3d Printing Workflow

This is the process I go through when creating a new model. I update it occasionally as the process is evolving.

The Model

Design your model in Blender or whatever.

Make it hollow, with holes that will allow resin/air to enter and exit from the bottom (that is, the bottom in your slicing software, which will be the top when printing).

Walls should be 1-2 mm thick. Nothing should be more than 5 mm thick. Details that jut out from a wall can be as thin as 0.1 mm, details not attached should be no smaller than 0.2 mm if small, and maybe as must as 0.4 mm if long.

Back-up your Blender file - hard-drives do fail occasionally.

Export STL File

Export it as an STL file.

If you are printing it as a number of parts, I suggest each part in a separate STL file, as it makes it easier to just print one part later if required, plus you have more freedom to arrange the parts on the build-plate of your printer. In Blender, I would put the parts in different collections, and then hide the other parts. Press A to select everything, then when you export tick the "Selection only" box on the right side.

If you do export several parts as one STL file, make sure they are all more-or-less on the same baseline, otherwise you will need long supports on the high up parts.

Repair STL File

Open the STL file up in Microsoft 3d Builder. Does it look right? If this is just part of the model, is it the right part and nothing else? Have any hidden parts been included that should not?

If it briefly flashes up on screen, then closes, you probably have an empty file; you exported with "Selection only" but had nothing selected!

Click "Import model" top left, then click to repair, bottom right if required. This can take a long time  for complex models, and it will get stuck at about 80% done. Just be patient; I have not had it crash it yet - and I have had it take over an hour on a pretty high spec computer.

Save the repaired file as an STL file again. I suggest doing so in a subfolder called "repaired" so you know which are repaired files and which are not. Alternatively, give it a file name with "fixed" or whatever appended. I do this even if the file did not need repairing so I know where there is a printable version for everything.

ChiTuBox

Open up ChiTuBox, and import each STL file by dragging the file into the ChiTuBox window. You can drag in several in one go

The STL format does not include information about units, so it guesses. Blender actually works in meters, but ChiTuBox will guess that should be millimeters to fit the print volume. For really small parts, it will guess cm, and the part will be huge. Scale it to 10% and all will be good. For tiny parts, it may even guess inches, and you will need to scale it to 3.94%.

You can print directly onto the build plate, but I prefer to have it raised. I think it is far easier to get the model off the build plate without damaging it - though of course it does use more resin.

Get the orientation right. It can be good to print items on their side or at an angle. Large flat horizontal areas rarely come out flat, so change the angle. If the item is on long spindly legs, you might be better off doing it on its side or even upside down to reduce the supports required.

You also need to ensure hollow areas have holes at the bottom. These are generally called drain holes, but are really vents, allowing air to enter as the model is lifted (remembering that it is printed upside down). Failure to do so will make your model much heavier during printing, and hence more likely to  fall off or otherwise fail. Having the model raised off the build plate helps with this.

If you need to scale, do that now too.

Now to add supports. This is something of a black art... Too few supports, and the model will get pulled off the build plate during the print. Too many, and you waste resin, have a bigger job removing them at the end, and can get artefacts in your model.

For each part, I typically click the supports tab, top right, select "Light", then click "+All" to have it automatically add supports. Then select "Medium" and add extra supports at the bottom of each corner of the model, but this is dependent on the nature of the model.

Even the smallest part should have at least three supports. One is not enough, even if ChiTuBox says it is!

If it has added supports high up your model, check they stand free of your model, so can easily get removed.

Click the other tab to return.

If you want more than one of a part, select the part and click Copy from the tool bar (after adding supports). Arrange the parts so they are evenly spaced. It is best if the bases do not touch so each can be removed and handled separately later. You can rotate objects round their z-axis too (if you rotate around the other axes you will need to do the supports again) or mirror them.

For tiny parts, you might want to do some extras. They are more easily broken, and will not use much resin. It is annoying to get to assembling your model and to be missing that one tiny bit.

Save the project.

Check ChiTuBox is set to your printer by clicking the up arrow just left of the "Slice" button. It will remember for next time.

Click "Slice", and ChiToBox will convert your model to a series of slices to be printed. Once it has done, it will tell you how much resin will be used. You can compare that to the capacity of the tank (for an Elegoo Saturn, that is 620 ml to the max line). 

It will also estimate how long it will take, but I find it tends to underestimate by maybe as much as 20%. Hmm, maybe its estimate of material used is just as inaccurate? The printer will also give the same erroneous estimate, and you would think it should know!

Click the "Save" button on the right. Although you need the file on a USB stick, save to your local drive first.

Wait patiently. When it tells you at the bottom of the screen "Write successful", click the "Back" button.

