Mendel Troubleshooting

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If your issue isn't listed below, consult the Build documentation. There are some useful little pieces of information scattered throughout the build docs.

Troubleshooting Hints-n-Tips

  • I cannot figure out why my Z axis is binding.

If you remove the belt you can tell if one of the Z drive screws is more restricted than the other by feel.

Measure that your Z drive screws are parallel to each other. The X bar measurements in the spec make them a little longer than may be ideal. You may have = to loosen the 2 x-bar-clam-m4 on the motor end and slide the assembly containing the x-vert-drive-nut-trap toward the center of the machine . The x-motor-bracket-spacer does not fill the gap between the bracket the motor is bolted to and the next assembly.

The x axis needs to be level once sitting on the Z screws. If your machine is on a (near) level surface, placing a spirit level on the extruder carriage will help you get the x axis close to correct.

The belt may not have sufficient clearance. If there are issues with the printed parts you may need an additional M4 washer or two with the idler bearings for the Z belt. The belt may be incorrectly routed.

Nuts may not be seated right in the x-vert-drive-nut traps.

Check the Z screw for grit and/or paint (usually nearer the ends, but can happen elsewhere).

  • Bearing Isues

Some 608 bearings may bind when the washers are placed either side. You might try using a nut directly on the bearing instead.

  • Washer Issues

Some 8mm washers are too big (diameter). The 8mm washer then catches on the 4mm washers that hold the bearing in place as the Z screw turns. If necessary, you may remove the 8mm washers (as above), use different washers (15.8mm or smaller diameter seems to work), or mechanically adjust the 4mm washers (trim or file off a piece of the washer).

  • How do I move the extrude hole in reprap host software? The software thinks its on the right side and mine is on the left.

You need to add the settings for your build platform to the file - <Your Home Directory>/.reprap/

You need to add:



or replace the 5s with the correct coordinates for where you want the extruder to purge before prints for your machine.

  • Nozzle Wobble

How much "wobble" is there on the tip of your nozzle.? Put your hand so it is palm-upwards, and put the tip of your finger over the nozzle hole, press firmly upwards, but not hard. Move your hand and finger around in the X & Y direction, applying some sideways force to the nozzle tip. Does it move around? Does your X carriage wobble in either direction ( ie bearings move away from rods) Try applying more or less force upwards through your finger while repeating it, and see if that affects it.

  • Y Axis binding

The Y-belt bearing/washer combo at the very front of your mendel Y belt, which has "a big washer" on it to constrain the belt from falling off the bearing may actually be appling too much friction to your belt. ( ie the side of the belt rubs on the side of the big washer). lubrication, and/or a tiny bend in the washer reduces friction here.

  • Belt Tension

You may have your belts *too* tight, and somehow be causing the carriage or bearings to bind on direction changes?

You may have your belts *too* loose, and be getting backlash?

Check that the belts are not damaged (ie: the teeth do not change distance or are missing). Note that the supporting wires in a belt can break over time, and this can lead to slipping.

  • X-Carriage Bearing alighment/s

Disconnect the X belt entirely as a test and make sure that the carriage rolls easily with gravity when you tip the mendel.

  • Loosing Steps?

your electronics may be loosing steps because they are coming "too fast" ( just like my old chinese stepper drivers did before I didtched them), try disabling microstepping entirely as a test of this.

  • Uneven Resistance

Remove power from your axes ( turn whole unit off ), and gently push the X-carriage and Y-bed-carriage through their full motion, checking for any changes in the resistance across the motion. If it's uneven, check to see if it still happens with the belt removed, if not, its the printed cog on the motor being eccentric.

The results of (fairly large) backlash can be seen in these photos: (In this particular case, the backlash was caused by a very stretchy belt. Steel wires hidden inside the rubber belt are supposed to keep it from stretching ...).

  • Strange behaviour of electronics, resets etc.

A running reprap can cause quite some inductive and EM effects. Also the open cabling could become antennas for surrounding equipment (think dremels etc) which can potentially cause the electronics to get confused. To reduce the impact of this, you should put ferrit beads on all your motor leads. You should also think of putting the electronics in a shielded box and make sure you use known good cables for the USB connection.