18" Machinist's Prism Newly Cast

Discussion in 'Sand Casting' started by Melterskelter, Jul 12, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I just thought I'd put up a few pics of prism casting I made today. It is 18" long and the two long flat faces are 3/8" thick.

    Its end use will be as a machine scraper's 1) Straight edge 2) Prism (both flat surfaces are precision scraped to allow reaching under dovetail ways that are being reconditioned. The prism, after precision scraping, is used to determine flatness of dovetail ways on lathes, mills and the like) 3) Machinist's level incorporating a very sensitive vial 4) Parallel as the top rail will be milled and may be then ground flat and parallel to the bottom face or scraped flat and parallel.

    Getting the sprue, runner and ingates right took a couple tries, but the current setup seems to be working OK. I am not sure it is ideal. I welcome comments or suggestions. You can see vent "pins" at each corner and near the mid portion of the apex of the faces. They extended fully 2 inches into the sand prior to me breaking them off---should have taken pic prior to clipping them off.

    The whole casting weighs 18 pounds with about half of that being in the gates, runner etc.
     

    Attached Files:

  2. That looks pretty good Denis, do they end up with much of a hard skin?. I see Luckygen made a flat from disc brake rotors by using additives to get a decent iron. Every time I see one of your castings it reminds me of how much equipment I need before I can scrape in my lathe saddle, cross slide and compound. :rolleyes:
     
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  3. Melterskelter

    Melterskelter Gold Banner Member

    The casting is allowed to cool in the sand minimizing any surface hardening and avoiding formation of "white iron" I think all iron castings have a subtle skin of harder iron that is generally not even detectable in normal machining. But, under some circumstances if trying to take a few thousandths skim cut on a small (not too rigid) machine, might be detectable. It is similar to the commonly-encountered skin on hot rolled steel but much less noticeable on the castings I have machined.

    I have not tried using scrap iron for castings as I have found it challenging enough to manage all the variables when using certified grey iron melting stock! If I were making casual items for my own use, I wouldn't hesitate to use whatever was at hand and add enough ferrosilicon to make it flow well and machine well. As it is, I add as much ferrosilicon as I can while staying within specification to optimize flow on the patterns I cast as they are generally fairly thin in section.

    Denis
     
  4. Great castings! I need to learn how to scrape.
     
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  5. DavidF

    DavidF Administrator Staff Member Banner Member

    The casting came out great. Youll have to post up some pictures of the machining and scraping when you get to it.
     
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  6. Melterskelter

    Melterskelter Gold Banner Member

    Incidentally I tried something today which may well be the oldest idea in the book, but it's something I have not read about.

    I carefully cut the runner and gate from the pictured casting keeping it in one piece. After removing the sprue, I cleaned it up some to get rid of its worst lumps and added some draft to the cut ends of the gates. Then I used it as a pattern for gates and runner for today's mold and expect to use it at least ten more times for this pattern in the next couple months.

    In the past I have made wooden patterns for the gate and runner and usually use a wood catch basin/ sprue combination to form them. But just cutting off the hand-cut runner and gate and reusing seemed like a time saver. FWIW.

    The top image shows the CI runner with a magnet attached as a means of drawing it out of the sand. The other just shows it prior to molding sand. As presently made it does require carving out the last 3/8" of the gate by hand. Easy and quick enough.


    The red bits of tape keep sand out of the boss holes used with screws to lift the pattern out of the cope.


    IMG_4783.JPG IMG_4782.JPG
     
    Last edited: Jul 13, 2018
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  7. PatJ

    PatJ Silver

    I am just getting caught up reading all the threads I missed while I was busy with work.

    That is a great idea.
    What is your core and pattern made of?
     
  8. Melterskelter

    Melterskelter Gold Banner Member

    The pattern is lacquered Baltic Birch Plywood. There is no core as such. Just a green sand cope and drag.

    Denis
     

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