Pattern Making for the Mechanically Challenged

Discussion in 'Pattern making' started by mrhomescientist, Dec 4, 2019.

  1. I used your method on the second coin, pictured in my last post. The first one I think I just wasn't careful enough, and it must have shifted while I was ramming.
    Thank you for the advice!
     
    Melterskelter likes this.
  2. I finished one coin!
    IMG_20200414_180944.jpg IMG_20200414_180958.jpg IMG_20200414_181006.jpg

    I know it isn't a perfect casting, but I think it came out looking pretty nice. I smoothed the edge but left some grinder marks in because I think they add a little character.

    Any recommendations on reducing that porosity, or whatever is causing those pits?
     
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  3. DavidF

    DavidF Administrator Staff Member Banner Member

    Could be a bit of sand wash. After watching old foundry man on YouTube I noticed he likes to dust everything with talc, and then lightly brush the surfaces with a soft brush, followed by a light shot of compressed air. He does this on every mold. That old man has some skills learned long before we ever had a spoon in our mouths... might want to watch him and try it..
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Something else to consider might be be excess moisture in your sand as the pinholes look to be quite widely distributed. It looks like you may have abraded the background areas of the coins to reduce them there?

    On easy way to check your moisture content is to simply take a sample (maybe a cup cup or so) of mulled sand and carefully weigh it on a sensitive scale. Then put it in 350 degree oven spread out on a cookie sheet until is is well dried---I imagine 30 minutes would do. Then reweigh the sample. Your moisture should be in the 4% range.

    One other experiment that might be interesting and would be easy to do would be to mold up your coin at least a couple times. Then close one mold up but leave the other open a few hours allowing it to dry. That might result in disastrous washing of the sand or might not and might reduce pinholes if they are due to moisture. Not much lost either way.

    I think the coins are very very handsome as they are. Way to go.

    Denis
     
    Last edited: Apr 15, 2020
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I concur. Well done. Completing a project is very satisfying........and so is starting the next one!

    Best,
    Kelly
     
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    Agreed!!
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Was this green sand or Petrobond?

    Best,
    Kelly
     
  8. Patrobond. It's old, though, and has lost much of its green strength. I bought a fresh batch of it, and used that as facing sand for another coin with the old sand to pack the rest of the box. The difference in the two is crazy - the new sand sifts out like Play-Doh, and the old stuff like regular sand (although it still holds shape when pressed). The coin I made from this setup appears much nicer, but I still need to clean it up later today and do a full inspection.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I would expect well condition Petrobond to reproduce the pattern detail very accurately. Have you spritzed a little Isopropyl Acohol onto the old stuff? Sometimes that will pep it up quite a bit.....but don't get carried away with it. Let's see the coin from the fresh facing sand.

    Best,
    Kelly
     
  10. Here you go! About to start cleaning it up.
    IMG_20200416_201856.jpg IMG_20200416_201900.jpg

    I think the D side looks perfect. I'm really happy with the wood filler repairs.
    Zooming in on the pictures, I see the K side has quite a few pits. That side was face down, in the drag. That might suggest sand wash?

    I haven't tried anything to refresh the old sand yet. After some deep research I found that propylene carbonate is used as the catalyst in the sand, so I bought some and was going to try a spritz of that. Just haven't gotten around to experimenting yet.
     
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  11. DavidF

    DavidF Administrator Staff Member Banner Member

    That's going to look really good cleaned up.
    You can probably just add a teeny tiny bit of synthetic 2 stroke oil to the old petrobond and mull it for a few minutes to bring it back to life...
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Nice work. Bet that would clean up nicely in some tumbling media.

    Best,
    Kelly
     
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    They look great!

    Jeff
     
  14. OMM

    OMM Silver

    Yes, he has a lot of experience.
     
  15. FishbonzWV

    FishbonzWV Silver Banner Member

    Those look good, are you going to patina them?
    Regarding your sand...http://www.alloyavenue.com/vb/showthread.php?14184-Petrobond-Waste-or-Recondition
    I moulded up a couple patterns yesterday. My sand was probably 45*F so plunged the heater into the bin. It sure wakes it up. One of the patterns was a house number plaque so I thought I would use some new PB for facing. I popped the lid off the bucket and it looked like the sand had crystallized. It felt like sea salt. I guess it will go into the mixer for tumbling.
     
  16. Here it is! This was much harder to polish because of all the intricate details. I think next time I'll try leaving the background tarnish intact and just polish the raised bits, and see how that looks.
    IMG_20200418_121627.jpg IMG_20200418_121644.jpg

    I absolutely agree that tumbling media is the way to go. I have a nice tumbler for my rockhounding hobby, and I recently bought some corncob and polishing compound for just this purpose. This coin is for my mom's birthday, though, which is today so I don't have the time to try anything else. I might try a few different experiments on my third one, the YouTube coin.

    Thanks for all the advice and support!
     
    Melterskelter likes this.
  17. dennis

    dennis Silver

    Perhaps use hand wire brushes?
     

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