Fine Calibration.

When I first started 3-D printing I found the calibration process difficult as there were few online resources or information about this critical process. I have now built quite a reasonable experience of 3-D printing after working with my machine for 18 months, and have improved my calibration technique. I will discuss the calibration now to add another online resource for newcomers to 3-D printing.

There are three elements which are critical to the fused deposition modelling (FDM) process, bed levelling, first layer height and plastic flow rate, underperformance in any one of these can cause total failure of the printed model. 

Bed Levelling:

Most 3-D printers on the market currently use a three point bed levelling system, where the adjustment of three nuts changes the height of the bed in relation to the Printer Heads. It is imperative that the printheads move parallel to the bed in both the X and Y axes. So that the space between the extrusion nozzle and the bed is constant. If this distance changes the amount of adhesion between the printed model and the bed varies, causing the model to lift from the bed and/or distort. Some 3-D printers are starting to appear which have automatic bed levelling removing this time consuming process. 

The tried and tested technique is to slide a business card between the nozzle and the bed and then, with the mains power disconnected, manually move the printhead across the X axis. Rather then see the gap between the printhead and the bed you feel it with the business card, if the card becomes tight then the bed needs to be dropped by tightening the nuts on the underside. This process is then repeated in the Y axis direction. It is worthwhile repeating this process many times and devoting a large amount of time as a unlevelled bed can prevent sticking of the first layer and cause unsuccessful printing. 

First Layer Heigth:

For good adhesion of the printed model it is best advised to have a thicker first layer to aid adhesion, but this layer should be compressed to help it bind to the bed, especially important when printing on blue tape which relies on the physical bond between the tape rather then heat. The height of the first layer can be controlled in the slicing software, software which converts 3-D model into layers and generates commands for the printer to follow, both Cura and Slic3r allow variable inputs. A value of between 0.15mm to 0.2mm has good results. To compress the first layer you manually move the position of the Z axes home. This varies from printer to printer but usually involves an adjustable component which breaks a light to gate telling the printer it is at zero for that axis. So the position the printer thinks is zero on the Z axis is actually minus  0.1mm, for example, so when the printer is making a line which is 0.2mm thick, it is actually 0.1mm and is being compressed onto the bed, providing a solid foundation for a long print and reduce the risk of the print model curling and lifting. 

Plastic Flow Rate:

The plastic flow rate effects the wall thickness of the printed models, and is affected by the material feed stepper motors rotational speed, the filament thickness and the nozzle diameter. It is important that the exact diameter of the nozzle is known as this value is used by the slicing software to calculate the number of lines required for a specified wall thickness. 

If the flow rate is too low and then the walls thin and can break causing a failed print. The most common cause of this problem is the filament jamming in the printhead, due to the printhead not being at, or slightly above, the glass point temperature (The temperature at which the material starts to become a liquid and flow, the higher the temperature above this point the less viscous the liquid) of the printing material or that the feed stepper motor is forcing too much material into the head causing it to jam. Both issues I have experienced. 

Temperature is easily fixed when using Printrun software to control the 3-D printer as it can be manually changed. When working with a new batch of material I manually push some filament through the Print Head, varying the temperature and testing the resistance to find a suitable temperature for good quality printing, as each batch of plastic can vary. 

If the material feed stepper motor is forcing too much plastic into the head this is usually due to the diameter of the nozzle diemention being inaccurate, and the Slicing software calculating the flow rate to be greater than it is, so the material enters the head at a greater rate than it can exit, thus causing jamming. This highlights the importance of an accurate measurement of the nozzle diameter. 

The flow rate also affects the precision of the printed models, if too much plastic is being extruded then the wall thicknesses will be greater than designed thus the model's dimensions will be larger than expected and this can affect the assembly of multiple components. 

Getting the Printer up and running again.

I have now got the 3-D printer up and running again and will discuss some of the maintenance I carried out on it.

Firstly I attended to the wiring, checking all the connectors on the central processing unit and in some cases reworking the connections to prevent errors such as oscillating stepper motors which the machine has suffered from. The thermostats on the printheads then needed reglueing in the correct position, with high temperature glue, so after calibration, they now read the temperature of the Hotends very accurately. 

I then brought each print head up to operating temperature, 200° C, to clean the inner channels from the buildup of plastic and any carbon residue. The primary printhead which has become blocked with carbonised denatured nylon is proving very difficult to clean out and will require the full disassembly of the head, in the meantime I am going to use the secondary head to print with. This is not an easy change over and I will have a blog entry explaining how I achieve this. 

Finally I then checked all the moving components were well lubricated, tightened the belts which control the X and Y movement and tightened the Allan screws to prevent any vibration during operation. 

I then moved to fine calibration. 

Projects.

I have several projects that I am looking forward to getting my teeth into and getting the 3-D printer up and running again. Firstly I've got a lot of work to do on the printer maintenance wise, during the technology projects I jammed up the primary printer head with nylon which I think has denatured and carbonising formed a solid block inside the head. After cleaning that out, some of the wiring around the printheads has become loose which needs attention to have reliable printing. Then I'm going to work on maximising the precision of the 3-D printer aiming for 40 µm resolution and 0.05 mm layer thickness, using a series of complex test prints with peculiar curved shapes and high detail to really push the performance of the printer. To give a comparison the Makerbot replicator, a commercial product, has a precision of 100 µm, which I am aiming to surpass. 

I have another few smaller projects I didn't quite finish over Christmas which I'm going to work on before starting some big projects which I've been looking forward to for a long time. 

The first project is to enter some of the Makerbot STEAM (Science, Technology, Engineering, Art and Maths) challenges. You can check them out here: http://www.thingiverse.com/challenges/  I will have future blog posts showing my entries. 

The next project is to build a 3-D scanner. I backed a 3-D scanning project on Kickstarter called Atlas 3-D. It was successfully funded in February and I am looking forward to the delivery of the electrical components sometime in July to build the scanner. The parts include the stepper motor, wiring and lasers and then I will use a Rasberry Pi and Rasberry Pi camera and print of the other components to assemble a DIY style Open source 3-D scanner. The 3-D scanner will run on Open source software, which I have been following the development of, called FreeLSS. (https://github.com/hairu/freelss)

I then will be designing and 3-D printing a range of small models of classic commercial vehicles, in 1/50 scale. I have collected vintage vehicle models for some years and I am going to develop my own models of vehicles and trailers which are not available as commercial models. 

So it's going to be a busy summer holidays.

Long time no printing.

 I have been somewhat plagued with ill-health and exams so have been unable to carry out any 3-D printing  related  projects. Struggling with  arthritis it  is going to be very difficult for me to work on all the projects I planned to complete this summer however I will fight on.  Typing is very difficult however I am now making use of the dictating feature on the iPad so I can still complete my blog posts.  I have completed my A-level technology project and will write a post about it and then have a series of projects I am looking forward to working on over the coming months.