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  1. #21
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    Default Re: Ram-type milling machine

    Hi IHNF - I have just downloaded Sigmaselect as its called. I have had a play with it and by the time I have waded through the menus I would have calculated the torque required manually. Using sigmaselect I still have to calculate the rotational inertia of the ballscrew and I have to select a motor vs use the known motor inertia. It does do some things that are more difficult like inclines and cranks and flywheels. So IHNF I'm not trying to give you a hard time. I'm just presenting easy stuff for people to use to design their machines.... I tried to match it up to my earlier calc but its difficult I will continue to look at it. It also includes jerk which is quite interesting (to me anyway) cheers Peter



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    Default Re: Ram-type milling machine

    more importantly, it lets you define motion paths, and it will size motors based on the aggregate path, not just one portion. for example acceleration usually takes a few hundred milliseconds... so you dont need a 4nm continuous motor if you only need 4nm when accelerating.

    everyone knows the basic math, that's the easy part. applying it to a practical end use is where it gets tricky.



  3. #23

    Default Re: Ram-type milling machine

    Quote Originally Posted by peteeng View Post
    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
    Depends on the motor manufacturer. For example, Yaskawa servos can be run at 110% of rated torque for 30 min, 130% of rated torque for 90 seconds, or 150% of rated torque for 30 seconds. Fanuc rates their Alpha motors at 110% for 30 min, 130% for 15 min, and 210% for 30 seconds. You are painting a very broad brush.

    None of the major servo manufacturers (Mits, Fanuc, Yaskawa) make liquid cooled axis motors, as far as I'm aware. The large majority of motors don't even have a fan. Torque motors are sometimes liquid cooled and used in rotary tables.

    Liquid cooling bearing mounts are sometimes done by machine tool builders.



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    Default Re: Ram-type milling machine

    Quote Originally Posted by footpetaljones View Post
    Depends on the motor manufacturer. For example, Yaskawa servos can be run at 110% of rated torque for 30 min, 130% of rated torque for 90 seconds, or 150% of rated torque for 30 seconds. Fanuc rates their Alpha motors at 110% for 30 min, 130% for 15 min, and 210% for 30 seconds. You are painting a very broad brush.

    None of the major servo manufacturers (Mits, Fanuc, Yaskawa) make liquid cooled axis motors, as far as I'm aware. The large majority of motors don't even have a fan. Torque motors are sometimes liquid cooled and used in rotary tables.

    Liquid cooling bearing mounts are sometimes done by machine tool builders.
    siemens does water cooled servo motors, above 10kw or so. not generally something in a "standard" milling machine axis.

    in machine tool application, where the load varies wildly every second for axis motors, you can often use an average duty cycle. a 750w yaskawa motor needs to stay at an average of 2.34NM for 10 minutes while adhering to the peak torque time curve. you can accelerate in a cut at 8.5nm, and then cruise in your rapid moves at 0.2nm, as long as it averages at 2.34. so in sigma size/select you add motion paths to simulate say, a section of an adaptive clearing move. accelerate, cut, decelerate, reverse, rapid back, and repeat. set the cut force to be the most your spindle can put out in tangential load. it will give you the motor you need based on load and inertia.

    What you usually find (especially if you are used to steppers), is you don't need any where near as big a motor as you might have thought. The brother TC225 with 2005 screws on x and y used 400w servos, accelerated at 0.25G, cruised at 787ipm.





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    Default Re: Ram-type milling machine

    I have checked Sigmasizing calculator and it looks simple to use but still you have to manually input acceleration time that you wish to have.
    And here is problem I don't know what to input here. What is recommended speed or what others use ?
    For rapids I'm inputting 20m/s and for weight 600kg
    If I input acceleration time 0.3s than 1kw servo is ok if I input 0.1s, than needed force goes much higher.
    The supplier of servo is saying that I should have 1.5kw (10NM peak 25NM) servo for moving 600kg on 2510 ballscrew but to me that is rather high and I think it is not needed.
    At first they offered me 1kw servo (4Nm peak 12Nm) but when I said that I will move 600kg of weight they changed it to 1.5kw - is that necessary ??



