Jump to content
 

3D Printing in 2mm Scale


TomE
 Share

Recommended Posts

I can't remember how long ago I started this design for a GER 10t vent van, but I finally got it finished enough for a test print last night. I hadn't looked at RMweb for a while though, and several of the things mentioned this week in this thread would have helped!

 

IMG_20201204_181720__01.jpg.c92d4893be613f6c05e6ac89f24f5471.jpg

 

I'd used sacrificial skirts as Tom illustrated, on a previous design, but forgot to add one here - you can see the distortion from the supports along the bottom of the solebar. The uplift from the build plate was 8mm - but I don't think it was enough - the bottom edge is still a bit distorted.

 

The orientation is the "magic" 22.49 degrees that supposedly minimises visible layering by matching the pixel size with the layer height at 0.02mm - but I'd left the layer height at 0.025mm after a previous experiment, so it didn't work out. I've also heard that 0.025mm doesn't actually correspond well to the original Photon's stepper motor full steps, which might explain why I'd had better results at 0.02 or even 0.05 in the past.

 

The supports here are Chitubox medium - but I'd forgotten that I'd tweaked the "contact depth" to be very shallow for something else previously, and it had defaulted to that again - which meant many of these supports simply didn't attach at the model end - which must have made some of the distortion worse.

 

The other issue that I keep getting are "stretch marks" where the cross section changes. I'm hoping better supports will minimise this, but I'd be grateful for any tips or advice in avoiding it?

 

In terms of the design itself, the test print really shows I didn't make the outside framing deep enough, so I've tweaked the design to increase the depth by which the planking is recessed from the framework from 0.3mm to 0.5mm. I also realised I'd forgotten the vents (it is a vent van, after all!) and the rain strips - both now added.

 

The discussion of resin curing reminded me of this video I stumbled across a while back. I found it really helped understand what's going on!

 

 

Justin

Edited by justin1985
  • Like 3
  • Informative/Useful 1
Link to post
Share on other sites

17 hours ago, justin1985 said:

[...]

The orientation is the "magic" 22.49 degrees that supposedly minimises visible layering by matching the pixel size with the layer height at 0.02mm - but I'd left the layer height at 0.025mm after a previous experiment, so it didn't work out. I've also heard that 0.025mm doesn't actually correspond well to the original Photon's stepper motor full steps, which might explain why I'd had better results at 0.02 or even 0.05 in the past.

[...]

Hi Justin,

 

It looks like this "magic angle" is actually 22.942 degrees? At least according to this diagram I found online:

 

slice_angles-van_kesteren.jpg

  • Like 1
Link to post
Share on other sites

1 hour ago, Valentin said:

Hi Justin,

 

It looks like this "magic angle" is actually 22.942 degrees? At least according to this diagram I found online:

 

 

 

Of course - thanks for catching the typo! Chitubox only seems to allow precision to two decimals, but I can't imagine it would really make that degree of difference. The diagram does nicely illustrate the principle, and at least anecdotally it does seem to minimise stepping.

Link to post
Share on other sites

The number of test prints to get to something I'm happy with never seems to get any smaller, no matter how many things I design! (which makes me very grateful not to be relying on Shapeways!)

 

Version two tweaked the design to increase the depth of the outside framing, but I forgot to increase the overall thickness of the sides commensurately, so they they came out translucently thin and wavy like a tarp! I also realised I'd forgotten the gap between the two halves of the door. Version three I thickened the sides - but forgot the ends, which have come out a  bit bulgy! (other things drying out here are replacement chassis and bogies for Märklin Z).

 

IMG_20201206_111848.jpg.27bb6a4710069e721d763b6e03541268.jpg

 

I'll run version 4 overnight tonight. Thought I'd show how I've tweaked the interior of the model to try and minimise risk of warping, and also now I'd added fillets to all the internal joints and corners to make the changes in surface area as gradual as possible to hopefully minimise the tear/stretching lines.

 

GERVentVanInside.jpg.05c96785a26e130e0cc97acc364a1f70.jpg

 

Justin

  • Like 7
  • Informative/Useful 3
  • Interesting/Thought-provoking 2
  • Friendly/supportive 1
Link to post
Share on other sites

  • RMweb Gold
2 hours ago, justin1985 said:

The number of test prints to get to something I'm happy with never seems to get any smaller, no matter how many things I design!


One of the benefits of home 3D printing I suppose :D 

 

Some interesting looking other items there too Justin! 

 

Tom. 

