3d printing process

[Patrick Matthews]

Phil- re: the white crud... it's a totally different process, with resin droplets being spritzed (like from an inkjet printer head) onto a wax support base. When done, the wax is (mostly) washed away, leaving a free part with no supports. But all surfaces that were in contact with the wax look frosted, while the top side is clean and smooth. 
Illustration depicts the wax support (red) under one of my chain-stopper sprues.

[Kevin-the-lubber]

Pat, how expensive have you found MJF? I think you've had hulls made haven't you, if so what would be a ballpark figure for a 1 metre long hull? And getting back to the issue, how smooth and accurate are the contact surfaces in reality?

[Patrick Matthews]

Multijet printing at Shapeways has just gotten more and more expensive, to the point I avoid it now in favor of my home resin printers.

 

Never did an entire hull in it, would be thousands of dollars, and in many pieces, because the platform isn't so big.

I did do a 27" hull in one piece on a big industrial (true) SLA machine, but that was through a special relationship that no longer exists...  

 

 

[Patrick Matthews]

Accurate? More accurate than anything we whittle in wood!

Smooth? As with wood, allow all surfaces to be sanded or scraped smooth. Molded plastic parts from Tamiya are smooth, but those steel dies have been laboriously polished to achieve the smoothness. Someone is going to do the work somewhere.

 

For precision parts, I treat printed parts like metal castings... which need to be machined for precision work.
Here's a 1:8 scale DUKW axle printed in pieces on a little Photon Mono. Parts were machined for fit and for bearings, and glued together. Works fine.

 

[Patrick Matthews]

Another use for printing: Rubber tires, as shown above. 

There are some flexible black resins, but they are difficult to work with and produce a material more like vinyl.

Instead, I printed a mold for the 5 inch OD tires, and had a friend pour polyurethane rubber into it.

 

[Patrick Matthews]

And let's not forget another thing you can do- print metal parts! 
Actually, you have a service print waxes for investment casting, and they outsource the parts to a casting house. You can also print your own waxes at home, but have to deal with the casting process yourself.
Here's a 3 inch Federal-Mogul "weedless" prop for that same DUKW, cast in bronze:

Edited February 20, 2022 by Patrick Matthews

[Dr PR]

Pat,

 

Your DUKW "duck" drive train brings back memories. I grew up in Hot Springs, Arkansas. It is a tourist trap - it had about 270 hotels and motels (individual businesses, not rooms) when I was a kid in the 1960s. The town is surrounded by lakes on two sides (actually it has grown around the lakes these days). There was a company with a fleet of "ducks" to take tourists on rides around the lakes.

 

I never rode on one. But I worked for an auto parts house in high school and college driving a delivery truck. The DUKWs had a bunch of universal joints in the drive train (I don't remember the actual count but I can see eight in your model), and they wore out fairly quickly. And of course there were the engines and lots of other parts. I made a delivery or two every week to the "duck barn." Hauling the engine blocks back and forth for rebuilding in our machine shop was the most difficult part.

 

I think they are still using some of those things that are older than I am!

[Dr PR]

The "wire" in the CAD model anchor chain is 0.6615 mm diameter and a circular cross section. The printed parts are oval in cross section, 0.62 to 0.65 mm on the vertical and 0.71 to 0.74 mm on the horizontal. So I am getting about a 2% to 10% reduction in the width on the film, but an additional 10% to 12 % thickness on the vertical.

I expected the parts to be a bit too thick on the vertical dimension. From past experience I knew that the very thin parts are translucent so additional resin gets cured on the upper surfaces of very thin slices.

But I can't explain why the parts were thin on the horizontal dimension. I would expect resin to be cured over the entire pixel width but this apparently is not happening.

Increasing the exposure time probably would increase the horizontal width, but it might also cure more resin in the vertical dimension. Increasing the step size would reduce the total exposure time, and perhaps reduce the vertical thickness.