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    Default Re: Ram-type milling machine

    well, ill give you the spec of my bother machine in that video:

    screw - 2005
    acceleration - 0.25G / 2.5m/s/s
    max speed - 787 ipm / 20m/m (4000rpm)
    table mass is about 250kg maybe (its pretty light)
    max work piece weight was 100kg on that machine
    this machine HAS jerk control which lessens stress on the machine accelerating. linuxcnc and mach 3 do not have jerk control.
    it ran happily with 400w motors.

    as you can see in that video, 0.25G is pretty fast on a small machine like that. thats "cutting" in the 400ipm range.



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    Talking Re: Ram-type milling machine

    Quote Originally Posted by ihavenofish View Post
    well, ill give you the spec of my bother machine in that video:

    screw - 2005
    acceleration - 0.25G / 2.5m/s/s
    max speed - 787 ipm / 20m/m (4000rpm)
    table mass is about 250kg maybe (its pretty light)
    max work piece weight was 100kg on that machine
    this machine HAS jerk control which lessens stress on the machine accelerating. linuxcnc and mach 3 do not have jerk control.
    it ran happily with 400w motors.

    as you can see in that video, 0.25G is pretty fast on a small machine like that. thats "cutting" in the 400ipm range.
    Thank you for this information, yes this speed looks pretty fast, if I can achieve same speed with my heavy 600kg moving column I will be extremely happy
    I have received also quote for servomotors and electronic and there is really not much of a difference in price between weaker and more powerful servomotors so I guess I'll take stronger motors.

    Still working on overall design, but for now it looks like this
    Ram-type milling machine-eg-v1-jpg

    Would be ok to make mold out of high density XPS Styrofoam with imbedded steel ground surfaces for linear rails ?
    I could easily make molds like this on my old CNC machine . I think that XPS Styrofoam is enough compact so it would not deform under weight and it is easy to form.

    Merry Christmas !!!



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    Default Re: Ram-type milling machine

    Merry Christmas Lukahr - Jingle bells jingle bells.... styrofoam will not be stiff enough for the moulds. I'd be thinking 16mm MDF with melamine coating.... If you have FE on your CAD you can model the EG pressure on the mould and figure the deflection out. Use a hydrostatic pressure profile... Peter



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    Default Re: Ram-type milling machine

    I would use XPS not standard styrofoam.
    XPS has compressive strength of 500 kPa or 700kPa.
    That would be only for internal shape. Around that I would build box out of plywood or something similar and connect everything with thread rods so it does not deform.
    I will try to make smaller scale model to test this out, or test in FE if I figure out how to simulate this



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    Default Re: Ram-type milling machine

    Happy New Year !!

    So little update about machine
    I have pulled the trigger and ordered :
    - servo motors + drivers (X,Y axis 2.6kw and Z axis 1kw 2500RPM with 23bit Tamagawa absolute encoders. )
    - spindle motor + driver (5.5kw servo motor 12000RPM)
    - 5 axis controller
    - TBI 2510 C3 ground ball screws + double offset ballnuts
    - Bearing blocks for ballscrews FK20 and BF20
    - MPG pendant
    - optical linear scales with 1micron resolution for XYZ

    Now the waiting game begins



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    Default Re: Ram-type milling machine

    Little update
    Had much other work to do these days so not much progress on 3D model, for now I have added ballscrews, servomotors and motor mounts on Y and X axis.
    Also machine got legs
    (Ignore Y axis servomotor and mount floating in air I still need to extend saddle)

    Ram-type milling machine-egv2-jpg


    Now I'm thinking about steel inserts for linear rail surfaces.
    they will probably be 45x45mm square steel bar imbedded in mold.

    But now I'm in dilemma as I have couple of options for what type of steel to pick.
    - Hot rolled, cold rolled or cold drawn?
    - s355 or c45
    What grade steel machine better ?

    Or this really doesn't matter much as it will be imbedded un UHPC and wont be able to move after milling/grinding



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    Default Re: Ram-type milling machine

    Hi Luka - The machine is looking "severe" as my German friend would say! Looking very robust. Are the cars flanged? Its unclear how you are going to bolt them to the parts? Also modern machines are usually three point mounted. Then a couple (or more) of stabiliser feet. This makes it easier to level. I think the bed should be thicker to keep to the rest of the proportions.... Keep at it, Peter

    afterthought - Looking at your model I see that the Z will be quite a big cantilever and will be the weak link in the design. What about making the table go up and down for the Z? Will be extremely stiff. And make it a separate part which will make casting lighter.... ??



