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35340Re: [hobbicast] Engine crankcase

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  • Lyle Landstrom
    Nov 1 11:22 AM
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      I gotta ask. If you have cnc capability, why not just
      machine permanent molds or diecast molds from steel
      and pour the aluminum directly into them? You could
      machine a cylindrical sprue and use a steel rod
      fitting into the sprue as a primitive pressure
      If your running a program like solid works, you can
      design the whole thing, coreboxes and all and convert
      to G-code.

      You can, and some foundries do, make aluminum machined
      molds for wax. But you need to think about how the wax
      part will be withdrawn from the mold without breaking.
      We just finished a run of motorcycle heads here last
      summer and I had a terrible time keeping the wax fins
      from breaking when I tried taking them out of the
      mold. And my mold was rubber. I had to melt and
      re-attach fins back on quite a few of them.

      Depending on the shape of the part you may need to
      make ejection pins for die casting your aluminum
      engine cases. You can buy premade die pins spring
      loaded from wholesale tool for pretty cheap.

      1000 psi is way way too much pressure for wax
      injection. 20 - 30 psi is the highest I've ever heard
      of. But that's in the jewelery industry

      Good luck with the experiments.


      --- hobbicast@yahoogroups.com wrote:

      > There are 4 messages in this issue.
      > Topics in this digest:
      > 1. Model engine crankcase.
      > From: tom hollis <cimarron_06@...>
      > 2. Update on my furnace
      > From: "Jeff" <janderson@...>
      > 3. Re: AL356 casting for Model Airplane
      > crankcases
      > From: david cam <davidcam406@...>
      > 4. Re: Re: AL356 casting for Model Airplane
      > crankcases
      > From: david cam <davidcam406@...>
      > Message: 1
      > Date: Mon, 31 Oct 2005 14:51:26 -0800 (PST)
      > From: tom hollis <cimarron_06@...>
      > Subject: Model engine crankcase.
      > Dave Cam,
      > A little terminology clarification first. 1. I
      > assume that when you say mold you are talking about
      > an actual model of the part? Then you will cut a
      > mold from the model to inject the wax into. 2. I
      > also assume that you will cast these parts yourself?
      > If indeed you will cast this yourself, do a trial
      > run with a model piece, say a round rod of a
      > measured length, say 2". Make the rod, measure it.
      > make a mold out of rubber/silicon or whatever you
      > want to use, inject the wax you want to use, cast
      > the part and measure the resulting rod. Original
      > length divided by final length is the percentage of
      > desired size that the model needs to be. That is
      > the only real way to know what you are working with.
      > If you are not going to cast this yourself pick a
      > foundry and use their desired wax and their
      > shrinkage factors. Also make sure they will accept
      > and be responsible for results on waxes that you
      > shoot yourself.
      > Wax injection pressure is not terribly important as
      > long as it is the same every time. In industry they
      > use aluminum molds and inject at higher pressures to
      > enable using cooler wax temperatures that result in
      > less shrink, among other things.
      > I actually prefer using rubber molds with any of the
      > silicone based releases the jewelery supply houses
      > sell because the mold release serves as a
      > debublerizer on the wax during investment. The
      > silicon mold compounds work fine also.
      > Yes, waxes vary a lot. Enough to cause problems if
      > you are trying to hold tight tolerances.
      > contact me off line if I can help more.
      > Tom
      > Tom Hollis
      > cimarron_06@...
      > ---------------------------------
      > Yahoo! FareChase - Search multiple travel sites in
      > one click.
      > [Non-text portions of this message have been
      > removed]
      > Message: 2
      > Date: Tue, 01 Nov 2005 03:20:37 -0000
      > From: "Jeff" <janderson@...>
      > Subject: Update on my furnace
      > Well, time for an update on the progress of my
      > effort to melt lots of
      > aluminum. Long note follows.
      > The last time I wrote, I reported on my 1 ΒΌ inch
      > burner from Mike
      > Porter's book. With Mike's and others help, its
      > running very well and
      > in control. I've also take some pictures (static so
      > far, no shots of
      > flames) and posted them to the pictures section of
      > Yahoo group
      > hobbicast1 under Jeff Anderson's Furnace.
      > I just finished the furnace for this burner, also
      > with lots of help
      > from these lists and put the heat to it this
      > weekend! Boy that burner
      > throws some heat, vitrified the lining quite nicely!
      > Pictures of the
      > furnace are at the site mentioned above.
      > Some details on the furnace.
      > - Its designed around a #35 B crucible or a #50 A
      > crucible. It has a
      > 12 inch inner chamber, and 4 inches or so of
      > refractory.
      > - The outer insulating layer is 2.5 inches thick
      > made to the recipe
      > on Lionel Oliver's BackyardMetalcasting.com website.
      > A mix of
      > Portland cement, fireclay, sand and Perlite. Don't
      > know how high a
      > temp it can stand, but it seems stable and strong
      > since it set. It's
      > faced with 1.5 inches of a higher temp recipe from
      > these forums, a mix
      > of grog, kyanite, clay and wood dust. Seems OK so
      > far, but it wants
      > to shrink away from the outer layer a little. Only
      > time will tell.
      > - The furnace body itself is split into three
      > halves. The top is
      > mounted on a cam operated pivot to allow it to move
      > up and then swing
      > away allowing full access to the crucible for
      > loading, etc. The middle
      > portion is a hollow cylinder mounted to a wheeled
      > carriage which can
      > be winched up and down the frame. This allows the
      > hot crucible full
      > of melted metal to be accessed directly instead of
      > having to lift 100
      > lb or so of hot crucible and Al several feet
      > straight up (seemed like
      > a sure back ache or spill to me!) before moving to a
      > pouring position.
      > The bottom portion is fixed to the base of the
      > lifting frame and
      > contains the tuyere for the burner and a drain hole
      > for oops.
      > - The frame is designed with a frame and winch for
      > lifting the body, a
      > base with three removable extension legs to provide
      > a wide tripod
      > support while melting, and wheels for
      > transportation.
      > Now, some questions if I may.
      > While operating the burner in the air with its
      > stainless nozzle, I had
      > no trouble with flame stability. In the furnace,
      > the tuyere is
      > designed so the refractory acts as the nozzle. But,
      > I had trouble
      > with the flame stability. As the tip of the burner
      > tube heated up,
      > the flames wanted to climb back into the tube and
      > the thing would
      > start chuffing. I think this was because the burner
      > tube got so hot
      > that it self-ignited the flame in the tube. I now
      > think this is
      > because I didn't follow the instructions in Mike
      > Porter's book and
      > left the space at the end of the tube. This
      > directly transferred heat
      > from the refractory to the tube till it was redhot!
      > The book on page
      > 27 says to move the spacer back away from the tip so
      > you don't get
      > that heat transfer. Any thoughts, if I move the
      > spacer back will that
      > solve the problem?
      > Next, being cheap (and being an hands on engineer
      > who really liking a
      > challenge), its time to design and build the lifting
      > and pouring shank
      > for those big crucibles. I've looked at the designs
      > at Budget Casting
      > Supply and Mifco so have an idea of the features I
      > want to build in.
      > But, there are a couple of things that aren't
      > evident from the
      > pictures, so I'm seeking some guidance from these
      > forums. First, how
      > long do I want to make the shank handles, ie how far
      > away do I want to
      > be from the hot crucible? Second, where on the
      > crucible do I want the
      > axis of the handles to fall? Obviously it needs to
      > be
      === message truncated ===

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