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    Default 6-axis Horizontal Machining Center for Education

    This projects consists in developing a DIY kit for a 6-axis Horizontal Machining Center initially targeted at the education sector (CNC departments of community colleges, mechanical engineering schools, R&D labs), with a Public Domain design.

    The machine is based on a relatively simple mechanical design:

    - Static vertical column for Y axis
    - Box-in-box X-Z table with built-in B rotary table
    - Fixed Y column with A-C spindle head
    - Focused on non-ferrous metal
    - Focused on minimum quantity lubrication

    The base and column are made of two solid pieces of granite (real stone, not epoxy composite). While relatively unconventional for a machine tool, the use of granite is expected to bring the following benefits:

    - High precision.
    - Excellent stability, rigidity, and vibration dampening characteristics.
    - Easier to design for than weldments or epoxy granite.
    - More affordable than epoxy granite.
    - Strong enough for machining non-ferrous metals.

    If granite stone turns out to be impractical for some reason, it will be replaced by epoxy granite.

    The design offers 6 axes for the following reasons:

    - 6-axis can offer better accuracy than 5-axis alternatives.
    - 6-axis can offer faster speeds than 5-axis alternatives.
    - 6-axis can improve ergonomics.
    - 6 axis can simplify kinematics.
    - 6-axis can turn the HMC into a VMC.
    - 6-axis can turn the HMC into a turning center.
    - 6-axis would benefit from more research & development in order to receive more mainstream adoption.
    - 6-axis is the next frontier in CNC machining now that 5-axis has become relatively mainstream.

    The focus on education is motivated by the following factors:

    - Schools need affordable training aids.
    - Aluminum is more suitable than steel for learning high-axis kinematics (cheaper, faster, easier on cutting tools).
    - The education market does not require production-oriented features like chip collection.
    - Schools cannot afford high operation and maintenance costs, which are reduced by replacing traditional coolants with Minimum Quantity Lubrication.
    - More research & development are needed in the area of 6-axis machining.
    - The release of the machine's design into Public Domain makes it easier to support experimentations and add-on distribution.
    - The 6-axis design makes it easier to understand the benefits and trade-offs of horizontal and vertical machining.
    - The machine's ergonomics are especially-well suited to an academic environment.
    - Labs in training schools are usually space-constrained.
    - Today's students are tomorrow's designers and operators.
    - This machine is developed as a learning experiment in the very first place.

    The machine has the following characteristics:

    - 64" × 64" × 80" footprint
    - 30" × 20" × 20" cutting envelope
    - Box-in-Box X-Z 30" × 20" table
    - Built-in 20" direct drive 225rpm 1870Nm/3490Nm rotary table
    - Cast iron boxes for X-axis carriage, Y-axis head, and Z-axis table
    - NSK roller guides
    - NSK ground 32mm ball screws with 6mm pitch
    - HSD HST310 2-axis head with ES368 HSK F63 Synch 13kW spindle with encoder
    - Dual Siemens SIMOTICS 1.5kW servo motors for every linear axis
    - Brakes on servo motors for vertical Y axis
    - Direct drive torque motors for every rotary axis
    - 700ipm rapids on every linear axis
    - Heidenhain LC 495 S linear encoders with 3?m accuracy for every linear axis
    - Absolute encoders with 30 arcsec accuracy for A, B, and C axes
    - ±120° rotation on A axis
    - Endless rotation on B and C axes
    - 50-tools automatic tool changer with carousel and double arm
    - ELTE ELT 12 water chiller
    - Unist Quantum minimum quantity lubrication system
    - Siemens SINUMERIK 840D sl controller
    - Blum TC52 touch probe
    - Blum ZX-Speed toolsetter
    - Blum IC56 IR receiver

    A detailed description of this project can be found there:

    https://docs.google.com/spreadsheets...NTo/edit#gid=0

    The goal of the project is to build and demonstrate a successful prototype, then make kits available to schools for less than $150,000 in North America and €150,000 in Europe. This project is developed by a first-time builder, but he is advised by highly-experienced engineers working for various suppliers and distribution partners, across all technical aspects of the project (software, electronics, mechanics, mechatronics, ergonomics, and logistics).

    This project originated from another thread that took many twists and turns before a final design was selected:

    https://www.cnczone.com/forums/diy-c...62576-cnc.html

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    6-axis Horizontal Machining Center for Education-head-left-jpg   6-axis Horizontal Machining Center for Education-head-right-jpg   6-axis Horizontal Machining Center for Education-head-back-jpg  
    Last edited by ishi; 07-12-2018 at 03:59 PM. Reason: Added brakes for servo motors on Y axis


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    Default Re: 6-axis Horizontal Machining Center for Education

    Quote Originally Posted by ishi View Post
    This projects consists in developing a DIY kit for a 6-axis Horizontal Machining Center initially targeted at the education sector (CNC departments of community colleges, mechanical engineering schools, R&D labs), with a Public Domain design.