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    Default Re: Ram-type milling machine

    Quote Originally Posted by peteeng View Post
    Hi Luka - The machine is looking "severe" as my German friend would say! Looking very robust. Are the cars flanged? Its unclear how you are going to bolt them to the parts? Also modern machines are usually three point mounted. Then a couple (or more) of stabiliser feet. This makes it easier to level. I think the bed should be thicker to keep to the rest of the proportions.... Keep at it, Peter

    afterthought - Looking at your model I see that the Z will be quite a big cantilever and will be the weak link in the design. What about making the table go up and down for the Z? Will be extremely stiff. And make it a separate part which will make casting lighter.... ??
    Yes it should be heavy and rigid when done - like the ''old'' good ones

    Cars are RGW-CC (roller) flanged in rails are size 30mm
    Bolted will be from bottom up into embedded steel plates
    Ram-type milling machine-egv3-jpg
    This is good idea about three point leveling system I need to check if I can implement it in my model.

    Z axis will probably really be the weakest part in machine. I need to carful design it to make it rigid as much as I can.
    Whole z axis beam will be 1000mm long as motor will be direct drive. Z axis travel will be 550mm
    I will try to move cars of Z axis as wide as it will be possible.

    I don't want to make moving table, that is why I went with moving column design like this, I want fixed table on this machine.
    Table is now 130mm thick - 100mm of UHPC and 30mm steel on top
    Steel plate will be resurfaced and T slots milled in after everything will be aligned and trammed.



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    Default Re: Ram-type milling machine

    Is this rail mounting method good enough ?

    Ram-type milling machine-mounting1-jpg

    Or should I make reference edge on both rails ?
    Is there any big advantage with using double reference edge other than quicker installation.



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    Default Re: Ram-type milling machine

    Ok so for rail mounting method i went with one side full reference edge other side just flat.

    Now I'm sitting at this.
    I need to figure out how to lower z axis height - servo motor with direct coupling comes to high.
    My ceiling is 2400mm and z axis servo is sitting at 2460mm, I will probably need to mount servomotor with ballscrew on column instead on z axis.

    Also I'm still figuring out where to put ATC and what type would be best for this kind of machine.
    As my work table is centered i have little space on each side, maybe it would be better to make it off center and leave on one side more space for ATC .... will see

    Ram-type milling machine-egv4-pngRam-type milling machine-egv5-pngRam-type milling machine-egv6-jpg



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    Default Re: Ram-type milling machine

    How high is your table?

    Why direct drive for servo.
    You can use a belt and have the servo out the way.



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    Default Re: Ram-type milling machine

    Quote Originally Posted by pippin88 View Post
    How high is your table?

    Why direct drive for servo.
    You can use a belt and have the servo out the way.
    Table - working surface is now sitting at 735mm from ground.

    I was thinking of direct drive so i don't have to make transmission with belt drive and that way i have one less variable to look after.
    But yes i think best solution will be to make belt driving and move servomotor on column out of way.

    Like this, but to flip servomotor around and add belt for driving

    Ram-type milling machine-z-axe-png



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    Default Re: Ram-type milling machine

    I have made it under required 2400mm

    Now I need to find timing belt and pulley combination that is suitable for this application. I'm thinking GT2 timing belt in 20 - 30mm width
    Transmission will be 1:1 on 1kw servomotor.

    Also I will need to reduce weight of column somehow as it is sitting at 460 kg. If I add saddle weight and z axis weight I think it will be too heavy - somewhere in 700kg range.
    I will reduce weight later when I will have roughly final design. I will try to make couple of holes for weight reduction.

    Ram-type milling machine-egv8-jpgRam-type milling machine-egv7-jpg



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    Default Re: Ram-type milling machine

    Hi Luka - Move your front feet forward a bit. You need to maximise the ground support. There's a lot of mass moving around and the more geometric support the better... Keep at it...Peter

    Attached Thumbnails Attached Thumbnails Ram-type milling machine-mill-jpg  


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    Default Re: Ram-type milling machine

    Yes I will try to move feet a little more apart, I have also extended table more in front to allow z axis reach back side of table and haven't really correct table support accordingly.

    But as far as center of gravity goes it looks pretty much centered between front and back legs no matter where a put column.
    Base weight is one huge mass so center of gravity really doesn't move much with column extreme positions.

    Ram-type milling machine-egv9-jpg

    Last edited by lukahr; 01-23-2021 at 08:09 AM.


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