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Linear Rail OX

Discussion in 'CNC Mills/Routers' started by sgspenceley, Feb 13, 2015.

  1. sw3Dp

    sw3Dp New
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    After following the trails in literally every milling build here I found answers and wanted a mulligan. This is a great cnc build forum but isn't a cnc forum thank god, cnczone left a horrible taste in my mouth. Openbuilds is exponentially better but the computer still says no, Aluminum cnc diy is still $4k (same cost of having molds cut.) My background is from 3D printing and I'm intimate with the $350,000-no-thinking necessary mechanical, that is resolution=$ and no in-house machines. So, because lead times in good shops round here are still 7-9 months that gives me time to do the CAD myself and clone a version of katran's or a heavy weight extrusion version of yours. I learned welding at art school ... what did flo call it, "stress", well precision don't do well with stress, so fasteners for me.

    You got it right, no offense China but the well dried up about three years ago. I'll have to bite the bullet and find a US supplier for the ball screws and bearings but and I hope I'm wrong, the US retailers are just buying up the good international production and doubling the cost. Still if the part store gets them in I'll keep the Nema 23 as the limiting factor and drop my 'tax refund' on the electronics and commit to this fantasy and post.

    Ah ... Rhino just finished downloading, I can finally see katran's CAD, hope there's a bom ... I'm off to make some coffee and monkey with his design. Thanks again for morphing your ox hybrid and giving me some optimism.

    jack
     
  2. sgspenceley

    sgspenceley Journeyman
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    Hi Jack, much of this design could be made bolting together the Y axis to the X axis base cross beams. The inserts in the tube ends could be bolted vs welded with some creativity. The same design could also be made easily from 80/20 aluminum extrusion.

    The key problem with mild steel tubes is straightness, none are going to give you real precision direct from the hot rolling process. Aluminum extrusion also does not garantee straightness, after shipping and handling. In the end no one can claim any DIY build machine can be used for true high precision work, because we avoid the expense of surface grinding faces of parts because it's expensive.

    What most shocked me the most on the OX build was how much aluminum flexs when under load of nema 23 stepper motors. I love the look of the Aluminium extrusion, I love the ease at which you can cut it and bolt it together, it's an ideal machine for light cuts in wood or plastics. The OX is best in it's class of relatively cheap DIY machines, it meets a real need in the market place.

    Can you provide a link of Katrans cad you like? I assume this was a cnc machine?

    Rhino is a good surface modeling solution for complex 3D surface shapes. I hope you enjoy learning surface modeling. Surface modeling vs solid modeling both have advantages and disadvantages, all depending upon what your building.
     
  3. Tweakie

    Tweakie OpenBuilds Team
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    To get both the X and Y level and square I bonded on aluminium strips to the box section then machined those (easier to machine / abrade than the steel).
    To get them true I used oversize holes in the box section /aluminium strips and steel 'nut-strips' on the inside of the box section to secure the linear rails. The whole process took forever (best part of two days) to complete.

    Tweakie.
     
  4. sw3Dp

    sw3Dp New
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    We spend so much time fretting over shipping and vat when what we need is a new kickstarer for bulk screws, bearings and plate, co-op supplier in the part store? One Datron M10 running 24/7 and everyone has to work 8hrs a month in the shipping department, scratch that it'll be a new religion, tax exempt Church of the Cut! I'm in charge of collection baskets. There is a market for designs, kits and finished CNC but the only prophets come from the supply chain and shipping and handling is the only real evil. Deerhoof says "Don't be mean to see the green." Every supplier now gives away off the shelf parts cad, machine design can be reduced or merged to the OX caculator. Of course designing, proving that it is reliable and worth the build will be the miracle: moses the AsexualOx , my first build (... too far?)

    Here is the Katran design I got from grabcad https://grabcad.com/library/cnc-router-frame-2 but I had issues importing/exporting into my other cads and viewers and had to download the Rhino 90 day trial.

    Onshape is another young cad, browser based or on your smartphone.
    https://www.onshape.com/

    Neil - Do you need ebay for extrusion? I thought Misumi and 80/20 were international direct sales, custom cut like home depot, (extruded aluminum rail going from Indiana to Florida, then to New York then to Ontario, good luck staying true.)

    jack
     

    Attached Files:

  5. sgspenceley

    sgspenceley Journeyman
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    Sorry Jack, I forgot the builders name who's design I posted earlier in the thread. I love his attention to detail and his workshop. My last major revision was a blend of his ideas and some really good ideas from CNCzone threads, related to builds which are very stiff.

    For the CNC builder's who don't want to adopt the welding approach, I thought I would provide some inspiration using 3060 extrusion for the beams and some 30 * 30 for the cross braces.

