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  1. #1
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    Ram-type milling machine

    For quite some time I'm planning to build my second machine.
    The First machine is made Alu extrusions and is good for wood and light aluminium work.
    This machine is serving me really good but it's really not meant for milling anything beyond aluminium.
    I see that I could do much more work if I had the option to mill steel and other hard materials. *

    So last year I had the idea to make a heavy gantry build milling machine.
    After some time and some research I have come to the conclusion that gantry build is really not meant for heavy milling of steel.

    I want a VMC that has a fixed not moving table and this is what I came up with. *

    My design has shifted over to a Ram style milling machine.
    I want heavy multipurpose machine with ATC
    Milling table size of 700x1200mmx500mm
    Everything will be welded and surfaces for linear ways and ball screws will be milled after.

    I have started gathering offers and sources for parts, and this is what i have for now

    - welded base construction from 150x100mm tube 10mm wall thickness
    - linear ways 30 mm HIWING RGW roller type for XYZ
    - ballscrews 2510 TBI ground C3 with OFU/DFU double ballnut for XYZ
    - Bearing blocks and motor mounts for ball screws from SKY
    - controller SZGH-CNC 1000 MDi-5 (5 axis)
    - servomotors from SZGH 1kw with tamagawa 23 bit absolut encoders
    - Spindle servo motor SZGH 5.5kw 12000RPM
    - Spindle cartridge jsswft / FUKA FKS1203 12000 RPM direct drive
    - absolute linear scales on all exes

    Now I can't decide what style of x axis should I proceed with.
    What is better, lighter and stronger and also easier to make.

    For now i have those two options

    1. Welded 15mm plates with some holes for weight reductions and additional ribs inside.
    2. Welded frame from steel rectangular tubes

    I have in mind also a simpler version of number 2.


    Attachment 454392

    Inspiration is this - dmg DMC v


  2. #2
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    Re: Ram-type milling machine

    For now i think that this design for x axis is my favorite.
    Thick 15mm steel plates and ribs inside, it should be plenty rigid
    Together it weights 250kg and that is pretty much the same as welded tube version.
    I could probably cut some weight down more if needed.

    Attachment 454416Attachment 454418

  3. #3
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    Re: Ram-type milling machine

    Hi Luka - With a steel fabricated machine made from relatively thin parts like you have drawn, vibration will be an issue. If you have FE capabilities run a modal analysis and you will see all those thin sheets will vibrate madly. Two options. 1) make everything very thick 2) make a steel shell and fill with UHPC or epoxy granite such as this company... (do not use Portland cement it shrinks and changes shape research UHPC or CSA concrete)

    https://www.rampf-group.com/en-us/

    The Mori machine is called a moving column configuration. Your Y700mm will be a challenge for it. Its a long way out for a cantilever. I have been working on a similar but smaller machine and came back to a gantry style machine due to the Y axis length. See the Milli thread.

    Plus a fabrication like yours will not be straight after its welded. So can you stress relieve it? If no stress relief, it will move again when you try to machine it. So consider SR you will need to figure that out.

    The Mori weighs 15 tonnes, so will yours if you require the same stiffness. The holes in castings are not lightening holes and you do not need them in a plate machine. The holes in castings are called "prints" These holes are the part of the sand core that hold it in place. Once the core is broken out this leaves a hole. In your case thin edges can vibrate so any free edge needs to be looked at carefully. I assume your parts will be laser cut. So holes actually cost money as this is laser time... Keep at it. Peter

    Many of Moris machine bases are mineral cast so don't be shy in using it... its the best material for the job and you can do it in your garage. For instance you can make plywood moulds on your current router then fill them with UHPC or similar and you will have a stiff damp part much better then steel fab...

  4. #4
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    Re: Ram-type milling machine

    Hi peteeng
    I tought that using 15mm thickness steel is considered thick walls I have capabilities to make stress analysis i just lack of experience to do it properly.
    Everything welded will be stress relieved and milled after.

