Replicator 2X pulley slip

[KrazyJim]

I have had the same problem with my 2X. This also applies to the Replicator 2 as well. I received a replacement carriage for the 2 not the 2X in error where I observed the grippers are identical. The length and shape is the same. The impact on the Replicator 2 is less because there is less weight on the carriage. The result is the same, just not as noticeable. Also the Replicator 2 tends to have lower print temperatures and no heated bed.

Background
If you measure the length of the belt gripper on the carriage you find it is about 14mm. It is in an area of the printer that is affected by heat.

The main gantry end plates each have two belt gripper areas. Each of these 2 grippers is about 18mm long. That means that each side of the main gantry has about 36 mm of total belt grip for a total of 72mm. If they need 36mm on each side, they need more than 14mm on the carriage.

Diagnostic process.

I pinched the belt together to lock it from moving. Then I tried to move the print head. The head moved in excess of 0.5mm. The belt was not moving, but the print head was.

The problem is the length of gripper on the print head carriage is way too short. Also the heat makes the plastic slightly flexible.

I sent a video to MakerBot showing this problem earlier this month. They sent me a new belt and carriage so I could experiment. Adding paper on the smooth side of the belt would probably be only a temporary fix. The plastic would gradually flex and you would have to add more paper until the part would fail.

My solution:

Put a bolt through the gripper and the belt. I wanted to use a 4-40 bolt. I mistakenly made the hole off center and could not fit the 4-40. I ended up using a 2-56 bolt. I suggest that you use a 4-40 Allen Head cap screw. If that is not available use a 2-56 bolt. Metric users can use a 1.5 or 2mm socket head cap screw.

Steps:

First remove the belt from the gripper. If you can get the carriage off the rails do so. Then carefully drill from the bottom of the carriage up through the gripper, exactly in the center of the gripper reinforcements on the bottom. I did not get this exactly centered so I could not use the bolt I had planned to use. Once you have the hole make sure the bolt goes through cleanly and is snug in the hole. Clean out the bits of plastic from inside the belt gripper area. Place the belt back in the gripper and center the belt. Then carefully drill through the belt while it is in place. Finally install the bolt from the bottom up, as probably the nuts won't fit on the bottom. I used 2 nuts to make sure they were locked together. Reassemble the print heads back on the carriage. Test print.

After I had assembled the bolt and nuts I tested the fix by gripping the belt as in the diagnostic process. The head did not move.

Now holes in parts are very close to round. The remaining out of round is caused by resonance. The resonance is worse on a 2X because the mass of the dual print heads is much higher than the single head on the Replicator 2. The steel rods on the Replicator 2 are barely large enough for the single head. The steel rods are undersized on the 2X with the dual heads. Without a massive redesign, the resonance will not go away. Carefully changing the acceleration settings in the machine preferences would help. I trust MakerBot will come up with new acceleration and deceleration settings to reduce the impact. At this point the options are in the software, I suspect they just need more testing and changing to get close to being resonance free.

If detailed documentation for the settings was available, particularly for those new settings in the the latest version of the MakerBot Desktop that affect acceleration, then we could test and determine better settings for the 2X. Hint Hint MakerBot.

Maybe someone will design a new carriage with a longer gripper, that we can 3D print. Maybe with two bolt holes already in the design.