Link to post
Share on other sites

7 hours ago, TomE said:

Some interesting looking other items there too Justin! 

 

I bought a whole load of Märklin Z wagon bodies as "spares or repairs" on eBay to build up a range of stock for my German project much cheaper than usual, even for second hand. The catch is that Märklin don't do wagon chassis or bogies as spares (clearly why these had ended up as they did). So ...

 

IMG_20201206_221601.jpg.af4bf83c567b52fd3bf5e9397eac1e05.jpg

 

Just waiting for more spare wheels to arrive from Märklin in Germany, and body mount magnetic couplers from Micro-Trains in the US. (Repaints into authentic Interfrigo livery clearly also needed for the "Christmas" wagons!)

 

2 hours ago, queensquare said:

They look great Justin

 

Jerry

 

Cheers Jerry! I'm sure they ended up in Somerset occasionally ...

 

Latest test print (with the bulging ends) peeking out behind the Z wagons in the pic above.

 

Justin

  • Like 1
Link to post
Share on other sites

  • RMweb Gold
15 hours ago, justin1985 said:

 

 

Cheers Jerry! I'm sure they ended up in Somerset occasionally ...

 

Latest test print (with the bulging ends) peeking out behind the Z wagons in the pic above.

 

Justin

 

Oh no doubt about it! :rolleyes:

 

Jerry

  • Funny 1
Link to post
Share on other sites

5 hours ago, TomE said:

Continuing the PALVAN chronicles, @missysuggested trying out a honeycombe style internal bracing to combat the diagonal ‘stretch marks’ that occur when the surface area of the print increases in size. This seems to have done the trick, with perfectly smooth sides and ends from the first test:

 

 

That looks like the perfect solution! Did you extrude a design of a lattice up/down? 

 

I did have a try at doing something similar with the GER wagon, but I think I've designed myself into a bit of a corner in terms of overhangs and levels in the floor to accommodate the etched W irons etc, that would make it tricky without a pretty comprehensive redesign, alas. But I'll definitely try and design it into the next van I start fresh. 

 

Justin

Link to post
Share on other sites

  • RMweb Gold
5 hours ago, TomE said:

Continuing the PALVAN chronicles, @missysuggested trying out a honeycombe style internal bracing to combat the diagonal ‘stretch marks’ that occur when the surface area of the print increases in size. This seems to have done the trick, with perfectly smooth sides and ends from the first test:

 

4EB023FF-B1C4-43BE-9A14-4E52807533B1.jpeg.e976339aed2f06f4634bf10d65c2d361.jpeg

 

F088AAC8-DFAE-4317-A5DE-D64BF808AC44.jpeg.c5c93bedba7765cb25a4ea487ff8be3d.jpeg


The phone camera makes it appear slightly bowed out in the middle but it isn’t in reality. 

 

This also negates the need for the floor and reduces the risk of trapped resin. 
 

Tom. 

Hi Tom,

 

A quesstion - based on my degree of ignorance (so far) on 3d design and printing.

 

The honeycomb within the body - Are you able to create this as a separate drawing and then insert it into the main drawing?

 

or

 

Does it have to be drawn as part of the main drawing?

 

Thanks

Phil H

Link to post
Share on other sites

  • RMweb Premium
5 hours ago, TomE said:

Continuing the PALVAN chronicles, @missysuggested trying out a honeycombe style internal bracing to combat the diagonal ‘stretch marks’ that occur when the surface area of the print increases in size. This seems to have done the trick, with perfectly smooth sides and ends from the first test:

 

4EB023FF-B1C4-43BE-9A14-4E52807533B1.jpeg.e976339aed2f06f4634bf10d65c2d361.jpeg

 

I will admit to having been quite sceptical about 3D printing for various applications in the past, but this is seriously impressive.

  • Agree 6
Link to post
Share on other sites

  • RMweb Gold
32 minutes ago, justin1985 said:

That looks like the perfect solution! Did you extrude a design of a lattice up/down? 


I’ll defer to Julia ( @missy ) on that one as she made the modification to the CAD for this experiment! 
 

24 minutes ago, Scottish Modeller said:

The honeycomb within the body - Are you able to create this as a separate drawing and then insert it into the main drawing?


Dependant on the software you are using that should be possible, it certainly is in Fusion 360 which is my program of choice. 
 

16 minutes ago, Nick Mitchell said:

I will admit to having been quite sceptical about 3D printing for various applications in the past, but this is seriously impressive.