    Your Y700mm will be a challenge for it. Its a long way out for a cantilever.
    Yes its long way that is why moving column is 1500mm long and bearing blocks are 800mm wide. I think that should be enough if column is rigid and stable

    At first i had idea to make thin wall shell and just fill with epoxy granite or UHPC
    This was fist idea
    Attachment 454422

    But with design like this only column is cca 450kg and with saddle and z axis it will be quickly over 600kg and i don't know if my 1kw servo is capable to move weight like this on 2510 ballscrew.
    Also if I cast this myself I will need to get someone to machine this huge block of casting for linear guides I don't think there is any other way of getting surfaces flat enough for linear rails (0.01mm).

    I assume your parts will be laser cut. So holes actually cost money as this is laser time
    Yea that is correct, I didn't think of that maybe i shouldn't make so much holes

  5. #5
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    Re: Ram-type milling machine

    Hi Luka - I said "relatively thin" if you do a modal analysis you will see the edges vibrate (or not). Thin or thick is relative to the structure size...Good you can SR so at least you can investigate this approach thoroughly. The inertia of the "solid" design maybe greater then the "shell" design so you need to establish stiffness required then make the casting sized down (or more hollow) to achieve the stiffness. Then adjust the steel fab to the same stiffness and compare the two. Stiffness is the first thing, then damping is the second thing to consider. The EG casting will be 20x damper then the steel fab. Both processes have pros and cons you have to decide the path...

    Easy to make light machine but hard to make stiff light machine. Your size machine will need to be UBER stiff. I have struggled for months with Milli and still no joy yet... (plate aluminium, welded steel, composite, EG, UHPC looked at them all in detail...) Your answer may lie in a hybrid, fabricated steel shell for the mould and stiffness, SR fill with concrete for full stiffness and damping. Maybe best of both worlds. And no holes cause the concrete will leak

    You have to machine guide lands both designs so that's even I think... Peter

  6. #6

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    Re: Ram-type milling machine

    Quote Originally Posted by lukahr View Post
    For now i think that this design for x axis is my favorite.
    Thick 15mm steel plates and ribs inside, it should be plenty rigid
    Together it weights 250kg and that is pretty much the same as welded tube version.
    I could probably cut some weight down more if needed.

    Attachment 454416Attachment 454418
    I'm more interested how something like this would be welded, a hand has to fit through the holes not to mention the welding head.

  7. #7
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    Re: Ram-type milling machine

    I think that welding this should not be much of a trouble.
    You can leave top plate off and weld all internal ribs and then weld top on, also top holes quite large.

    I have commercial producer of welded constructions and they can do everything at their place from stress relieve to milling surfaces and deliver construction to my doorstep.
    And the price is reasonable.
    That is why i'm considering welded structure, i will not diy weld this as my welding skills are more or less rubbish

    I'm doing some calculations about servo motor sizing at oriental-motors site. If servomotors (4Nm) would allow me to move 600kg on 2510 ballscrew i would go with steel shell and concrete cast structure.
    And it looks like critical parameter is Acceleration and deceleration of machine.
    What value should i input here to get good performance machine ??

    Attachment 454488

  8. #8
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    Re: Ram-type milling machine

    Design has shifted over to cast base, as I really want rigid machine and after doing some stress analytics on my welded base i decided that it will not work optimal.
    Now my base is one huge casting. Base is cca 2400kg 1m3 of material.
    Also moving column is one casting cca 360kg of material.
    For now material of choice is 52.5R concrete reinforced with glass fiber with added superplastificator - this may change when i get prices from RAMPF for products from them.

    Only thing that still worries me is how to make straight flat surfaces for linear rails. - I'm researching DIAMANT DWH as this maybe solution for my problem.

    Click image for larger version. 

Name:	cast base.jpg 
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ID:	454690

    If any moderator is reading this maybe you can move this Thread to section CNC "do-it-yourself"

  9. #9
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    Re: Ram-type milling machine

    Hi Lukahr - Since you have access to machining get the mould lands machined. The part will be the exact replica of the mould. Its always best to make the mould as best as possible vs rectifying the part. What do you intend to make the moulds from? Peter

    what is the spec for 52.5R concrete? I looked it up and its probably a portland cement. Not recommended for machine building as it shrinks and cracks. Use a CSA grout or UHPC mix...