    The machine is based on a relatively simple mechanical design:

    - Static vertical column for Y axis
    - Box-in-box X-Z table with built-in B rotary table
    - Fixed Y column with A-C spindle head
    - Focused on non-ferrous metal
    - Focused on minimum quantity lubrication

    The base and column are made of two solid pieces of granite (real stone, not epoxy composite). While relatively unconventional for a machine tool, the use of granite is expected to bring the following benefits:

    - High precision.
    - Excellent stability, rigidity, and vibration dampening characteristics.
    - Easier to design for than weldments or epoxy granite.
    - More affordable than epoxy granite.
    - Strong enough for machining non-ferrous metals.

    If granite stone turns out to be impractical for some reason, it will be replaced by epoxy granite.

    The design offers 6 axes for the following reasons:

    - 6-axis can offer better accuracy than 5-axis alternatives.
    - 6-axis can offer faster speeds than 5-axis alternatives.
    - 6-axis can improve ergonomics.
    - 6 axis can simplify kinematics.
    - 6-axis can turn the HMC into a VMC.
    - 6-axis can turn the HMC into a turning center.
    - 6-axis would benefit from more research & development in order to receive more mainstream adoption.
    - 6-axis is the next frontier in CNC machining now that 5-axis has become relatively mainstream.

    The focus on education is motivated by the following factors:

    - Schools need affordable training aids.
    - Aluminum is more suitable than steel for learning high-axis kinematics (cheaper, faster, easier on cutting tools).
    - The education market does not require production-oriented features like chip collection.
    - Schools cannot afford high operation and maintenance costs, which are reduced by replacing traditional coolants with Minimum Quantity Lubrication.
    - More research & development are needed in the area of 6-axis machining.
    - The release of the machine's design into Public Domain makes it easier to support experimentations and add-on distribution.
    - The 6-axis design makes it easier to understand the benefits and trade-offs of horizontal and vertical machining.
    - The machine's ergonomics are especially-well suited to an academic environment.
    - Labs in training schools are usually space-constrained.
    - Today's students are tomorrow's designers and operators.
    - This machine is developed as a learning experiment in the very first place.

    The machine has the following characteristics:

    - 64" × 64" × 80" footprint
    - 30" × 20" × 20" cutting envelope
    - Box-in-Box X-Z 30" × 20" table
    - Built-in 20" direct drive 225rpm 1870Nm/3490Nm rotary table
    - Cast iron boxes for X-axis carriage, Y-axis head, and Z-axis table
    - NSK roller guides
    - NSK ground 32mm ball screws with 6mm pitch
    - HSD HST310 2-axis head with ES368 HSK F63 Synch 13kW spindle with encoder
    - Dual Siemens SIMOTICS 1.5kW servo motors for every linear axis
    - Direct drive torque motors for every rotary axis
    - 700ipm rapids on every linear axis
    - Heidenhain LC 495 S linear encoders with 3?m accuracy for every linear axis
    - Absolute encoders with 30 arcsec accuracy for A, B, and C axes
    - ±120° rotation on A axis
    - Endless rotation on B and C axes
    - 50-tools automatic tool changer with carousel and double arm
    - ELTE ELT 12 water chiller
    - Unist Quantum minimum quantity lubrication system
    - Siemens SINUMERIK 840D sl controller
    - Blum TC52 touch probe
    - Blum ZX-Speed toolsetter
    - Blum IC56 IR receiver

    A detailed description of this project can be found there:

    https://docs.google.com/spreadsheets...NTo/edit#gid=0

    The goal of the project is to build and demonstrate a successful prototype, then make kits available to schools for less than $150,000 in North America and €150,000 in Europe. This project is developed by a first-time builder, but he is advised by highly-experienced engineers working for various suppliers and distribution partners, across all technical aspects of the project (software, electronics, mechanics, mechatronics, ergonomics, and logistics).

