VMCs. Traveling column VS moving tables for X axis.
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    Default VMCs. Traveling column VS moving tables for X axis.

    VTCs seem to have longer X axis in a given footprint, compared to moving table types. Just curious about your thoughts. I have 2) VTCs with 65X x 30Y and my oldest VTC 30C fits through a 120x120 inch door. Almost 30" under the spindle.
    Why moving table more popular?

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    Most traveling column machines have pretty poor rigidity. MTB's generally get a much better performance/price ratio out of table/table machines. The best of both worlds would be a really robust bridge mill, but those tend to be massively expensive relative to machines with a moving table. Look at the sticker price on some of the 40x20 bridge style machines for mold making.

    There are of course some interesting compromises, like some Okumas, Makinos, and Matsuuras that are built like a wall, so the X axis travels on a column with a Y axis that slides through a portal in the wall. I don't think that design has a huge space savings though, it's just a cost/performance thing.

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    Traveling table seems like a better balance of speed and rigidity for a given mass and HP to me.

    I've looked at a lot of traveling column aerospace machines with around 16" Y and 20+ feet in X. The only smaller traveling column machines I have seen are Mazaks and they strike me as pretty whimpy.

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    My guess would be price/cost to manufacture.
    I don't think the structure of the VTC is narrower. As a matter of fact, I bet it is significantly wider.
    But, the enclosure on a regular C-frame VMC needs to be a lot wider to accommodate the length of the table at the X extremes.
    Where the H-frame only needs to accommodate the width of the spindle.
    It is probably cheaper to make the table move X on a saddle, than the whole spindle move X. That is my guess anyway? IDK? Just a guess.

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    Quote Originally Posted by Garwood View Post
    Traveling table seems like a better balance of speed and rigidity for a given mass and HP to me.

    I've looked at a lot of traveling column aerospace machines with around 16" Y and 20+ feet in X. The only smaller traveling column machines I have seen are Mazaks and they strike me as pretty whimpy.
    Traveling table does not seem rigid to me at all.

    Are we talking traveling column like a Brother pallet-changer? Or H-frame like an Okuma Genos?

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    Quote Originally Posted by boosted View Post
    There are of course some interesting compromises, like some Okumas, Makinos, and Matsuuras that are built like a wall, so the X axis travels on a column with a Y axis that slides through a portal in the wall. I don't think that design has a huge space savings though, it's just a cost/performance thing.
    This is what I picture when somebody says traveling column. Is there another design structure I am not aware of?
    I mean sure, I've been around a few gantrys. But, I don't think that is what the OP was referring to.

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    Less mass for a moving table...it can hang over while a column need a heavy table, heavy suppory under the vtc and heavy casting for the VTC rigidity. The fastest cnc in the world is a Mazak SVC which can be found in 120 inch to 200 inch rapiding at 4700ipm with linear drives. Makes a lot of great machine tools look like dinosaurs. They run 500K+

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    Quote Originally Posted by wheelieking71 View Post
    This is what I picture when somebody says traveling column. Is there another design structure I am not aware of?
    I mean sure, I've been around a few gantrys. But, I don't think that is what the OP was referring to.
    Yes. What I would consider a true traveling column has a completely fixed table. The spindle and Y axis ride on a saddle that travels back and forth on the X. This is a very popular design among European builders. It's also the same design used in the infamous Mazak VTC machines.

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    Interesting thoughts. The moving mass in a VTC machine is a known amount and servos are tuned for that mass. The mass is only the column, and with many, tool magazine. Weight of table and workpiece not in the equation. Any they are available in 50 taper as well.
    For reference the Mazak VTCs have what looks to be the top part of a C machine, but that moves in X and Y.
    No affiliation, just curious. I favor longer X machines for what I do.
    And a moving table in a 65 x 30 travel machine is not so light.

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    Quote Originally Posted by boosted View Post
    Yes. What I would consider a true traveling column has a completely fixed table. The spindle and Y axis ride on a saddle that travels back and forth on the X. This is a very popular design among European builders. It's also the same design used in the infamous Mazak VTC machines.
    What makes them infamous? I have 1 over 20 years and 1 very close to that.

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    Quote Originally Posted by Scruffy887 View Post
    What makes them infamous? I have 1 over 20 years and 1 very close to that.
    Infamous to me, because Mazak sold a bazillion in the 90's and early 00's. They are so often found squirreled away in the back of larger shops, and many are showing their age.

