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MendelMax 2.5 the future on your desktop

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Wednesday, 27 August, 2014

MendelMax 2.5 the future on your desktop

Printer selection

After much searching and asking for advise, a MendelMax printer looked like a good candidate as a 3D printer. Ordering the kit from the US would add a pretty steep shipping charge and add VAT and import duty to the price. But then I found the "MendelMax 2.5" kit at http://reprap.cc.

It is a kit based on the MendelMax 2.0 with some changes. Don't know about the name though, and judging from all the noise on the fora, a lot of people don't agree the kit should be named MendelMax 2.5.

Based on the price and the good reviews of the MendelMax 2.0 I decided to buy this printer.

Ordering

After mailing a bit with reprap.cc I got quick responses with explaination of a few questions I had regarding electronics assemble and required skill level for this kit. I also got some advise regarding extra's I might need.

So I ended up odering the following:

  • MendelMax 2.5 complete kit
  • 1 roll of white PLA 1.75mm (1kg)
  • 1 roll of black ABS 1.75mm (1kg)
  • 1 roll of kapton tape (33m)
After ordering it took 22 days for the kit to be produced and arrive at my home.

When it arrived the box was pretty beat up and torn.

Fortunatly upon opening of the box the contents looked ok, nothing seemed to be lost.

I also mailed reprap.cc about the box and they replied very positively that if anything was to be lost they would send out new parts.

In global the kit contains the following:

  • 4 x Stepper driver A4982
  • 1 x Arduino 2560 Mega
  • 3 x opto endstop oe-r1 (to be soldered)
  • 1 x Ramps v1.4
  • 1 x 400W 12v powersupply
  • 1 x extruder (0.50mm hotend + direct drive coldend)
  • 5 x Nema 17 steppermotor (44 N.cm holding torque)
  • All aluminium extruded profiles
  • Cable wrap
  • Heated printbed
  • Solid state relay
  • Glas plate for printbed
  • Clamps to fasten glas to printbed
  • All metal plates painted black
  • Threaded and untreaded rods
  • Printed ABS parts
  • M3 and M5 nuts and bolts
  • 230V power cord (x cm, way too short to be useful)
  • USB cable (x cm, also way too short to be useful)
What to expect

Now before going on about the build of the printer, I want to explain what I was expecting. As I bought a printer as a kit I was expecting something along the lines of an Ikea build: a manual explaining how to put all the parts together. Of course I expect some ambiguity in the documentation and I was expecting to make some assembly errors, needing to take things apart and put them together again. Also, I was expecting aligning all the parts and getting everything square would be a bit of a challenge.

Building the mechanical part

I had downloaded the build documentation for the MendelMax 2.5 from their website. All documentation is in German, so you need to do a bit of translation.

Mounting the feet

Starting the first part of the build I immediately ran into a small issue. The feet that go below the frame needed to be secured with M5x6 bolts according to the documentation. However, those will never reach the slide nuts in the rail, they are just too short. Not wanting to switch over to M5x10 (don't know if there were any spares in the kit) I emailed reprap.cc about this. They told me just to use any bolt that would fit.

The lenghts of the bolts used in this kit is a bit of an issue for me. A lot of M5x6 bolts are being used to fix parts to the rails. However, those bolts are so short that even without washers they barely get 1 turn of thread in the nut. This doesn't give a good connection and when you want to adjust parts (sliding them in the rails) the bolts almost immediately fall out when you loosen them a tiny bit.

To illustrate, below is an image of one of the M5 sliding nuts in the alumiunium rail.

You can see the space between the flat surface of the nut and the flat surface of the aluminium rail. Now, below is an image where an M5x6mm bolt is fully threaded in the nut with the calipers beside it to measure clearance between the top of the nut and the bottom of the bolt.

So 1.3mm excluding the space to bridge in the aluminium rail, excluding the to be fitted part excluding a washer.

Assembling the printer base

Although not specified in the documentation, don't forget to insert 2 M3 slide nuts in the left top and bottom rails and move them all the way to the back. At the end of the assembly you will need those two nuts to fix the solid state relay to. Otherwise you'll have to remove the back plate which is a shame if you've already done all the aligning.

Parts list

Each section of the documentation starts with a list of parts that is required to complete the section. Very useful, it give a handy overview if you've got everything complete before starting the build of the section. Unfortunately the parts list is often not complete or lists items that aren't used in the section (or that should be used but no assembly information is in the instructions). This is really a shame, it would make the build so much easier if everything would just check out.

Driving the X and Y axis

When you're done assembling everything according to the documentation, there is no drive for the X and Y axis. The documentation lists the use of the toothed timing belts in the parts list, but there is no information on how to assemble this. I ended up pulling information from the MendelMax 2.0 documentation. That shows quite clearly how to mount the belts.

Missing parts

When following the build instructions, you will run out of M3 slide nuts for the aluminium rails. You can save a couple by reducing the amount to use to fasten the sliding rails on the X axis. Still, it is a shame the few extra nuts aren't included.

To mount the 230V power socket to the frame you need reasonably long M5 bolts. There aren't enough of these in the kit. I ended up cutting some M5 bolts I had lying around to the right length and using those.

Left over parts

After having everything assembled which is in the documentation, you're left with quite a lot of parts: some bearings, aluminium extrusions, threaded rod etc. It turned out these last parts were for an optional spool holder on top of the printer. A shame it wasn't listed in the documentation.

