gr5 2,167]

By the way - even though it makes a horrible noise, it seems not to cause any damage. This has happened to me plenty of times (when homing on the left side - not the right side) and many many other people. The printer is designed to withstand this kind of abuse. Some people call it the "death rattle" when it happens over a few seconds.

 

[eldrick 65]

It is the extruder carrier head hitting the right-side black slider block on the rod. I'm pretty sure that either Marlin or Cura should be preventing this from happening.

 

[illuminarti 18]

Well, since there is no hard endstop on the right side, the only way for the printer to know when it should stop moving right, is to measure movement from the left end stop.

However, the exact position of the left endstop isn't particularly well fixed; it has changed slightly over the evolution of the printer (early ones had a slot allowing the position of the endstop to be adjsuted slightly. More recent ones have a fixed hole instead.) Furthermore, depending on the exact shape of the fan ducts, and angle of the endstop, the exact left stop position can still be vary between printers a bit (and, indeed, may need to be). So, there's not really an exact dimension for the width of the printable area (at least not without picking a conservative value which deprives a few folks of the last few mm that they might really want). So, currently, it's possible that the value is a bit off for your printer. Also, as you mention, the printer is set up to allow dual extrusion, so valid coordinates for the second nozzle (when it exists) are greater than for the first nozzle. Cura might need to be smarter about that too.

In the meantime, as George suggests, install Pronterface, and drive your head around the bed to figure out what the exact safe dimensions are for your printer, and then set those as the bed size in Cura.

 

[gr5 2,167]

Can you please do the pronterface test and measure how far X can move?

I just looked at the code and it doesn't agree with official specifications:

 

#define min_software_endstops true // If true, axis won't move to coordinates less than HOME_POS.
#define max_software_endstops true // If true, axis won't move to coordinates greater than the defined lengths below.
// Travel limits after homing
#define X_MAX_POS 230
#define X_MIN_POS 0
#define Y_MAX_POS 230
#define Y_MIN_POS 0
#define Z_MAX_POS 230
#define Z_MIN_POS 0

I got that snippet from here:

https://github.com/Ultimaker/Ultimaker2Marlin/blob/master/Marlin/Configuration.h

Official specs are 230mm width, 225 depth, 205mm height. That info is here:

https://www.ultimaker.com/products/ultimaker-2

And also in cura "machine settings".

So obviously the software endstops disagree with the literature and Cura settings.

I'm thinking your machine can only go to 229mm or something and to get the full 230mm you might need to move your X limit switch slightly more to the left. You can bend the limit switch arm or you can loosen it and slide it a little.

 

[eldrick 65]

In the meantime, as George suggests, install Pronterface, and drive your head around the bed to figure out what the exact safe dimensions are for your printer, and then set those as the bed size in Cura.

 

Excellent idea - I'll use Printrun and report back. The print that brought this to my attention, as sliced by Cura with stock UM2 settings, was a good 5mm wider than the machine would do without collision. The head hit the rod still printing the skirt, and slid along it, basically truncating the skirt along that side.

 

[eldrick 65]

Here's what I got when trying to evaluate actual printable volume using Cura: http://umforum.ultimaker.com/index.php?/topic/5447-um2-does-not-meet-its-build-volume-specs/%C2%A0