I am happy with the results I got - no one (except me) is going to be taking a micrometer to the chain on the model. But I might try printing them again with a different step size and exposure time.

With a model diameter of 0.66 mm the 0.02mm step size gave 33 slices and exposures. A 0.03 mm step size would give 22 slices, 0.04 mm would give 16 and 0.05 mm would give 13 slices.

So I might try the 0.04 mm step size to halve the number of exposures and try to reduce the vertical diameter, but use an exposure time of 3 seconds to expand the horizontal width a bit.

****

The reason I want to control the printing better to get a circular cross section is that there are many yards/meters of life rails on the model. They real parts were made of pipe 1.25", 1" and 0.75" diameter. At 1:96 this comes out to 0.013", 0.010 and 0.008", or 0.33 mm, 0.25 mm and 0.20 mm. This is less than half the chain link "wire" diameter.

I have successfully printed 0.20 mm diameter pieces, but they are extremely fragile. I really don't want the parts to come out any smaller, but 10% oversize would be OK. But I want them reasonably close to cylindrical.

I have been reading up on some of the flexible resins. I would think these would be less susceptible to the accidental bumps that happen while assembling models. But several sites say they are not suitable for thin walls, and the minimum thickness should be 1 mm, or 125 times the thickness of the smallest pipes!

Furthermore, because they are flexible they may not separate from the plastic film evenly and become bent while printing. This is also probably true for regular resins, so lots of supports will be needed!

[Kevin-the-lubber]

9 hours ago, Patrick Matthews said:

For precision parts, I treat printed parts like metal castings... which need to be machined for precision work.

What resins are you using for parts that will be machined, Pat? I guess if the wall thickness is substantial enough you don't run into problems with brittleness. Unfortunately I don't have a hobby lathe/milling machine and although it would certainly solve many problems, I'll leave that until / if I reach a point where it would be more worthwhile.

 

I looked at having the main body of the stern I made for the Victory professionally printed as I was having endless difficulty at this end, but it was too expensive. Eventually I found a way, as you do. Likewise I looked at making the vic stern available via shapeways but I wouldn't have been willing to pay the net price so wouldn't expect anyone else to either. When I go back and finish it off I'll look at another, more affordable way.

 

Phil, one thing I learned on the Vic stern was that resin either shrinks or loses accuracy in the printing. I was losing about 0.5% with elegoo ABS-like. I haven't measured the loss with syratech but think it may be more as I've had a couple of parts that wouldn't fit as intended, but I think Pat's approach - treat as needing machining - is the best solution. I chased my tail a lot on the Vic trying to compensate through scaling but, in the end, adapted the design to work around the issue and am doing the same with the Cutty Sark.

 

I think once you're printing walls/objects down at 0.3mm or so, they'll be fragile whatever resin you use. However if anyone is going to find the work around it'll likely be you, with this methodical approach. 

 

[Patrick Matthews]

I like any of the "hard/tough" resins for just about all parts I make. And yes, a thick wall, 2 - 3mm, provides a lot of strength without building excessive internal stress. There are ways around that issue too if needed... plastics can be "tempered", but I haven't needed to resort to that.

 

1:96 railings: That's a tough one for printing. I did some in 1:87, with 1/32" printed stanchions and brass wire rails. Those stanchions were really delicate and I was terrified of breaking them simply by threading the wires through. They really want to be metal.

 

 

 

[Dr PR]

Pat,

 

Nice railings. I have been thinking about how to make railings for the OK City model for about 12 years. They have extremely small diameter sections. I have been planning the purchase of a small high tolerance milling machine just to drill 0.008" holes through 0.013" brass wire to make the stanchions. Even with a very good mill I foresee a lot of broken bits and scrap pieces. There are between 450 and 500 stanchions that will have to be prepared!

 

****

 

I ran the chain prints again, using a 0.04 mm step size and 3 second exposure (as opposed to the earlier 0.02 mm step and 2 second exposure). Half as many exposures but 50% longer exposure time.

