Gridplate

Discussion in 'CNC machining projects' started by ESC, Nov 8, 2019 at 8:18 AM.

  1. ESC

    ESC Silver Banner Member

    I needed a gridplate that would mount in the mill vise to machine the disc brake mount and other flat pieces. Since it is also the axle bearing retainer it has a shallow relief where it retains the bearing.
    I made a quick pattern with the intention of using up some of my junk bifilm infused ingots since their appearance was unimportant due to them being a sacrificial surface for drilling. I rammed a couple molds with the sprue directly into the base with an 1.5" shrink bob.
    I added the ingots to a hot crucible and added fresh wheelium to have enough metal and poured at 1200*. I ran low on metal had to go back to the furnace to pour the second plate. After shutting down I dunked the first casting and started machining. Beautiful chips and no detectable bifilm.

    I set up a surfacing program in Mach 3 and then followed with a 2" dremel disc with three .001" passes. It is flat, those are just the swirl marks and no visible inclusions.

    IMG_20191107_133553.jpg

    I followed with a grid drill program and threaded the holes for hold downs.

    IMG_20191107_143509.jpg

    Here is brake bracket ready for bolt holes and circular relief. the bolt head is center drilled for 0,0 location although I used the center hole as the start point for the grid and can always pick up from there.

    IMG_20191107_163115.jpg
     
    Tobho Mott and joe yard like this.
  2. Petee716

    Petee716 Silver Banner Member

    Did you sprue near the center of the casting or nearer to the edge? I can't see the base, I'd be interested to know where the metal came in. I always get swirls in my flat castings, probably from multiple fronts meeting, but I think I tend to pour hotter than I need to. Your plate machined up nice.

    Pete
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Pete, ever try to slightly tilt your mold so the low point is at the sprue/gate end and top end is vented? -Helps

    Best,
    Kelly
     
  4. oldironfarmer

    oldironfarmer Silver Banner Member

    So you've discovered what I've been saying all along. Hydrogen does not build up from multiple melts, and remelting a bifilm filled ingot results in a cleaner ingot or pour. I have speculated on the reasons, but regardless the results are great. All my scrap now goes into ingots to be remelted later.
     
  5. ESC

    ESC Silver Banner Member

    Pete, I double rolled the mold and sprued into the base at one end with the riser closer to the midpoint.
    Andy, I had multiple melts on some of the ingots I used and had been no improvement in quality even with a tablet treatment. In this case the difference seems to be from a quick melt and adding virgin wheelium and I did skim the dross before I poured.
     
  6. oldironfarmer

    oldironfarmer Silver Banner Member

    Interesting. I've never used tablets but think there is some anecdotal evidence they add porosity, of course depending on the tablet.

    I have had great success, and always skim dross regardless of whether I'm pouring a casting or an ingot. I have seen consistent improvement and never deterioration having sectioned and polished maybe 50 ingots.
     
  7. ESC

    ESC Silver Banner Member

    I don't always skim, it depends on the amount. From Puhakka's comments you never see molten aluminum, it is always Aluminum Oxide. Yesterday with half a crucible I tilted and watched the new oxide layer form as the molten mass advanced to the lip. Since I couldn't get it any cleaner by a mechanical method, I poured and so far haven't found any unfurled bifilms.
    I'm inclined to agree with you regarding the tablets. They sure create a lot of turbulence, but I think Ironsides has demonstrated some of the fallacies of their use.
    It still comes back to not understanding all I know about this stuff.:D
     

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