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In the early days of SLA, each layer of film was controlled by a wiper bar that wiped across the previous layer and then a round laser was used to trace the outline of each slice (how accurate were the stepper motors then?) to trap the resin and then the internal area of the slice was cross hatched to sinter the last layer to the previous. Thankfully this is all done in one DLP flash which is why parts can be printed in hours instead of day, I digress.
As I understand the X and Y dimensions are permanently fixed since the UV light is simply projected through pixels of a screen (like screens used in smart phones) sitting directly under the clear FEP film. There are no XY stepper motors - the screen is stationary.
My boxcar ended up printing flat with no tilt. The roof is peaked so the whole thing doesn't stick all at once. But it does leave a boat to hold resin so when done printing I tip it for a while to drain.I drew up a similar gondola, but haven't tried it yet because the deck is flat. Maybe some heavy supports will keep it from ripping off? I don't want to print at an angle because it comes out soooo much better flat. Some surfaces look machined.
Have you messed with that ChiTuBox slicer yet? Once sliced you can play it like a video and can even zoom in on each slice to look for problems.
@narrowminded Here is what I want to know. What is the accuracy of the screen's projected section (layer, slice, or whatever one wants to call it)? This accuracy (inaccuracy?) has much more effect on the dimensional stability of printing the nominal design. Much like an old time projector surely there must be some way to adjust the X and Y slice dimensions to calibrate its accuracy?If not, this is a major flaw in the design or software of the printer, IMHO. This will also be exacerbated when slicing at an angle because now the dimension is no longer lateral to the plane of the screen but foreshortened by the angle when sliced and printed. I mention this because the tender shell that Mark so kindly printed and mailed to me, unfortunately would not fit the mating, sintered metal printing of its chassis floor., critical to my kit.Can you find anything about that? No one should have to redesign a part or scale it in either direction for dimensional accuracy.
Yes. And there's a fixed percentage adjustment to the program, unlikely to be needed as they are set up from the factory, that can be made if needed to correct those axis if for some reason you were consistently printing with an error in any of the planes. And John, as far as forces from the Z axis movement, while something is surely there, it is so low that it doesn't really matter to the process. If you look at the pictures of the tipper chassis, take note of the saddle coming off of the frame and the two guides that project upwards from that saddle. Those were printed with no supports whatsoever, hanging out in the breeze. What forces exist aren't enough to hurt those parts where the largest dimension in any plane is .03", then .015" for the tee with both of them .008" thick. The two vertical supports are .028" wide and it all printed VERY nicely. I was amazed to see that too but the original test pieces and every one in the twelve piece group after that printed flawlessly. That was part of what made me think this through further, coming to the realization that the print process was as I understood and now observed first hand. There was no real force applied to those parts to make them NOT print straight and true. 100% success rate so far, tipper hoppers and chassis. No rejects after the very first test print, the lower section of the chassis only. That print was done with their automatic support placements and the failure was anticipated just from the review of the support placement, with zero experience, the first print ever, and utilizing my first ever 3D drawing, done in Sketchup. One thing I have seen in these threads was a problem with a very broad face printed flat with full surface area printed on each layer. Those had a problem remaining stuck to the build plate but I suspect that was due to the z axis upward move with that much area effectively sealed to the bottom of the vat by the viscous resin, much as two flat faces will stick momentarily with an oil or grease layer on their face. The resin creates a seal around the perimeter so the atmospheric pressure keeps force against its removal. That might be able to be fixed by adding some holes to an inconspicuous place if that were possible so it would afford more opportunity for the resin to flow through, breaking that seal easier. Otherwise, just slowing down the Z upward movement might help but that's not an adjustable parameter, at least on the menu. But the conventional fix is to print the part at an angle, not engaging the whole face at once. BTW, my chassis prints were tipped 30 degrees and 15 degrees in X and Y, not recalling which was which. The hopper was tipped 15 degrees in only the X axis. The chassis is open enough that it might print just fine flat but I don't know that. Afterall, I'm brand new at this with much to be learned.
Yes a trial and error is always required to establish a dimensional baseline, but please look above. I have dimensions that should be parallel and off by roughly the same amount, but the clearly are not. This leads me to believe that in addition to dimensional adjustment, there is something else at play.
John, I'm new at this and don't have the definitive answer to your specific question about this machine printing to your specified number as it sits. I don't have that experience yet. I'm also not proposing that your part should be made in this way or any other way. What I do know is that the parameters are adjustable both in the machine primary settings as well as in the slicer, adjusted per individual print. As I run this more I will know what those capabilities are for certain. But from what I DO know, speaking not just for this machine but from parts manufacturing in general, all I need to make properly dimensioned parts is a consistent, repeatable process and that is the SINGLE thing that will matter, all measurement numbers be damned, metric, English, or cubits. All else is adjustment from the start point whether in the machine basic parameters, a secondary adjustable parameter, (the most convenient ways) or even if the dimension that is inserted from the drawing isn't the result, BUT it is, ALWAYS some other very exact number, change that number. (Pattern makers do exactly that as a key tool of their trade.) And that's ALL I need to cover that requirement, a repeatable process. With the repeatability requirement in mind, as I measure these pieces, 16 of one and 20 of the other, all I have made over a few runs, most measure comparatively within a half thousandth in x, y, and z, splitting the dial divisions on a set of 6" dial calipers, and the two excursions are no worse than +/- .002". That's ALL I NEED to repeatedly make good mating parts as your example requires.What I will do with running time is confirm the details of what's happening over the range of part dimensions in each axis. If adjustments are warranted they will be made. If it's something that varies with different resins, that will be recorded for future compensation and as required. And if it's a single thickness adjustment, that too will be made when required. Point is, if the process is repeatable, so CAN the parts be that are produced by that method. I will know with experience but the small sample this far suggests that the process is VERY repeatable with various options to compensate as needed. I hope that helps clear up my claim and if not, sorry, it's all I've got at this point.
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