    For fun I will get quotes for the extrusion version and publish them...
    3QuarterViewGold.jpg 3QuarterRearViewGold.jpg
     
    #95 sgspenceley, Apr 27, 2015
    Last edited: Apr 27, 2015
  6. sgspenceley

    sgspenceley Journeyman
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    Tweakie. If you were to build again would you still build a steel frame? I was "thinking" about using cold rolled steel as face plates. I always assumed the cost of surface facing them would be very similar to aluminum or steel because it's the labor charge for setting up the machine which is costly.
     
  7. sw3Dp

    sw3Dp New
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    Ask and you shall receive, you are closer to my thinking. My thinking is that the gantry plates can carry the load well especially with gravity supported linear rails. With your welded steel there is no way that a nema 23 would torque anything but itself. That is my current fear, now that I have a rigid enough gantry support the weight will stall the stepper. There is no nice part management in my free cads like inventor or solidworks so I can't easily calc the weight. Any idea on what your spindle and gantry assembly will be? Someone suggested to me today that my application would benefit from a 3kw spindle, but adding 25lbs isn't going to help anyone.
     
  8. Tweakie

    Tweakie OpenBuilds Team
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    There are some pictures of the construction of the router here:- http://hobbycncart.com/forum/62-216-1
     
  9. sgspenceley

    sgspenceley Journeyman
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    Tweakie thank you for posting your build thread. Truly outstanding work, we are very lucky to have your skills and knowledge here.

    Jack I will look into SolidWorks weight calculations. The large Aluminium beam is not light in weight either! In the end I will buy the required size motors, because I want a robust machine, it will just require more time to save, making the project longer to complete.
     
    #99 sgspenceley, Apr 28, 2015
    Last edited: Apr 28, 2015
  10. sgspenceley

    sgspenceley Journeyman
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    Material Mass Comparison of 1/4" wall steel tube VS aluminium extrusion

    aluminium weight 2640 kg/cu.m
    steel weight = 7850 kg/cu.m

    Mass properties of 3060-X-Axis
    Volume = 225.122 cubic inches
    Surface area = 2446.799 square inches

    Mass properties of X-Axis-Steel 1/4" wall thickness
    Volume = 132.80 cubic inches
    Surface area = 1058.35 square inches
     
    Joe Santarsiero likes this.
  11. sw3Dp

    sw3Dp New
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    Thanks for posting.

    I'm knee deep in costing and more importantly understanding the engineering behind the infinite variables of screws, back when ebay was cheap the cost savings made the knowing irrelevant, at these prices I need to get my wits. I keep adding info to your "discussion" that you posted last month, I have to start using the stalking app here to get a better idea of what has already been answered ... sorry, just remind me to keep diggin.

    hillbilly weights: 22lbs in Al and 38lbs in steel, if my cipherin is correct? I can live with those moments or the nema 23 should be able, but physics is still just a silly superstition to me.

    We seem to be hunting in the cracks between the ox and something like tweakie's or this one http://www.embeddedtronics.com/cnc_gantry.html
     
  12. Florian Bauereisen

    Florian Bauereisen Well-Known
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    Hi sw3dp,
    if we are talking (still) leadscrews:
    At 5 mm pitch, on a 16mm leadscrew, a stepper only needs to put out 1,65 Nm to generate 800 N of moving force at 1000mm/min.
    Assuming 25 kg gantry, a 100% Safety margin and 0,1sec accelleration as well as the use of the square type of linear rails.

    800 N force should (roughly) suffice to mill aluminum at aprox 6mm endmill / 1,0- 1,3 mm deep per pass.

    Hope that helps

    greets

    flo
     
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  13. sgspenceley

    sgspenceley Journeyman
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    Thank you Flo for this very valuable information.

    I have what might be a silly question. I assume 1,65 Nm is equivalent to 234 oz stepper motor here in North America?

    My Nema 23 380 oz stepper = 2.68318 Nm

    I ask because I as planning on putting both nema hole patterns in the end plates "just" in case I need to go to the larger format motors. I have been assuming my OX motors were too small... but would be good enough just to get things moving!
     
  14. Florian Bauereisen

    Florian Bauereisen Well-Known
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    Hi,
    problem with steppers beeing their rpm/torque curve.
    With the 5mm pitch leadscrew in the example above the motor only turns 200 revs per min. At that rpm one could easylie mill some aluminum with a smallish motor like a kress 1050 . But at say 1000 rpm or 5m/min it hardly puts out any torque at all.
    So it is a design-aim game.
    While beeing strong enough to cut aluminum, this example would still cut balsa at fast speeds and say 2mm ply to 1500mm/min...2,5 D would require some time as the roughing at high speeds and feeds only will allow 5or 6mm millbits.
    The finishing cut on the other hand will be as fast as anything, as the ballnose bit being smallish as well as its stepover. The nema 23 allows for high accelleration and the milling parameters allow for high cutting speeds..

