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IndustryArena Forum > MetalWorking > General MetalWork Discussion > Holding round objects vertically!
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  1. #1

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    Holding round objects vertically!

    Hello guys and girls, I'm somewhat new to the art of machining so be gentle!

    Ive recently purchased a small 5 ton injection molding machine called a rabit 2/3 and I'm looking to build my first mold. Interestingly, these machine take a 3.15" round mold X 3" total thickness.

    Anyway, my question is how do you fixture and accurately locate a round object to be milled in a cnc. The mold halves need to be flipped to add features that match up with the other side. These need to be real accurate as you can imagine. I do have a touch probe that can locate outer bores and whatnot. I've gotten some 3.25" 7075 T651 aluminum that I am going to use as my stock. I asked the seller to include a mold with the sale of the machine so i could get an idea on how to make one. Attached are some pics of it, the platens, and a picture of my cnc machine that I built. Let me know what you guys like to do! I'm all ears and am eager to to learn from the masters!

    Thanks!
    -Will

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    The best way for that size of part is to make soft jaws for your vice. Can be steel or aluminum. Just chew out a pocket to hold the part. I normally close the vice on a couple of 1/4'' dowel pins, then make the pocket in the jaws.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3

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    Re: Holding round objects vertically!

    Thanks for the reply! How would you locate the part when it is flipped to know its true with the other side? Thanks

  4. #4
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    Quote Originally Posted by ypmcnc View Post
    Thanks for the reply! How would you locate the part when it is flipped to know its true with the other side? Thanks

    Not sure what you mean by ''true with the other side'', but you could certainly create a clocking feature or use a dowel pin to clock it.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5

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    Quote Originally Posted by Jim Dawson View Post
    Not sure what you mean by ''true with the other side'', but you could certainly create a clocking feature or use a dowel pin to clock it.
    Thanks for the reply!
    So for example, the mold features will be made on one side of the part. It will then need to be flipped over and things such as mounting screw and ejector pin holes will be milled. What are the options for accurately flipping the part and making sure the x and y axes line up still. It’s hard because it’s a round object with nothing to reference off of.

    There is the a part and b part of the mold. Everything needs to fit together like an accurate puzzle. But like I said it’s a round object so how do you line it up to be milled when flipped.

    Hopefully I’m explaining it right or maybe I’m not understanding. What would a clocking feature look like?

  6. #6
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    Clocking is locating a part radially, so this could be anything from a locating pin, to a flat on the OD of the part, even a bolt hole.

    I see in the picture that there are already locating pins and holes in one of the parts. Just do the work on the back side first, then use one of those features to locate the part in the fixture to carve out the mold cavity.

    I normally use a dowel pin in a reamed hole when something needs to be accurately located.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7

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    Re: Holding round objects vertically!

    Thanks so much for the advise! Really clears things up!

  8. #8
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    I'm happy I could help.

    About 80% of machining is work holding and setup. You are only limited by your imagination.
    Jim Dawson
    Sandy, Oregon, USA

  9. #9

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    Re: Holding round objects vertically!

    Jim, so i got to thinking (oh no). So you would clamp the round stock vertically in a vise using the soft jaws, mill the features on the back of the mold along with the dowel pin through holes. Once the part is ready to be flipped, you basically make a small fixture plate with the male dowels sticking up to receive into the dowel pin through holes.

    The question I have is: How would you attach the mold to this fixture plate? I guess you would bolt the fixture plate down with the dowels sticking up, to the table. But how do you attach the mold. Nothing can be on the top surface because it needs to be face milled. Again, thank you for any wisdom Master Jim.

  10. #10
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    You machine a mating dowel pin hole into the soft jaws for locating while you are making the soft jaws. That way you only need to flip the part over and tighten the vice again. I would probably start by machining both faces of the part, before starting any other work on them. In fact I would most likely make several blanks and face them on the lathe and have them ready to go for the next mold. The pocket in the soft jaws only needs to be 1/4'' deep or so.

