Building my Repstrap Smartrap 3D Printer... and the setbacks (Part 4)

Before I can do a test print, I needed a glass of course.  I had a headed build plate but it's a little warped and arching in the middle. And I don't think I was supposed to print directly on it. I looked around the house and found an unused picture frame!  :)  I took out the glass and it fits perfectly with the length of my rods. Even if it's just 1/16 inch thick, it will do for now. When I installed it in the printer, the glass gives and bends a little during probing but not enough for it to break.

By this time, I have already gotten over some printing issues through trial and error. But not without some frustrations.  I agree that 3D printing is not for everyone because it takes a lot of troubleshooting before and during each print. One variable you change and your print will turn out differently.

Slicer Software 

Commercial printers come with the software you need to print but if you're just building from scratch reprap style, there are alternatives. You will primarily need a slicer - as the name suggests, it slices your 3D models into layers depending on the setting you provided and gives out a set of instructions for the printer to follow.  The settings can be overwhelming at first but when you get the hang of it, you will know which ones you need to adjust for every model you print. There could be times when you will forget to change something and only realize it after the print has already started. Sometimes, it would be okay to continue but there are times when you really need to stop the print and start over with the new gcode.

The first slicer I tried was slic3r but after using is for a while, I find it too slow so I tried Cura. Cura's user interface is better in the sense that you can visualize the gcodes and make adjustments immediately.  Unlike when I was using slic3r, I used to open the generated gcode file in repetier just to see if everything looks right before I print it out.

Semi-automatic bed probing

After assembly of the printer, the first problem I had was how to get servo to work. I tried to follow the guide and traced where the wires go. The RAMPS board has pins dedicated to servos but for smartrap, the servo wires go to the end stop max of z axis. I double and triple checked but the servo still doesn't work.

I happen to have a spare arduino uno board so I hooked up the servo with the sample servo sketch and still didn't work. I probably got a broken part. I am not willing to send it back to the seller in the U.S. so I needed to think of a way to manually or semi-automatically probe the bed.

My solution was to manually put the servo arm before probing the bed and remove it after the probing sequence.  To do this, I modified the slic3r start gcode so that after probing the bed, it will raise the nozzle 10mm and pause for 5 seconds.  This gave me enough time to remove the arm from the servo before it prints. It took took some effort but It works. I did this until I was able to print the parts for the mount without a servo.

Edit:
Here's how bed leveling is currently done on my smartrap with a broken servo

Z offset setting

Alright, it probes the bed, but when it prints, the nozzle was more than 5mm away from the glass. The filament comes out so I was sure it was just an adjustment somewhere. Turns out, there was a setting on the firmware to set the offset between the tip of the nozzle and the probe. X and Y were easy but I found it difficult to get the Z offset right and I didn't want to keep uploading the firmware whenever I change the value so another way to adjust the Z offset was through the slicer software. Different slicers have different ways of dealing with this.  Slic3r's Z offset setting is straightforward.  But in Cura, the only way I was able to adjust the offset was to modify the start gcode using the G92 command.

Getting the Z offset right needed a lot of patience and took a lot of trial and error. But when you get it right, you won't need to change it until you take your printer apart or make some adjustments that will affect the z offset.

First print issues

The first thing I wanted to print was the shaft adapter for the X motor. I got those motors with D shaped shaft but a little short especially on the X axis. This is the first successful print of the adapter.

 

Filament flow rate

I had the issue of the extruder motor springing back once in a while during a print. I thought the extruder was having a hard time pushing the filament because the nozzle was too cold. After some trial and error, the best thing to do in this case is to dial down the feed rate. It springs back because the extruder is giving too much filament than what can come out of the nozzle.

Print speed

No matter what I do, I couldn't print at speeds more than 20mm/sec reliably.  I guess that's just the limitation of my hotend nozzle and the heater element that came with it. If I go just about 1mm/sec faster, the heater could not keep up and the temperature quickly cools down.

Temperature

The suggested temperature for PLA was between 180 to 200 degrees but I just couldn't go lower than 230 degrees. At 220 degrees, it can still print slower but it comes out rough so I have to set it at 230.  I sometimes went too far and set it at 240 degrees.  I believe I stressed the heater too much because after just a few prints, the resistor broke.=(  I ordered the 30W heater cartridge but it will take a month to arrive. I will find fix but that will be for another post.

Right now, at least I know I can print! :)

To make it easy to follow this series, the links are here:

• Part 1 - Sourcing parts and building the base/frame
• Part 2 - Electronics  
• Part 3 - Power supply  
• Part 4 - First prints and modifications