    If one desires to go faster on that 2,5d example one would need to have higher torque at higher revs...leading to a longer Nema23 as mentioned above.
    raising your voltage suppy will give you higher torque at higher rpm as well.

    If one desires to simply aply more brute force to aluminum ( 3kw spindle and say a 20mm bit) one would need more torque at low rpm leading to a Nema 34 setup. The "ocasional" 2,5D mould or plug still beeing possible but the inertia of the big diam rotor will slow the process down ... especially at the finishing cut using small bits and stepovers.

    So as anything in live it is a tradeoff...

    Servos beeing the ultimative solution, i have the clearpath ones on order for my new mill.

    greets

    flo
     
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  15. sgspenceley

    sgspenceley Journeyman
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    Thank you Flo, it's always a pleasure to read and learn from your posts.

    Can you share some pictures of your new mill?
     
    #105 sgspenceley, Apr 28, 2015
    Last edited: Apr 28, 2015
  16. sw3Dp

    sw3Dp New
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    Hey flo,

    Yes and thank you. At this point I'm going to pretend I understand everything you said, there's that 3kw beast again and clearpath as in $300 nema 23s?

    I was playing with the idea of the 2.2kw or slightly smaller spindle as the Chinese ones in my price-point are rumored to have exaggerated specs. On the x with two 5mm pitch 16 mm x 1000mm lead screws and 20mm flat linear rails, 76mm nema 23s that supposedly pull 3.5A, allowing for "max" holding torque of 3.0Nm(425oz.in) but I would rather drop down to the 1.8A, 2.4Nm(340oz.in) for lower voltage/heat and backlash? Higher spindle speeds with 4-12mm end mills and .75 mm depth per pass (calculated solely on acceptable machine time per mold as I have no real experience with realistic feeds and speeds) for 750mm x 300mm x 15mm 6061 mold parts. 8+hrs machine time/4days per week. Running in a enclosure at low enough decibels to listen for that missing cat. That was just the initial hurdle. If the improbability drive was capable, I would have a machine for the cost of the molds ... and still better education than community college working on a 5 axis machine.

    Those were the economic and arbitrary assumptions I had going into the minimum specs for the build design after throwing the Chinese fortune sticks. Like I said too little experience and way too many variables but I will build something and find out the hard way for the fun.

    Steve, sorry for the hijacking of your discussion, I swear to migrate these opinions and specualations to my build once the extrusion and stepper motors arrive (I, me, mine.)

    jack
     
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  17. sgspenceley

    sgspenceley Journeyman
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    No problem Flo, it all adds to the education and information process.

    I publish to give and receive knowledge.
     
  18. Florian Bauereisen

    Florian Bauereisen Well-Known
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    Sorry Steve to, again answer to Sw3Dp within your build:

    The Servos had only been mentioned as these offer the best solution if you are willing to pay....alot...

    As i wrote before it is the best to use a as high as possible voltage supply, in order to get the most out of your steppers ( or servos)

    There is no gain at all to run them at lower voltage. Quite contrary, having some overhead will prevent missing stepps and stalls.
    I merely tried to point out the difference of a nema 23 to nema34 drivetrain..

    Backlash has nothing to do with the power output of your steppers... it is a mechanical thing...

    greets

    flo
     
  19. sw3Dp

    sw3Dp New
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    flo,
    thanks, got it, backlash is on the screw not the holding torque of the stepper motor.

    Steve,
    In your early iteration you had the stepper motors off set with spacers on the y gantry I assumed to gain some routing space inside? I've been thinking about that today was the change a stability thing?

    jack
     
  20. sgspenceley

    sgspenceley Journeyman
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    I honestly enjoy the questions and answers because they are relevant to building a linear rail CNC machine. This thread was created not out of personal pride showing off my build.

    I thought it was more interesting to show a design process, of ideas and suggestions. A CNC machines can be built in so many different ways, so many opinions and finding the right balance between cost, strength, and ease of building.

    For example, I love the servo motors, highlighted by Flo. If I was building a production machine then I could justify the increased costs, but my machine is for personal use and some small production work on a weekend. So with great sadness no servo motors in my plans..

    It's honestly a really fun design challenge and very satisfying process designing your own machine. You start with so many open questions, and you slowly come to a design that works for you.

    After reading more and more about linear bearings and the best use of them, I noticed that they are supposed to work more efficiently if the weight is evenly distributed over both bearings. When using the 2" * 6" steel beam, the Z was pretty central based on the length of my bearings . The second key concept I wanted to preserve was the X beam sitting directly on both Y axis carriages.

    I'm trading off X axis gantry stiffness VS chances of debri on the linear rails! I might regret this choice!

