Cast iron crank

Discussion in 'Pattern making' started by ESC, Oct 23, 2017.

  1. ESC

    ESC Silver Banner Member

    I started on a pattern to cast a crank for the 1/3 scale smallblock. The original steel crank took 300 hrs to make and I wanted to cut the time down a little. I am in the process of making a follower and will have to add some additional draft where the counterweights are deep, but with a straight vertical pull I believe it will draw from linseed oil bonded sand.

    IMG_20171023_161333.jpg

    P1010589.JPG
     
    Last edited: Oct 24, 2017
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Tuned in, looking forward to seeing your progress...
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That should be a fun one. When you say the first one in steel took 300hrs in steel, is this your second 1/3 scale engine?

    Best,
    Kelly
     
  4. ESC

    ESC Silver Banner Member

    My first was a cast iron engine, then I used a double shrink pattern to pour an aluminum block which I will use the blower on. P3170619-1.JPG blockandheads.JPG
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    ESC = sand crab???
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes indeed. Alias/AKA Sandcrab......you got me. Nice to see you E.

    Best,
    K
     
  7. PatJ

    PatJ Silver

    Beautiful work.

    I think a crankshaft could be cast. Worst case you could make a couple of SS molds and cement them together.

    I saw a photo or video of Ford casting their 1960's vintage crankshafts vertically.
    Does not seem like a vertical cast would work, but obviously it did.
     
  8. ESC

    ESC Silver Banner Member

    I don't plan to use SS. I had a failed casting with the Indian heads in a SS mold that fused with the iron and created an unmachineable surface. I thought I had a photo, but PB might have eaten it. Checking back I made some comments then that I used a 60 mesh sand. Since then I have used Okie 90 and perhaps it was the first sand's refractariness (sp) that caused the failure. All my successes have been with the linseed oil bonded molds, but with the better sand. I am able to pour vertically and might be able to horn gate the mold, but I expect to pour conventionally the first time.
     
    Last edited: Oct 24, 2017
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    How many cranks are you planning to cast?

    K
     
  10. ESC

    ESC Silver Banner Member

    At least one. I'm also building a crankshaft grinder with a Themac tool post grinder so I will be able to grind away from the lathe.
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Seems like a good piece for expendable pattern casting. Having a one track mind, in an afternoon I think I could knock out the fixtures and a few patterns in foam and assemble them on an 1/8" rod. The rod could be extracted after molding/b4 casting or left and trimmed. Sprue and feed it right down the crank snout? May have to be invested, burn out, and vacuum cast to travel the length of the crank before freeze.

    Looks like fun. I cant cast iron but I'd make a few foam patterns for you if you supplied all the dimensional data and had a go at casting them.

    Best,
    Kelly
     
    Last edited: Oct 24, 2017
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    My one track mind jumped right into investment casting it as lost wax.. LOL
    I have yet to attempt cast iron in investment molds but it is on the to do list and I have the materials...
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There ya-go ESC, we have a volunteer ;)

    K
     
  14. ESC

    ESC Silver Banner Member

    At least one. I'm also building a crankshaft grinder using a Themac tool post grinder to keep the grit away from the lathe. This isn't a very good photo, but I use an old Craftsman table saw for a platform and then cast a sliding base that I mount on a dovetail with gib.
    I have done cast iron in lost wax and that is a possibility, but believe it or not the parting line of the crank is less complex than the water pump and should only need a decent follower and some good sand to pour in petrobond. The main challenge will be inclusions, but I screen the sprue and have had good luck controling the slag with the gates and runners.



    IMG_20171023_161616.jpg
     
    Last edited: Oct 24, 2017
  15. DavidF

    DavidF Administrator Staff Member Banner Member

    Hey now!!!
    Man he would be waiting forever for me to get a round tuit...

    ESC, any concerns about warpage???
     
  16. ESC

    ESC Silver Banner Member

    I don't think so David. I added 1% shrink to the length and journal diameter and it will have a lot of machine allowance when I finish adding draft. One thought is feeding from a large parallel runner with about the same cross sectional volume as the casting so they both cool at about the same rate.
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not to worry David. Having built the pattern and follower I doubt ESC will be having anyone horning in on his fun.....you need another project so I'll volunteer ya for something else.

    Best,
    Kelly
     
  18. ESC

    ESC Silver Banner Member

    Kelly, I might take you up on that. With your hot wire cutter it would be a piece of cake. I had also thought about lost foam but felt it would require several attempts and since I'm not set up as well for fine foam construction, I passed on that. I had thought that with the pattern I might be able to cast a mold in aluminum and then use the polystyrene beads to make a foam pattern. The mains are 1" and the rod journals are .750" and they overlap at the counterweights so there is a fairly straight path with just the filling of the counterweights themselves as a horizontal run. The crank is just over 7" long so with cast iron that is a short run and will have no problem filling. Cast iron goes faster, but fills the same as aluminum especially with a coated pattern.

    This also goes to HT1's question of detail. Surface finish is not an issue, but dimensional accuracy is critical over the length so the journals line up with the bearings.
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'm willing to have a go just to see how well it works out but would need a detailed sketch and a profile of the throws and the clocking of each. What's the stroke?

    Best,
    Kelly
     
  20. DavidF

    DavidF Administrator Staff Member Banner Member

    UT OH, things about to get real!!!

    Clocking could get interesting... Fortunately the journals are large enough to give you something to work with, like maybe using hexes or squares (depending on the degree of separation) to align the segments?
    I also wonder if it would be better to attempt it with a full length center segment (mains) to hold the crank true to the c/l... Yea one straight rod through the center to be cut of of the rod throw area after cast is what im trying to say...
     

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