  10. #10
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    Re: Ram-type milling machine

    Yes i'm thinking how can i make machined mold part of linear guides and replicate shape into part.
    Only problem is i will cast whole part upright, i dont have option to turn part over (it will be 3tones) this is not an option.
    Would be OK to drop machined part into soft material from top down, would that work ?

    I will make mould from waterproof plywood or we have local company that makes framework panels for concrete molds.

    I have option for superplaster additives and anti shrink additives this should help with shrinking and reducing water use. Also i can leave part to cure for couple months no problem.

    Cant find what CSA grout would be or where to get it in our part of world - Europe
    Yes i'm looking into UHPC concrete or mineral casting from RAMPF, but price might be problem, will see when i get quote
    I have found also Creteo®Repair CC 194 M - this should me with minimal shrinking

    Edit* .. i have just found NANODUR® Compound 5941 -this looks like good stuff, will see what prices i can get from Germany

  11. #11
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    Re: Ram-type milling machine

    Hi Luka - Portland cement shrinks over a period of years and is UNSUITABLE for machine parts, but people have used it but long term I'm sure it would lose modulus due to microcracking. Nanodur 5941 is perfect and not expensive compared to epoxy.. Use that... Peter

    I tried to get 5941 to Oz but the company won't ship out of Europe Peter

    People do screw up the release agent, Use PVA release (NOT PVA glue) common in boatbuilding and concrete industry. Cheap very good release, easy to use...

  12. #12
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    Re: Ram-type milling machine

    Yea i'm pretty much decided to go with Nanodur 5941.
    - Its easily available to me
    - i can use local source of aggregates
    - price is good cca450€/ton

    Is this release agent right one, i have this one locally available.
    https://www.revivo.si/pva_blu_release_agent_1l

    For moving column i think it wont be problem to make precise milled mold- cast it as one part and then flip it over.
    But for base i'm thinking to make split part. Only top section (section where linear guides are) cca 20cm thicknes with milled mold and then flip it and glue it somehow onto base ...

  13. #13
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    Re: Ram-type milling machine

    Hi Lukahr - yes thats the one. Use a wax first to protect the mould and then PVA. Its water soluble so you can "float" a part out. Lots to learn for you. But you are probably going to break up the mould so using PVA direct on surface is OK. Do a small test to check out how it will go first...Probably cheaper from a concrete place then an art supplier...Peter

    you can make in small sections and then epoxy together will be easier...

  14. #14
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    Re: Ram-type milling machine

    Quote Originally Posted by peteeng View Post
    Hi Luka - With a steel fabricated machine made from relatively thin parts like you have drawn, vibration will be an issue.
    My maho (dmg mori) has the main base/column made of welded steel plate, 10mm thick. vibration was not on the radar when cutting with 250NM torque. This was at the time their top of the line machine, 6000kg, twin pallets, 4 axis, 600ipm, 8000rpm spindle, 1 micron glass scales, $250,000usd.

    you dont need to inject everything with concrete
    wotzBotz

  15. #15
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    Re: Ram-type milling machine

    Quote Originally Posted by lukahr View Post
    I think that welding this should not be much of a trouble.
    You can leave top plate off and weld all internal ribs and then weld top on, also top holes quite large.

    I have commercial producer of welded constructions and they can do everything at their place from stress relieve to milling surfaces and deliver construction to my doorstep.
    And the price is reasonable.
    That is why i'm considering welded structure, i will not diy weld this as my welding skills are more or less rubbish

    I'm doing some calculations about servo motor sizing at oriental-motors site. If servomotors (4Nm) would allow me to move 600kg on 2510 ballscrew i would go with steel shell and concrete cast structure.
    And it looks like critical parameter is Acceleration and deceleration of machine.
    What value should i input here to get good performance machine ??

