Honest question: Why do we need "super" rigid machines?
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  1. #1
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    Default Honest question: Why do we need "super" rigid machines?

    Ok, this might sound like BS, but I honestly question why we need the super rigid machines* - box ways and million pound castings when modern cam lets you do so many different varieties of HSM (high speed machining) techniques? I mean, in the 'olden' days (LOL ) when cam wasn't as prominent, and making the code by hand fast and accurate and compact, sure it would be much easier to program that slot / cut burying the cutter to minimize programming time and code lines / size. But why now?

    I can sort of see with surface finish, but I thought that was more related to tool holder / and cutter runout and geometry, and processing speed-look ahead of the control..?

    The reason I thought about this was all the recent Haas bashing about not being able to take a cut and all that stuff... I've run mostly Haas, with a smattering of Robodrill (30 taper so a different animal IMO), and Mazak and some old china type iron.

    When I was in a job shop we cut tool steel, 4140ph, and hardened toolsteels all the time with Haas machines. Maybe not as fast as some other high end machines, but very doable, and we were loaded with work mostly so apparently we did ok on our quoting and making parts... We had an SL 30 that ran 4140 10-12" diameter blanks all day every day. We made good money on those parts as I recall. These were big enough we needed a crane to get them in the machine, and light enough when done to unload by hand so we removed ALOT of material (in a timely manner if I say so, but I don't have a metric to compare it to...)

    We made alot of the flywheel portion of these (in our Haas SL30 and VF2-3) , but unfortunately not seeing any good pics of them.
    South Bend Clutch | We Motivate The Shiftless

    edit: before tom shows up to tell us we are running toys, I am more specifically talking about the general ranges of 40x20 machines

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    I'm with you. I used to be on that bandwagon and anti haas...

    The Japanese machines really are great, and the surface finish is much better on the Jap machines I have/had but man the price of the haas machines and even robodrills make it not a big deal at all.

    Slowly we are moving away from big heavy machines and instead going smaller robodrill with pallet changers and dm1/2 machines with pallet changers. Cheaper machines and maybe a little longer cycle time compared to a makino, okuma, etc... but the cost to run a haas and own a haas is so damn cheap!

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    Rigid machines will typically allow you to cut harder and faster with the same tool life as a "flexy" mill, or cut the same speed with a longer lasting tool. Better side taper too, and usually (as mentioned) surface finish.

    Not all hard-and-fast rules, but generally the above is true. The stiffer machine minimizes the "bouncing" the cutter does as the edges enter and leave the work, and that lowers the micro-fractures that starts dulling tools. So stiffer machines are more critical with harder materials or heavier cuts.

    Yes, you can do the same work with a Haas, but it means lower cutting rates and more time. I'd blame the spindle stiffness (or lack of) for a lot of that, but don't have proof.

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    When machine is super rigid everything works better. Literally everything.
    Spindle bearings last longer.
    Tooling ( endmills, drills, etc) last longer.
    Electronics in the back panel last longer, less vibrations.
    Part is more accurate, less taper on walls, less deviation.

    Many parts you can get away with making with any type of machine. Rigid or not so rigid. But there are parts that litterally can only be made with nice rigid machines. Parts with 3" deep pockets and nice side walls required and is stainless or D-2 steel.

    I've had many HAAS machine in my lifetime. Great machines. Maybe not the most rigid but not a pasta noodle either. I've made a shit ton of fancy, big, demanding parts on them.

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    Quote Originally Posted by as9100d View Post
    I'm with you. I used to be on that bandwagon and anti haas...

    The Japanese machines really are great, and the surface finish is much better on the Jap machines I have/had but man the price of the haas machines and even robodrills make it not a big deal at all.

    Slowly we are moving away from big heavy machines and instead going smaller robodrill with pallet changers and dm1/2 machines with pallet changers. Cheaper machines and maybe a little longer cycle time compared to a makino, okuma, etc... but the cost to run a haas and own a haas is so damn cheap!
    Proportionately a Robodrill can be pretty rigid. I.e. small machines (that are not super heavy) can be rigid versus a large heavy ponderous machine. Measures of deflection.

