The LittleRP – A review and Getting Started guide

We needed a printer to test Nün&Noot designs without having to cast them, so we got a LittleRP 3D printer. It took a while to calibrate and get good results, so I decided to write a review and a “getting started” guide. Here it is.

What is the LittleRP?

The LittleRP is a kit for building a resin based 3D printer, also called an SLA or DLP printer. It uses a DLP projector (hence the name) to cure special resin that hardens when exposed to UV light.


The LittleRP assembled, without the projector mounted.

So it’s a kit, you say

Yup, that means you have to put it together. It’s not terribly complicated, but it will take you 3-6 hours. There are assembly instructions on LittleRP’s website, but they are slightly out of date. There are two sets of instructions, be sure to scan through both before you start. Here is a timelapse of me assembling the kit.

The projector

The kit is just half the story here, you will need a projector. A DLP projector, to be specific. LCD projectors won’t work, as they don’t put out enough UV light. LittleRP has a list of projector models that are known to work. I tried the Acer H6510BD but found that I could not get it to focus sharp across the entire build area. These projectors are not designed for this kind of use. They have manufacturing variances that are not noticeable in normal operation but come into light (har har) when you try to focus on an object that is 10cm in front of the lens. The projector also died after 10 hours of use, so I returned it and got an Acer X152H instead.

The Acer X152H

Compact, HD and relatively cheap, The X152H is a good choice for the LittleRP. However, unlike the H6510BD, the X152H needs to be modified to allow focusing on a close target. Actually, most projectors will need to be modded to work with a DLP printer. The projector lens module needs to be moved forward about 5mm. This sounds scary but actually it’s a simple process that took me about 10 minutes to complete. If you want to know how it’s done (the process is very similar with all the projectors), I will describe the process (with pictures) in a separate blog entry. Once the projector was modified I was able to get a sharp image across the entire build plate.

The LittleRP needs to be modified a bit as well, to accommodate for the X152H height. The projector is thicker than most, so the printer needs to be moved up by about 18mm, and you will need to drill new mounting holes for the projector on the base plate. Send an email to LittleRP support and they will send you a template to help with the hole drilling.

The Build Plate and Printer Operation

The projector projects an image, it is reflected off the mirror (angled exactly 90 degrees) and goes up through the vat, through the resin, and onto the build plate. The vat is a transparent Teflon foil held in a bracket, and holds about 100cc of resin. The picture above was shot mid-print, when starting the build plate should be pressed right into the vat (more about that later). After each layer is cured, the build plate moves up a few mm to allow resin to flow into the gap, and also to peel the print off the Teflon foil, than moves down (by a few mm minus the layer height). The next layer is cured and the process repeats itself.

Some numbers and printer specs

The build plate of the LittleRP is 40x70mm. If you use an HD projector you can achieve feature size of about 36 microns (0.036mm). That is the size of a single pixel on the build plate. The smallest layer height is about 30 microns. This is very, very small. You can print objects with an incredible level of detail and complexity.

Layer cure time varies greatly with the resin being used, but overall it’s not a fast process. Anywhere between 5 and 20 seconds per layer is the norm. An object the size of a ring will take 1-2 hours print. Actually, I should say “an object the height of a ring”. The projector will always cure a full layer, and the cure time is constant, so it doesn’t matter how many objects you are able to cram into the build plate. Printing one ring takes the same time as printing 5, as long as they all fit on the plate. Print time is a function of layer count, and not volume.

Objects rising out of glowing resin. Pretty cool. 

Resins and operational cost

There are several resins on the market for DLP printers. Some work better than others, some will work better with your projector & printer. The best way to know which works best is to experiment. I had great success with Vorex Orange by MadeSolid. I also tried MakerJuice, and while the objects look nicer and come out cleaner, I’m having difficulty getting it to render small features.

Resins sells for about $100/kg. This seems a lot, and it’s certainly a lot more than the $20/kg you can expect from FDM printers (plastic filament) but remember that DLP printers are designed and suited for printing small items. 1 kg of resin is enough to print about 200 rings. Castable resin is more expensive, and can go up to $250/kg.


A mouse sitting on a quarter.

