3d printing process

[Egilman]

36 minutes ago, CDW said:

Most of what you're describing has a vague similarity to the differences in CAD drawings and mapping software. What works just fine in CAD won't cut it in mapping software, even though they are similar in many ways.

Absolutely sir!

 

Cad is cad, just like sculpting is sculpting, but in sculpting, the material your working with can be very different, from solid stone to soft clay so the tools and techniques are different... Cad for machine parts is vastly different than cad for geomapping... They are both cad, but they work with different subjects so have a different workflow and process....

 

That's exactly the point I'm making, 3D software is 3D software, some of them are optimized for 3D imagery others lean towards the physical cad side... There are quite a few well developed programs for 3d imagery, while software for physical 3D printing design is still working on a way forward....

 

The main problem is figuring out what works best for you...

 

Eventually as best practices and methods to accomplish a creation develop, they will all start becoming similar, with the same functions and processes like the basic cad and 3D imagery software has become... We aren't there yet....

Edited October 12, 2021 by Egilman

[Kevin-the-lubber]

40 minutes ago, Egilman said:

Blender 1.9... It was a real issue trying to find anything out there for learning it though, everything was run through user groups and forums.... It's much better now along those lines but the learning curve is still like trying to climb an overhanging cliff with out a rope.. {chuckle}

Chuckle here too, partly because that's exactly what the younger me used to do... but with a rope; I'm not entirely stupid! But also partly because I simply cannot get through the initial hump of blender. Like you I'm an engineer, by nature, training and temperament. When in Paris, while my wife viewed the Eiffel tower as a fabulous piece of art, I was looking at the castings, the webs, the compound angles, visualising the drawings and processes to make them. A different kind of heaven. So F360 makes perfect sense to me; when it says ' no can do', I understand that it is my fault because I haven't, for instance,  correctly expressed my design intent. But Blender... currently still beyond me. Which is irritating because I sure could do with being able to do some basic sculpting.

 

I see your point about FDM vs resin, I guess that's how I treat them these days. Filament for when the properties matter more than the aesthetics, resin the other way round. Which is why I'll probably hang on to the FDM, as a tool just like the rest of my workshop machines. besides which I wouldn't get very much for it anyway.

[Egilman]

2 hours ago, Kevin-the-lubber said:

I see your point about FDM vs resin, I guess that's how I treat them these days. Filament for when the properties matter more than the aesthetics, resin the other way round. Which is why I'll probably hang on to the FDM, as a tool just like the rest of my workshop machines. besides which I wouldn't get very much for it anyway.

I was given a piece of advice, (and a demonstration of it) back in my tech school days that has always served me well.... My instructor, a retired toolmaker, told me that it isn't the tool that the craftsman uses, it's how he uses it.... Then, he took a 4 inch dia. bar of 4130 and cut a perfect #2 morse taper on it.. The lathe he used was a 150 year old South Bend that was converted from overhead belt drive....  It had 1/8" of lash in the cross slide lead screw.... 

 

What he said after the demonstration was it isn't the tool it's the operators knowledge of the tool and his skill in using it... The 3D Printer is a tool, the software is a tool.... WE need to learn how to use them correctly....

Edited October 12, 2021 by Egilman

[PRS]

I am pretty happy with the detail you can get with the resin printer.

 

This is with the Elegoo black water washable resin. The finish is dull and I have purchased some Anycubic standard grey resin to try.

 

 

I am still in an early learning stage and find that Lychee Slicer is a lot more user friendly so I will stick with that.

 

Here is a few things I have learned:

 

Do not use paper towels on the FEP as they will scratch it.

Run a vat clean and removing the piece of cured resin is the best way to clean up after a print failure and might not be a bad idea between prints.

To do a plate level on the Mars 2 use two pieces of paper and home it with the bolts loose. Then slowly snug them down back and forth then remove one sheet to check and you are done. The spring is quite strong in the build plate.

Make sure you get the build plate back on all the way when you remove it.

More supports are better than less to avoid failures.

 

[Kevin-the-lubber]

I only used one bottle of water-washable and have a feeling I mixed half of it with standard resin to use it up. I think I just found that the surface finish seemed fractionally less sharp. I also wasn’t too keen on washing prints in the kitchen sink, I really don’t want a blocked drain down the line. 

 

I find FEP gets dimples from supports and this makes fails a little more likely. I had a terrible problem with supports breaking halfway through a print until I was told that extending the exposure time was the cause; reverting to recommended settings, and beefing up the supports, sorted that out. But I agree, more and stronger supports is safer. Same wrt paper towels, though to be honest, I haven’t found hazy FEP making any difference.

[PRS]

On 10/16/2021 at 6:26 PM, Kevin-the-lubber said:

I only used one bottle of water-washable and have a feeling I mixed half of it with standard resin to use it up. I think I just found that the surface finish seemed fractionally less sharp. I also wasn’t too keen on washing prints in the kitchen sink, I really don’t want a blocked drain down the line. 