 

The design diameter of the chain "wire" was 0.66 mm. The horizontal links came out 0.75 mm to 0.84 mm thick, 14% to 27% oversized. The vertical links were 0.63 mm to 0.66 mm, or 95% under size to 100%. Most of the links were free or slightly fused, but when I gently twisted the chain around the long axis almost all of them separated. So this was near the limit for getting a flexible chain. However, I printed three chains and one did not print completely.

 

I think the 2 second exposure was better because it have thinner vertical layers - even though I was printing layers twice as thick as before, so only half the number of exposures. I can see no visible difference in the surfaces of the 0.02 mm vertical step and 0.04 mm step parts, so 0.04 mm is adequate. Actually, these things are so small that if there was a difference it wouldn't be noticeable.

 

There really wasn't much difference in the thickness of the vertical links between the two runs, so the longer exposure time made no difference there. But it certainly did make the horizontal link thickness greater even though there were only half the number of exposures. And that was causing the links to fuse.

 

So it looks like the optimal settings for these tiny parts 1s about 0.04 mm step size and 2 second exposures with the Anycubic Basic Grey Resin - which they call "Colored UV Resin" on their web site - on the Photon Mono printer.

[Kevin-the-lubber]

I did these a week or so back, just to see if it would go, which it obviously does. The wire is 0.5mm dia, the stems a very generous 1mm or thereabouts. The wire holes closed up during printing but there was enough of an indent to make drilling out easy. I wouldn't want to have to do 500 though! I think I only broke one stanchion head along the way.

 

As you can see I've gone back to FDM for some parts. I'm finding that it is better than resin for larger flat surface parts and comes up well with a little light sanding. 

 

 

[Dr PR]

Fellows on The Ship Model Forum have been experimenting with printing large flat surfaces without any supports - just flat on the print platform. This produces very flat thin pieces like decks. The initial long exposures for the base layers will create a small wider bead around the part on the print platform,  but this is easily filed/scraped/sanded away. Because the contact surface on the plate is so large you don't need many long exposed base layers. Some have made successful prints without them.

[Kevin-the-lubber]

The main thing I’ve been printing in FDM is a four section 500mm long deck with staggered, interlocking joints using the plank lines to disguise that there’s a joint. As there’s only 0.2mm clearance the elephants foot effect meant I couldn’t do this successfully in resin on the plate. But I have to admit it didn’t occur to me to reduce the cure time for the initial layers so I might try that next time round. I also had another problem that I simply couldn’t figure out; when printing large rectangular sections on supports and tilted, the straight leading edge was not coming out straight, it always had a slight curve to it, regardless how hefty the supports. It’s as though the resin shrinks slightly during the print and gradually pulls the outer edges towards the centre.

[Mldixon]

I've been printing parts for the Winchelsea. I started this process out of frustration with not being able to buy figures in the poses I wanted.

It's an Anycubic Mono X  printer. I've attached a pic of the Swivel Cannon. I had to print this with a flexible resin in order to get the handle to print without breaking off with handling

 

🔻The raw unpainted part.

 

But the primary reason I turned to 3d printing was for scale figures for the ship. It is a 1:48 scale. This sailor is posed for a chain pump gang.

 

 

I'm using many of the methods you have outlined. However I always print a reference file with any resin I use and make that my starting point. Saves a lot of hair pulling and anguish.

🔺️Three figures printed for Captains Quarters. 

[henrythestaffy]

I like your figures. Did you design them yourself?

[Kevin-the-lubber]

39 minutes ago, Mldixon said:

However I always print a reference file

Good stuff - can you tell us more about the reference file, I have very little hair left but would quite like to hang on to it 😬.

 

That looks like the Syratech  resin? I’ve discovered this week that either it or my baby printer (elegoo mars2) is way out dimensionally, but bigger rather than smaller.

[Mldixon]

1 hour ago, henrythestaffy said:

I like your figures. Did you design them yourself?

