DRG #168 - More Printing Lessons Learned...

I've finally have a printing setup where I can start experimenting with parts. What took a while was assembling all the ancillary things to support the workflow, like LCD screen protectors (saw too many leak pictures over at reddit/resinprinting...). I still have a few things on order, like a silicon spatula and spray primer, but I can now print test articles.

Here's today's batch, on 1/4" grid paper:



I picked these to get a sense of how supports would work, and the cylinders so I could start to consolidate the frame. First thing, the smokebox course is WAAAY too thin! I ported over my CAD for the metal layout and didn't think twice about the 0.02" wall thickness. The print is thinner than a soda straw, and it flexes like one. Okay, decrease the diameter of the subtracted cylinder, that'll make the wall thicker.

I'm finding out a lot about the extent of "exaggeration" needed to accommodate the material. The number plate is one example, I did a previous print where the numbers were extruded from the surface by an amount that looked appropriate to the photos I have, but you can barely see the numbers (the translucent resin doesn't help, can't wait for the primer...). So, I extruded them even more for this print, with my paint strategy to be to airbrush gloss red on top of a primer coat, then puddle a little thinned gold paint on a glass surface and lightly press the face into it. I made the extruded numbers the same height as the rim, but they printed a bit less tall than it; I may have to further exaggerate them to make them print level with the rim.

If you look at the end of the smokebox adjacent to the supports, you'll see some curling. I'm not sure if that's due to the thin material or the spacing of the supports; for the next print I'll keep the supports the same and see if the increased thickness of the wall keeps that from happening. I'm also considering consolidating the smokebox cylinder with the front plate, but that'll require a bunch of internal supports. I may try both ways in the same print, what's a little resin to learn stuff...

The bottom of the cylinder chest definitely suffered due to lack of support. Also, I printed it solid; it may need to print hollow with holes to drain the uncured resin inside. The rest of it looks quite nice, even the color. I'm not going to prime it yet, see if it cracks.

The detail in the rivets, dogs, and hinges of the smokebox front are there, but the hinges kinda fade into the center, so I'll extrude them a bit more.

The two-part wash bath and toothbrush scrubbing seem to be working to keep crystallization from happening, but I think there are scratch marks from the toothbrush on the smokebox face. This might drive me to an ultrasonic cleaner. Yeah, I'm accumulating quite a collection of tools and accessories here, but the cost is far less than outfitting a lathe.

Anyway, much fun is being had...

 

I re-printed the smoke box with thicker walls, 0.05", and i also incorporated the smokebox front in the same print. Here 'tis, sitting on the cylinder saddle, along with the better-cleaned compressor; for sense-of-scale, the compressor is about 1/2" in length:



Note the concentric layers in the smokebox door, these are more-finely gradated in the previous iteration which was printed vertically. I have some available discretion in the slicing layer height, but that requires an exposure adjustment away from the recommended settings (I've already dialed in such for using a LCD screen protector), and I'm also trading that off with just printing it separately and gluing it on afterward. This becomes one of those decomposition questions, that is, what level of print integration vs assembly integration and the considerations behind each. In that regard, I'm considering just adding the rest of the boiler to the print, and then trading orienting the whole thing horizontally or vertically for print and the associated trades in gradation. Geesh...

I also did some comparison measurements, printed size vs. modeled size. The assertion is that cured resin shrinks; what I see in the couple of measurements taken on these parts is about 0.001-0.002" difference. That's about .2" in 1:1 terms, so I'm not going to compensate for "decoration" parts, at least with Elegoo plant-based "Tough" resin.

I'm also really interested in seeing the detail in the locomotive's builder's plate, on the smokebox side. I modeled it based on the available font's default size, scaled it to HO, and just moved it into position on the smokebox. I can't really see or photograph it well in the current semi-transparent state, need to shoot it with primer but I'm afraid that's going to fill stuff in. In any event, I'm probably going to have to rely on the failing eyesight of my audience...

 

I'm actually quite surprised at how well it's going this early. The Mars 3 is just that, a third iteration, and it seems they've really designed-out a lot of the earlier headaches. I also have read and considered a lot of "Why did my print fail?" threads over at reddit/resinprinting...

Oh, and shout-out to Stephane Savard here and Jeff Kraker at the MRH forum for their chronicles of building scale model locomotives with resin printing. A lot of heuristics in those threads...

 

I've been using Fusion 360 to design some Tscale rolling stock. I'm also printing them on a Mars 3 in resin. Building stock in F360 can be addicting, and it's amazing how the hours can fly by. Here's a link to the Tscale forum where I posted about those STL files this morning. https://www.trainboard.com/highball/index.php?threads/some-tscale-models.144249/ .