    Attachment 454488
    try yaskawa sigmasize tool. even if you dont buy their motors. it allows alot of input to determine what you might want as far as motor size.

    for 2 opposite end comparisons:

    my maho had a 4010 vertical screw to lift the Y axis and rotary table and work piece - about 1000-1200kg. motor was 24NM, belted 2:1, so 48NM at the screw (7kw).

    My brother TC229 had a 2510 vertical screw, lifting only the head - about 200-250kg. motor was 4nm direct drive (1kw).

    they brother had 4 times the acceleration of the maho. the main difference is that the maho maintained 10000N for cutting, where the brother had only about 2000N.
    wotzBotz

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    Re: Ram-type milling machine

    Hi Luka - Here's the math for the torque calcs on a screw drive. You have to solve incrementally unless you set up a spreadsheet an use an optimised solver. But one or two goes at it you get there. ie the linear accel and rotational acceleration have to be solved separately but they have to have same basis if that makes sense.... Peter

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    Re: Ram-type milling machine

    Hi IHNF - Thats interesting. From your numbers the Maho has over twice the capacity it needs but the brother is close to its static needs. The Z axis usually does not need the accelerations that the X&Y do, so accel not as important for the Z. Plus The Z has to lift the mass against gravity vs the X&Y just has to slide the loads around against inertia.... Peter

  18. #18
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    Re: Ram-type milling machine

    Quote Originally Posted by peteeng View Post
    Hi IHNF - Thats interesting. From your numbers the Maho has over twice the capacity it needs but the brother is close to its static needs. The Z axis usually does not need the accelerations that the X&Y do, so accel not as important for the Z. Plus The Z has to lift the mass against gravity vs the X&Y just has to slide the loads around against inertia.... Peter
    the brother in this case has near 1G acceleration, 1400ipm. "needs" is relative. this machine wants to change a tool in 1.2 seconds chip to chip. new brothers have 2g z acceleration, 2000+ipm, and 0.8 second tool changes.

    the maho has a completely opposite target. tool changes take 15 + seconds, so, it's 0.25G acceleration is only to get around the cut. but then it wants to push an 8" face mill through steel at 250rpm so you need motors that would easily run a car. maho is box ways as well, so that needs even more force out of the motor.

    the trick with servos, on "light" machines like the brother that prioritise dynamic movment over heavy cutting is you use the intermittent torque of the servos. that 4nm brother servo really only uses continuous torque when its holding the head up, and drilling a deep hole. for acceleration, short moves, plunges, peck drills, it uses dynamic torque up to 11nm.

    the maho wants cutting force, so it wants continuous force. it actually has clutches on the motor to e stop the machine in overload - in a crash basically. they were set to about 37nm if i remember, so actually a bit less than the constant torque of the servo at 0rpm. the servo has i think closer to 37nm at 3000rpm belted down to 1500. (if the brother crashes, you have a heart attack!)

    point is, if you know what you want the machine to do, an app like sigmasize will give you a proper idea of the motor you need, vs your basic x nm = y force math.
    wotzBotz

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    Re: Ram-type milling machine

    Hi IHNF - All of the motor calculators use the equations I have just used manual calcs are just as proper as a calculator. No more and no less. If its constant velocity then the prior eqn is fine as there is no accel. If there is accel then it needs to be included. The "dynamic" torque you speak of is for very short periods. If you look at the dynamic torque curves you will see you can cook a motor in a few seconds if you go into that territory for too long. The continuous rating means the heat generated by the motor can be dissipated safely. The dynamic range means the heat is building up and can cook the motor, so it needs some down time to get rid of the excess heat then it can get back to thermal stability. This can be a fine line between smiles all day and fried motors and unhappiness for a while. Machines like Mori's and Brothers have thermal overloads, current overloads and mechanical overload control.... (clutches as you say) so this sort of thing is managed properly.. Are these motors liquid cooled? Peter

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    Re: Ram-type milling machine

    sigh.

    you're wearing me out here. have you used sigmasize?
    wotzBotz

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