 

I find FEP gets dimples from supports and this makes fails a little more likely. I had a terrible problem with supports breaking halfway through a print until I was told that extending the exposure time was the cause; reverting to recommended settings, and beefing up the supports, sorted that out. But I agree, more and stronger supports is safer. Same wrt paper towels, though to be honest, I haven’t found hazy FEP making any difference.

You are correct on this. 

 

Here is the difference between the same print of some canons. The black is water washable and the grey is regular resin. Also the water washable just seems softer than the standard resin and the detail is less.

 

Something the black I have is good for is small detail parts. Here are some hooks I drew up and printed. I tested the strength and they are mighty strong. I left them on the supports to cure and they come off easy and I don't loose them

[Kevin-the-lubber]

I haven’t tried any colours at all, always gone grey as everyone says it’s the easiest for seeing the detail before painting. I was thinking of getting some brown for making blocks etc, but maybe black is worth a go. It certainly has a nice look to it.

 

I’ve just begun a new run of printing and, oddly enough, the elegoo ABS-like is coming out a bit softer than previous batches. So I wonder if mixing resins was, after all, quite a good thing to do. I only did it because they were test prints and the end result didn’t matter, but I think I’ll try a standard and abs mix again shortly, and be more scientific this time.

 

Out of interest, presumably you printed the cannons vertically, with supports on the muzzle? Any issues with that? I had planned on printing vertically with the muzzle flat on the plate, to avoid support dimples, but am conscious that there’s nowhere for the resin to drain from the barrel.

[PRS]

1 hour ago, Kevin-the-lubber said:

I haven’t tried any colours at all, always gone grey as everyone says it’s the easiest for seeing the detail before painting. I was thinking of getting some brown for making blocks etc, but maybe black is worth a go. It certainly has a nice look to it.

 

I’ve just begun a new run of printing and, oddly enough, the elegoo ABS-like is coming out a bit softer than previous batches. So I wonder if mixing resins was, after all, quite a good thing to do. I only did it because they were test prints and the end result didn’t matter, but I think I’ll try a standard and abs mix again shortly, and be more scientific this time.

 

Out of interest, presumably you printed the cannons vertically, with supports on the muzzle? Any issues with that? I had planned on printing vertically with the muzzle flat on the plate, to avoid support dimples, but am conscious that there’s nowhere for the resin to drain from the barrel.

Here is how I did the canon prints.

 

 

[henrythestaffy]

Kevin, if you were going to print it as a solid model and then drill the barrel later then putting the muzzle on the build plate is ok. Otherwise putting the muzzle on the build plate will create a suction which is something i try and avoid. Models can work their way loose and the FEP can be damaged. An angle and 5mm off the plate is a good way to print.

[Kevin-the-lubber]

Tell me about it! I’ve gone through a fair few FEP’s through bad judgement and still have cold sweats whenever I’m trying something marginal! I wouldn’t be anywhere near brave enough to have so few supports as you, Paul, at least not with 40 or 50 cannons on the plate.
 

To be honest I’m not sure what benefit there is in angling these cannon (but am very open to being educated). Whether plumb vertical or angled, you’re going to have an annulus pulling on the FEP, in effect a suction cup, and the only gain I can see in angling would be to more naturally put a few supports up the hidden side of the barrel. Please do tell me if I’ve missed something though, FEP is expensive!

 

In passing, I bought the large Anycubic wash and cure machine a couple of weeks ago and used it for the first time yesterday. What a joy, I’ve gone from a tedious, quite messy wash process to something quick, clean and easy. It’s also great for washing out the vats when changing resin - I’ve been using up some standard resin but wanted to switch to ABS for the current run.

[mtaylor]

Hmmm.... question then.  Since it prints from the bottom up, if the barrel were bored out by the software it would be hollow and have drainage, right?   Then sealing off the end of the bore would create a suction or would it?   I'm not into 3d printing (yet) but just looking and learning a bit.

[Kevin-the-lubber]

No Mark, Paul’s picture of the setup is upside down when it comes to the actual printing, so there will come a point when the barrel hole gets closed off and a small amount of liquid resin will become trapped.  I doubt the curing light rays would reach that far up the barrel so, in principle it may remain wet forever. I don’t know if, at this scale, this is really much of any issue, but it’s why, when messing around, I’ve gone for a two part assembly, as it’s easy to hide the joint.

[henrythestaffy]

Mark, what you say is correct if the barrel is attached directly to the build plate. This something you should avoid. Too much suction is bad for printing. That is why in Paul’s example the barrel is lifted from the build plate with supports. Angling the print also helps as it is better to start small and have the model fan out, if you can, as it prints. It pays to look at each model before printing and work out the most beneficial way to position it on the plate. If you wanted to print a pyramid for example placing it flat on the build plate or even 5mm off the plate would not be as preferable as putting one of the edges at the lowest point and printing up from there. I don’t hollow any of my prints anymore because it creates too many bad prints due to either suction or misplaced supports. The placement and size of supports is another whole different kettle of fish when it comes to success or failure in 3d printing.

[Egilman]

Simple solution?

 

When you design your cannon, drill out the barrel, AND the touch off hole, making sure they intersect like on the real thing.... (create a vent for the bore of the gun, just like in real life)

 

And then of course raise it off the build plate and angle it a bit as well....

