Belt Failure

[brhub...@gmail.com]

I don't know the root cause of this failure, so I'm just throwing everything I have on here for reference and help troubleshooting.

About two weeks ago I was running a print and experienced a strange motor skip (of about 1 inch) midprint. This occured on my U motor and completely ruined the print. Photos and description here.

Today, I was running a 6 hour print - just a basic bed for a mass balance I'm developing with Dr. Pearce. The print began with garbage that I have gotten used to, but still do not understand (random slight changes in the bed leveling that make the first layer or two terrible):

Notice how the dragging is relatively sudden on the horizontal edge..

The print was about 4 hours in when my roommate called me to let me know the print had failed. This is what he saw:

There are a few interesting details.

• For one, its printing wayyyy off to one side. The same motor jumped - the U motor. This time in the opposite direction (compared to the first time I had this type of failure), and much farther.
  
• The print started working its way upward, as to be expected from a misalignment of the motors.
• You'll notice a few points where the tip was seriously driving into the plastic, just to the left of the two thru holes. It's unclear why it was driving into a single point, or why the end effector's magnets didn't simply disconnect.

When I got home, I was greeted with this busted belt on my U motor:

That's a serious snap. I didn't think these motors could put out that kind of torque - mine are set at around 470 mV, but still hardly get warm to the touch during continuous printing. Regardless, I think I'll back that off some once I replace the belt.

Inspecting the belt, I noticed some discoloration on the side of the belt facing away from the bed plate (nearer to the wood).

Its tough to photograph, but its that pale coloring on the lower side of the belt in this picture.

My suspicion is that the belt was rubbing against the side of the drive gear due to the drive gear being not quite centered under the steel guide rods. What I don't understand is why this would have snapped while the end effector was up in free air (seemingly facing no resistance to motion). This could potentially also explain the wavering I saw in all of my prints (not printing straight up) and the weird loss of home explored here.

While this seems like the easiest explanation, I'm not quite satisfied with it. Curious if anyone else has thoughts on the matter.

[Dr. Bas Wijnen]

Hi,

I haven't looked at your pictures, but just a quick thought about the
situation:

In my experience, the drive gear is the not problem with the belts. If they rub
against something, it's the idler end. The usual reason that this happens is
that the M8 nut holding the M8 idler axis is loose.

As for the weird first layer with the sudden dragging: this is what I normally
see as well. While the nozzle is too close to the bed, there is no extrusion
but some pressure builds up (until steps start missing). When it gets slightly
higher, the pressure is released so more plastic is extruded than should be.
It's never been a problem for me. If you need a smooth underside, print on a
raft.

Thanks,
Bas

On Mon, Dec 02, 2019 at 09:26:24PM -0800, brhub...@gmail.com wrote:
> I don't know the root cause of this failure, so I'm just throwing
> everything I have on here for reference and help troubleshooting.
>
> About two weeks ago I was running a print and experienced a strange motor
> skip (of about 1 inch) midprint. This occured on my U motor and completely
> ruined the print. Photos and description here

> <https://groups.google.com/a/mtu.edu/forum/?hl=en#!topic/most-delta-users-l/-zZALAhbxtY>.

>
>
> Today, I was running a 6 hour print - just a basic bed for a mass balance
> I'm developing with Dr. Pearce. The print began with garbage that I have
> gotten used to, but still do not understand (random slight changes in the
> bed leveling that make the first layer or two terrible):

> Notice how the dragging is relatively sudden on the horizontal edge..
>
> The print was about 4 hours in when my roommate called me to let me know
> the print had failed. This is what he saw:

> There are a few interesting details.
>

> - For one, its printing wayyyy off to one side. The same motor jumped -

> the U motor. This time in the opposite direction (compared to the first
> time I had this type of failure), and much farther.

> - The print started working its way upward, as to be expected from a
> misalignment of the motors.
> - You'll notice a few points where the tip was seriously driving into

> the plastic, just to the left of the two thru holes. It's unclear why it
> was driving into a single point, or why the end effector's magnets didn't
> simply disconnect.
>
>

> When I got home, I was greeted with this busted belt on my U motor:

> That's a serious snap. I didn't think these motors could put out that kind
> of torque - mine are set at around 470 mV, but still hardly get warm to the
> touch during continuous printing. Regardless, I think I'll back that off
> some once I replace the belt.
>
> Inspecting the belt, I noticed some discoloration on the side of the belt
> facing away from the bed plate (nearer to the wood).

> Its tough to photograph, but its that pale coloring on the lower side of
> the belt in this picture.
>
> My suspicion is that the belt was rubbing against the side of the drive
> gear due to the drive gear being not quite centered under the steel guide
> rods. What I don't understand is why this would have snapped while the end
> effector was up in free air (seemingly facing no resistance to motion).
> This could potentially also explain the wavering I saw in all of my prints
> (not printing straight up) and the weird loss of home explored here

> <https://groups.google.com/a/mtu.edu/forum/?hl=en#!searchin/most-delta-users-l/skirt%7Csort:date/most-delta-users-l/GFf-6fwPUO8/90lchHdSDgAJ>
> .

>
> While this seems like the easiest explanation, I'm not quite satisfied with
> it. Curious if anyone else has thoughts on the matter.
>

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