    Don't get me wrong though - it's a great platform. Not the most rigid machine, but very versatile and simple/reliable.

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    Quote Originally Posted by boosted View Post
    Infamous to me, because Mazak sold a bazillion in the 90's and early 00's. They are so often found squirreled away in the back of larger shops, and many are showing their age.

    Don't get me wrong though - it's a great platform. Not the most rigid machine, but very versatile and simple/reliable.
    Got it. I make products, not parts. Any fixture I make are for the long haul and seeing the table covered with parts gives me a woody. I like to push the green button and walk away. 30C was made as a 40 taper only machine, but the 300C series can be had with a 40 or 50. Much more iron in the column and Z head.
    I do tons of HDPE and plenty of Acetal so no worries about rigidity here.

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    Quote Originally Posted by Scruffy887 View Post
    And a moving table in a 65 x 30 travel machine is not so light.
    My bigger VMC has 60x26 travels and weighs about 38k lbs. The saddle and table are surely heavy, atleast several tons I'm sure. in comparison though, I would put the column, headstock and toolchanger combined near 10 tons.

    In a traveling column machine the head and column are considerably lighter so they can move quickly with reasonably sized servos. That lighter weight means less rigidity.

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    I can tell you after buying that Junkford fixed table I wont have another because of the leveling issues. 7.5 meter X travel machine had 260 leveling pads. After you get the table level you have 2 rows of pads on each column and its an absolute week long bitch to bring it in. And one decent bump to a heavy part and it's repeat all over again.

    Our Ingersoll traveling table gantry was a fixed gantry with 80' of travel in X and a breeze to bring it in.

    One nice thing about a fixed table is since its not attached to the gantry you can install the table deeper and use a riser. We had the pit poured to set the table an extra meter deep and was quite nice having the extra Z height.

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    Quote Originally Posted by g-coder05 View Post
    I can tell you after buying that Junkford fixed table I wont have another because of the leveling issues. 7.5 meter X travel machine had 260 leveling pads. After you get the table level you have 2 rows of pads on each column and its an absolute week long bitch to bring it in. And one decent bump to a heavy part and it's repeat all over again.

    Our Ingersoll traveling table gantry was a fixed gantry with 80' of travel in X and a breeze to bring it in.

    One nice thing about a fixed table is since its not attached to the gantry you can install the table deeper and use a riser. We had the pit poured to set the table an extra meter deep and was quite nice having the extra Z height.
    Ingersoll are simply machines from another world. Back in 1986 I had opportunity to visit their factory in Rockford, dealing with technical aspects of purchase of big 5 axis bridge machine with nutating head. This visit definitely change the way I am judging the engineering of the machines in respect of accuracy and endurance. Yes, price, price. Diamonds are expensive ...

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    It might come down to load paths through the structure. A "standard" VMC looks like a big C clamp. And main cutting forces are generally in the middle of the machine, regardless of where the table is. Managing table "nod" due to heavy weight out on the ends may be easier than having a good load path for a cutting loop that moves.

    Seems to me that VTCs, fixed-table-verticals, bridge mills, gantrys - aside from mold machines, they're all Very Large. And floor space issues on the customer site start to matter (a 30ft x 5ft table that moves around in a 60ft by 10ft space will draw the ire of the facilities planners....)

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    Quote Originally Posted by g-coder05 View Post
    I can tell you after buying that Junkford fixed table I wont have another because of the leveling issues. 7.5 meter X travel machine had 260 leveling pads. After you get the table level you have 2 rows of pads on each column and its an absolute week long bitch to bring it in. And one decent bump to a heavy part and it's repeat all over again.

    Our Ingersoll traveling table gantry was a fixed gantry with 80' of travel in X and a breeze to bring it in.

    One nice thing about a fixed table is since its not attached to the gantry you can install the table deeper and use a riser. We had the pit poured to set the table an extra meter deep and was quite nice having the extra Z height.


    Oh man that has to suck releveling after a bump. I wonder why there were no anchors. Most of these bigger VTC mills have at least 4 anchors

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    Quote Originally Posted by Speedie View Post
    Oh man that has to suck releveling after a bump. I wonder why there were no anchors. Most of these bigger VTC mills have at least 4 anchors
    The gantry on those things run about 40-50K pounds. That much weight running around and hitting something on a table that is separate from the machine is going to move somewhere even with anchors.


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