[Kevin-the-lubber]

I agree about avoiding suction cups, hadn't considered that, less so about angling and supports. There is always a balancing act when using supports; they need to be strong enough to resist the separation force but you want the least surface imperfection possible. If I was printing a pyramid and didn't care about the lip arising from the over-cured initial layers, I would attach directly to the plate. I'd do so because the surface area of cured material attached to the plates will, by definition, always be greater than the new layer that has to be pulled off the FEP and adhesion failure is highly unlikely. If I wanted precision across the base, I'd put it on supports, accepting the resulting surface imperfection. I would angle the pyramid if doing so meant I could reduce the surface area of each layer, but remain conscious that there is going to be a 'fat' stage in the process when the surface area is at it's maximum and support to suit. If the surface area arising from tilting was going to be larger than a horizontal base I don't think you gain anything. If I was printing a perfect cube for instance, I wouldn't angle since by definition the smallest surface area will be a face.

 

I think all of my print failures - certainly all the 'OMG' one's - have been due to supports breaking under tension, but (touch wood) I haven't ever had anything detach from a plate. All I'm really saying here is that I don't think angling is a 'must do' in it's own right, it can be a very important risk mitigator but you could actually increase the risk by angling as well.

 

Coming back to the cannons, I will now use supports to avoid the suction cup issue but orientate for a balance between holding power and surface finish. I wouldn't angle unless I had to, for support purposes, because angling increases the surface area. (All of which is probably over-thinking things for 1:100 cannon barrels!).

[PRS]

This is such a small print and I have a lot of supports on the bottom so I have no failures with this print.

 

Let me try printing it with the muzzle flat on the plate like this as see how it works.

 

 

[Egilman]

7 hours ago, Kevin-the-lubber said:

All of which is probably over-thinking things for 1:100 cannon barrels!

I think that given our backgrounds and experiences over decades have driven this more than anything else... we are constantly re-thinking things in pursuit of scale accuracy and how to get there....

 

Sometimes to our own hindrance.... {chuckle}

[PRS]

They printed fine standing up and very little support was needed.

 

 

[Kevin-the-lubber]

I ran my own experiment as well today, as I've been wanting to test out making spars and yards with a carbon fibre insert for stiffness. So, I printed this in 5 parts, a hollow centre section, two long hollow sections either side and two end caps (forget about these, not relevant here). I printed the centre section vertically, using supports and this came out fine. A little not fully cured resin in the tube but dimensionally true throughout the length. I printed the other two sections vertically but straight on the plate. Not good! They printed fine externally, no problems in that way but, due to the suction cup, the tube gradually closed up and is very gooey inside. You'll probably find the same with the cannons. Obviously this doesn't matter if you don't need an accurate tube but it's no good for my purposes.

[mtaylor]

Thanks for the answers Kevin and Henry.   

[Kevin-the-lubber]

ps. Just while it's in my mind and in case you don't already know - today I've discovered the need for calibration of resin prints. I have what is now a complex kit with about 40 parts. 39 of them have to fit to the other 1, which is a 'main body'. All very precise, very tight tolerances, using tiny locating pins. And most of the 39 seem ever so slightly too big. Headscratching moment. A bit of research throws up that resin can shrink and you need to allow for this by scaling. Quick bit of measurement of the main body shows it's shrunk by about 1%. So tomorrow I'll try scaling up by the correct factor and if necessary do the same with the parts so that, hopefully, everything will fit as planned.

[Dr PR]

I have been working with an Anycubic Photon Mono since Christmas and thought I would pass along a few things I have learned.

 

I have used the CAD program "DesignCAD" since 1988. It is a surface/mesh program with true 3D solid capability, but most of what I have done has been just planes and meshes (grids) that have zero thickness. I combine these to create the 3D object but they often have leaks and are unsuitable for 3D printing without some "repair."

 

Microsoft's "3D Builder" program is free for Windows 10/11 and does (almost) perfect repairs. The only catch is that it will place a surface over any closed opening in a single plane/grid. So I have to be sure I create separate surfaces around holes. I don't know if this is a requirement for STL files that some programs do automatically. It is not a problem for solids that I have "drilled" by subtracting a tool solid, so it is just a problem with the way I made some of the objects.

 

I use the Chitubox slicer program, and it does a pretty good job with the default settings. More about this in another post.

 

Here is a link to a 3D model I created. I am now printing many of the parts you see on this ship.

 

https://modelshipworld.com/topic/19321-uss-oklahoma-city-clg-5-1971-3d-cad-model/?do=findComment&comment=590228

 

https://www.okieboat.com/CAD model.html

 

I started a 1:96 scale physical model about 16 years ago but stopped until I finished the CAD model. I have started the build again and am 3D printing parts for the model.

 

https://www.okieboat.com/Ship model page.html

 

I have been amazed at the resolution I can get with the Photon Mono printer! Here are a couple of examples of 1:96 scale parts. These are straight off the printer (after curing) without any touch-up.

