Inconsistent Tool Pickup

This issue can be tricky to diagnose, but the main symptoms are:

• monochrome prints look good.
• multicolor prints appear to have small layer shifts that affect one or more tools.
• if printing with a purge tower, the layer shifts will also be present there.

Here's an example.

What's Happening?

In the image above, the silky gold filament looks fine, but the marble filament is displaying what looks like inconsistent extrusion. Assuming the above symptoms hold, this issue is likely to inconsistent tool pickup.

In principle, the tool should only seat into the coupling in exactly one way where the twist lock applies only a downward nesting force through the wedge plate that pulls the tool into the carriage. In practice, however, the tool may twist on pickup, causing the twist lock and wedge plate to form a reference feature. In this case, the tool will wiggle, since it is not fully engaging the coupling.

Some tool plate designs are more susceptible to this issue than others. The printed tool plates are especially susceptible to this issue since the wedge plate layers are a source of added friction that can twist the tool on pickup. E3D tool plates are less susceptible to this issue as their wedge plates features are smoother.

Fixing

To solve the inconsistent tool pickup issue, adjust the parking post location. The key idea is to ensure that the tool does not twist while it is being picked up by the carriage.

Checking the Fix

After adjusting the parking post location, do the following:

1. Pick up the tool
2. With your hand physically try to wiggle it. Did it wiggle? Did it click or make any audible noise? A properly engaged tool should not wiggle at all, nor should it make any audible noises. If the tool still wiggles, readjust the parking post location. Ideally, when tools are picked up and put down, they should not show any signs of play.

Other Notes

Every time you disassemble/reassemble the machine's xy moving components, you should check to ensure that tools are being picked up consistently.

This issue has been discussed in and is related to Github issues #43 and #44