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picclock's modified i3 3d printer attempt
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Pete49:
picklock just a thought re the glass bed .When the bed on the Da Vinci chipped (cheap glass) I got a replacement borosilicate with the heater attached from a guy in Dallas Tx for about $Au70 including shipping. I am thinking about getting 1 for the CTC kit printer as it will heat the whole plate without needing to worry about it not being uniform heat.
Pete
picclock:
@ PeterE
I've just done a run through on some of the other slicers. Some are a pain to use or have other snags. Slic3R is OK, but the dimensional error is much larger than Cura ~1.6 times. However the finish is the best I have seen. It also seems to round all the corners, which looks very good, but not suitable for accurate parts. Cura have a new beta version which I may have a go with as it seems to offer lots more controls for tweaking. My current thinking is that the error may be fixable by specifying an oversize nozzle in the slicer - say 0.43mm - which will hopefully alter the final size. I may have another go with craftware to see if I can get it to finish the test piece as it seems by far the most accurate.

@Pete49
Do you have a link for the borosilicate glass/heater site ?. I know that borosilicate expands far less with temperature, which causes less stress on the glass when heating, so hopefully no more cracks. Its thermal conductivity is still fairly poor, so it will not do well at spreading the heat. With 200x better thermal conductivity even a thin layer of Aluminium will be effective. Have read differing things on the internet about borosilicate durability though, with some suggesting abrading the surface to get grip. To  to avoid warping (nylon  :palm:), especially on larger parts, would seem to require an enclosure to prevent localised cooling from drafts. I have thought about using a balsa wood rim extending about 1" above the edge of the printbed to try to contain the hot air (or at least keep out the side drafts) as the bed moves. Problem is that hot air is less dense than cold, so it will always try to escape upwards. Heated enclosure anyone ??  Tricky stuff !!

Good luck with solving your new printer issues.

Best Regards

picclock
Pete49:
I can't find my invoice with the details but here is his email address jdholbrook33(at)yahoo.com
If that doesn't work here is the link I used to contact him originally
http://www.soliforum.com/topic/9642/da-vinci-borosilicate-glass-with-heater/
Hope it helps
Pete
picclock:
@ Pete49
Thanks for the info, I'll see if I can track him down.

Slicer Success  :ddb: (finally)
Using the new Cura 2.1 beta slicer, (it has some bugs). I have found an adjustment for horizontal expansion which allows calibration of the XY sizes. Tried it with -0.15mm and the test piece came out 0.3mm smaller than the original oversize one - so it just needs half to correct the overall size error. Also tried another tricky piece and it worked just fine. Quite a relief after all the slicers I have tried.

Hope this helps

Best Regards

picclock
picclock:
Hi all

So I have my printer up and running (mostly). I have replaced the original X carriage and extruder, and fitted a bed levelling servo, all very worthwhile. The extruder upgrade allows instant changing of filament and jams are a thing of the past. The bed leveling system is worth persevering with and works really well. Main snag I found was that the cura slicer preamble inserts an G90 absolute positioning code which destroys the bed levelling settings in marlin - so I edited the cura definition files to remove it.
 
But (there always is one  :scratch:) the performance is poor by my standards, probably aggravated by the use of ABS, needed for its higher temperature stability. The problem is warping of the part caused by the differential expansion of the plastic. The initial layer is stuck onto the bed by a combination of heat, pressure and a certain amount of magic  :med: in the form of ABS juice, PVA, hairspray, or whatever works for you. Bed adhesion does not seem to be a problem using just dilute PVA, and if you add ABS juice to it you will have a very hard time removing the part, however I digress. Once the initial layer is attached the next layer is added. The temperature of the subsequent layer is determined by temperature of 1st layer, surrounding temperature, and radiation/convection of the same. Subsequent layers therefore experience a different temperature depending of the heat losses of the layer, layer size (more time to cool for larger parts) to which to adhere. If the plastic is extruded from the nozzle at 240C, and the temperature at which it hardens is 100C then the surface temperature to which the subsequent layer attaches is very poorly defined. Once removed from the bed the temperature of the layers will becomes equal and warping occurs, because at the same temperature the layers are different sizes. It always seems that the bottom layer becomes convex which implies that the temperature of the plastic when deposted, bonded and hardend is higher than that of the bed, presumably because the heat maintained in the previous layer is greater than the bed temperature. So the upper layers shrink more and warping occurs.

ABS has a glass temperature of around 100C so one would think that provided all the layers were bonded at that temperature warping should be a thing of the past. I have already taken steps to guard the print bed from drafts but this does not seem to have improved things much, despite having an internal temp of ~ 40C.

It occurred to me that it may be possible to solve two problems with one solution. Instead of using a heated bed which adds to the Y axis movement mass, why not heat the whole interior of the machine to 100C using circulated air to even out the temp differential. Could use heat bed controls with fan for circulation. This would eliminate the need for an underglass aluminium heat spreader as the whole interior would be at one elevated temperature. To prevent heat damaging the extruder, belt, motor etc a plastic oven bag or sliding fibreglass/srbp heat seal could be used, attached just above the print head as a possible solution, minimising heat loss.

Still at the thinking stage on this so if anyone has tried this or has any further thoughts on this solution please contribute.

Best Regards

picclock. 
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