Why your resin printer only prints supports and no model, and how do you fix this?
So you might have run into the issue where you go to run a supported print on your resin printer, only to find a few hours later as the print is finishing up that the supports printed, but your actual object is no where to be found--as if you were printing a ghost.
This tends to be a common and mildly infuriating resin print fail that is relatively easy to troubleshoot and ultimately fix. So lets jump into potential causes of this type of print fail.
Not enough supports at the start of the print.
At the early stages of a resin print, the supports tend to act as a foundation to not only connect the miniature or other object you are printing to the base layers and the build plate but also to ensure that it stays rooted in place and not shift or wobble during the peel phase of the print. The supports also need to be able to withstand the force exterted on the print while the newest layer is being peeled off the FEP sheet.
We often commonly see undersupported models failing quickly early on in a print job because either there are no supports or because the contact diameter and contact depth are too small for the print to reliably hold the part.
When you start troubleshooting ghost prints, supports is usually the first thing we recommend looking into. You can do this easily by pulling your supported model into your slicer of choice and inspecting the supports that would be closest to the the build plate.
As you can see there are no supports at the very lowest points of the this object, which means there is nothing to pull the initial layers of the print off the FEP sheet. Which means that the supports further up on the model will likely not be able to hold the main object, causing the supports to print but the actual object to stick to the FEP sheet as a flat silhouette of the the model.
To fix this we would recommend adding ample supports to the lowest edges, specific support settings and placements would vary depending on your model which we will cover in its own blog post about resin printing supports.
You can see here an example of supports that would likely have better results with printing in the real world.
Similar to no supports, having supports that are too thin can also cause issues where the part prematurely breaks away from the print because of the strain of the FEP sheet peeling off the newest layer is higher than the ability of the supports to hold it. This can be resolved in one of two ways. You can add more supports to evenly distribute the strain much in the same way that more beams would hold up a ceiling with ease in a building. Or you can increase the contact diameter width and contact depth so that existing supports could have a firmer hold on the part.
Suppose you know that the supports work fine or that you supported the print to use very thick supports and ruled out that supports could be a factor in causing your supports to fail. The next step to troubleshoot would be your layer exposure times because it could be that your resin is not getting enough UV light energy to fully polymerize and "connect" to the the supports.
Here, you ideally would want to consult your resin manufacturers' resin exposure settings spreadsheet and make sure the layer cure times match what they recommend. If they do you may want to use a calibration print like the XP2 Validation Matrix to figure out and fine tune your layer exposure times. On fast mono screen printers the difference between a success or a fail can be as small as tenth of a second.
Final fix ideas to troubleshoot
Most hobby level resins tend to have high shrinkage rates, e.g. that is the percentage that a resin might shrink while its polymerizing from a liquid to the hard solid piece. So a print that might be 10 cubic millimeters may come up slightly smaller than the dimensions of the actual model are. This can have an impact your supports if you are using very fine supports under .15mm contact diameters where a non zero shrink rate could mean that your real supports are smaller than expected and fail to hold or connect to your part.
Fortunately both Lychee and Chitubox have a tool built into their slicer that allows you to compensate for a known shrinkage rate without having to adjust supports, settings or anything else that might throw off your goove.
That covers much of what we know and have experienced about this particular type of fail and how to troubleshoot and resolve it like a pro. We'll be back next week with another type of resin print fail and how to fix it.
See you next week!