 

 

The CAD model was created 1:1 scale from the original blueprints, including all the proportional angles and dimensions of the real thing. At 1:96 scale the blades are only 0.25 mm (0.0095 inch) thick. This is far too thin to try to machine and much too thin to try to cast. But I just scaled the file to 1:96 and printed it! The diameter of the propeller is 1.46 inches (37 mm). They printed perfectly the first time using the default supports added by Chitubox. For this print I used a vertical step of 0.01 mm, 0r 0.0039 inches. The surfaces are smooth to the naked eye, but with 10X magnification I can detect a hint of the digital "jaggies."

 

 

The anchor was also created 1:1 in CAD from Navy drawings. It is made up of dozens of individual complex curve surfaces. I figured if this would print anything would! It also came out perfect the first time! This was a 0.05 mm vertical step and some slight jaggies are visible on the bottom surfaces of the flukes.

 

So this was the result of my first attempts to print with this printer. It just seemed too easy, especially since I already had all the CAD files prepared!

 

But this was just beginner's luck, as I will explain in another post.

Edited February 16, 2022 by Dr PR

[Dr PR]

As I said earlier, I am a novice at 3D printing, having started after last Christmas when I received an Anycubic Photon Mono printer as a (totally unexpected) gift. The Admiral's youngest son gave it to me, and he readily admitted that he did it because he has one, and wanted me to figure out how to use it and be his tech support!

 

I have been into digital photography for decades and had a pretty good idea about pixel density and image quality. But with 3D resin printing there is another dimension, the vertical step size. And there are a few complications due to this third dimension that I hadn't thought of and learned the hard way.

 

First let's consider the basic 2D pixel size. This is what the LCD display produces, and is the fundamental limiting factor in print resolution or surface smoothness. You might think more pixels in the LCD display is better, and basically it is. But there is a catch. Larger displays tend to have more pixels, and they allow larger things to be printed. But more pixels does not automatically mean better resolution or smoother surfaces.

 

Consider a 3" x 2" display with 100 pixels per inch (300 x 200 pixels). Each pixel is 0.01" x 0.01" (0.25 mm x 0.25 mm). Now imagine a 4" x 2.6" display with 100 pixels per inch. There are 1/3 more pixels but they are still the same size. It is the number of pixels per inch/cm that determines resolution, not display size. If you had a larger 4" x 2.6" display with the same 300 x x200 pixels, each pixels would be larger, and the resolution/surface smoothness would be less.

 

On the Photon Mono the pixels are 0.05 mm x 0.05 mm and this determines the minimum horizontal resolution for the printer. Here is a picture showing how pixel size determines resolution:

 

 

The "circle" on the left has pixels 1X the grid spacing, and the one on the left has pixels 2x the grid resolution, or an area 4 times as large as the one on the left. It is clear that the larger pixels cause larger "jaggies" than the smaller pixels. But it may not be obvious that the smoothness of vertical surfaces is limited by pixel size. If the circles are extruded (printed) vertically, the resulting cylinder on the right will have deeper grooves in the sides than the one on the left. So smaller is better, and this may be more important than the total number of pixels.

 

Less obvious is the effect the vertical step size has on surface smoothness. Of course the smoothest surfaces are either perfectly horizontal or vertical flat surfaces. But with non horizontal or vertical surfaces things are different.

 

 

The smoothest angled surface you can get is at a 45 degree angle to horizontal with the horizontal pixel width and vertical step size the same. Again, you can see the 1x pixel/steps create a "smoother" surface than the 2x and 4x pixel/step sizes, so again smaller pixels produce smoother surfaces. But not perfectly smooth because pixel size will always be finite, producing finite sized steps. So to get the smoothest angled surfaces the part should be oriented as close as possible to a 45 degree angle from horizontal. For the Photon Mono with 0.05 mm pixels the step size would be 0.05 mm.

 

But this one to one pixel/step size smoothness rule applies only to 45 degree slopes. For shallower slopes the step size is all important for getting smooth surfaces.

 

In this picture the red line is angled at 10 degrees from horizontal. The horizontal "pixel" size is 4x, and the vertical step size is 1x, 2x and 4x.  Clearly the 1x vertical step size produces a "smoother" surface. It has more jaggies, but they are smaller. On the Photon Mono the minimum vertical step size is 0.01 mm (0.0039 inch), about the thickness of a sheet of printer paper.

 

This isn't just a theoretical conclusion. Look at these pictures:

 

 

 

In both images the capstan (above) and wildcat (below) were printed at 0.05 mm and 0.01 mm vertical steps.  The 0.01 mm vertical step parts (right) are clearly smoother than the 0.05 mm parts (left). This is most apparent on the near horizontal surfaces. Of course, you can't get something for nothing. You have to print 5 times as many slices at 0.01 mm step size as with a 0.05 mm step size, and that takes 5X as long for the exposure process. However, as described below, this does not mean 5x as long total print times.

 

Things aren't as simple for vertical surfaces.

