Water Based Resin 3D Model Problem And Solution

Discussion in '3D Modeling Projects' started by gormo, Dec 16, 2021.

  1. gormo

    gormo Staff Member Administrator

    Messages:
    5,991
    Likes Received:
    4,140
    Joined:
    Dec 5, 2015
    A joint effort topic posted by Gormo and Chris M.

    A Brief History

    Chris has been learning and working his way through the fine art of 3D printing. He has been
    producing models in various scales to develop his skills and some of those models have been
    displayed in various posts on this forum. Chris has also been working on OO/HO models with his
    future railway in mind.
    He has asked me (Gormo) if I would be willing to test some of his models on my railway, basically
    for evaluation and constructive criticism.
    Recently, we have been focused on a buffer stop design that Chris acquired through a down load, so
    that`s what this post will focus on.
    Testing
    The original test buffers were FDM (Fused Deposition Modeling) prints, however a nice crisp
    model was also produced in Water Based Resin (WBR).
    The first installation consisted of 2 x FDM buffers and 1 x WBR buffer.
    They were painted with Acrylic Paints and Chalk Pastels and glued in place with neat PVA.
    Later ballast was added, mist sprayed with water and diluted PVA was added with a dropper.
    The WBR buffer distorted after 24 hours....the FDM`s were OK.
    Note the bowed rail and sleepers.


    1.png

    Chris re-designed and strengthened various parts of the model to counter the distortion issue.
    The pic below shows the improved design once again using WBR.


    2.png

    The second installation followed the same processes as the first yet still yielded a similar result,
    with the buffer stop model distorting within 24 hours. Note the sleepers curving upwards.


    3.png

    Both of these events were followed by exchanges of detailed PM`s and telephone conversations.
    I will hand over to Chris now to explain how he solved this issue with a controlled experiment.

    My Investigations
    Thanks Gormo ... this was puzzling as no other resin prints I have printed have distorted like
    this. I like the water based resin as it is much easier to handle, less smell, easy clean-up and
    seems to print as well as normal resin.
    SO ... WHAT IS GOING ON HERE ... !!!....:scratchchin:

    FIRST THOUGHT
    Thin resin prints can sometimes bend after printing due to heat stresses as it is exposed by the
    laser and subsequent UV curing. Other 3D modellers have found that the orientation of the
    model on the print bed can cause bending. I had the same problem when printing some HO
    power poles. Printed at an angle they bent, hanging vertically they printed straight.
    BUT ... this bending happens soon after printing. Gormo had the resin buffer stop for some
    months and it had remained stable.
    SECOND THOUGHT
    I used WATER BASED resin for this print. Does water affect water based resin ???? BUT the
    model had been sprayed with acrylic paint which should have sealed it.
    THIRD THOUGHT
    I did not remember spraying paint under the sleepers ... HMMMM !!! Some testing was
    required.

    FIRST TEST

    4.png



    2 water based resin buffers both painted silver as before. The NOT SEALED model has been
    left unpainted underneath.


    5.png

    Both buffers glued down with PVA on a piece of pine board.


    6.png

    After 24 hours the unsealed buffer was distorting slightly (see front sleeper). Not as extreme as
    Gormo’s but definitely happening. Gormo also used lots of water when ballasting and grassing
    around his buffer.

    SECOND TEST


    7.png

    Unpainted water based resin buffer stop left sitting in some water.


    8.png


    And “VOILA” ... after 24 hours sitting it water MAJOR distortion and delaminating of the
    model.
    CONCLUSION
    Well obviously, water based 3D resin absorbs water and IS NOT WATERPROOF ... unless
    you seal it with a non-water based paint.
    I assume that normal 3D resin would not have any water issues. I will have to print some buffer
    stops in normal resin to confirm this but I do not expect any issues. I now have to consider
    whether to continue using water based resin or change to normal resin.
    FINALLY
    Gormo subsequently sealed 2 more buffer stops with enamel paint and glued & ballasted them
    into Bamford as before.
    NO DISTORTION.


    DSC01603.JPG



    DSC01601.JPG
    :tophat:Gormo & Chris M
     
  2. paul_l

    paul_l Staff Member Administrator

    Messages:
    9,848
    Likes Received:
    5,902
    Joined:
    Dec 5, 2015
    I would also add

    All resin prints should be sealed after the curing and clean up process are completed, preferably with a non-translucent coating - I use Black, Grey or White acrylic primers. This stops any further curing caused by light - no so much of an issue up here in Scotland, but in the land of the 365 days a year sunshine this will be more of an issue.

    May be worth increasing your print cure time to see if this effects the result as the delamination appears to be on the layers, in general the cure time appears to be the same as that of standard resins.
    Also post cure time may be worth increasing - allow time for the models to cool between exposures.