Those originate from Daz a posing program. Its free. But a learning curve. I design the parts of the ship they interface with and import them into the program. Then I pose the figures into whatever action I want the involved in. Then I export them in scale to an stl file. I repair that file to make it watertight, then print. I also use a program called z brush to add details I otherwise couldn't get. Accessories to figures, hats for example

[Mldixon]

1 hour ago, Kevin-the-lubber said:

Good stuff - can you tell us more about the reference file, I have very little hair left but would quite like to hang on to it 😬.

Yes if you search the net, you can find the files everywhere.  I use the files provided with the anycubic printer. It prints eight different models, all at once. The eight models are different settings set up by whatever genius figured this all out. I have no idea how they do it, but the eight different models are numbered, you pick the one that prints the highest details and use its settings for your resin and printer. I used to cuss up a storm until I ran across this technique.  Now I never print with a new resin until I run the reference files. I use Syartech and like it, but this was printed with

ANYCUBIC 3D Printer Resin, 355-410nm Fast UV-Curing Photosensitive Wax Resin for SLA/LCD 3D Printing, Rapid Precise Printing Craftsman Liquid for Jewelry Anime Figure  and Character Design

its flexible and holds paint and primer.

[Mldixon]

1 hour ago, Kevin-the-lubber said:

Good stuff - can you tell us more about the reference file, I have very little hair left but would quite like to hang on to it 😬.

 

Edited February 26, 2022 by Mldixon
Double post

[Mldixon]

Anycubic Photon S - Resin Exposure Test - R_E_R_F with custom timing
YouTube · Jonathan Carroll
 

 

[Patrick Matthews]

On 2/26/2022 at 7:19 AM, Mldixon said:

Those originate from Daz a posing program. Its free. But a learning curve. I design the parts of the ship they interface with and import them into the program. Then I pose the figures into whatever action I want the involved in. Then I export them in scale to an stl file. I repair that file to make it watertight, then print. I also use a program called z brush to add details I otherwise couldn't get. Accessories to figures, hats for example

 

Nice find, I'm trying it out now for a big 1:8 scale driver I need for my DUKW. 
And yes I see that much repair is needed for the STL. Not only removing bits that are too small to print (like shoe laces), but also filling gaps under the layers of clothes. 
I have to look if any of the mesh programs have a "shrink wrap" function, like I had in some high end software at my previous employer. Does what it sounds like, covering a messy mesh with a new mesh that bridges holes and gaps under a set size. That would make life easier!

I also need to find out how to import a CAD seat and steering wheel to Daz, that I can then use to position the figure correctly... a learning curve!

 

Cross section through the STL reveals gaps that would cause print problems:

Edited February 27, 2022 by Patrick Matthews

[Kevin-the-lubber]

More’s the pity there isn’t a reference file like this for the elegoo series, but I have found a good single setting alternative on the syratech site. I wasn’t even aware of such things so thanks for the tip, likewise the resin, I may try that one presently.

[Mldixon]

2 hours ago, Patrick Matthews said:

Cross section through the STL reveals gaps that would cause print problems:

Download windows 3d builder, it also is free. When you open it use the import feature to bring in your seated figure, then when you import it, it will ask you if you want to repair, say yes. Then when it's done you will see multiple objects on the right side panel. Use the edit feature, select all the objects and then merge them.  This creates a solid figure, save this as new stl file. Open in Chitubox, also free, and you will see that your figure is solid. Also in edit you can then resize the figure to the appropriate scale. This took me a lot of headbanging to get to, as their is no one source for doing these things. 

As far as printing little things, like laces, my Anycubic mono has no problem with this a very small scales. See cannon handle. If you don't want print it, when you see the objects in windows 3d builder just delete the laces and they'll be removed from the final merge. 

The steering wheel import into Daz is only for reference for positions.  I would print it separately and then add seated figure.

