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| picclock's modified i3 3d printer attempt |
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| picclock:
@PeterE Thanks for your interest. Hope your daughter is now settled and work can progress on your printer. The glass that cracked on mine was only held by the 4 clips at the sides. The end clips hold the bed heater to the glass. The fittings that touch the glass underside are all fibreglass to act as a heat break. Borosilicate is without doubt an improvement, but have also read about that breaking, not sure what the mechanism for that could be. Several things spring to mind. It may be that adding an insulating layer to the top at warmup would cause the heat to be more evenly distributed, the layer could be removed prior to start of printing. An aluminium heat spreader under the glass could improve heat transfer. Alternately a slower warmup period would allow the heat to spread more evenly. Thicker glass would also help by increasing the heat conduction path to the outer edges. If I can get hold of some borosilicate glass I have no doubt that would also improve things, but I doubt it will be easily available. Best Regards picclock |
| PeterE:
Yes, now the lass is in place in her first own apartment :ddb: I got a glass sheet similar to this http://www.ebay.com/itm/Geeetech-Borosilicate-Glass-for-Heatbed-MK2-MK2A-of-3D-Printer-Reprap-Mendel-/221661533512?hash=item339c0e9548:g:srgAAOSw-W5UtPEE and at about the same price but from a local seller in Sweden. It is 3mm thick which increases its strenght quite a bit and it evens out the temp spread as well. Just have to get my foot in order after spraining the ankle carrying furniture bits down some stairs :palm: Work will proceed during the coming weekend. /Peter |
| picclock:
Hi. I have managed to print some usable bits but things have been difficult. I replaced the mirror glass with some 4mm glass liberated from a skip behind a window shop (with there blessing). I heated it to 115C and all seemed fine, but after the first print it had cracked again :palm:. prior to the print I had been monitoring the temperatures with a thermocouple type thermometer. The nozzle temp was exactly correct - quite impressive really. However the bed temp is all over the place. The centre area, on the surface of the glass was about 95-98C measured, however an inch or two from the edge it had fallen to 55C or so. With that kind of temperature gradient over a couple of inches I am not surprised the internal stresses caused issues. Also as the bed moves small distances cold air is pushed onto the edges but the centre always has warm air, exacerbating the thermal gradient. So I have thought of several fixes which will hopefully improve the situation. Firstly, use an aluminium heat spreader directly above the heater below the glass (will try 1mm as I have it around). In the centre area of this I could put some kapton tape to further reduce the centre temperature and increase the heat to the outer edges. Secondly, I could fit an air dam around the bed, basically just a 25mm high strip of an insulating material, which will prevent cold air from reaching the outer areas so readily when the bed moves. Thirdly, a form of enclosure to prevent external drafts from having an effect. If I'm lucky this will bring things under control and resolve the issues. Pictures of my first real parts follow. As you can see, the cable chain links were printed with a large raft to promote adhesion. The bed cracked part way through printing, though it was held together with the tape. Use of the tape likely increased the thermal differential even further, promoting the failure. The yellow stuff around the edge was from some attempts I made to print with ABS juice, which did not seem to work well. For printing, bed temp was set 110C, and nozzle temp 260C. Sliced with Cura, 0.1mm layer thickness. Layer adhesion was excellent, although it struggled with the bridge across the top of the links, as can be seen from the top right hand link in the 'chain links on raft' picture. Hope you found this informative and of interest. Onward and hopefully upward. Best Regards picclock |
| RussellT:
Can you find an oven door window the right sort of size? Russell |
| BillTodd:
Does the bed need to be glass? was glass suggested because it readily available and flat to a few thou? the model is stuck to a layer of tape or lacquer so , would any flat surface work? Tooling plate anyone? |
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