 

In these three examples the red line is angled 10 degrees from vertical and the vertical step size is the same, 1x. But you can see the surface smoothness is very different for the three examples. The vertical step size has no affect if it is smaller than the pixel dimension. The reason is simple - no matter what the vertical step size is, the horizontal "step" size is determined by the LCD pixel dimensions, and smaller pixels are better. You can print as many steps as you want (smaller or larger vertical step size) and the jaggies are still determined by which pixels are turned on or off in the LCD display. However, using vertical step sizes larger than the pixel dimensions will produce rougher surfaces. So for objects with vertical surfaces angled 45 degrees or greater from the horizontal you should use a step size equal to the pixel dimension.

 

Again, this is not just a theoretical conclusion:

 

 

Again, the chock on the left was printed with 0.05 mm vertical steps and the one on the right had 0.01 mm vertical steps. You can see the near horizontal surfaces are much smoother in the 0.01 mm print on the right, but the edges of the vertical supports are about the same roughness because the LCD pixel dimensions were the same.

 

If you have mixed near horizontal and near vertical surfaces, use a smaller vertical step size to make the near horizontal surfaces smoother.

 

There are a few more things to keep in mind. First is total print time. The actual exposure time for each "slice" is a fairly small part of the total print time. More time is spent raising and lowering the print stage. I have been using the recommended lift speed (4 mm/second) and retract speed (6 mm/second) for the Photon Mono. So for each slice that is printed 10 seconds expire while the stage is moving. I have used 5 second and 3 second exposure times for each slice. So the exposure time is only 1/3 to 1/4 of the total print time. Smaller step sizes do increase total print time, but not as much as you might think.

 

Another thing to consider is the effect of exposure time on the surface smoothness of very small objects. This is tricky! The resin I have been using is the Anycubic Basic Grey. In quantity it looks opaque, but for very thin layers/slices like 0.01 mm it it translucent - some light passes through it. And this means that any resin that accumulates on top if thin horizontal surfaces may be exposed even if it isn't a part of the slice that is being printed. I have noticed that very thin horizontal cylindrical objects (0.05 mm or less) tend to print thicker in the vertical direction than in the horizontal with 5 second exposures. Reducing to 3 second exposures reduces this over thickness (the minimum recommended exposure of the Basic Gray resin for the Photon Mono is 2 seconds).

 

A third thing to fiddle with are some "advanced" features in Chitubox. These are in the "Settings/Advanced" tab. The "Anti-aliasing Level" is an attempt to minimize the jaggies effect. It has three settings 2, 3 and 8 that cause the pixels at the edges of objects to be shades of grey instead of black or white. 2 is the grayest and 8 is just black and white. The result is that you get less exposure of the gray edge pixels than for the white interior pixels. This seems to harden less resin on these outer surfaces and it pools in the grooves, making them less noticeable. But this is a very subjective thing!

 

The other "Advanced Tab" feature is "Grey Level."  It ranges from 1 to 8, and as far as I can tell it works just like the "Anti-aliasing Level." Step 1 is the grayest and step 8 is black and white.

 

I have been experimenting with 3 second exposure times, 0.03 mm vertical step size and an Anti-aliasing level = 2 and Grey Level = 4.

 

There is also an "Image Blur" option, with "Image Blur Pixel" sizes of 2, 3 and 4. $ blurs the edges of the surfaces the most and 2 the least. I haven't experimented with this yet.

 

Finally, exposure time affects the hardness of the printed slices, and that affects the success or failure of your prints. That is the subject of the next post.

Edited February 16, 2022 by Dr PR

[Dr PR]

PRINT FAILURES

 

OK, take a deep breath! This is complicated.

 

As I said at first, I had a lot of beginner's luck just using default values for the printer and resin. But that didn't last. I finally met my nemesis!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This is the TALOS missile launcher on the USS Oklahoma City CLG-5. My CAD model is on the left and the 3D print is on the right. I had a LOT of print failures with this thing before I learned a few important tricks. I still haven't ironed out all the problems, but here is food for thought.

 

 

 

On the left is the base ring and trunnion support (launcher body), showing the "lock and key" arrangement to allow the launcher to rotate on the base without falling off. Both pieces are cylindrical and hollow, with thick walls. On the right is a picture of the default support arrangement that Chitubox created. Notice the very large number of supports under the trunnion support and the small number under the base ring (using the same slicer settings). The trunnion support prints every time with no problems. The base ring failed to print every time! The reason for the failure is VERY important!

 

The printer works by lowering the print platform so there is a very thin gap between the platform and the previously printed layers and the thin UV transparent plastic film at the bottom of the resin tank, right above the LCD display. The gap between these objects is the vertical step size, generally between 0.01 mm and 0.05 mm. Liquid resin in this gap is exposed to UV light to harden the resin and create another "slice" layer on the printed part. Then the print platform is raised to allow more resin to flow in, and then lowered to set another vertical step gap for the next exposure.

 

When the resin is exposed it hardens and sticks to both the part being printed on the print platform and the plastic film at the bottom of the resin vat. Then when the platform rises a tug of war ensues between the print platform and the plastic film. Something has to give, and it is supposed to be the bond between the printed part and the film.