The tech has come a long way in a very short space of time. It’s perhaps not quite there for some 2mm applications, but within the next 5 years almost certainly will be, and I’ll probably still be printing PALVANs...

 

Tom.

  • Funny 1
Link to post
Share on other sites

  • RMweb Gold
4 minutes ago, TomE said:


Dependant on the software you are using that should be possible, it certainly is in Fusion 360 which is my program of choice. 

 

Tom.

Hi Tom,

 

Thanks for the fast response - much appreciated.

 

I'm right at the beginning of learning 3dCad - fortunately it is Fusion 360 that I've chosen.

 

now, just have to remember this for when i get that far.

 

Phil H

  • Like 1
Link to post
Share on other sites

10 hours ago, TomE said:


I’ll defer to Julia ( @missy ) on that one as she made the modification to the CAD for this experiment! 

Tom.

 

Thanks Tom!

 

I generated the pattern in AutoCAD (Attached just in case anyone would like to use it).

 

image.png.702688a34590e394d60c259876cc326d.png

 

A section of the pattern was then copied then pasted into a sketch on the required surface (in this case, towards the bottom of the wagon), then trimmed to suit the aperture.

 

image.png.ae2e6b0aeeed6273ece8d853ede8d160.png

 

This was then extruded to the underside of the roof profile.

 

image.png.90a59dc63d8086978938e306fba32828.png

OK, this pattern is different from Toms original but I had to regenerate it for the pics.

 

Simple really!

 

Julia :)

honeycombe fill template.dwg

  • Like 6
Link to post
Share on other sites

By following this tutorial, I managed to create a very similar pattern straight in FreeCAD. One of the advantages is that the size of the hexagons and the gap / wall between them can be very easily adjusted.

 

I have attached the FCStd file dor those interested (I had to add the .stl extension to "trick" the RMWeb's interface to allow me to upload the file; this extension should be removed befpre opening the file in FreeCAD).

Hexagonal_Pattern.png

 

Hexagon Pattern.FCStd.stl

Edited by Valentin
  • Like 3
Link to post
Share on other sites

Switching away from design methods, to materials.   Does anyone have any longevity data for the cured resin ?   I'm wondering if a cured item degrades over time (maybe years, maybe decades), and whether this is worse if kept in the light (and worse again in direct sun), or any other environment factors.    And following on, if there is age decay, do certain paints or varnishes improve the life expectancy ?   And, how does the material age (eg. some injection moulded plastics become more brittle with age) ?    

 

Whilst the home printing machines are a new thing, UV curable resin has been around a while, so aging data ought to be available somewhere.  

 

 

- Nigel

 

 

 

  • Like 1
Link to post
Share on other sites

24 minutes ago, Nigelcliffe said:

Switching away from design methods, to materials.   Does anyone have any longevity data for the cured resin ?   I'm wondering if a cured item degrades over time (maybe years, maybe decades), and whether this is worse if kept in the light (and worse again in direct sun), or any other environment factors.    And following on, if there is age decay, do certain paints or varnishes improve the life expectancy ?   And, how does the material age (eg. some injection moulded plastics become more brittle with age) ?    

 

Whilst the home printing machines are a new thing, UV curable resin has been around a while, so aging data ought to be available somewhere.  

 

 

- Nigel

 

 

 

I've not found much of a formal nature, but the consensus seems to be that strong UV light (e.g. sunlight) is the main danger, causing brittleness.

 

Possibly of interest to the dentists among us is http://www.sdclucknow.com/Journal2012/Dental materials/298_303_Longevity-of-materials-for-pit-and-fissure-sealing—Results-from-a-meta-analysis_Kühnisch.pdf

This seems to suggest UV-cured resin is significantly less long-lasting than some of the alternatives.

 

Yes, painting seems to be a good defence, but little information on what characteristics are needed in the paint. I've seen epoxy recommended, but that doesn't seem suitable in the typical use-case here.

 

David

Link to post
Share on other sites

4 hours ago, -missy- said:

I generated the pattern in AutoCAD (Attached just in case anyone would like to use it).

 

image.png.702688a34590e394d60c259876cc326d.png

 

A section of the pattern was then copied then pasted into a sketch on the required surface (in this case, towards the bottom of the wagon), then trimmed to suit the aperture.

 

This was then extruded to the underside of the roof profile.

 

OK, this pattern is different from Toms original but I had to regenerate it for the pics.

 

Simple really!

