Rob's Resin casting thread

Discussion in 'Wagon Builds' started by Rob Pulham, May 1, 2021.

  1. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    I will post this on the wagon thread because I suspect that most of what I might cast will be wagon related starting with some NER No2 Axleboxes and springs

    I made some masters by modifying some Slaters Midland Railway Axleboxes and attaching MR springs to them (they cone as independent mouldings.

    Next comes creating the mould. Since I wasn't expecting to show this I took the photos in reverse order.

    Stick your masters to a sheet of glass using a small dot of superglue to hold them in place while you pour the resin.

    IMG_0001_1.JPG
    You will note that there are only three this is because the 4th one came adrift as I removed the mould from the glass.- this was taken after the event.

    Then build a box around the masters to contain the mould compound. Some people build the box from sheets of plasticard but old lego is the easiest.

    IMG_0001_2.JPG

    This is the stuff that I am using to make the mould. Bought from eBay a couple of years ago. There are lots of options to choose from but I was advised by Kerry to get one that you weighed out 50:50 as being the simplest to work with.

    Weigh it out in a suitable disposable pot. I used the top from a tub of cotton buds that was handy in the workshop and for this particular mould I mixed up 30 grams of each part.

    IMG_0334.JPG

    As you are mixing try to minimise the amount of ar bubbles but do ensure that you give it a decent mix - I named this my comedy resin casting because for a while I thought I hadn't mixed it enough for it to go off but id did eventually.
     
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  2. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    Once it's set peel it from the lego. This is where I made a couple of errors I forgot to also add a couple of spots of superglue to hold the lego in place and I also didn't press the bricks completely together in some places. This resulted in my nudging it as I poured in the silicone which allowed some to run under the edge of the box and between the bricks. Not much, but enough to make releasing the mould a bit harder than it need have been.

    This is what it looked like when I first removed it from the Lego and glass sheet.

    IMG_0001.JPG

    IMG_0003.JPG

    Because the silicone is clear you cant really see the mould apertures but once the resin has hardened I will take another photo before removing them from the mould.

    IMG_0002_1.JPG

    This is the resin that I am using again bought from eBay and is a 50:50 mix. I have just mixed some for the mould but my hand slipped as I was measuring the second part so I have probably double what I needed. I have filled a couple of seat moulds that I have to use up any excess but I still have a small pot left over. I am sure I will get there in the end but as I said on my NER Perishables van thread, I have only done this once before under Kerry's watchful eye.
     
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  3. Mossy

    Mossy A classic grump Yorkshire man Full Member

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    Rob,
    Thanks for putting this thread together as I suggested - it's very interesting and hardly a comedy.
    I'm really interested to see how the casting process goes.

    Mossy
     
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  4. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    Next time I create a mould I will take photos at every step. I have some seat moulds to make so it shouldn't be too long before I get to it.
     
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  5. jakesdad13

    jakesdad13 Staff Member Moderator

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    This is an interesting topic, I watched a chap doing some resin casting at Doncaster model rail show some years ago. He was using bathroom mastic for the mould and 24 hour araldite for the casting. I had a go at casting some brake parts for my Andrew Barclay scratch build and must say they turned out really well. I wouldn't recommend it for larger castings but I was happy with mine.

    Cheers, Pete.
     
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  6. paul_l

    paul_l Staff Member Administrator

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    Great thread Rob

    I purchased some silicon measuring cups for resin measuring and mixing

    upload_2021-5-2_12-41-12.png

    8 of them for £8.99 from Amazon.

    The casting resin (inc normal fibre glass resin) does'nt stick to the silicon cups, so once set breaks away from the inner surface.

    Resin casting is not a tecnique I tried yet, but will possibly go down that route for making some larger parts, I'm lucky enough to be able to 3D print most of the parts I need (if I can actually create the model - but thats a different challenge :whatever:), but ...... there's always a but.... if I need to assemble several parts to make a larger item, and I need several of them then resin casting becomes a serious contender.

    Paul
     
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  7. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    They look brilliant, thanks Paul.

    I also need to get myself a set of scales as Chris is frowning upon my using the ones from the kitchen.... I may as well get both from amazon.
     
  8. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    [QUOTE="Mossy, post: 90047, member: 2624"hardly a comedy.
    [/QUOTE]

    Hi Mate,

    You would think so if you had seen what came out of the mould this morning, quite a bit of the resin hasn't set. I am reasonably sure that it's a combination of my hand slipping with the resin and not getting the two parts equal and then possibly not mixing it enough. Or I have kept my ingredients too long (I do hope it's not the latter as it's a lot to waste...).

    I will order some scales and silicone pots and have another go.

    The good news is that despite none of them being whole there is enough that's recognisable to tell me that the mould looks like an NER No2 Axlebox so that's something.
     
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  9. Mossy

    Mossy A classic grump Yorkshire man Full Member

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    Rob,

    In most sports its 3 strikes and out so you have 2 lives left. Seeing that you bought 2 kilos of resin I really hope it isn't life expired
     
  10. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    Hi Mossy,

    Me too, that was the minimum I could buy at the time and was about £30 if I remember correctly. I have ordered some of the silicone meauring cups and a set of scales which should be delivered on Tuesday so I will have another go then.

    I was talking to a chap that runs a bit plastics company yesterday and he says that he has used resin that they have had for 3 or 4 years without issues so it;s probably me. I need to take a bit more time when measuring, mixing, etc.
     
  11. paul_l

    paul_l Staff Member Administrator

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    Hi Rob

    Better heavier on the hardener (part B) than the monomer (part A), shortens the working time tho'

    For the silicone, if you pour gently from height into a corner of the mould, the bubbles will burst and should give a bubble free mould.
    Next up you'll be after a vacuum vessel to degas the resin, and a pressure vessel for the casting.

    And you thought this was going to be simple :avatar: - who's laughing now :giggle:

    Paul
     
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  12. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    I am really happy to say that last night's casting efforts are much improved. There are a few air bubbles but the resin set reasonably quickly (I did leave it overnight to be sure but they felt firm before I went to bed.

    A couple of the axlebox/spring castings took a bit of cleaning up of flash where I had slightly overfilled the mould and there are some tiny air bubbles but at normal viewing distances they are all but invisible.

    IMG_0002.JPG

    IMG_0003.JPG

    I had reduced the amount that I poured to 20 grams in total but it was still too much for the moulds that I have at the minute even after pouring some coach seats as well.
    IMG_0001.JPG
     
  13. paul_l

    paul_l Staff Member Administrator

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    Time to make up multiple moulds, so when you cast the ones you want, the extra's are available to use up the remaining resin.

    For the air bubbles, placing the mixed resin in a vacuum chamber will degas the majority of the bubbles from the mixing process. Placing the moulds with resin in a pressure chamber will compress any remaining gas into miniscule bubbles.

    Knowing your Yorkshireman heritage (as the Scots would say cannie with money), I thought this may be of interest.




    Paul
     
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  14. paul_l

    paul_l Staff Member Administrator

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    And a comparison between Vacuum Chambers and Pressure Pots

     
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  15. Mossy

    Mossy A classic grump Yorkshire man Full Member

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    Hi Rob,

    They certainly look like NER Type 2 boxes. I hope when you have got the process off to a tee your up for a commission to make me some (I need about 6 sets) or alternately create me a mould that I can cast from.

    Mossy
     
  16. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    Hi Mate,

    I am sure that we can sort something out.:thumbup:
     

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