    This project originated from another thread that took many twists and turns before a final design was selected:

    https://www.cnczone.com/forums/diy-c...62576-cnc.html
    You seem to have a lot of T-Slots, but over that 20" diameter it may not be very many, just looks a lot in this small drawing

    Is the C axes the spindle, that would rotate, if so that would serve no purpose for a horizontal spindle like this

    Mactec54


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    Default Re: 6-axis Horizontal Machining Center for Education

    Quote Originally Posted by mactec54 View Post
    You seem to have a lot of T-Slots, but over that 20" diameter it may not be very many, just looks a lot in this small drawing

    Is the C axes the spindle, that would rotate, if so that would serve no purpose for a horizontal spindle like this
    mactec54,

    The spindle head has two axes: A and C. You can find more information about it on our drive:

    https://drive.google.com/drive/u/3/f...kwBI-?ogsrc=32

    Having A as an axis on the spindle's head is what makes C useful.

    Regarding T-Slots, we're not sure about which size we should go for. We know that it should be DIN 650 compliant, but sizing has yet to be defined. What is your recommendation? M6, M8, M10, M12? In the current design, slots are spaced by 50mm center to center.



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    Default Open Questions

    The current design raises several questions. Among them, the most pressing are:

    1. Vertical counterbalance
    There is some debate among advisors to the project regarding the need of a counterbalance for the vertical Y axis (the axis driven up and down the vertical column). An earlier version of the design included a hydraulic counterbalance made of two gas tanks and two hydraulic pistons. Later on, we decided to remove this apparatus, with the assumption that we could achieve similar results by using larger servo motors for the Y axis and a proper motor module (Siemens SINAMICS S120 Smart Line). From a performance standpoint, specifications would be the same or better. From a design standpoint, things would be greatly simplified by using mechatronics instead of hydraulics, and the same would be true regarding maintenance (tanks and pistons need to be replaced on a regular basis). Nevertheless, one advisor raised the issue of safety, which is also critical to us, especially within an academic environment. Therefore, this issue raises the following question: can we get an equivalent (or better) level of safety with mechatronics only?

    2. Number of servo motors for the vertical Y axis
    The X and Z axis will each be driven by two motors directly coupled to two ball screws (4 motors and 4 ball screws in total). The vertical Y axis alongside the vertical column could be driven by one or two servo motors directly coupled to one or two ball screws. Each option has its pros and cons. Using a single motor with a single ball screw reduces cost, design complexity, and assembly complexity. Using two motors with two ball screws increases rigidity, performance, and accuracy. Considering all other aspects of the project, which option should be selected?

    3. Rails extension
    A reader pointed out that our rails extend all the way to the edges of the base, column, and X-axis carriage, and considered this a design flaw. Is there a proper justification for this, and if so, what amount of clearance should be added, knowing that it would reduce travels on all linear axes?

    4. Travels on X and Y axes
    With the current design, travels are:

    X: 30"
    Y: 20"
    Z: 20"

    Travel on X can be increased by making the machine wider. Knowing that we want to keep a small footprint, would that be desirable? If so, by how much?

    Travel on Y can be increased by making the machine taller. It is likely that we will need to use the space on top of the vertical column for the Automatic Tool Changer. In such a context, we cannot increase the height of the machine by much if we want to keep a total height below 80". If we relax this constraint, we could increase travel alongside the Y axis by 5" to 10" without significant changes to the machine's design. Is that desirable? In other words, is increased travel on Y more important than total machine height?

    Travel on Z cannot be increased without compromising the rigidity of the vertical column (as far as we can tell).

    5. Automatic Tool Changer mounting
    The Automatic Tool Changer should have capacity for at least 30 tools, possibly more. It could have any design as long as it does not increase the machine's footprint (64" × 64"). With that in mind, we can think of three configurations for it, assuming a double arm for tool exchange:

    - Vertical, alongside the left side of the vertical column, parallel to the Y axis.
    - Horizontal, attached at the top left of the vertical column, parallel to the Z axis.
    - Horizontal, attached on top of the vertical column, parallel to the X axis.

    Which configuration is the most practical for it?

    6. Tool maximum dimension and weight
    The machine will offer two options for tools: HSK E40 and HSK F63. Ideally, the design of the Automatic Tool Changer will support both options. Assuming the larger tool size (HSK F63), what should be the maximum length and maximum weight of tools that would be handled by the Automatic Tool Changer?

    7. T-slots dimensions
    The table will use DIN 650 T-slots. With that in mind, and considering that the diameter of the rotary table is 20", which screw dimension should we use in order to be compatible with the most popular fixturing tools for a table of that size? M6, M8, M10, M12?

    8. Spindle options
    The machine will offer three options for the spindle, outlined there:

    HST310

    Which one is most likely to be the most popular for an academic environment?