 

The first few layers that are printed are exposed much longer than the rest of the part. This creates a strong bond between the printed layers and the print platform. In addition, the bases of the supports are much larger than the supports themselves, increasing the contact area between the printed part and the platform. The contact area of the support bases must be greater than the largest slice section area if the platform and printed part are to win the tug of war. So be sure to use fairly large  bases for each support. In the picture above I have used "cubic" (actually square) bases 15 mm x 15 mm. This size is assignable in Chitubox.

 

It is always the weakest part that gives. And in some cases it is the connections between the supports and the printed part. Each support can take only so much stress, and if that is exceeded it breaks. In the case above, there were a lot of supports under the launcher body, and they were enough to take all the stress of pulling the printed layer from the plastic film. But there were not enough supports under the base ring, so when the platform lifted the force of pulling the printed layer away from the plastic film was too great and all of the supports broke. When this happens, after the print is done you find the base of the supports stuck to the print platform and a part-shaped blob stuck to the plastic film. After I manually added about 4x more supports in Chitubox I finally got a correctly printed part!

 

The moral of the story is that you have to have enough supports to take the strain.

 

But of course, there is more. The force necessary to separate the printed layer from the plastic film is directly proportional to the surface area in contact with the film. And the number of supports needed to take the strain is equal to the total force divided by the amount of force force needed to break one support. So if the total force was 100, and each support will break with a force of 2, then the number of supports needed is 100/2 = 50. The larger the surface area, the larger the number of supports needed.

 

In the case above the launcher body walls were thicker than the base ring, meaning that the forces would be greater, so Chitubox added a lot of supports. But for some reason the program guessed the necessary number of supports for the base ring too low, and they weren't strong enough to take the total force. You can't always trust the software (more about this later)!

 

However, there is no way to predict the actual forces involved with the information supplied with the resins, and we don't want the complications, expense and time of setting up and running a laboratory experiment to determine these things. But I think it is a safe bet that you can just divide the surface area of the largest print slice by the cross section area of the supports and get a good idea.

 

Chitubox allows you to set the contact diameter where the tip of the support contacts the printed part. Contact area = diameter x pi (3.14159). And you should be able to determine the cross section surface area of the printed part in your CAD program. So divide the slice surface area by the support contact area to get the minimum number of supports needed.

 

But even I am  not anal enough to want to do that, so I just start with Chitubox's default supports and if it looks like there aren't enough I add more. If the print is a success I guessed right, and if not I start over and add even more supports. This is called a learning curve!

 

But that s just the start of this problem. I did manage to print the base ring and launcher body to my satisfaction. But the launcher arms were another thing!

Edited February 16, 2022 by Dr PR

[Dr PR]

PRINT FAILURE PART 2

 

The launcher arms turned out to be my nemesis!

 

 

 

The arms are printed in two parts, right and left. They slip into openings in the launcher body and fit together in the middle using the same "lock and key" arrangement in the launcher body and base ring. Stops molded into the interior of the launcher body and grooves in the launcher arms limit the angle of rotation of the arms from horizontal to plus 55 degrees just like the real thing.

 

The left photo shows some successful parts. Very tiny details were printed correctly. The photo on the right shows some of the 14 print failures during the learning process. I finally got two usable prints of each arm -  a not too spectacular 22% success rate!

 

I first tried printing them horizontally. After a lot of failures and suggestions from more experienced people, I tried printing them vertically. No joy!

 

 

 

Here is an example of the support arrangement for the vertical prints. They were total miserable failures! So what was the problem?

 

Not enough supports, of course.  The problem is that Chitubox and I were putting a lot of supports along the very bottom of the part, But because the arm is shaped like two truncated cones attached at their base, the cross section are increases with each slice. And that means the forces involved increase. So what is needed is more supports for each printed slice. A LOT more.

 

But there is a way to reduce the slice contact area. Chitubox has a hollowing feature that works very nicely. And it also can add internal supports so the top of the hollowed object also has plenty of support.

 

 

This is an image from Chitubox showing a cross section through the hollowed launcher arm. The slice surface area is the darkest blue layer. You can see the internal "X" braces the program adds. This solved most of the problems. I also used Chitubox's "Hole Punch" tool to add drain holes to allow resin to escape from the interior cavity and avoid suction caused as the part rises from the plastic film.

 

The original parts were solid and as the print progressed the s;ice surface area increased and increased until the supports failed. But with the hollow parts the surface area was much smaller and the supports held. But this wasn't the end of my problems!

 

 

This is an example of one of the failures. The interior part of the arms is supposed to be cylindrical and you can see how the ends of these arms "collapsed." But it wasn't a collapse - the failed surfaces were attached to the supports. If the supports failed why didn't the succeeding layers remain stuck to the film? After the job was finished there was nothing on the film! Mystery #1.

 

This is my guess how this happened. First, as the separating forces increased with each pass, the supports broke, leaving the printed part unsupported on the ends. When the print platform rose to print a new layer the separating force between the plastic film and the printed surfaces pulled the thin flexible print layer down, adding a curve to the surface. When the print stage descended this downward curved part contacted the plastic film and prevented more resin from filling the gap. So the parts still attached to the supports printed the correct thickness, and the part on the end was too thin. At each subsequent pass the existing curved printed part served as the support for a bit more of each slice, extending the curved part. Weird!

