Mad Max - Fury Road Shifter Knob

Discussion in 'Investment casting Block method' started by Mach, Jul 5, 2020.

  1. Mach

    Mach Copper Banner Member

    I use the long weekend to dial-in my casting setup with mixed results and a few lessons learnt. Any advice is appreciated.

    About the casting, the movie Mad Max Fury Road has its share of iconic vehicles. Gigahorse is a monstrosity made from stacked '59 Cadillacs powered by twin supercharged 502s. I've got mixed feelings about the demise of the Cadillacs but it fits the story.

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    This is the shifter knob from Gigahorse as seen briefly during a chase scene.

    [​IMG]

    This is my take on it. I started with the stl file from Thingiverse (https://www.thingiverse.com/thing:841218) Credit to questpac. I tweaked the lower jaw to my liking in Meshmixer and then printed it in four parts in Polysmooth filament. Then molded it using Smooth-On Rebound 25 and cast it in wax. The wax is made from a sculpting wax mixed with sprue wax. I could have gone directly from the print instead but wax meant I could make several quickly with easier clean-up.

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    The casing turned out ok (see the pics below). Not perfect but usable. I'm still getting the kiln dialed in. The cone sitter accidentally switch off at the 500 c stage and the the PID quit sometime after reaching 730C. The wax burnout appears to have been complete. My PID controller failed for some reason. I'm using 5x8" flasks that are too large. I can only fit two in my kiln at a time. I'm going to step down to smaller ones for future attempts.

    [​IMG]

    The jaw area shows some flash where the mold cracked. All the teeth are there and should clean up. Not sure if it cracked due to thermal shock with the temperature fluctuations or burnout stress.
    [​IMG]

    The grainy texture was definitely a WTF moment. I think its sawdust. I had to switch over to a large pressure pot for vacuum investing instead of my vacuum table because of the flask size. Instead of releasing the pressure at the pump, I hit the valve on the top of the pressure pot and sucked saw dust into the mold. Its an interesting effect but not what I was looking for. We'll see if it grinds off ok.
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    Unlike the burnout, the casting itself was uneventful. I poured about 3 minutes after the last ingot melted. I used "new" ingots that I got from Art awhile back.

    The mold was not completely cooled. I was able to quickly transfer it to the vacuum stand with welding gloves on. My gloves were toasty but not bad. I'm guessing the kiln was off for 6 hours but closed in before casting.

    The vacuum stand worked well. I've got two pours on it. I'd like to have a longer internal chamber for long flanged flasks but it works well for non perforated ones on top.

    Lessons learned (Notes for next time.)
    Get a better blower for the furnace. I'm using two hair dryers but I don't have any top end. I'm going to try a 12v bilge blower with a speed controller next.

    Rewire the kiln for 220. Its an old Cress kiln that I don't mind using for burnout but my setup is error prone and manual. I'm looking to add 220 coils and a ramp soak controller. I've got 220 service with 50 amps for welders and only 20 amps on 110 though.

    I could use with another set of tongs. Getting the large flasks out of the kiln was exciting on an earlier pour.
     
    Tobho Mott likes this.
  2. Jason

    Jason Gold Banner Member

    Where's a photo of the face of this thing?
     
  3. Billy Elmore

    Billy Elmore Silver

    Pretty damn cool!
     
  4. Mach

    Mach Copper Banner Member

    Thanks Billy. Sorry Jason, I thought that I posted these already. Here's the face before cleanup:
    [​IMG]

    A little work with a dremel and files to rough it in. On to polishing this weekend.
    [​IMG]
     
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  5. Jason

    Jason Gold Banner Member

    Yeah, now we're talking! He looks cool and should be easy to clean up any of those issues. I need a pair of those for my throttle levers in the airplane. Somehow I doubt the feds would approve that modification!
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Good result Mach. Should clean up and polish well.

    Though you may have indeed ingested some saw dust, to me the size and location of surface finish irregularities look like your investment wasn't sufficiently degassed. The flaws are eruptions into the investment and I don't think dust could have done that. They seem to be concentrated on the top surface of your mold which is where buoyancy would tend to make entrained air gather. Might be aggravated by surface tension on the wax pattern so application of a surfactant before investment may also help. -Just thoughts for next time.

    Good job!