    My other original assumption was the lead screw and bearings need to be the same length as the Y axis support rail. Then I thought about just making the Y axis beam longer without needing the rail to be longer. This caused me to reverse the end the leadscrew and motors attach, so they are now on the back side of the X gantry. In the end the machine base is a little longer, without having any additional expense on rails or leadscrew. Earlier my design had the router with the ability to machine over unsupported base, which is a waste, but good for changing spindle bit!

    I know the OX has a real problem with particles landing in the v slot and the wheels running over the top! But now I have the linear bearing in hand my design assumptions changed.

    I hoping the wiping seals on the bearing will remove and small particles! The bearings don't actually run on this top rail surface, they actually slide along 4 ball bearing tracks on the side of the rail. So it's a very small surface area that can collect dust and debri.

    My suggestion to anyone at the planning phase, choose and buy the key components before you finalize the design. Detail ideas become more refined when you have the rails and leadscrews in hand.

    Building a 3D CAD model is worth the time and effort. It forces you to think and question design assumptions. Don't rush the process, let the machine evolve naturally.
     
    #110 sgspenceley, Apr 29, 2015
    Last edited: Apr 29, 2015
  21. Joe Santarsiero

    Joe Santarsiero OB addict
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  22. sgspenceley

    sgspenceley Journeyman
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    A very interesting read Joe, thank you for posting this.
     
  23. Joe Santarsiero

    Joe Santarsiero OB addict
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  24. RAVINARAYANAN

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    Hello friend,

    It's very nice job, but we need some what the max pay load ?
     
  25. Neil Rosenberg

    Neil Rosenberg Journeyman
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    HI Steve, and wow has your design evolved! There's probably a business somewhere in there if you can compete with China-Incorporated (who are mainly putting out pretty but low performance cheap machines). Where you at lately, I've seen so many different renderings here, which one or ones have you actually built at this point?

    My hat's off to you!

    Neil
     
  26. stylewarz

    stylewarz New
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    Fist of I would like to congratulate you to the great design! I'm very new to the CNC world but the design caught my eye.

    I've been trying to find the size of your machine and was not able to. How big will you create it?
    At the moment my experience with CNC is at the level of building a Rostock Max V2, printing finished designs to get used to the printer and the CAD. Some small own mode designs mostly for the household or my workshop.
    A CNC mill like the one you are working on would be perfect for my intention to design my own models. The mill to make negative forms which can then be used to make full carbon fiber airplanes instead of making the forms from an "accurate" hand made markup.
    Next to that I love building machines like this one so I'll be checking once in a while on the status of your build. I guess the aluminium extrusion version would suite my purpose and build skills as I cant weld.

    Anyway.. Thank you for sharing and looking forward to maybe build one on my own.

    Phil
     
  27. MartinTurner

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    Hey man.

    Your designs look amazing.
    I am looking at upgrading my existing OX now and I have studied your designs in detail.

    One thing I noticed with your design evolution is that you moved from to 2 SBR round rails mounted on each side of the Y Axis to the 1 Bosch rails per side mounted on the top.
    This seems much better, from what i can see but how will you keep the crap from going into those slides ?

    Obviously most of the rail / ball screw kits that come from china only come with one Y Axis rail, so this is a problem for me.
    Also i am struggling to find any Bosch or Hiwin rail kits that A) Are the right size for me, or B) Are not to expensive.


    Hope you don't mind me asking you a few questions...
    I think you could save me a lot of time and money.. :)

    1. Are the Bosch bearings that much better than the SBR Rail ?
    1a. Do you think your design would work if you mounted a single SBR rail on the top of the Y Axis instead of the Bosch rails?

    2. What was the quality of your Chinese ball screws / SBR rails like. Did you use a particular ebay supplier?

    3. How are you planning on cutting your plates and what material do you spec ?

    4. What steppers and drivers have you spec'd. Will the Nema 23's still cut it do you think ?

    5. What router head unit do you plan on using ?

    Thanks man
    Best of luck
    Martin
     
  28. MartinTurner

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    PS. What made you decide to move away from rack and pinion ?
     
  29. Joe Santarsiero

    Joe Santarsiero OB addict
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    Hey Flo,
    I know it's been a while, but can you run through the math with us on this one?
    I'm coming up with different figures.
    somewhere near 110N of force at the ball nut at hold.

    Joe
     
  30. Florian Bauereisen

    Florian Bauereisen Well-Known
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    HI,
    its a little xls. sheet. Unfortunately i do not know how to post the results..
    well anyway that is just a quick calc... of course that assumes that friction and all other factors really are
    what you type in and of course it assumes a real ballscrew with 80% efficiency.
    If i change that to trapezoidial screw than figures will change dramatically. Your 110 N sound to me like that.
    screwlenth.. motor inertia friction ....onandon....
    so if you change a few factors you will see dramatically different figures.


    greets

    Flo
     

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