Replicator 2X pulley slip

[Feliks87]

well :/

just received a response from MakerBot support... I have to send back the machine so they can repair it... yay

[Mouser]

Makerbot's paying the bill I assume ?

[Feliks87]

just waiting for them to send me the shipping label... good that I kept the box my Rep2X came in...

I really hoped it was simply a stepper or pulley problem which I could've switched by myself...
but since I have to send it back I assume it's a problem with the whole gantry :/

[Feliks87]

well thank you MakerBot....

they don't pay for the shipment regardless the fact that, according to MakerBot support, my brand new carriage is faulty.... the connection between belt and carriage is the problem and obviously not tight enough :/

I think I can fix it myself with some layers of paper just so that the belt and carriage connection is tighter

this is why I can't have nice things

[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.

[Feliks87]

thanks a lot for this big technical comment KrazyJim !

I did notice now, after 30h of printing, that my temporary "piece of paper" solution is starting to fail again
what I noticed too when implementing that solution is the major design flaw in the carriage that you also mention: the single short "belt gripper"

my original plan was to upgrade to an aluminium carriage from Raffle but that's out of stock for some time now so I think I might bolt the belt to the carriage as you suggested (with two M3 screws and self locking nuts maybe)
right now there are new linear ball bearing bushes on their way (ordered from here http://www.amazon.de/gp/product/B00OCK50YK) so I think I'll do the modification to the belt when the bearings arrived

I already tried pulling the carriage off the rails but with no success... is there any special trick for that except of brute force? I don't want to damage the only carriage I have :/

[KrazyJim]

Those LM8UU bearings may be too long. The LM8SUU are only 17mm long. I just measured the length of the bearing support in the carriage and it is slightly over 17mm. So the 24mm LM8UU will probably not fit. The LM8SUU is what you require for a MakerBot 2 or 2X.

Using eBay.com and searching for LM8SUU found many, most with free shipping from China.

Also maybe Igus makes a stiction free plastic replacement of the right size.

I could only fit a single bolt in the gripper. I used two nuts to form a lock nut. You may have a hard time fitting a 3mm bolt. Probably not enough room. Also the belt is only 6mm wide. If you drill a 3mm hole it may weaken the belt and cause it to break.