I have found ChiTuBox crashes sometimes. At one time I had issues with it crashing when saving the .ctb file. You can just reload your project, and try again. If it crashes a second time, I would advise re-starting your computer. I have not had it crash after a restart yet. 

Print

The build plate of the printer needs to be level, though you do not have to do this every run. I would suggest that if your last run was a success and you have not done anything to the printer (besides removing the vat and/or build plate), it should be alright this time (ETA (Nov/24): it is getting on for a year and a half since I last levelled it). To check the build plate is level, the best way is to repeatedly press the home button as you test with a sheet of paper in each corner (with a clean base plate and the resin tank removed). Full instructions here (note that you tighten the right screw before the front one). The instructions that come with it are best used as levelling paper, which mine did not have.

Remember to add more resin to the tank if required. Note the resin is very viscous, and if you pour in a lot at the front, it takes a few moments to reach the back where the mark is, so take care not to fill above the level.

Make sure the resin tank is secured with the bolts and the cover is in place.

I use a heater to keep the resin warm, and turn it on at this point, then leave it a while to get to around 25°C.

Transfer the .ctb file to a USB stick (remember to remove safely), and put the USB stick in the printer. I use a USB extension lead to save wear and tear on the USB port, and two USB sticks so I can swap between them.

Select the file and print, as per your printer.

You can top up the resin during a run if necessary, but it is not easy to see when that is just by looking at the printer. If you do top up, do not pause the printer. I would also warm up the resin before adding so it is the same temperature as the stuff already in there. I have never got anywhere near needing to do this.

Wash

Once printing is done, leave for a few minutes for excess resin to drop off. Note that it is safe to leave the model in this state for days.

Remove the build plate, and as you do tilt it so any remaining resin will drop back to the tank. Hold it like that until it stops dripping. On the Saturn 8K you can put the build plate back in place, but rotated 90°; you can then leave it to drain without holding it, as long as the models are not tall.

If any drips outside the vat, wipe it up immediately before it gets anywhere it should not. Have kitchen roll on stand-by!

Once the resin has stopped dripping, prise each part off using the metal scraper. The ChiTuBox raft does help with this, but getting started can be awkward. Once you have the scraper under a model, it is a lot easier.

Use a pair of tweezers to handle the parts. I would suggest a large pair that you keep only for doing this job, as they will get resin on them. If you only use the tweezers to handle the parts until they are cured you can pretty much avoid contact with the resin.

Wash each part in iso-propyl alcohol (IPA). I use a plastic tub with a well-sealing lid, that is a little bigger than  the build plate and three quarters full of IPA. Using the tweezers to hold the model, just shake the model in the IPA, then let the IPA drain off. Repeat a few times. 

The IPA can be reused. Every so often, put it in a clear container in the sun, and the dissolved resin will cross-link and drop out of solution. You can decant off the IPA, and dispose of the resin. It can be a good idea to shake the contain to break up the solid, and then allow to stand for days to get the last of the IPA out.

You can get resin that can be washed with water; I have no experience of that. Some people suggest using acetone rather than IPA. Be aware that it is significantly more flammable, and incompatible with more plastics. Some people claim it is not compatible with FEP or PFA, but that is not true.

Leave the items in the open while the solvent evaporates. Do not cure it until all the solvent has gone; this may take hours - I like to leave it over night. Curing when there is still solvent on the model can lead to patches that are shiny and do not take paint well. It may be possible to use a hairdryer to speed up the process, but using a hairdryer with a flammable solvent would worry me.

Note that the model may be quite flexible at this point, so leave it in a place where it will not warp.

Are any parts missing? If so, you need to recover them from the vat. This is best done straightway, while the resin is warm, as it will filter faster. You will need to: Drain the tank into a suitable container (an old resin bottle is best) via a funnel with an oil filter. Use the plastic scraper to get the last of the resin out - never use metal on the base of the tank. A shadow of the missing part will be on the base. With some prying it should come off with the plastic scraper, try gently pushing on the bottom of the film to raise the edge. If this happens a lot, re-level the build plate. Note that you do not need to clean the vat; no need to rinse with IPA or wipe with a cloth or anything like that.

Cure and remove supports

UV cure each part. You can do this by leaving in the sun, and turning occasionally, or with a curing station for about 3 minutes.

Cut away the supports. I use cutters especially designed for cutting parts from a sprue, which lets you get right up to the surface. Be careful; the parts can shoot off, and you do not want to lose them - or get one in the eye!

I usually do a second cure, with the model the other way up, to get the parts that were obscured by the supports.

Finish

Then assemble, prime and paint, or prime, paint and assemble.