    Best,
    Kelly
     
  7. Billy Elmore

    Billy Elmore Silver

    I think gas and foreign matter would leave inclusions and not protrusions...voids in the mold or metal penetrations cause protrusions.
     
    Jason likes this.
  8. Jason

    Jason Gold Banner Member

    Billy is right, if I have voids in my ceramic shell, it will leave "proud" areas on a casting. Easy to knock them off as opposed to filling in craters. That always sucks.
     
  9. Mach

    Mach Copper Banner Member

    I was thinking saw dust because the voids are angular and barely stuck to the surface. They reminded be of rock salt on a pretzel. They could be collapsed bubbles that we're caused by the investment partially setting during vacuuming.
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    The other thing that was puzzling was some seemed to float and others settled. Anything organic like sawdust would have burnt out. The orientation of the investment was upside down to pour. The red arrows are the angular defects. The blue arrows are bubble vugs. There was one small one of the back of the lower jaw. Another bubble was in the blind hole on the back of the skull marked in blue also. Those two locations and the teeth are where I've seen bubbles when casting this before.

    [​IMG]

    Its kinda funny. I first started trying to cast this thing 5 years ago at a local hackerspace where we had limited control over burnout and pouring. That caused me to find AA and build my own furnace. 5 year later, here we are. I don't have much in the way of speed but I got stubborn for years. :) Here's the first cast. I've hopefully learned a little more since then. I'll invest some more when I get my kiln fixed. I'll give the surfactant idea a go then.

    [​IMG]
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Based upon your post, I thought you ingested saw dust after you had invested the pattern in your flask thus my comments. Are you saying it occurred before you invested the mold? If so then debris on the pattern before investment could cause eruptions on the casting, but even so, it still looks like air bubbles and aggravated by surface tension. Before I started dipping foam patterns in surfactant prior to dipping them in slurry I would often get similar (but finer) beads on the casting surface.

    Best,
    Kelly
     
  11. I don't have anything to contribute to the technical side of this project: I just wish I had one of those castings to fit to the T-bar shifter of my first car, a 1973 XB Falcon coupe.

    XB-3.jpg
     
    Jason likes this.
  12. Mach

    Mach Copper Banner Member

    During - I vacuumed it, sucked in sawdust that was on the pressure pot lid and it went into the unset investment. I could see it on the bubbles on the top of the flask and tried to scrape it off but doesn't appear to have got it all.

    I can make that happen. It may take awhile and you'll have to drill and tap it.
     
  13. Sadly I had to sell it: the rust was getting into it and I didn't have the time nor money to do a full restoration. Still it was fun to have a "V8 Interceptor" for a few years, it turned out to have originally been an unmarked police car with heavier duty stiff springs on the rear and a diff ratio that gave it good acceleration.
     
  14. Jason

    Jason Gold Banner Member


    Why did you guys get all the cool cars in the 1970's. We got ugly shit here in the states! Even with that ugly 2 tone paint job, that thing has some excellent roof lines. I love that small side window.
     
    Mark's castings likes this.
  15. Mach

    Mach Copper Banner Member

    Steady....
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  16. Jason

    Jason Gold Banner Member

    That's pretty cool too... but according to wiki, they made less than 1000 XB Falcons.
     
  17. I could be wrong but I think they made more than that, 1000 might be the XB GT numbers, I seem to recall either 3000 or 6000 coupe's. The truly rare Falcon was the XA GTHO Phase 4 of which only three or four were made, they sell for a million or so. Mine originally came with with metallic brown paint and the vinyl roof that some said was used to hide panel ripples where the roof welded to the rear quarter panel during production. It had weird options and was in the Brisbane floods of 1974 as it had a high tide mud mark halfway up the door skins ( I bought it in Brisbane ). A cop pulled me over once and told me the original number plate showed it was an ex police car....it had weird suspension options and the diff ratio would be ideal for racing around streets but not that fast on the highway. You could fit 295 (12") wide wheels on the rear under those wide hips. The neighbour two doors down had an emerald green 1972 Mach 1 Mustang, the cops used to focus on him a lot so it lived in the garage most of the time.

    Everyone who owned an XB dreamt of modifying it into a Mad Max pursuit special:

    V8 XB.jpg

     
    Last edited: Jul 24, 2020
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