 

This is how I positioned the powder monkey for my ship model. The stairs were made in cad and imported into Daz. Then figure was set to that scale position 

🔻and the final result.

[Mldixon]

2 hours ago, Kevin-the-lubber said:

More’s the pity there isn’t a reference file like this for the elegoo series

I'm not familiar with that printer, so maybe those timed cycles won't with their LCD screens. I'll check and post if I find a solution. 

[Mldixon]

4 minutes ago, Mldixon said:

More’s the pity there isn’t a reference file like this for the elegoo series

Yep, but you can still do it, by downloading a reference model as an stl. Then printing them individually one at a time for your resin. Then observing the best result and using those settings.  This is labor intensive and a Pain in the a**. But if you use the same resins over and over well worth the effort. Much better than making wild guess only to have repeated failures. 

I'm still amazed that the Anycubic can print all eight at once with those different settings. 

[Mldixon]

 

8 minutes ago, Mldixon said:

like this for the elegoo series

 

I found this article, good explanation to get you going

https://3dprinterly.com/how-to-calibrate-resin-3d-prints-testing-for-resin-exposure/

[Dr PR]

I use a somewhat out of date CAD program that produces poor quality STL files, and many of the things I build are made of zero thickness surface meshes and planes. Lots of leaks!

 

I import the STLs into Microsoft's 3D builder and click the "repair" box and presto - leak free solids!

 

There is one caveat. 3D Builder doesn't like closed circles around openings - it fills them in with a plane, blocking the holes. The solution is to be sure all holes are surrounded by two objects (solids, surfaces, etc.). Then the solid that is generated will have the proper hole in it.

 

I suspect this is only a problem with my CAD program generating incorrect STL files. When I use the Chitubox "Hole Punch" feature to make a hole into hollow interiors there is not false closure over the hole, and I haven't heard anyone else complaining about the plugged openings.

 

****

 

If you are experiencing leaky STL surfaces I highly recommend 3D Builder. But it is only available for Windows 10-11. CAUTION: Be sure to select the proper measurement units in the top bar in Builder. STL files do not contain any measurement unit information. Builder may default to the wrong units -  it scaled my millimeter unit parts to centimeters, and everything was 10x the correct size until I realized what was happening.

 

Also, I HIGHLY recommend using the Chitubox "Hollow" feature. I was designing objects in my CAD program with manually created interior hollow spaces, trying to achieve a uniform wall thickness. It was a lot of work! Than I just redesigned a part that wasn't printing well with only the exterior surfaces. I used the "Hollow" feature to generate parts with 2mm thick walls, and the program added the interior lattice supports needed for correct printing. Then I "punch" holes in surfaces that would normally be hidden (bottom, etc.) to let resin drain from the interior. The results were a lot better!

[Patrick Matthews]

OK, I tried 3D Builder. Was pleased at first- it worked! But upon closer examination, the "fixed" model was still loaded with issues. Maybe because I'm working in a very large scale, so it tried to leave details like his trouser pockets and gaps under his collar and a number of other issues. I went ahead and printed it. Mostly OK, but some very visible areas lost detail or fell apart in printing.

 

I poked around and found another way:
https://integralrealitylabs.com/gameprint

These folks want to print (and paint!) high end game figures for you. But you can also use their plug-in for Daz to merely upload and clean a downloadable STL, for the princely sum of $2!
I tried it and was much happier with the result. All gaps filled, all thin sections beefed up. 

Two gripes though: 
1. They insist on resizing the STL as a standard (to them) figure size, like 6 or 12 inch, thus losing the original size. You'll have to rescale to your own needs.
2. The mesh is heavy- many many triangles. Mine was 430 MB. If it's a problem, the mesh can be decimated in Blender. 

This will be my workflow, until something better comes along. I'm amazed that a powerful application like Blender doesn't have such a feature.

My new fixed driver:

[Kevin-the-lubber]

Meshmixer, also free, fixes leaky stl’s, but I assume you all know this and it somehow doesn’t do what you want.