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    Default Re: Open Questions

    Quote Originally Posted by ishi View Post
    The current design raises several questions. Among them, the most pressing are:

    1. Vertical counterbalance
    There is some debate among advisors to the project regarding the need of a counterbalance for the vertical Y axis (the axis driven up and down the vertical column). An earlier version of the design included a hydraulic counterbalance made of two gas tanks and two hydraulic pistons. Later on, we decided to remove this apparatus, with the assumption that we could achieve similar results by using larger servo motors for the Y axis and a proper motor module (Siemens SINAMICS S120 Smart Line). From a performance standpoint, specifications would be the same or better. From a design standpoint, things would be greatly simplified by using mechatronics instead of hydraulics, and the same would be true regarding maintenance (tanks and pistons need to be replaced on a regular basis). Nevertheless, one advisor raised the issue of safety, which is also critical to us, especially within an academic environment. Therefore, this issue raises the following question: can we get an equivalent (or better) level of safety with mechatronics only?
    Now that there is no gantry, using a standard counterweight also becomes more practical. I don't think I'd use hydraulic, seems too complicated. Not sure why straight pneumatic wouldn't work. May require more maintenance to the cylinders? If you go without counterbalance, you'll need a brake on the servo(s). You might want a brake anyway as a heavy tool in the spindle may be enough to overcome friction. Brakes on servos are a very common option.
    2. Number of servo motors for the vertical Y axis
    The X and Z axis will each be driven by two motors directly coupled to two ball screws (4 motors and 4 ball screws in total). The vertical Y axis alongside the vertical column could be driven by one or two servo motors directly coupled to one or two ball screws. Each option has its pros and cons. Using a single motor with a single ball screw reduces cost, design complexity, and assembly complexity. Using two motors with two ball screws increases rigidity, performance, and accuracy. Considering all other aspects of the project, which option should be selected?
    I'd go with one screw per axis. Not sure why you're going with 2?
    3. Rails extension
    A reader pointed out that our rails extend all the way to the edges of the base, column, and X-axis carriage, and considered this a design flaw. Is there a proper justification for this, and if so, what amount of clearance should be added, knowing that it would reduce travels on all linear axes?
    I think he was pointing out that the rails were spaced too far apart, not that they were too long. Moving them in should not affect travels.

    Last edited by skrubol; 07-12-2018 at 03:23 PM. Reason: Fixed quotes


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    Default Re: Open Questions

    skrubol,

    The servo(s) for the Y axis will have a brake, and the Siemens SINAMICS S120 Smart Line module can play the role of braking module and braking resistor. With that in mind, would you still put a counterbalance? Also, if straight pneumatic is enough, why do most vendors adding a counterbalance go for hydraulic? This does not make much sense to me, especially considering the cost of these setups ($2,000 for parts, $4,000 if you buy them directly from vendors like Haas).

    I'm going with two screws on X and Z because it provides more rigidity and accuracy. They're more difficult to assemble and they increase mechatronics costs quite significantly, but they're the way to go when spacing between rails goes beyond certain dimensions. If you look at box-in-box designs for many DMG MORI machines, they always use two ball screws on their linear axes. Assembling them horizontally is not too difficult, but it's much more of a pain for a vertical axis. And for Y, the spacing between rails is reduced, therefore this really begs the question of whether two ball screws are really necessary there.

    Regarding the spacing of rails, I think I'm starting to understand what pippin88 had in mind, and this makes perfect sense. I always thought that you want to space rails as much as possible in order to reduce torsion, but you actually want to strike some balance between spacing and rigidity of whatever the rails are supposed to support. If they are too far apart, you'll get deflection in the middle of the supported assembly. That makes a lot of sense! Thank you pippin88, and sorry for not having properly understood your original comment. I know you asked the same question twice, but I did not understand what you meant, both times. So, without going into complex mechanical calculations, what should be the rule of thumb there? 1/4 - 1/2 - 1/4? 1/3 - 1/3 - 1/3? If I want to keep two ball screws on each of the X and Z axes, I think 1/4 - 1/2 - 1/4 would be about right. Thoughts?



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    Default Closer Rails

    skrubol, pippin88,

    Here is an updated design with rails for X and Z being placed closer to each other, yet with enough spacing for two sets of motor and ball screw on every axis. Please let me know if this is what you had in mind. In any case, this feels a lot better to me. Thanks a lot for pointing this design flaw out!

    Attached Thumbnails Attached Thumbnails 6-axis Horizontal Machining Center for Education-screen-shot-2018-07-12-1-08-a   6-axis Horizontal Machining Center for Education-screen-shot-2018-07-12-1-08-a   6-axis Horizontal Machining Center for Education-screen-shot-2018-07-12-1-09-a  


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    Default One or two ball screws on Y axis?