The dark side of resin

Coming from FDM 3D printing, where a finished print is yanked off the build plate and is ready to be used, working with resin can seem like a huge pain in the ass. That’s because it is. Uncured resin is a skin irritant, whenever handling anything about the printer you should be wearing gloves. You will burn through a lot of gloves. The resin is also very viscous, it’s hard to pour without dripping, it gets everywhere and it’s hard to clean. A failed print will leave floating bits of cured resin in your vat, which are really hard to fish out. If you leave them in there they can stick to your prints and/or ruin the print completely. Changing resin is also an involved process, requiring cleaning the vat with Isopropyl alcohol. Luckily you can leave the resin in the vat most of the time, just remember to close up the printer cover. Some resins will require stirring before use, I use a brush to mix up the pigments in the vat if it sat there overnight or longer.

 
3D Benchy and baby. That’s a penny under the smaller boat.

Flexvat

This is an add-on to the LittleRP but I highly recommend that you get it. It replaces the petri dish with a vat that has a transparent yet flexible bottom. This allows the print to peel off easily when the build plate is moving up, instead of just sticking to the glass and ripping off the build plate.

The downside of the flexvat is that the first few layers will be squished and funky. If those layers are important to your print’s geometry, you will need to raise the object it a bit and print support structure. I will write more about support structure and preparing objects in a later blog post.

Calibration and first layer woes

As any 3D printer, the LittleRP needs to be calibrated. These tips and procedures apply to almost any DLP printer. Also, like most 3D printers, printing the first layer is the hardest and most important part. There are several parameters you will need to work on:

  • Flexvat tightness – The foil needs to be taut just the right amount. It should sound like a drum when you tap on it. Yeah, that’s hardly scientific but it’s all I got. You’ll need to experiment.
  • Getting the right cure time for initial layers – If you under-cure it will detach from the build plate. Luckily, with the flexvats over-curing is not a problem. I usually cure the first layer for 1.5 minutes, than 10 layers at 25 seconds each.
  • Getting the right cure time for the rest of the layers – Again, experimentation is key. I found that the Vorex Orange needs about 10 seconds per layer, while the MakerJuice needs at least 20.
  • Z movement speeds and distances – You might need to change this if you have issues with layers detaching. Start with LittleRP’s recommended settings (4mm travel distance at 100mm/s).
  • Build plate leveling – It has 3 screws, use them to make sure it’s perfectly parallel to the flexvat.
  • First layer height –  I manually move the build plate down, pushing it right into the vat and extending into the foil, then using the threaded rod I move it up a bit, until it’s still pushing down the foil but only a little bit. You will need to do this several times to get a feel for it.


Two vases printed in Vorex Orange, total print time about 2 hours.

Starting a print

Make sure the manual shutter is inserted before turning on the projector. You don’t want the projector logo and splash screen cured into your print. I will make a blog post about how to prepare a 3D model for printing, which software to use and how to execute a print.

Post Processing

When the print is done the objects are not ready to be handled, as they are covered and infused with uncured resin. This is my post-processing routine:

  1. Detach objects from build plate using an exacto knife. Don’t forget to wear gloves.
  2. Put prints in a small container with isopropyl alcohol
  3. Put container in an Ultrasonic Jewelry cleaner for 3 minutes
  4. Remove items, dry, and put in cure box for 10 to 60 minutes, depending on resin.
  5. Snap off support structure (more about this in a later post)


Ultrasonic Jewelry cleaner. Get one with a stainless steel container.

Cure box

When the objects come out of the Ultrasonic cleaner printer they still have some uncured resin in them, that will eventually seep out and onto your hands. Post-curing is mandatory. You can place them in sun light for an hour, or you can build a cure box from UV led strips ($20 on ebay). I use a nail polish lamp, can be found in Walmart or amazon. Depending on the resin, prints need to be cured for 10 to 120 minutes. Some special resins need to be post-cured for many hours. Over-curing is not a problem, so feel free to just leave them in there for as long as you want.


Nail polish lamp box

Conclusions

DLP 3D printing is a great way to get incredible detail on a budget. For less than $1000 you can have a setup that generates professional quality prints. The LittleRP is an excellent kit if you are willing to invest some time in putting it together and learning how to use it. Their support is excellent and responsive, the documentation on the website is adequate although it does need to be updated and reorganized (as of Jan 2016). The LittleRP price can’t be beat, it’s one of the cheapest DLP printers on the market.


The Shrine, printed in MakerJuice resin.

 

Nün&Noot

Check out our neat 3D printed sculpture jewelry at NunAndNoot.etsy.com

 

 

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