 

Julia :)

 

Much easier with AutoCAD - I'd been trying to do the whole thing with the Fusion sketch tools, which quickly reach their limits with this kind of thing! I've nabbed your DWG, Julia, will try it next time :)

 

40 minutes ago, Nigelcliffe said:

Switching away from design methods, to materials.   Does anyone have any longevity data for the cured resin ?   I'm wondering if a cured item degrades over time (maybe years, maybe decades), and whether this is worse if kept in the light (and worse again in direct sun), or any other environment factors.    And following on, if there is age decay, do certain paints or varnishes improve the life expectancy ?   And, how does the material age (eg. some injection moulded plastics become more brittle with age) ?    

 

Whilst the home printing machines are a new thing, UV curable resin has been around a while, so aging data ought to be available somewhere.  

- Nigel

 

 

Very good question! The common answer to this seems to be that once UV cured to the specified amount (whatever that might be for an individual resin) then the photo-initiator is "used up" so the resin should act like a comparable casting resin. But I don't find this particularly convincing!

 

Everything I've found on this in more scientific contexts seems very much focused on mechanical properties like compressive or tensile strength which seem difficult to translate into our contexts. I did see this article recommended, which takes a more subjective view for an art-history audience:https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-016-0097-y - not really much of a conclusion though. And of course even then the Chinese manufacturer branded resins we're mainly using are are almost certainly not formulated to the same standards as the ones mentioned in the article.

 

On the other hand, I think literally every case I've seen of models degrading/splitting/exploding on the various user forums has been the result of prints that are under cured - usually hollow objects with insufficient drain holes either trapping liquid resin, or simply not allowing enough UV to penetrate into interior surfaces during post-print curing. I'll be shining a UV "laser pointer" light into the holes in the bottom of my van, for example. 

 

Justin

Link to post
Share on other sites

It's very easy indeed to do with fusions sketch tools. You can even draw hexagons as a straight off the bat shape (the same as in autoCAD). I would much sooner do this in Fusion than autoCAD for sure.

Edited by RBE
Link to post
Share on other sites

1 hour ago, Gingerbread said:

Possibly of interest to the dentists among us is http://www.sdclucknow.com/Journal2012/Dental materials/298_303_Longevity-of-materials-for-pit-and-fissure-sealing—Results-from-a-meta-analysis_Kühnisch.pdf

This seems to suggest UV-cured resin is significantly less long-lasting than some of the alternatives.

This meta analysis (a bringing together of data from a number of studies) seems to have been primarily concerned with the retention of the resin, which depends upon a number of factors, not just the strength of the resin and so really gives little by the way of pointers to the longevity of models.  UV cured materials are rarely used in dentistry nowadays (as far as I am aware) as there were a number of drawbacks to them from the clinical point of view - poor colour stability and the risks to patients and staff from the carcinogenic properties of UV light, to name but two.  Modern filling materials are cured using light at the blue end of the spectrum, 400-500nm wavelength.

 

Jim

Edited by Caley Jim
  • Like 1
  • Agree 1
  • Informative/Useful 2
Link to post
Share on other sites

1 hour ago, Caley Jim said:

This meta analysis (a bringing together of data from a number of studies) seems to have been primarily concerned with the retention of the resin, which depends upon a number of factors, not just the strength of the resin and so really gives little by the way of pointers to the longevity of models.  UV cured materials are rarely used in dentistry nowadays (as far as I am aware) as there were a number of drawbacks to them from the clinical point of view - poor colour stability and the risks to patients and staff from the carcinogenic properties of UV light, to name but two.  Modern filling materials are cured using light at the blue end of the spectrum, 400-500nm wavelength.

 

Jim

 

The resins sold for use in 3D printers are all rated to cure at 405nm so technically not in the UV range, but just in the blue light range that you quote, Jim.

Link to post
Share on other sites

  • RMweb Premium

I think it’s fair to say that all plastic materials degrade over time if exposed to strong sunlight.  However, models that are painted seem to survive perfectly well, as this acts as a good UV barrier.  The short deep blue wavelength used in the polymerisation process will give a limited depth of cure, which is part of the mechanism for increasing vertical resolution. UV is incredibly dangerous and of course the deep blue isn’t good for your eyesight either. Dental curing lights use a 470nm wavelength (nominally). 
 

Tim

  • Agree 1
Link to post
Share on other sites

15 hours ago, CF MRC said:

UV is incredibly dangerous...
 

Tim

Living in the melanoma capital of the World - aka Queensland - I can vouch for that.  It does mean however you get lots of post production UV for free!  

 

Cheers

Kevin

  • Agree 1
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...