Building the electronic parts

Unfortunatly the electronics side of this build is hardly documented. I found it invaluable to use the pinout of the RAMPS module as listed on the reprap.org wiki. At least it gave me a starting point on how to wire this.

The endstops

The kit has 3 optical endstops that need to be soldered. If I would have paid attention I would have seen that the shop lists a soldered version of the endstops for 2 euro's extra per endstop. As I'm colour blind and no direct reference in the documentation can be found which value resistor goes where, I would have gladly paid 6 euro's extra for the completed parts to be in the kit.

When done assembling the endstops there is no information in the documentation on where to put them exactly. When I contacted reprap.cc about this I got 3 photo's on where they should be. Unfortunatly the images weren't very clear. So I will put some images below showing how to mount them.

First the X axis.

Next the Y axis.

And last the Z axis.

Wiring 230V

When first powering on my printer nothing happened. Troubleshooting led to a quite simple problem. The fuse that was in the kit wasn't a spare, it needed to be inserted in the 230V connector block, DOH.. But after fixing the fuse still nothing happened. After testing the wires with a multimeter, I found the live wire wasn't conducting. It turned out that the length of copper crimped to the plugs was so short, there wasn't much of a connection.

I ended up replacing all the 3 wires (live, neutral and ground) by new wires with longer copper in the crimped connectors. After that, the powersupply ran without a problem.

Wiring power

You'll notice the amount of cables in the kit is insufficient to wire up everything to the powersupply. You'll need to make an additional cable to wire the output of the RAMPS module to the solid state relay.

Wiring the extruder

There is 1 paired wire which you're left with. This is supposed to go to the temperature sensor on the hotend of the extruder. But the extruder has 4 wires, none of them labeled or documented. Turned out that the thicker two are for the heater. As no cabling is included for this, you'll need to get some cable, isolation and solder to connect the wires to the hotend. Also solder the dual wire to the thin wires of the hotend (temperature sensor) and connect them to the RAMPS module.

Wiring the heated bed

I was (again) slightly confused here. Based on the information of the pinout of the RAMPS modules, the heated bed should be connected to the RAMPS module. But it turns out the solid state relay is supposed to switch the heated bed directly from the powersupply. Not difficult to wire, but it's not very obvious either.

Summary of extra parts required

In order to do any serious build of this kit you will need the follwing:

  • a supply of longer M5 bolts (8 or maybe 10mm)
  • a 4x2 header to solder the wires to of both z-axis motors and be able to connect to the RAMPS
  • a drill to drill out the nuts in the USB connector plus some m3 bolts to bolt it to the rear of the frame
  • extra wire plus crimp connectors to assemble all power connections
  • probably extra wire to replace the 230V wires to the powersupply
Also, get the MendelMax 2.0 documentation and the generic RAMPS 1.4 documentation. It will help you a lot to get some pointers on how to assemble al the missing pieces.

Calibration

After the build was done the calibration began. You're on your own here, no information is supplied on how to calibrate. It takes a lot of searching the internet, reading and trying to guess which information applies to your printer.

When adjusting the Z axis parallelism of the threaded rods and the smooth rods you run into the issue that the delrin nuts are quite wide. You have to remove one of the bolts holding it in place to actually get it slightly parallel with the smooth rod.

Even more problematic, the Z axis uses flexible couplings between the threaded rods and the motors. The bottom side of the threaded rods aren't supported. So the whole weight of the X axis (including 2 350 gram motors) is not supported by anything but the flexible couplings. This results in a lot of flex and an almost impossible to adjust Z axis.

After leveling the printbed for the 100th time, I found out that the set nuts are glued to the heated bed! Glue and heat don't seem to mix very well, it lets go :(

After having tried a few weeks myself I enlisted the help of a friend who has years experience in building and calibrating 3D printers. After an initial session quite a few issue's came up:

  • X and Y bearings have a lot of play. Reducing the play results in bearings that run with a lot of resistance.
  • The Z axis threaded rods aren't straight, introducing wobble in the print.
  • The X axis weight is quite high and distributed unevenly over the axis which results in tilts when adjusting the Z axis
  • The extruder hotend is very sub par, it seems to have a lot of trouble distributing the plastic
For me the final straw was the Y axis drive. There does not seem to be a combination of low bearing friction and no play. Combined with a printed Y axis drive coupling, this just doesn't work:

After the build

It was only after the build was done and I was doing a lot of test prints with PLA that I noticed the colour of the ABS I had ordered when I wanted to start testing ABS. I ordered a roll of black ABS with the printer kit, but I got a roll of blue ABS.

I sent an email about this three times, but unfortunately never got a response.

Conclusion

For a kit in this price range I would have expected:

  • complete assembly instructions (including how to assemble all parts that are in the kit)
  • a complete set of bolt/nuts etc
  • printer alignment and calibration information
  • configuration files for this printer for the Marlin firmware
  • configuration settings for this printer/extruder configuration for a slicer
  • email support
  • no cost cut on simple parts
The last one might need some explaining. I can't imagine that the cost of the kit would have been much higher with a normale length power cable and a usb cable that would actually reach from the back to the front. Below are images from the cables in the kit.

I really understand it isn't easy to create a kit to build a printer. But the current level of the kit gives the impression of an early beta. And then I'm not even going into the quality of the used bearings. For a kit naming itself Mendelmax 2.5 you would expect big improvements.

This is really not the future on your desktop.