    Translucent resins will cure better than opaque resins, both during the print and post cure process as the UV light can pass through the models. It's just harder to see the detail before paint.

    For gluing the resin prints I use super glue.

    From your testing I may need to change from an acrylic based primer to a non-water based primer.

    Paul
     
  3. Chris M

    Chris M If 2 wrongs don't make it right ... try 3 Full Member

    Messages:
    156
    Likes Received:
    182
    Joined:
    Mar 14, 2019
    Thanks Paul,

    A couple of questions.

    I found the best exposure for these buffers is 1.8secs on my AnyCubic Mono. Higher exposures cause some loss of definition on the layers facing the bed (a shiny/wet look which gets worse the higher the exposure) ... do you see this?

    I generally cure for 6 to 8 minutes (depending on how my items) in my AnyCubic Wash & Cure station. I would be interested in your cure times.

    Of course, all the above may be different when using normal resin which I will use when I reprint this model (probably after Christmas).

    Chris
     
    Rob Pulham and jakesdad13 like this.
  4. Andy_Sollis

    Andy_Sollis Staff Member Moderator

    Messages:
    3,894
    Likes Received:
    3,621
    Joined:
    Aug 4, 2018
    6-8 mins??

    wow. I’ve never gone over 3-4 sometimes even 2 mins for small items Like that? Maybe your over exposing? (That’s a question not an answer… I don’t know. I may be under exposing at the cure stage)
     
    Rob Pulham and jakesdad13 like this.
  5. gormo

    gormo Staff Member Administrator

    Messages:
    5,991
    Likes Received:
    4,140
    Joined:
    Dec 5, 2015
    Knowing nothing about 3D printing.....:scratchchin:
    But as an observer, it seems to me that there is some fundamental equation missing from the process, that would calculate and determine the correct exposures and cure times for any particular model based on its mass, material and overall size and shape, with a floating variable allowing for climatic conditions and material used.
    Now that is quite an equation, however as 3D printing develops over the years, I can see it being built into the machines of the future.
    In the meantime, you early starters (pioneers) in the hobby are doing the groundwork to enable improvements to be made that will take the guess work out of it eventually.
    :tophat:Gormo
     
    Rob Pulham, Chris M and Andy_Sollis like this.
  6. Andy_Sollis

    Andy_Sollis Staff Member Moderator

    Messages:
    3,894
    Likes Received:
    3,621
    Joined:
    Aug 4, 2018
    If only it were that simple..

    theory is sound, but we also have to take in to account the material type (ie clear or opaque resin and even type and possibly even brand!) and obviously it’s thickness.. even harder should it be something that tapers.

    I really don’t think there is a hard and fast rule and much of it is trial and error. Some don’t even use the UV curing lights and choose to leave in direct UV sunlight, depending on where you are in the world (couldn’t do that in Nottinghamshire at the moment!)

    But I think that is part of the fun - the challenge to see what rabbit you can pul out the hat.. sometimes it’s an absolute failure, but with luck it could be the most proudest moment in your day. :tophat:
     
    Rob Pulham and Chris M like this.
  7. paul_l

    paul_l Staff Member Administrator

    Messages:
    9,848
    Likes Received:
    5,902
    Joined:
    Dec 5, 2015
    Hi Chris

    The glossy surface surface texture your getting on flat surfaces is derived from the surface texture of the FEP sheet - which is as smooth as they can make it to help with the peel process (reduces the contact area). As your detail is good, stick with 1.8sec for the time being.

    Wash n Cure

    Small items I tend to give 2 min, then flip them over and 2min on the other side. Even with larger parts I don't give more than 4 min in a single shot.
    Check the temp of the part before and after cure, if it feels warmer after 2 min, then allow to cool before curing further.
    On the underside of the part, run your finger nail over the surface, if it scratches, then further curing is required.

    The clear resin is easy to see if the cure time is correct - overcuring and it starts to discolour and gets a brown tint.


    It was an unstained clear before.

    As with the print cure times, cure times for Translucent / clear resins are lower than opaque resins.
    I have seen youtube video's of parts being put in a jar of water (jam jars seem to be appropriate), then cured in the machine, the water helps keep the parts cool and also defracts the UV light to give a more even cure - well thats the theory, not tried it yet myself, but I do now have some jam jars.

