Ultimaker 2+ extended: crossbars have come loose

[RogerBW 0]

The crossbars on which the print head sits ride on pairs of brackets, each bracket attached to its drive belt.

 

All of a sudden, both of the crossbars are loose in their brackets and can become entirely disengaged, which obviously causes a print failure.

 

Haven't seen any mention of this. Has it happened to other people? Any recommendations for a fix?

[Enigma_M4 119]

Hi RogerBW,

this seems a very common issue which is simple to fix.

There's a good tutorial by @fbrc8-erin:

The video refers to an UM3, but as the sliding blocks are the same for the UM2, you can refer to it 1:1.

Regards

[fbrc8-erin 272]

Are the printhead shafts refusing to snap solidly into the blocks? Do you enclose your machine? If you have heat wear and tear on the blocks, it may be time to replace your sliding blocks if reseating them doesn't do the trick.

[capcotechuser 0]

My guide X and Y rods are popping loose on an Amazon Basics ABS print that requires unusually high bed and nozzle temperatures (215 degC and 248 degC).  User reports on Amazon say that it takes a very high bed and nozzle temperature and I also blanket the printer to ensure a warm, stable environment because the shrinkage and warpage have been crazy.  I've re-seated the rods several times and they pop loose within an hour of two of starting the print job.

 

"Heat wear and tear" is a curious concept since the printer should be designed to handle a heated build enclosure.  Thermal fatigue usually only applies to extremes in temperature and particularly when those extremes are reached rapidly, such as from turning a high-powered light on and off repeatedly.

 

What's the story behind this "heat wear and tear" that the bearing blocks may be experiencing?

 

Do the bearing blocks expand at print enclosure temperatures above 180 degC or something?

[fbrc8-erin 272]

@capcotechuser are you sure about the bed temperature? 215C is about 100 degrees too high for the bed. What model Ultimaker are you printing on?

Are the sliding blocks on your machine black or white? If it's an older machine with black plastic blocks, those machines didn't come with any enclosures and the blocks are made of ABS, so they will take wear and tear from heat if you enclose the machine and don't leave some avenue for excess heat to escape. The blocks (especially on your Y axis) spend a lot of time close to the bed during your first few layers.

For the later machines (S3, Connect, etc), the blocks are made of a different material--it's more heat resistant. However, the enclosures Ultimaker makes for those machines are also designed to control the ambient temperature and keep it from overheating. I think max recommended build chamber temperature is around 55C.