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Thread: Valve Shroud Pattern via CNC

  1. #1

    Valve Shroud Pattern via CNC

    Its been awhile since I have posted anything. Its amazing how life can get in the way! This past October I acquired a Tormach PCNC 440 mill for my
    Drafting & Engineering Technology classroom. Having never worked with CNC its been an interesting learning experience both for me and my students.

    We currently have a couple of projects going - the big one is milling out all the parts for a small steam engine. Every year the University of Maine at Orono's
    first year Mechanical Engineering Technology students build steam engines - the idea being to familiarize them with machine processes and to
    teach the application and importance of fit and tolerances. At the end of the year they hold a contest were they run them on compressed air
    and measure which engines achieves the highest rpm at a set pressure. Anyway... my students embraced the project and were hoping to compete against
    the college students but we won't be done in time.

    Another project is creating a set of patterns and core boxes for the valve shrouds for a Wisconsin Model 'A' T-head engine in a 1917 FWD truck. The "Client"
    provided us with a original part to use as a go-by. From this we created a 3D model and generated a modified file for the pattern which includes
    allowances for shrinkage, draft, machining and of course the core prints. We used Fusion 360 to generate the tool paths and then post processed it to
    Pathpilot (Tormach's proprietary controller).

    Here is the first trial run. We have since optimized some of the tooling and paths to address a few issues apparent in the photo. I could have easily turned the required two halves in the lathe but I wanted to
    explore the 3D capabilities of the mill. For stock we used a chunk of 2x4. (note the knots) For the final patterns we will use laminated hardwood. Next we will try the core boxes.

    Best regards,


  2. #2
    Moderator DavidF's Avatar
    Join Date
    Jan 2012
    Wilmington DE
    Welcome back. The test pattern looks great, I'd be tempted to primer it and use it.
    Congrats on the 440!
    A calm sea does not make a skilled sailor...

  3. #3
    Are these more or less the same as the shrouds we did with the borrowed pattern? I think I still have the banged up originals you left me, haven't melted them down yet...
    Vade Libram Harenae.

  4. #4
    Hello Peter,

    They are similar but much smaller and a bit different shape.


  5. #5


    Over the past couple of days we milled out the patterns and core boxes using the
    Tormach PCNC 440. To say I am pleased would be an understatement!

    We used pine for the patterns - it worked ok but a harder wood would have been better. There are a few areas were due to the straight grain
    and soft nature of the wood it flaked - for lack of a better term. For the core boxes we used some well seasoned Hemlock which cut very nice.

    Now I just need to mount the patterns on a backer board, fix a couple of nicks and seal them with shellac. The core boxes will
    be joined together in a frame and sealed with shellac as well.

    I would say they came out adequate. In the background you can see the original part we used as a "go-by".
    Last edited by Tharper; 06-01-2017 at 12:19 AM.

  6. #6
    Here are the finished pattern and core boxes. All I need to do is add some cross pieces to the bottom of the core boxes.

  7. #7
    Senior Member Jammer's Avatar
    Join Date
    Nov 2007
    Very nice.

  8. #8
    Senior Member
    Join Date
    Dec 2010
    Vienna, Austria
    Blog Entries
    Nice pattern work. Look forward to seeing the finished castings.

  9. #9
    Very nice work. One curiosity question. Apologies if posted elsewhere and not sure if these will be CO2/SS, air set, or green sand cores, but how do you invest the cores? Fill the two halves, glue, and/or just place them in the mold? Was just wondering why the end with the larger diameter core print wasn't left open so it could be pack and strike off (and potentially gas) as one piece.

    My furnace build ----- I toil and fettle then foam turns to metal!

  10. #10
    Hello Kelley,

    Since I only make the patterns and relay on Oddduck to cast them I am not sure if I can answer your question adequately.

    The parts we are casting is actually a shrouds composed of two separate halves. When installed on the engine they are held together with
    circular spring clips. The cores will not be joined together in anyway. Using the setup that we have we can cast two halves per flask.

    Here is a photo of the original part (aka one half of a complete shroud.)

    Here is a set fresh out of the sand Odduck cast for my several years ago - these were for a much larger engine.

    I hope this helps explain it.

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