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Friday, 8 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5c

This is the raw print of the chassis on the print bed of our 3D printer.

A few comments about the environment. Each time the machine is powered up the printer needs to be calibrated to take into account any deviation in levels between the X, Y, Z arms and printer bed. This may be a peculiarity of our printer design and I don't know if other printers have the same need. In theory it is simply done by loading a set up file into the controller but I go a step further and manually set the print head height above the middle of the bed. Too low and the first layer or two will be too thin, too high and the plastic will tend to float free of the bed.

The bed has a glass working area that is covered with kapton tape. This is a high temperature tape that has good adhesion properties for the plastic as it is laid down. The tape looses its effectiveness after a few prints and needs to be replaced, but its life can be prolonged by wiping vinegar over the surface before each print, which acts as a cleaning agent. Some people have cited success printing directly onto the glass.

The chassis component above shows thin plastic whisker deposits and it is a bit blobby. This is a common occurrence, particularly for small objects. I dare say further experimentation with printing parameters may reduce the problem but it is generally the case that some post processing with files, scalpel and drills to remove blemishes is required. Indentations can also occur and if undesirable will need to be filled with plastic padding.

I mentioned in the previous posting that a skirt is formed around the component. It can be seen in the photo above. In this example it is ragged and not suitable for rod and bar components. You'll have to read Part 5b to understand this.

Here is the finished component after the rubbish is removed. A one penny piece is alongside to show how small the chassis is. If you think it looks a bit rough then it pails into insignificance at normal viewing distances.

Sometimes the component printed may be very poor. In this case either the design would need rework, the printer parameters changed or simply print the component rotated through 90 degrees corrects the problem.

The cab canopy was a case in point.

The photo below shows two prints of the same cab canopy. The right hand version suffered badly. When it was printed turned 90 degrees it held its dimensions correctly. (version on the left).

Note the indentation on the left hand version. This could be filled with plastic padding but it is not necessary here. The canopy on the prototype is in fact canvas pulled over a frame and exhibits depressions between the frame bars. This I recreated with a file for the finished component shown below.

More component printing in the next posting.

To Part 5d.

To Part 5a.

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