Cross-layer Curing and Layer Bulging on Resin Printers: Enemy of Overall Dimensional Accuracy and Printed Threads

If you read my blog regularly, you might know that I try to push the accuracy of resin printing as much as possible, as I use resin printing for functional parts. We have already explored resin shrinkage, warping, blooming (part one and part two), and we also briefly touched on how temperature affects precision. However, I haven’t covered one of the most notable problems – cross-layer curing.

When you have geometry without overhangs, you don’t have to care. However, in practice, some overhangs are often necessary. In this post, we won’t look at techniques to avoid overhangs, and we will also not deal with overhangs that need to be supported. We will focus on the overhangs that are nicely printable – e.g., steep ones or such that cannot be supported, e.g., metric threads. Yes, you can actually print functional M3 threads right out of the printer. If you use the right resin and give the trial-and-error approach a chance, you can also get somewhat functional M2 treads.

How is a layer formed, and what is cross-layer curing

To fully understand the problem of dimensional inaccuracy caused by cross-layer curing, we first must understand how a layer in an LCD resin printer is formed. The general idea is – I hope ­– clear. A build plate sinks into the resin tank so that a thin layer of resin is between the resin tank film and the already printed part of the model. The LCD exposes this thin layer of resin to UV light and cures the resin. See the image below:

How a layer is formed and how cross-curing happens

The following observations are noteworthy:

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The Winter is Coming – B̶r̶a̶c̶e̶ ̶Y̶o̶u̶r̶s̶e̶l̶f̶ –Prepare Your Resin Printer And Prevent Print Failures

The summer is over, and winter is near in the northern hemisphere. What does it mean? The resin printing groups are getting full of questions regarding suddenly failed prints. Why is it so? What can you do to prevent the failures? Note that you should continue reading even if it is not cold outside but you experience print failures. In this post, I will summarize all my findings on various ways a resin print can fail and tell you what you can do about it. The advice I present is no random guess; it is formed from many experiments, and all of them are supported by data (you can read all my other posts that explain the topic in depth).

An example of all the problems shared in the FB groups. It is really not hard to find them.

I know this isn’t a flashy TikTok/Youtube video, and reading this post will take you about 15 minutes. But trust me, I think reading this thoroughly can save a lot of headaches, time, and money in the resin wasted on failed prints.

The short summary is as follows:

If you want the full story, continue reading:

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2 Months of Experiences with Peopoly Forge: Is it the Dream Machine? No More Chitu?

At the beginning of 2022, Peopoly announced their new Forge machine. It is a large format LCD printer (288×163×350 mm) with standard 50µm pixels. Besided large-format, the printer promises to deliver great build-quality, ability to print engineering resins reliably, convenient features and non-Chitu control solution. Partially because of my curiosity, partially to increase my production capacity, I decided to buy the printer. I’ve been using it for 2 months now. Let’s look at what I like, what I dislike and what am worried about. Does it deliver what it promises? Is the new control board good and does it solve all the problem we have with Chitu controllers? Let’s find out.

In this review, just like in my other reviews, we will look at how the machine performs. Don’t expect a traditional review when the reviewer prints a few minis and tells you that it prints nicely and basically rephrases the specs. I will only focus on my experience with the machine. I assume you have some notion about resin printers, and basically, you are just wondering if Peopoly Forge is worth the money. I use my printers to print precise functional components, we will explore the limits of the printer, and we will also look inside the printer and its construction.

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Making Elegoo Saturn 2 Silent

In my review of Elegoo Saturn 2 I mentioned that Elegoo Saturn 2 is very loud and the noise is unpleasant. The good news is that the silencer kits I make for Saturn 1 work with Saturn 2. In this blog post, I will show you how to install them.

Saturn 2 uses two 50mm fans powered by 24 V. The combination of size and 24V rating is extremely rare. You cannot find any quiet fans in this form (at least in Europe). There is only the SilentiumPC Zephyr 50. These fans are of high quality in my experience and are nearly unhearable (the manufacturer claims 18 dBA). However, Silentium fans require a 12V power supply. If you connect such fans to a 24 V supply, in the better case, they won’t be silent (as they will spin much faster), but also you will significantly shorten their life or immediately burn them. Therefore, you need to step down the voltage to 12V. If you are not afraid of soldering, you can do it quite easily. However, if you cannot solder or you want to support my work, you can use my silencer kits.

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Elegoo Saturn 2 Review: Is Pixel Size Everything? In-depth Look & Disassembly.