    You also need a locating feature off of the part area for locating your zero in the case of a power fail or some other disaster. This could be the edges of the fixed side of the soft jaws, or a dowel pin, even just a divot with a center drill that you could locate with the pointy end of your edge finder. Once you zero your machine to the soft jaws, you would not turn it off until you were done to insure you maintain the location through all of the parts.

    EDIT:

    Also mill a trough around the ID of the pocket, maybe with a 1/4'' end mill about 1/8'' deep or so. This breaks the corner of the bottom of the pocket so your part will seat properly and allows some clearance for any crud that gets in there.
    Jim Dawson
    Sandy, Oregon, USA

  11. #11

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    Jim that genius! I have to admit though, I do not follow the part about the pocket in the soft jaws and a trough around its I.d. (I’m more of a visual learner but I try haha). Your saying to have two pins sticking up vertically on each soft jaw so when the vice is tightened it “locates” the part. However, where does the pocket come into play? The sharpie in the picture is where I think you’d want the pins. Thanks again

  12. #12
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    I am not explaining myself well. Let's try pictures

    I just arbitrarily placed a .250 dowel pin hole at the center of the fixed jaw side, you of course would want to place and size it to fit your part.



    A section view showing the clearance trough in the soft jaws
    Jim Dawson
    Sandy, Oregon, USA

  13. #13
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    Re: Holding round objects vertically!

    Quote Originally Posted by ypmcnc View Post
    Hello guys and girls, I'm somewhat new to the art of machining so be gentle!

    Ive recently purchased a small 5 ton injection molding machine called a rabit 2/3 and I'm looking to build my first mold. Interestingly, these machine take a 3.15" round mold X 3" total thickness.

    Anyway, my question is how do you fixture and accurately locate a round object to be milled in a cnc. The mold halves need to be flipped to add features that match up with the other side. These need to be real accurate as you can imagine. I do have a touch probe that can locate outer bores and whatnot. I've gotten some 3.25" 7075 T651 aluminum that I am going to use as my stock. I asked the seller to include a mold with the sale of the machine so i could get an idea on how to make one. Attached are some pics of it, the platens, and a picture of my cnc machine that I built. Let me know what you guys like to do! I'm all ears and am eager to to learn from the masters!

    Thanks!
    -Will
    You don't have to use round inserts, ( what you have are very rough not made by a mold maker ) they can be square or any shape you want to make them

    There is always a center hole in both Halves of the mold if injected through the center of the mold ( 1 ) A side will have the sprue hole, and the B side will have an ejector pin hole or Cold slug hole

    You have in your case 2 locating pins these holes also go right through the mold, this can be used to indicate the location of the mold or the best way for round parts is to mill ( 2 ) flats on them and then you just indicate the center hole
    Mactec54

  14. #14

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    Hey guys thanks for the replies. I’m trying to think about what the best option is giving the limitations of both machines and my intentions. The point of going round is I guess to have more molding surface (and room for water lines). Also, I already bought the 7075 round stock haha. Although it’s a good idea, the machine is quickly running out of Z axis mounting the mold on top of soft jaws.
    So I got to thinking again.... What about getting a 3/4 x 4 x 5 aluminum block and making a fixture plate out of it. Two pins sticking up would receive the mold through holes. On the outer diameter of the 3” mold would be those mitee-bite fixture clamps. I’m no artist but maybe you get the idea.
    What do you think? Thoughts? Concerns?

    Edit: Also, I was worried about mitee bite Pressing up against the very bottom which could potentially damage the face?

  15. #15
    Community Moderator Jim Dawson's Avatar
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    Re: Holding round objects vertically!

    There is really no reason for the part to stick up above the vise too far. You just put the pocket inside of the vice for the most part.

    But I do like your idea of building a fixture that bolts to the table. If you have pre-faced the parts, then you can clamp them from the top, a couple of bolts and washers work well for this, I rarely use my clamp kit.

    Let me show you some soft jaws I have built for my work holding adventures.















    Jim Dawson
    Sandy, Oregon, USA

  16. #16

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    Re: Holding round objects vertically!

    Jim, that is an impressive amount of soft jaws. Thank you for sharing.

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