    If your tolerances are tight and your travels are long that's where things can get really difficult.

    Basically in terms of amount of iron or granite in a machine there is basically a cubic (x-cubed ^3 relationship )) to maintain a certain rigidity (lack of deflection) for a linear size and scale of machine (and beyond).

    That scaling can be pretty massive to maintain "rigidity" / lack of deflection. Much easier to make a small work volume rigid versus a large one.

    Interesting with some of the Hermle machines they are not super massive but not ultra ultra fast either but have synthetic granite "castings" that one does not bolt down to a foundation, i.e. it's a self supporting structure on a few legs... So the travels and geometry of the machine is not distorted by changes in it's foundation. And vice versa , they don't interfere with each-other.

    Some DMG Mori monoblock's on 3 legs use that idea also and are not what I would regard as "super rigid" but if they are not pushed too hard can do a nice job.

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    if you've ever had to hog out Rene41, you'll appreciate a big heavier than shit machine

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    Rigid machines are great so when you fat finger the .010" per rev feedrate as .100" the machine just makes a different noise and funny looking chips until you figure out what you are doing wrong. No crashes !

    Ask me how I know

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    Just talking BT30 machines here but I have ran many and own 2. My favorite is my 2001 Kitamura. 2000ipm and stiff as hell. I bought it used in 2011 or so, it has spent 9 years running 24/365 but was still in good looking shape. It took me several months to confirm the spindle had an issue. Instead of 15k it was programmed 6k max, but still displayed the programmed speed which was 15k max. At first, I thought the spindle must have too much runout because of the surface finish left when side milling, it was coarser than expected, duh the chip load was 2.5 times higher. I can run the chip load until the tool breaks or the part moves, the machine NEVER complains, ever. It just purrs with chip loads that would have any other drill/tap I have ever ran screaming bloody murder. When you mix that stiffness with high rapids and feeds then

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    The simple, short & sweet (very accurate) answer to your question?

    Thats easy: HARMONICS
    Vibration kills.......everything. It starts with surface-finish, but slowly and surely, it is killing everything.

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    HSM has made things a little easier for smaller milling machines, but more rigidity is still better if you have it.

    On a lathe nothing has changed. Even if you dont need the power and rigidity to take huge cuts, you eventually will run into problems when trying to cut coarse threads and long overhangs.

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    Quote Originally Posted by cameraman View Post
    Proportionately a Robodrill can be pretty rigid.
    When i had mine, i was ballbaring them and could not believe how flexible the base casting is.
    It's a 4x feet design, and with a spanner on one foot, i only had to breathe on it to throw the ballbar readings haywire.
    In desperation i phoned my Roboguru who laughed at me and told me don't worry they all do it, and to put a mag base on the base casting and a plunger clock onto the factory floor, so i actually knew how many thous the foot is lifting.
    Doing it this way worked like a charm.

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    Quote Originally Posted by fmari --MariTool- View Post
    When machine is super rigid everything works better. Literally everything.
    Spindle bearings last longer.
    Tooling ( endmills, drills, etc) last longer.
    Electronics in the back panel last longer, less vibrations.
    Part is more accurate, less taper on walls, less deviation.

    Many parts you can get away with making with any type of machine. Rigid or not so rigid. But there are parts that litterally can only be made with nice rigid machines. Parts with 3" deep pockets and nice side walls required and is stainless or D-2 steel.

    I've had many HAAS machine in my lifetime. Great machines. Maybe not the most rigid but not a pasta noodle either. I've made a shit ton of fancy, big, demanding parts on them.
    This. rigidity and vibration dampening are key no matter what you are doing, it's an old idea that has stood the test of time. Everything the light fast machines do well, they will do better on a rigid machine/setup.

    I have both and when it comes to holding tight tolerances and hard machining the big heavy bridge mills and box way lathes are hands down easier to work with. They make you look good, the noodle machines will make you a better machinist and designer because of all the tricks you need to make the same part.

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    Quote Originally Posted by Jaxian View Post
    Rigid machines are great so when you fat finger the .010" per rev feedrate as .100" the machine just makes a different noise and funny looking chips until you figure out what you are doing wrong. No crashes !

