Mechanics? Checked!

Another Sunday in the workshop is done :)

The work has gone much further. As a conclusion we can say that the mechanics are done, only some electronics to do the next time.

In the beginning we fixed the endswitch of the Y axis. As told the last time we used epoxy resin to glue a small piece of platic to the bearing mount. Now it makes 'click' when we move the Y carriage to the front. As ist should be :) 

the 'enhanced' endswitch

We had to disassemble the whole Y carriage once again, but thats fast done. Just pull the smooth rods out and thats it.

After that we could use a big angle to put it on the motormount of the Z axis. With that we can measure the exact position for the upper mounts of the Z mounts of the smooth rods. Hold it there, mark, drill and set the screw in place. What we got is a (nearly) perfect right angle with parallel smooth rods. The X axis carriage runs on it like in a dream.

while building

All the other Mendel printer got one major disadvantage in our opinion. Alle the cables are wild flying over the whole printer, winded around threaded rods... So another reason for us to build a Mendel90 was the clear routing of all cables. So we did care to do it clean.

Wires from the Y Motor

In the bag with the printed parts were also some cable clamps. So we used them to mount the cables on the ground plate. We devided the motor and endswitch cables to avoid interferences. To get this point further we also twisted the stepper cables in pairs.

Cables in the back - heated bed, thermistor, left Z stepper

In the back of the printer you can see all the cables for the heated bed. At this printer it's connected with a 26x ribbon cable. 12 wires for the +12V, 12 wires for the ground and 2 for the thermistor which measures the heated bed temperature.

Because we use a ribbon cable it can roll under the Y carriage without sharp bends while the carriage is moving.

The right  Z stepper - with printed couplings

To get all the cables to the electronics we had to drill some holes into the frame. It's a pity we got some chipping in the wood, but again some drops of paint will fix it. Maybe the drill wasn't sharp enough, sometime i thought Torsten wants to make fire and not a clean hole. Next shopping day we should by a new drill, together with some screws we are missing.
The BOM is full of details, and we suppose we didn't use all the screws in the places where they should be. But everything is fixed and working.

many wire to connect

All the wires ran together on the right side of the gantry, where we want to mount the electronics and the PSU. The fat black and red cables run to the hated bed, blue cables for the endswitches and the colored ones for the steppers. There we need to get some system in, some cables are running wild there.
What you can't see is the ribbon cable which comes from the X carriage and stepper. It runs over the upper edge of the gantry to get it to the backside.
When the printer is ready we will print some cable clamps to fix all the cables.

The X carriage with hotend - cables will be sorted

The extruder is assembled. The mount of the J Head Hotend can be improved. Currently it's held by the screws with washers while pressed into a notch in the Coldend. It works but is far away from pretty. Maybe we will make a solution from aluminum to get a better mount.

Once again the X carriage

Everything which is on the X carriage - Hotend, thermistor, stepper wires and power for the fan, is connected with a ribbon cable. This is reinforced with a small strip of plastic. Not as well a an energy chains but goot enough and much cheaper.
The carriage is connected with a 15 DSub connector to it can be disconnected if needed. One of our ideas is, that we can use this platform as an laser cutter / engraver. With this connector we can just take the extruder out and use the same connector to supply voltage to the laser. All thru the same electronics.
  

Electronics (RAMPS und Arduino Mega2560)

As mentioned before we put the electronics to the right side of the gantry, where all the cables came out.
As electronics we used an Arduino Mega2560, a widly used microcontroller board which is used in many electronics, not only 3D printers. Heart of it is an Atmel ATMega2560 processor.
Connected on this as a shield we use a RAMPS 1.4 (RepRap Arduino Mega Polulu Shield). This board offers all connectors we need to connect all heat elements, steppers and sensors. The top connectors are planned for the display which we want to use to print without a connected computer.
Also on the RAMPS are small boards as stepper drivers, the Stepsticks.
The green connectors on the lower are for the heated beds, the hotend and the fans. The longer green connectors connects everthing to the PSU.

The steppers we bought will need 200 steps per revolution, 1.8 degrees per step. Thats a lot but not enough. So we use microsteps to need even more. Microstepping is not easy if you try to do it by hand, and because of this the stepper controllers are used. So we can easily use jumpers to set it to 1/16th steps, 3200 steps per revolution.
To do some math: our Z axis is driven by a metric M8 threaded rod, with a inclination of 1.25mm per revolution. So we need 2560 steps to move the Z axis one mm. The other to axis use pulleys with 20 teeth, with a 2mm belt. So we got a accuracy of 0.0125 mm per step. This can be calculated the easy way with Josef Prusas RepRap Calculator3.

as far as we got now

After connecting all the cables, we were working on the printbed. On the small wooden plate which holds the linear bearings we drilled small holes to hold M4x40 screws with the heads up, held by nuts.
The printbed is a mirror from Ikea with 30x30 cm. In the corners are some magnets glued with epoxy. These magnets will hold the mirror on the Y carriage. With this we got enough room for some heat insulation underneath the printbed. The heated bed will be fixed with two aluminum pieces and bulldog clips - not mounted yet.

Next time we will solder all cables to the connectors to get them connected to the RAMPS. We hope the motors will then move the first time.