Ditching lathe and using VMC with rotary table
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  1. #1
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    Default Ditching lathe and using VMC with rotary table

    I'm asking around and trying to get an idea if this would be a good alternative before I present it.

    We lathe grey/ductile cast iron parts that have a circumference up to 2 feet and are relatively flat/stubby with features like tenons, bearing bores, and shaft holes, etc.: all needing to be concentric to withing a couple thousands between each feature for the tighter stuff; about 4-5 thou for the looser stuff. Then things like the bearing bores need to have a diameter that's tackling less that a thou on tolerance.

    Then we second OP all of these parts in a VMC to add bolt holes, drain ports, grease ports, etc.

    Wondering if it would be easier to lay a rotary table flat on the table; not standing upright like most? Add a chuck and now I can mill-turn parts so features are relatively concentric. Others were wanting to circle interpolate these features and I know that's not a good idea.

    The idea would likely work in a large lathe with live tooling but figure I have more room to grow in a mill with a rotary. Plus, like I said, we just machine short, flat parts. Nothing long like shafts. Figure a mill with a rotary is also cheaper to maintain than a large lathe with live tooling.

    I figure surface finishes would change but that's not a bid deal.

    Now we can essentially ditch lathes and just have VMC's. I effectively reduced some of our multiple OP parts to two OPs (one OP for each side verses two OPs in the lathe and 2 OPs in the mill).

    Certainly I'm not the first to think of this?

    Thanks

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    Good idea, but your rotary table will not spin fast enough to function as a lathe. You would only be using it to position the part if you didn't have enough Y-travel.

    Mazak makes a 5-axis machine that has an 1,100 RPM rotary table integrated into it called a Variaxis i-700T that sounds like it would be perfect for your parts. We bought one last year.

    VARIAXIS i-700T
    Attached Thumbnails Attached Thumbnails variaxisi-700t_smoothx_800-600jp.jpg  

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    Well, OP threw me a loop using circumference as a measurement... 24" cir = 7.64" diameter. Easily handled in most 'real' cnc lathes... If you are machine shopping, Philabuster has the right idea, but that machine is going to be pricey..

    I don't know of too many rotaries that can 'turn', and if they do, they are $$$ so might be cheaper to continue 2-3 ops... food for thought.

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    Derp, is it Friday yet? I meant 24 inch diameter, not circumference.

    I wouldn't use the rotary to turn like a lathe spindle. Just whatever rotation needed with whatever endmill I was using to machine the tenon, bearing bore, etc. I'd essentially only be using the X, Z, and A axis to do all my machining and in reality, the X axis would move a max of the parts radius. It also wouldn't have to rotate fast since I can take a bigger DOC with an endmill versus mutliple passes on a lathe. An endmill would clear most of the cast features so I'm not limited to lathe tooling. Assuming it's an even match on CT but now I don't have to remove a turned part and put it into a mill to do my second OP. Now I'm saving time on handling.

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    What is wrong with milling the parts concentric? Any decent mill should have no problem with this.

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    Sorry, forgot to mention roundness. We do have roundness requirements. Figure a rotary table is better at roundness than interpolation. Technically, concentricity would work with interpolation even if the roundness was out.

    I was told that a previous engineer tried to interpolate the round features like tenons and bearing bores and it didn't work.

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    Quote Originally Posted by rbmgf7 View Post
    I was told that a previous engineer tried to interpolate the round features like tenons and bearing bores and it didn't work.
    Maybe you should try a machinist instead?

    It just doesn't work like you're thinking. Sure, lathes make round parts, but mills can do the same thing. You just need the right machine and skill to do it (not really hard at all).

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    Quote Originally Posted by Garwood View Post
    Maybe you should try a machinist instead?
    I bounced this idea off of most of our machinists and they agreed and thought it was a good idea. I just want to reach outside our walls to see if this has been done before since it's not exactly conventional. But I thought machinists were supposed to think outside the box? I won't put down the last engineer that tried since he did his best with what he had. It's likely he left because of the bureaucracy we all face in the corporate lifestyle.

    Wish in one hand and you know what to do in the other. Getting a new machine won't happen which is why I'm seeking this alternative.

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    Quote Originally Posted by rbmgf7 View Post
    I bounced this idea off of most of our machinists and they agreed and thought it was a good idea. I just want to reach outside our walls to see if this has been done before since it's not exactly conventional. But I thought machinists were supposed to think outside the box? I won't put down the last engineer that tried since he did his best with what he had. It's likely he left because of the bureaucracy we all face in the corporate lifestyle.

    Wish in one hand and you know what to do in the other. Getting a new machine won't happen which is why I'm seeking this alternative.
    What machines are you trying to do this on? Any decent Jap iron will do that since the beginning of time.

    One of my machines came from a real big co and it was making parts a lot like what you describe, but from chromoly steel. Did it for 25 years 2 shifts a day. Was only replaced to run the same job on a monster HMC.

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    Several machinery manufs, make a "Bullard with a live head"
    (actually they have toolchangers)

    and have the ability to index the chuck for accurate placement of bolt holes, etc.
    And probably even helical interpolate.


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