Mineral in Resin

Discussion in 'Techniques' started by JimG, 5 September 2019.

  1. JimG

    JimG Western Thunderer

    While I'm waiting on all the bits to come from Steel River Engineering for the S scale wagon wheels, I thought I might have a try at printing a wagon body in S scale with maybe a thought about using it as a master to use for casting in resin. I had been working on an etched kit for a mineral using copies of Charles Roberts drawings which @AndyB had kindly sent me. But some members had suggested that a resin body might be a good option as well if they didn't want to have to build an etched kit.

    The etched body was to fit on an underframe produced by Justin Newitt at Rumney Models so the resin body has been designed to fit it as well.

    16TMineral-006.jpg

    16TMineral-007.jpg

    This is the third attempt. :) The wagon was printed at a 45 degree angle and you can see some evidence of layering in the upper picture. I dare say that the dead flat sides of a 16T mineral are not going to be the easiest to print. :)

    There are one or two other faults. The corner angle closest to camera on the end door has got as bit of a wiggle and I might have to make it a bit thicker - it's 0.2mm at the moment. The one on the other side - the same width - is perfectly fine so I suspect that is in between pixels and would probably improve if I moved the placement on the build plate - but then the other one might suffer. :) Adding another 0.05mm will probably suffice.

    I'm not sure what caused the small hole on the end door. There were also a couple on one side which you can see just poking over the top of the end in the upper picture. I suspect that this was down to me not ensuring that the resin was fully stirred.

    There are no details, like hinges, on the body as yet. I've been experimenting with thicknesses to see what I can get away with. A lot of the metal work on the mineral was 1/4" thick sheet and angle and this scales out to 0.1mm in S scale. The thinnest that the printer and the resin will reproduce is 0.2mm and even that can be pushing it as the door angle mentioned above shows. So it's a case of making parts as thin as I can and see how they look. I've made the body sides and ends 0.6mm thick at the moment. I did try thinner but the sides were much too flexible. I suspect that they will have to be even thicker for resin casting and I'm waiting on feedback from CMA about minimum thicknesses.

    It's not all that quick a process. I spend ages trying to persuade Fusion 360 to do what I want then the print takes nearly ten hours. :)

    Jim.
     
    john lewsey, Rob R, AdeMoore and 3 others like this.
  2. ScottW

    ScottW Western Thunderer

    Jim, could you not use one of the etched wagons as a master for resin casting?
     
  3. JimG

    JimG Western Thunderer

    Scott,

    The material used for the main body in the etch is 0.008" nickel silver and I think this is much too thin to use as a resin master. I'm waiting on minimum thicknesses from Tracy at CMA and I suspect that the minimum for the sides might even be a bit more than the 0.6mm I'm using at the moment. I opted to try a 3D print since that would give me the freedom to set whatever thicknesses might be required and would also allow me to mess about and try and disguise much overscale thicknesses.

    I've done a bit of googling and it looks as though the minimum wall thickness might be 1mm with down to 0.5mm in small areas. I've used 0.6mm for the sides and 0.2mm - 0.25mm for finer details like the angles so far, so it looks as though I'm going to have to thicken things up a bit. All good fun. :)

    Jim.
     
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  4. Rob R

    Rob R Western Thunderer

    Jim, don't worry about flat sides cos the the real thing didnt stay flat for long.
    That said, we are most grateful for everything you are doing.
    Were S leads others will follow.

    Rob
     
  5. JimG

    JimG Western Thunderer

    Rob,

    I've got a picture of a 16T mineral which I took in the old Fort William station in the 1970s when it was being demolished. I had never seen a more battered sample of the breed, completely covered in rust. I vowed to make a model of it some day but never got round to it. It would probably be the most difficult of models to make. :) I'll try and dig the picture out. It would have been a transparency so I'll have to find a way of scanning it.

    Jim.
     
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  6. matto21

    matto21 Western Thunderer

    Did you ever find the photo of the 16tonner?

    Matt
     
  7. Jim smith-wright

    Jim smith-wright Western Thunderer

    Why not print it as 5 parts? I’ve never really understood the apparent obsession of printing complete RTR bodies in one hit.
     
    michl080 and AJC like this.
  8. JimG

    JimG Western Thunderer

    So far, no. I was "on the road" in Scotland for ten years or more and I carried a small Rollie B35 around and shot a lot of transparencies and I have boxes and boxes of them. I've also no longer got a 35mm viewer. So the spirit is willing but the body is weak. :):) My daughter is chasing me to get a film scanner to digitise some family pictures so something might happen in the future. :):)

    Jim.
     
  9. JimG

    JimG Western Thunderer

    You might have a point. :) It could be a lot quicker since I could print flat on the build plate and the printing times would be measured in minutes rather than hours. The main problem with resin printing is that the parts have to be supported and oriented and that can create problems with straightness and flatness, and supports can also leave a problem of finish. In a lot of cases it is easier to print a complete body since these problems can be minimised since the floor, sides and ends provide enough support in themselves without the need for additional supports.

    I've found with 3D resin printing that supporting parts is the main problem that you have to learn how to overcome, and that is just by experience.

    Jim.