So far, all my resin printers are LCD printers, and all of them have approximately 50µm pixels. The pixel size is somewhat the ultimate limit to the precision and details it can print. I was considering buying Elegoo Mars 3 or Phrozen Sonic Mini 8K as they have roughly half the size of pixels, as they could improve the quality of my resin-printed models. However, they have a quite small build volume so most of my molds wouldn’t fit, thus, I decided not to buy them. When Elegoo announced Saturn 2 with 28µm pixels and a slightly large build volume than Saturn 1, I decided to pull the trigger, and I got one from the pre-order.

In this review, we will look at how the machine performs. Don’t expect a traditional review when the reviewer prints a few minis and tells you that it prints nicely and basically rephrases the specs. I assume you have some notion about resin printers, and basically, you are just wondering if Elegoo Saturn 2 is worth the money. I use my printers to print precise functional components, we will explore the limits of the printer, and we will also look inside the printer and its construction.

Note that this review wasn’t sponsored in any way, and I bought my Saturn 2 as a regular customer. All opinions are mine.

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Step-by-step Guide On Perfect Bed Adhesion and Elephant Foot Removal in UVTools 3

A while ago, I presented my finding on why the prints do not stick to the build plate and why is there an elephant foot formed on resin printed models. Then I made a follow-up post where I presented a plugin for UVTools that automates the process. However, a few months passed, UVTools 3 was released, and the script stopped working. Fortunately, the functionality I presented was built into the UVTools. Since I frequently receive questions on how to use it, I decided to write this short “how to” guide.

Using suggestions to add rest times in UVTools 3

I assume that you have already UVTools downloaded. Adding rest times is hidden under the suggestions tab. The suggestions are a set of semi-automatic sanity checks of your file. When they detect unusual settings, they allow you to fix them. The usage is simple, follow the image guide:

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Preventing Platinum-cure Silicone Cure Inhibition in Resin-printed Molds

If you follow my work, you know that I use my resin 3D printers a lot to produce soft silicone molds or pieces (original blog post and a follow-up). Resin printers can create precise and detailed patterns. You can quickly prototype, cast miniatures, dices, chocolate molds… There are plenty of uses for soft silicone molds. However, some silicones play well with resin-printed patterns, and some don’t. In this post, I will explain to you which silicones cause the trouble, why we care, and also, how to prevent the cure inhibition. The recipe I give you is surprisingly easy and doesn’t require any special equipment. It actually outperforms existing commercial solutions (e.g., Inhibit X) both in terms of price and performance.

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Short Prints and Squished Layers On Chitu-powered Resin Printers: Solution

Many users of Chitu-powered resin printers complain that when they print flat on the bed, their prints are shorter than they should be – usually around 0.3–1 mm. This forces the users to print on supports. Back in the days when I started with resin printers, I observed the same thing on my Elegoo Mars. The cause of that was poor construction (see full explanation). I haven’t observed such problems on Elegoo Saturn ­– until now. Let’s explore what causes it and how to fix it.

You see people fighting this problem by leveling against a paper folded various number of times, setting arbitrary numbers to Z-offset and similar. Everyone has a custom recipe. I will give you my recipe which I think works the best – and unlike the others, I will explain you why. I tested everything on Elegoo Saturn, but I believe it applies to all Chitu-based printers.

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Preventing Warping of Resin Printed Pieces: Alternative Way of Fighting Resin Shrinkage

In the previous blog post, we started the topic of resin shrinkage. We showed how serious it is and we presented a simple yet effective method of measuring the shrinkage amount and compensating for it.

However, the problem is more complex than the two numbers. Anyone who has ever worked with plastic injection molding can confirm this. There is a number of papers, models, and algorithms that deal with modeling shrinkage of plastics after molding. The same, unfortunately, applies to 3D printing as our material shrinks as it cures. What effects does it have? Is there something we can do about it? Yes, there is as we see at the end of the post!

Just to illustrate what we are trying to fight, there are a couple of posts from a single FB resin printing group:

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Getting Perfectly Crisp and Dimensionally Accurate 3D Prints on a Resin Printer: Fighting Resin Shrinkage and Exposure Bleeding

Most polymers shrink when they cure or solidify. That means that their volume shrinks down during the process. The simple consequence is that the models you print either on FDM or resin printer are smaller than you designed. Therefore, when you try to print, e.g., an enclosure for PCB or a hole for a pin or a screw, they might not fit.

Today, we will explore how serious the shrinkage is, whether it is the only source of dimensional inaccuracy and how to measure it and compensate. After reading this post, you should be able to calibrate your resin printing process such that the models you print will come out perfectly within the accuracy of a single LCD pixel. That is usually roughly 50 µm + the inaccuracies in your measurement setup. We will also show you that you can easily use this test to precisely tell if you overexpose your model or not.

However, since we print quite complex geometry layer-by-layer there are some interesting phenomenons that need to be taken into account. They affect how the printed part wraps. They are complex, so we will dedicate a separate blog post on this topic in the future; today we will start with the basics.

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