    Hi Gormo

    There appears to be more of a black art in this than DCC and electronics put together. Most of this is we are doing this in a home environment and not an industrial environment where we can control all parts of the process.
    The resins appear to have an optimum working temp - 21C to 24C, in the UK we struggle to get that temp, and I would assume in Oz you'd struggle to get it down to that temp. Under 21C and the resin becomes viscous. Also as the temp increases the cure time shortens, couple that with the UV lamps are hot, so they also warm up the resin. This gives rise to inconsistancies, if you start an 8hr print at 8am, the next 4pm and the final print at midnight, you may be lucky and all three could turn out perfect, but if one fails, was it due to a print error or a change in ambient temp causing the resin temp to change.

    The Mono screen printers have a big advantage over the older RGB screen printers, with exposure times of the Mono screens being between 1/3rd to a 1/5th of the RGB screen printers. This does have the advantage of the UV light source being on for shorter times, so the heat build up is less, however the RGB printers are more forgiving on exposure settings, for example a Mono printer with a 1.8s exposure - a 5% variation in exposure time is 0.09s, whereas with the RGB 8s exposure it would be 0.4s.

    The beauty of it is, starting with smaller items, the cost of mistakes isn't too bad, and once you get it right, it's easy to repeat.

    On the Mono X I can print three of these O gauge wagon bodies at a time (approx 8 hours), and with a wee bit of maths could re-scale them in to 4mm and print them to suit.



    I couldn't cut and scribe the plasticard in that time.

    Then we come to the smaller parts

    It is just so easy to make bits



    Parts costing a fraction of the cost of postage nevermind the part cost, once you get the hang of it, you can design, prep and print quicker than you can get the part sent out.

    The pain is worth it.

    Paul
     
  8. Andy_Sollis

    Andy_Sollis Staff Member Moderator

    Messages:
    3,894
    Likes Received:
    3,621
    Joined:
    Aug 4, 2018
    There is only one issue… printing such detail is a luxury.. but being able to paint it when it’s 0.25mm high etc is another matter! :facepalm: As I have found once or twice… but then, I have never confessed to being a painter. :giggle:
     
    Rob Pulham likes this.
  9. gormo

    gormo Staff Member Administrator

    Messages:
    5,991
    Likes Received:
    4,140
    Joined:
    Dec 5, 2015
    Ah....painting is like 3D printing Andy, in that it`s all about the process or the method if you like.....basically you have to plan it well.
    Think it through before you start and no smoking, drinking or strenuous exercise beforehand as those three things can make your hand shake when trying to do precise work........how do I know this ????.....well that`s another story..........:thumbs:
    :tophat:Gormo
     
  10. Andy_Sollis

    Andy_Sollis Staff Member Moderator

    Messages:
    3,894
    Likes Received:
    3,621
    Joined:
    Aug 4, 2018
    Indeed…
    I find it’s also down to eyesight. I can see a computer screen 2ft away but struggle now (at 45 years) to see as all item in my hand..

    Go on, what did you paint!!! :facepalm::scratchchin::avatar::avatar:
     
    Rob Pulham likes this.
  11. Mossy

    Mossy A classic grump Yorkshire man Full Member

    Messages:
    1,540
    Likes Received:
    2,320
    Joined:
    Sep 8, 2020
    Andy,

    At 45 your a spring chicken, try 66 with cataract replacements in both eyes. Long sight fine, get close up what a faff about, if you can see the tool at say 2 ft away when you switch back to the model its a blur. Its exactly the same when painting which is why I hate painting!
     
    Andy_Sollis likes this.
  12. gormo

    gormo Staff Member Administrator

    Messages:
    5,991
    Likes Received:
    4,140
    Joined:
    Dec 5, 2015
    Nothing in particular, but a number of projects over the years have given me experience and gradually I`ve learnt by doing.
    I am 70 years old now with eyes that still work and hands that don`t shake. But it`s only a matter of time before I go on the down hill slide.
    I have recently bought a digital microscope to help with the fine work......figures ( little people )....but am yet to try it out.
    :tophat:Gormo
     
    Andy_Sollis likes this.
  13. Chris M

    Chris M If 2 wrongs don't make it right ... try 3 Full Member

    Messages:
    156
    Likes Received:
    182
    Joined:
    Mar 14, 2019
    Hey guys ... if bits haven't started falling off yet ... you are still ahead :avatar:.

    Who knows ... in the future we may be able to 3D print replacement parts as we wear out.

    So I thought I'd have a go at 3D printing a Gormo ...

    Seems to be coming out OK ... :giggle:

    3D Gormo.jpg

    Chris :facepalm:
     
    Andy_Sollis likes this.
  14. gormo

    gormo Staff Member Administrator

    Messages:
    5,991
    Likes Received:
    4,140
    Joined:
    Dec 5, 2015
    OK
    Looks armless enough
    :tophat:Gormo
     
    Andy_Sollis likes this.

Share This Page