    When looking at the attached picture, the question of whether to use one or two sets of motors and ball screws for driving the vertical Y axis is obvious: because the spindle assembly goes through the middle of the vertical column, ball screws have to be installed on the sides. With a single ball screw, the ball screw mount would be offset from the center of gravity of the head carriage by quite a bit (175mm to 200mm), which is far from ideal from a rigidity standpoint. This is the reason why using two sets of motors and ball screws might be a preferable option. Of course, they would be more expensive and more difficult to assemble. So, how do we decide which trade-off to make?

    Attached Thumbnails Attached Thumbnails 6-axis Horizontal Machining Center for Education-screen-shot-2018-07-12-1-15-a  


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    Default Re: 6-axis Horizontal Machining Center for Education

    Quote Originally Posted by ishi View Post
    mactec54,

    The spindle head has two axes: A and C. You can find more information about it on our drive:

    https://drive.google.com/drive/u/3/f...kwBI-?ogsrc=32

    Having A as an axis on the spindle's head is what makes C useful.

    Regarding T-Slots, we're not sure about which size we should go for. We know that it should be DIN 650 compliant, but sizing has yet to be defined. What is your recommendation? M6, M8, M10, M12? In the current design, slots are spaced by 50mm center to center.
    Just your design the small size does not show the main spindle mounting very clear, I see what you are doing now

    Tee-slots should not be less than 12mm, check what other machines this size are using, most outside of Europe use 1/2"

    Last edited by mactec54; 07-12-2018 at 06:22 PM.
    Mactec54


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    Default Re: Open Questions

    Quote Originally Posted by ishi View Post
    skrubol,

    The servo(s) for the Y axis will have a brake, and the Siemens SINAMICS S120 Smart Line module can play the role of braking module and braking resistor. With that in mind, would you still put a counterbalance? Also, if straight pneumatic is enough, why do most vendors adding a counterbalance go for hydraulic? This does not make much sense to me, especially considering the cost of these setups ($2,000 for parts, $4,000 if you buy them directly from vendors like Haas).

    I'm going with two screws on X and Z because it provides more rigidity and accuracy. They're more difficult to assemble and they increase mechatronics costs quite significantly, but they're the way to go when spacing between rails goes beyond certain dimensions. If you look at box-in-box designs for many DMG MORI machines, they always use two ball screws on their linear axes. Assembling them horizontally is not too difficult, but it's much more of a pain for a vertical axis. And for Y, the spacing between rails is reduced, therefore this really begs the question of whether two ball screws are really necessary there.

    Regarding the spacing of rails, I think I'm starting to understand what pippin88 had in mind, and this makes perfect sense. I always thought that you want to space rails as much as possible in order to reduce torsion, but you actually want to strike some balance between spacing and rigidity of whatever the rails are supposed to support. If they are too far apart, you'll get deflection in the middle of the supported assembly. That makes a lot of sense! Thank you pippin88, and sorry for not having properly understood your original comment. I know you asked the same question twice, but I did not understand what you meant, both times. So, without going into complex mechanical calculations, what should be the rule of thumb there? 1/4 - 1/2 - 1/4? 1/3 - 1/3 - 1/3? If I want to keep two ball screws on each of the X and Z axes, I think 1/4 - 1/2 - 1/4 would be about right. Thoughts?
    You don't need a counter balance if the motors are sized correctly, and if you have 2 of them it's even less work, they won't be doing much work anyway, when you have 6mm pitch Ballscrew

    Mactec54


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    Default Re: 6-axis Horizontal Machining Center for Education

    Quote Originally Posted by mactec54 View Post
    Just your design the small size does not show the main spindle mounting very clear, I see what you are doing now

    Tee-slots should not be less than 12mm, check what other machines this size are using, most outside of Europe use 1/2"
    Great! Yes, it's not easy to understand how this 2-axis spindle head works, it took me a while as well. But now that I understand it, I love it. It brings so much flexibility from a kinematic standpoint... And it's two less axes that I have to worry about, since they come pre-packaged as a single unit.

    I'll go for M12 t-slots then.



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    Default Re: Open Questions

    Quote Originally Posted by mactec54 View Post
    You don't need a counter balance if the motors are sized correctly, and if you have 2 of them it's even less work, they won't be doing much work anyway, when you have 6mm pitch Ballscrew
    That was my expectation as well, and I would really like to get rid of the counterbalance, because assembly and maintenance would be a real pain... Plus, it would save $2,000 in parts, not to mention design and debugging time.



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