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Technical Shaving piston tops ... mill or lathe ??

Discussion in 'The Hokey Ass Message Board' started by winr, Jun 12, 2024.

  1. Rich796
    Joined: Nov 18, 2023
    Posts: 36

    Rich796

    Most piston vises I've seen, are vee jaw based. So they don't limit you to one piston size per fixture.
     
    winr and Unkl Ian like this.
  2. distributorguy
    Joined: Feb 15, 2013
    Posts: 113

    distributorguy
    Member
    from MN

    I'll tie 2 pistons together with 3 wrist pins, then clamp down on the outer ends of the wrist pins, if the skirts are square to the table. If they're not, some times I flip them over just to square them up a few thou. Quick and dirty but I've never had them come loose.
     
    winr likes this.
  3. Rich796
    Joined: Nov 18, 2023
    Posts: 36

    Rich796

    I was referring to the post directly above mine. Where it sounds like he just has stuff sitting on top of the vise. Rather than clamped in the vise or secured to the table.
     
    winr likes this.
  4. There’s a member here that has posted on this thread already .
    His company does this work,,,,,,he recently did the tops of my DeSoto pistons .
    They turned out top rate !
    Very reasonably priced work as well,,,,I was very happy with the cost and the quality !
    I don’t want to volunteer him,,,,,,,but if you ask him,,,he might help .
    Look back through the posts here,,,,,you might figure out who it is .

    Again,,,Thank you to my friend here that worked my pistons ! (You know who you are ),,,There are wonderful people here on the Hamb,,,,top rate .

    Tommy
     
    winr and Budget36 like this.
  5. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,887

    ekimneirbo

    Guess I didn't explain it very well. Think about it like this..........The pipe ring simply sets on top of the vise jaws. This is assuming someone has a decent vise with level top surfaces. Anyway, the ring simply sets on top of the vise and the piston is inserted into it until the piston ring comes to rest on the pipe ring.

    The piston skirt will be sticking out the bottom of the ring and you simply tighten the vise against the sides of the piston where the wristpin goes in. That way no pressure or marring should occur on the pistons skirt.

    Loosen the vise ....remove the piston and just insert the next one and retighten.

    As for the V shaped piston vise........if someone has one, it should work. I modified a vise to put valve reliefs in pistons. Its really just about finding a repeatable method of holding a piston without damaging it. Thats what machinists do, figure out how they can make the machines they have do what they need to do. If you are going to do a lot of pieces they design and make special fixtures so locating and changing parts can be done efficiently. When doing one part or a few parts, setting the job up often takes way more time than the actual machining process.
     
    winr likes this.
  6. Adriatic Machine
    Joined: Jan 26, 2008
    Posts: 701

    Adriatic Machine
    Member

    I’ve done this on a lathe using custom jaws. Once you get into the habit of using machinable jaws you open up a whole new world of possibilities.

    Doing this on a lathe makes it infinitely easier to deburr and preferably lightly radius the top edge of the piston.
     
  7. Beanscoot
    Joined: May 14, 2008
    Posts: 3,421

    Beanscoot
    Member

    Holding them in a milling vise at the piston pin area, I'd be worried about them moving when making the cut. It will be hard to hold them tight enough without crushing them.
    It's no fun when a part moves as it's being machined!
     
    winr likes this.
  8. Unkl Ian
    Joined: Mar 29, 2001
    Posts: 13,509

    Unkl Ian

    Imagine the pistons are custom made, "semi finished",
    and it takes 6+ weeks to get another set.
    Today is Monday, the domes and valve notches have to be modified,
    so you can race this coming weekend.
    AND you only get 2 weekends out of a set of pistons.
     
    Last edited: Jun 16, 2024
    winr likes this.
  9. Ericnova72
    Joined: May 1, 2007
    Posts: 664

    Ericnova72
    Member
    from Michigan

    Every time I've done the dished cut to a flat top deal, it's been with a 3 or 6 jaw chuck on the lathe.
    Put 6 to 8 wraps of masking tape around the ring land area to both protect them and it gives you a place for each chuck jaw to clamp down but not have to worry about pressing the small amount of taper in the skirt or collapsing the skirt.
    You don't have to clamp it gorilla tight, you're only cutting aluminum and you don't have to take it all in one cut.
    Doesn't matter if the piston runs concentric, since I'm not leaving any material on the crown to form into a dome, just cutting a flat top.
    All I have to indicate is face parallelism of the stock machined rim around the existing dish.
    Easy peasy, done it several times with SBC 400 forged pistons, back when there weren't any longer than stock rod pistons even made.
    I cut the TRW forged replacement piston with an .083" dish into a flat top, for use with longer 5.7" instead of the stock 5.565" connecting rods.
     
    Unkl Ian, hotrodA and winr like this.
  10. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 5,755

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    I took some pictures of my piston vise. I do not remember the company that I bought it from - Perhaps Williams Lo-Buck tools? It requires a unique pin arbor for each pin diameter. I have an arbor for the most common pin diameters I've needed, .912", .927", .975". The whole fixture should be simple for a machinist to duplicate. The end of the pin arbors have a tapered hole that a hex Allen bolt with a machined conical head that expands when tightened in the arbor and holds the piston securely. Surprisingly securely.
    To be clear, the flat surfaces of the heavy walled angle iron anchor plate have been machined flat and square.
    I must admit that I was skeptical when I first tried it, so I took light cuts, being worried about chatter. But as you can see in the attached photos and my previous post the machined surfaces are very smooth.
    To set it up I indicate the top of each piston in four spots to insure it is level. I can also set the piston on an angle if I need to machine valve pockets, as shown.

    piston vise 1.JPG piston vise 2.JPG piston vise 3.JPG
     
    Last edited: Jun 17, 2024
    bobss396, winr, Deuces and 2 others like this.
  11. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,887

    ekimneirbo

    The pipe ring should help prevent movement and the top surface of the piston is only a short distance above the ring, so there would be very little leverage. The cut could be made with the cutter moving from jaw to jaw rather than with the plane of the jaws. Being the piston is most likely aluminum and a light cut is being taken, there should be very little chance of movement.............but like any machining set up, its always a possibility that someone will mess up.

    Putting an oval shaped piston in a round 3 jaw chuck requires things to be done to protect the surface of pistons sides and any coating that may be applied. Tightening the chuck jaws will require good judgement on how tight. The same idea of using a top ring to square the part in the chuck could be utilized and help repeatability. People do it, so it does work.

    It's basically a matter of what machinery someone has available, and where they feel comfortable gripping their piston. In either case, not gripping the piston tightly enough will cause a problem......and gripping it too tightly can also cause a problem. From my perspective, I think there is less chance of damaging the surfaces by gripping the piston at the piston pin axis.... but I respect that others will feel differently.:)
     
    winr likes this.

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