 

The solution was to add a lot more supports under the end and inside the "keyhole" to be sure there were enough supports as the print proceeded.

 

But that wasn't the end of the problems!

 

 

 

The ends of the launcher rails are supposed to be squared off like the photo at the left. But many of the failures were as shown on the right. Both parts were hollow, and they had the same number of supports! What gives?

 

 

 

This was actually a simple fix once I understood the problem. On the part at the left there is a support right at the bottom front end of the rail. This supported the print so it didn't warp. The right hand part also had a support near the front bottom of the rail, but not right at the front. So the rail flexed as it was printing - exactly like the failure  in the cylindrical parts of the arms. I added a support at the end of the rail and it printed correctly.

 

And then there was this problem:

 

 

Same problem. An overhanging part failed to print in one case but not in the other. Looking at the supports tells the story.

 

 

In this case it was not Chitubox's fault. The picture on the right shows the correct default support provided by the program. But I moved the support on the left because it left a bit of the tip of the support on the flange of the overhanging part. Duh! But again, there was nothing left on the plastic film after the print. So the successive print layers remained attached to the printed part but just flexed with the separating forces. After the support connected to the part the rest of the part printed correctly.

 

This funny thing on the back of the launcher arm was the "Emergency Igniter." If the TALOS booster failed to ignite when we pulled the trigger we had a real problem! The 4000 pounds of class B explosive in the booster accelerated the 7500 pound booster/missile from zero to Mach 2.2 in 5 seconds, at a distance of 8 miles! It made fuel dragsters look like kiddie toys. The flame from the booster was 75-80 feet long. It was a real blowtorch, and we definitely didn't want that in a magazine containing 200,000 pounds of high explosives!!

 

The solution was the Emergency Igniter arm. The cylindrical can at the end held a black powder charge. The assembly could be rotated back and down, and the arm extended to shove the powder charge into the booster nozzle. Then we pressed a button igniting the black powder and that ignited the booster. End of problem (unless the igniter failed to light).

 

And the end (I hope) of my printing problems is the awareness that EVERY part must have a support, especially at the ends, and the total supports must be capable of withstanding the separation forces as the part frees from the plastic film.

Edited February 17, 2022 by Dr PR

[Dr PR]

Here is another example of playing with the printing parameters to get the job to come out right. I decided to try to print the anchor chain for the OK City. I have never been able to find stud link chain the right dimensions for the 1:96 model. The links are pretty small - 3.95 mm x 2.4 mm (0.155 x 0.094 inches) with a "wire" diameter of 0.66 mm (0.026 inches). In Navy terms the round bar that the links are made of is called "wire." The wire for the 1:1 links was 2.5 inch diameter.

 

 

 

These are images of the supports that I added manually in Chitubox (the automatic support add function placed too many and they were somewhat haphazardly positioned).

 

The first attempt used 0.01 mm vertical step size, 3 second exposures and the Chitubox Settings/Advanced anti-aliasing feature was enabled. The print was a failure - all the links were fused together.

 

I figured there might be several causes. The 3 second exposure was curing more resin around the parts. Using 0.01 mm step size meant more exposures. And the anti-aliasing function might be blurring the image a bit and causing some exposure in the space between the links.

 

Next I used 0.02 mm vertical steps to halve the number of exposures, and 2 second exposures (the minimum exposure time recommended by Anycubic for the Basic Grey resin and the Photon Mono printer). I also disable anti-aliasing.

 

Success!

 

 

The top "chain" has fused links. The lower chain has every link separate as they should be.

 

 

 

Here is a close-up of the chains. The upper chain links are smoother because of the larger number of steps and possibly because of the anti-aliasing. You can see the cured resin in the gaps between the links. You can clearly see the open gaps between the links in the bottom chain They might be a bit rougher than the top chain, but they are definitely good enough! Now I have to figure out how to paint them (black) without gluing the links together.

 

A really nice thing about being able to print the chains is that I can include the anchor shackle and a swivel link, and use the correct number of links between them to get the right configuration for the ship.

Edited February 18, 2022 by Dr PR

[Kevin-the-lubber]

Good R&D Phil, this will be useful to many of us as we progress our own printing journeys. The chain is especially useful for me as I've tried the same previously with the same result as your first attempt, so now know what to try next time. By and large I use factory settings. A while back I tried playing with exposure times, longer and shorter, but didn't achieve much other than getting through several FEP's in short order. But looking at your outcomes I should do some more testing of shorter times as you're getting better results than me wrt holes closing up.

 

I hardly ever use auto-support, in part because anything we're making (us modellers) is almost always quite fine and the placement of supports matters to the finish as well as print success. These days I try to put a few heavy supports on everything, to make sure the object doesn't get pulled off the supports, then pepper the remainder with medium and, if it's a delicate area that doesn't need much support, I'll use light one's.

