Hi All
Things have moved on a bit since last post.
The bed wiring is now complete, with it passing through the belt attachment for the glass bed. When fully operational one of the first things I will print is cable chains for the X and Y axis. The cork is attached to the heater pcb with a high temp silicon adhesive, and this in turn is attached to the glass with clips as shown.
The Z limit switch is sorted, and the Y axis switch fitted. The Z limit switch is one I reused from a scrapped photocopier. Although it is push to make, (default is push to break so that wiring integrity is maintained) the accuracy and repeatability are better than I can measure. I put one of them in my mill vice, connected to a beeping continuity meter and used the Z digital readout to detect the point of switch actuation. The reading at the switch point was exactly the same, so its easily as good as 0.5 thou of travel. Picture with simple mounting and adjuster below.
The distance between the print head and bed is an important setting to ensure the correct adhesion of the first level of plastic. Having powered it up, I was able to set this to 0.05mm, by adjusting the screw and re homing the axis. Once the left side was complete I manually adjusted the right side to the same gap. I intend to automate the bed levelling process by using a servo and a limit switch, parts on order.
Next, the filament feed calibration. This is achieved by simply marking a piece of filament and telling the extruder to extrude a given distance. For this I removed the extrusion nozzle and set the minimum extrusion temp to 1C in the Marlin firmware. I had an extrusion rate figure from the internet, taking account of the different gear ratios, and in an unusual stroke of good fortune this proved to be exactly correct. I extruded 100mm, and exactly 100mm was extruded
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So for a trial print. I thought I would try the blue tape adhesion method first with some hair spray to help things along. I loaded up a new reel of blue ABS filament, sliced the design for a cable chain link in cura, and dropped the file into the octoprint browser window. Had a quick think to see if I had missed anything, then clicked the print button. The bed started to warm to its final temperature (100C), once reached the print head quickly warmed up to its operational temp (230C), and the process commenced. I was very impressed with the fine detail of the outline and its accuracy. All seemed to be going well, with the first layer going down but after 4 or 5 layers the parts started to warp and come off of the bed, at which point I cancelled the print.
I thought I would try to improve the bed adhesion using abs juice so attempted to make some from the scrap printed parts and filament dissolved in acetone. I left this for several hours but was surprised to find that it had not dissolved, in fact was not even sticky. I took a piece of known ABS and dunked it and it went sticky almost immediately.
I was thinking that I had been supplied with the wrong filament type, so I checked out a roll of conductive abs filament, which I had ideas about using for plated items. In doing so I came across the original carton which clearly showed that my blue abs was in fact nylon, and further checking of the order indicated this was exactly as ordered. Its a terrible thing getting old .. .
I have ordered some other colours of abs and hope to show some first printed parts soon. I may have a go using the conductive abs, but this is far from typical due to the carbon loading, so will not be too good for calibration. The white roll of PLA I have may be useful for testing or prototyping but not very good for calibration or working parts.
I also think that it would be a good idea to fabricate an enclosure to maintain an even, elevated temperature throughout the printing process, as this would minimise warping.
Thanks for your interest
Best Regards
picclock