    Ask me how I know
    We must belong to the same club! LOL

    img_20150219_202533_zpsroosbyr7.jpg

    That chip: the wide part is the entire width of a CCMT insert. The narrow part is the boring bar body itself! LOL
    All because of a grossly fat-fingered offset. The material was 7075. It finished the hole.
    When I went to change the part, imagine my surprise when the hole that was supposed to be around an 1", was more like 2.125"

    That was a Nakamura Slant-1. No doubt in my mind, that would have stalled a haas SL10 (equivalent haas machine).
    And, if it didnt stall the spindle, it would have made so much racket (vibration) I would have surely known I screwed up way before I opened the door.

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    Quote Originally Posted by wheelieking71 View Post
    We must belong to the same club! LOL

    img_20150219_202533_zpsroosbyr7.jpg
    So you proved you could save an opp by eliminating the pre-drilling...

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    Better rigidity is always better, all else being equal. It also tends to be more expensive. Is it worth paying for, for your parts in your shop? That's up to you. It can also have some trade-offs; a box way machine is generally slower on the rapid, and the ways may not hold accuracy as long.

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    I think rigidity is a separate property from vibration dampening... They are interrelated (depending on how much mass of material and structure / design you throw at something. ).

    I "believe" that hand scraping and good precision surface contact between key joints of a machine are pretty critical to rigidity and maintaining long term machine geometry and alignment.

    On the other hand you can have rigid assemblies that "ring" like a bell but don't actually absorb that much vibration as compared to synthetic granite that has very different mechanical properties that do an excellent job of absorbing vibrations and better thermal properties..

    Use of shims rather than hand fitted and scraped joints is thought to reduce rigidity but some people 'Poo poo" that idea (also).

    Carbidebob once made a really interesting comment about how with very large gantry style machines that the masses behave in different ways and sometimes you don't want super rigidity between uprights and the base ? I'm sure he's right but I don't know the details as to why and why not ? He seemed to indicate that there are particular low modes of vibration that you don't want to interfere with ? [Something different about much larger machines + connection / contacting points and surfaces.].

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    Quote Originally Posted by wheelieking71 View Post
    That was a Nakamura Slant-1. No doubt in my mind, that would have stalled a haas SL10 (equivalent haas machine).
    And, if it didnt stall the spindle, it would have made so much racket (vibration) I would have surely known I screwed up way before I opened the door.
    Similar story, I was running some parts on a Hardinge T42 a few years back using a 10mm Ceratizit EcoCut drill to drill and bore out the part, part way through the run the bore size shifted and due to how short the cycle time was I didn't notice until after it had churned out a bunch of bad parts.

    I stopped the cycle and had a look at the drill to find that the insert screw had worked loose and the insert was no longer there, it had been drilling and boring out quite happily with no noticable change in noise or spindle load just with the steel drill body, luckily this was in 6082 T6 so the drill itself was pretty unscathed and even more amazingly I spotted the insert and screw in the swarf conveyor and was able to carry on using them.

    Pretty sure a lighter machine would have pegged the spindle load meter and screamed at me, things I'd do to get a nice late 90s T42 in my shop...

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    Load monitoring can be your friend.

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    Rigidity and mass are pretty much tied together when talking typical machine materials and not exotic carbon and Kevlar injected plastics and such.
    I’m sure there are some examples of heavy machines that had crappy engineering that made them floppy, but they are the exceptions

    If you want to machine heavier parts with high feed rates and fast rapids you need lots of iron in the base of the machine, or the base of the machine has to have a design that maintains its geometry while being securely bolted to a foundation that has lots of mass. The forces transferred to the machine and the foundation due to the table and work moving around at high speeds need to impact the geometry(shape) of the machine minimally or you will get crappy parts

    The short and simple answer is....
    Physics


    Sent from my iPhone using Tapatalk Pro

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    I rearranged 80% of my shop over the past 4 days. If I had light little fast machines I think I could have done it in a day. Fuck me. I think I moved a million pounds.

    So for me, I primarily have heavy rigid machines for the exercise. It keeps my heart healthy and I save on heating costs when I work harder.


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