 

I've been experimenting a little with resins lately. All I've ever used for the last year is Elegoo ABS-like, which gives a great finish and has a fair bit of flex. The downside is that parts can curl over a few days post-curing. So I've tried SirayaTech Fast, and Anycubic standard. I really didn't like the latter, the finish was nowhere near as good as Elegoo, but as I still have almost a litre left I'll give it another go like for like. On the other hand I love the SirayaTech. Excellent finish, a little bit of flex and very little curling. There are lots of others I'd like to try e.g. SirayaTech Blue, but they do start to become expensive when you're looking at pro-grade resins, so I'll save that experimentation for when I rarely need to print an object more than once.

[Patrick Matthews]

You're a brave man, Doctor.

I've done that small a chain with Shapeways, as their Multijet process uses wax supports, not the integral supports we're forced to use on home printers. Sadly, the Shapeways process proved to be too difficult for them to control. They even told me that they used my chain as a test for their machine prophylaxis! But they couldn't keep it up consistently, so the chain usually arrived fused.

I've never seriously considered trying it with integral supports- too much nipping and clipping of brittle supports on delicate parts, and I wanted to have a commercial go at it. The smallest chain below is the same size as yours... so congrats on making it happen!

BTW, I was able to print chain in lengths of about a meter at Shapeways. I was limited by the number of links, or actually the number of STL file facets, for which Shapeways had an arbitrary limit in order to control file sizes. I was getting down to optimizing the number of facets in each link!

The macro image shows the odd wax and/or unexplained crystal gunk that is found on these multijet parts. 

 

[Dr PR]

Kevin,

 

So far I have used only the Anycubic Basic Grey resin. I would like to try other resins so please post your results as you try new types. From posts other people have made on the Ship Model Forum (lots of scratch built modern vessels) I know there are some resins that are flexible when cured, and do not break as easily as the harder more crystalline resins. These are useful for very thin things like life rails that get bumped often while building the model .

 

I have yards of railings on the Okie Boat model and have been wondering how I can make them to scale. The thought of making thousands of solder joints too assemble the railing out of 0.008 and 0.010 inch diameter wire is not appealing! I do not think railings that thin printed with the Anycubic Basic Gray will stand up to any accidental bumps. It is pretty brittle when cured.

 

Pat,

 

I wonder if the white crud on the chains is the result of over curing? Some resins (including Anycubic Basic Grey) turn white and crusty if overexposed - I speak from experience! Since the chain is small and very thin I used only a two minute exposure, then turned it over, and gave it another two minutes. And I was afraid four minutes might be too long. I am using a 20 Watt 405 nm light with twelve UV LEDs and a small light powered turntable. They are enclosed in a box lined with crumpled aluminum foil to create surround lighting. For large parts I use 5-10 minute exposures.

 

I was surprised to see that very little material from the supports was left on the chain. There was some, often because I didn't get a clean cut when freeing the chain from the supports. I spent an hour or so examining every link (on three chains) and cutting/scraping the tiny bits of residue. There really wasn't much to remove.

 

Actually, I have been using Chitubox's "medium" supports but I do think I reduced the contact diameter to the smallest size for this job. Another fellow (on the Ship Model Forum) who printed a small chain like this said he just pulled it off the supports and it came away like a zipper opening. I wasn't that brave, but most of the links came free of the supports just as I was handling the thing while clipping some of the supports. I was able to remove the chain from the supports with just some sharp pointed tweezers. Just a slight twist on a link caused it to separate from the supports, and that usually freed the neighboring links too!

 

The first (failed) print had two supports under the vertical links and four (two each side) on the horizontal links. This left lots of residue at the points the supports contacted the links. But after separating the fused chain from the supports I decided that I really needed half that number for the second attempt, and it worked fine.

Edited February 19, 2022 by Dr PR

[Kevin-the-lubber]

Phil, I'd recommend both elegoo abs-like and sirayatech fast, each for different purposes. Take a look at my victory log, just skip to page 4 and you'll see the results I've been getting with the abs-like. There are some very thin sections, I think 0.2mm (0.008") is the smallest and I needed a bit of elasticity for which the elegoo is great. I've been using the sirayatech on the cutty sark but haven't posted any detail pictures yet, but I like it because it holds it's shape post-curing much better and is still a bit more elastic than standard resin. I've printed some very thin walled objects, about 0.2 or 0.3mm which are fine so long as I'm ultra careful when detaching supports. The technique I've developed for very delicate pieces is to make the supports longer than normal,10mm minimum, sometimes much more, and snip them off at the base first, as they then tend to come away from the object quite easily. Breakages have tended to occur when there isn't enough length for the support to bend when being cut, thus pushing upwards onto the delicate object.

 

Re' curing, I was doing much the same as you when I was using a nail polish dryer but since buying the big anycubic wash'n'cure I do everything at 2 minutes regardless of size, which seems fine. Occasionally I'll turn the object and do another 2 minutes. I think 10 minutes might be overcooking it.

 

Using medium supports but reducing the tip size is a good idea, I'll remember that. I was test printing railing at 10 thou or thereabouts last week but couldn't get it off the supports without breaking so will use 0.5mm wire instead.