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  1. #1
    Hi there,

    I am on the way of my 1rst real build. The idea is to be fast and sturdy. I am building it for a friend by order. Its a smaller variant of a sturdy machine i designed not long ago for my self which i would build after that build, which will serve also to figure some points of the process.

    I have a lot of questions and will appreciate any help with this one, as i would like to make it really right.

    From my part, once finished, i will provide the Sketchup plans for free here, so anybody can use them if wished so.

    Some of the design points:

    1. All steel soldered construction. Overbuild for stiffness, avoiding weak elements in the design.
    2. Money is not an issue for the frame or the length of the supported rails, so i am not going to go cheap to save 10cm of rail or steel profile.
    3.This machine is for continuous 3d jobs routing plastic or composite epoxy based materials so a desired stable routing speed of 300ipm is the goal
    4. Usual job size would be 800x400x160, hence that commands the gantry clearance and z design
    5. 3d continuous very detailed jobs, > 24h sometimes, made me choose a low power spindle like the 0.8kw water cooled one. Electricity cost is an issue here

    So i am at the point of finishing the design, still waiting for some details on the profiles. Already started purchasing the components. I hope in 3 months it should be making dust

    Here are some pictures of the design, still not finished:

    Click image for larger version. 

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    Profiles used 180x80x4mm
    gecko 540
    Nema 23 low inductance motors , CNC routerparts Pro Rack and pinion drives 1:3, mod 1 rails, Hiwin HG 20 rails with long wide bearing blocks on all axis,
    All plates are 10mm thick mild steel,

    The doubts:

    1. Now before i finish the design and order the profiles and plates , i wonder about the gantry weight. My design is 1000mm 180x80x4 profile with soldered over it at all sides 10mm steel plates. Basically the profile weight will be around 15kg ,reinforcing it will be another 50 kg+ the side plates another 10 + 2 motors and drives + Z another 12-15kg=more or less 100 kg. I am waiting for an advice from CNC routerparts about the gantry weight. If it heavy i can hollow some holes in the reinforcing plates to bring it to the desired weight , however i would like to reinforce it more than leave bare profile.

    2.Another point here is that i am not sure if i can bolt to 4mm profile directly threading it or should be 10mm plates below RP rails, Hiwin rails, as i designed it

    Notes:
    - the table would sit on 2 more rails same of similar size soldered. This should raise it for the cable guides and stiffen it, to avoid twisting . I am contemplating making a case there and all electronics mounted inside the base of the machine

    What do you think about the design?
    Last edited by Boyan Silyavski; 22-08-2013 at 10:53 AM.

  2. #2
    Hi,

    Well the design looks strong but you have some quite major conflicts going on here.?

    First the weight of the gantry really means your on the very edge of needing Servo's not steppers.!

    Next because your using R&P then efficiency is very low so larger Nema34 motors will usually be needed to deal with this and the weight of the gantry.
    The G540 is limited to 3.5A and 50V which isn't nearly enough for Nema 34 motors which you'll need at least 75Vdc or higher and more amps.
    Nema 23 motors (even low inductance) just will just not be able to handle the Inertia this gantry's weight will put on them. Plus combined with R&P they will also struggle to give fast acceleration with that heavy gantry which you'll need for 3D work.
    Even with larger Drives and higher 70Vdc voltage nema23 motors won't work with this weight gantry and high speed requirements.

    Really I wouldn't recommend R&P for a machine this size and with your requirements for accuracy and 3D work, Ball-screws are the only way to go.!!. . . .You'll seriously regret using R&P.

    Regards Steppers or servo's then I'd say lighten the gantry 20-30Kg and use Nema 23 motors running on 80Vdc drives with 70Vdc power supply and connected to 10mm pitch ballscrews.

    If you don't lighten gantry then I'd say choose Servos has they will handle the inertia and speed much better.
    Larger Nema 34 motors will handle the inertia at slower speeds but not do so well with the combination of speed and inertia has because they spin considerably slower than Nema23 motors they will struggle with reaching higher speeds anyway and the torque will be low at high speeds so with heavy gantry will struggle to handle inertia when changing direction.

    So Above 80KG gantry at speed will need servos.

    With Electrics in base of machine then I wouldn't recommend it has vibrations tend to loosen wires and don't mix well with sensitive electronics.!!

    The 4mm steel will be fine for threads with rails.!
    Last edited by JAZZCNC; 22-08-2013 at 06:54 PM.

  3. #3
    Thanks. I am starting to realize this.

    Let me explain something.

    This build is a rip-off of my design for my next build which is meant to ride on 34 name Rack and Pinion.

    I spend quite some time asking people around when i designed it, so it seems the overall opinion was that a 150kg gantry is quite well driven by 34 nema rack and pinion, i mean the acceleration and deceleration. There were even people on CNCzone that insisted that the gantry behaves well if is loaded more than 130kg so they made it heavy on purpose.

    So everything started as i would like to test the RP on a real build, The nema 34 would raise the price, so i went for Nema 23 and started slowly underrating my original idea.
    Now Just received an answer from CNCrouterparts and Ahron tells me what i suspected , that the g540 is not up to the task and i should couple their low inductance motors with better drivers, due to possible g540 overheating during long runs.

    So it seems i am insisting on the RP drives . I like to test them and could not help . I am at the point of ordering the RP drives , racks and the low inductance Nema 23 . That means i must lower the gantry weight.

    Ok, gantry weight.
    Lets see. I can go back to 50 kg, complete gantry with Z, still keeping some reinforcement. Only eventual twisting should be considered, z is 300mm wide so no worry there in the other directions. Another point is that normally the jobs will be done with rough cuts by 1/4 router bits and fine passes 1/8 router bits, with passes equal to the width, routing wood as i said and that easy going special cast materials which route like MDB , so this is not a factor that would play in the final design.

    Jazzcnc, i highly value your opinion. Why you believe the Chinese ball screws 2010 for example could give me better finish than the RP drives? All seem to be happy running RP drives, did i miss something? I know the table is not so big to really need RP.

  4. #4
    Quote Originally Posted by silyavski View Post
    Jazzcnc, i highly value your opinion. Why you believe the Chinese ball screws 2010 for example could give me better finish than the RP drives? All seem to be happy running RP drives, did i miss something? I know the table is not so big to really need RP.
    Those people on the Zone are probably only using R&P because.!
    A: They are large long machines so ball-screws are harder to use.
    B: They can't afford Us made Ball-screws and the Yanks are very reluctant to Import Chinese parts.
    C: The CNCRP R&P is US made so fits with above.
    D: They have never used ball-screws so they don't know the difference in performance and smoothness ball-screws make.

    My advise is just that "Advise" take it or leave it but I know thru experience with R&P that Nema23 motors with heavy Gantry is recipe for trouble if your wanting high feed rates.

    Yes I know Nema 34 will handle heavy gantry ok and that heavy helps with cutting but Heavy and high feed rates is a completely different issue.!
    Combine this with 3D work which requires Small fast direction changes and this issue becomes worse.

    Now the difference between R&P and ball-screws is several.

    Ball-screws are much more efficient so don't require has much power to turn, typical efficiency for Balscrew is 90%+ were R&P is 60% or lower.
    Ball-screws have much lower backlash so are far more accurate and repeatable. R&P is quite high backlash and not easy or cheap to make real antiback lash using correct pinions.

    R&P resolution is much lower and to get higher resolution requires at least 3:1 gearing this in turn means steppers need to spin fast and has you may or may not know torque drops off fast at higher speeds on steppers and even more so on Nema 34 motors unless running really high voltage.

    R&P is noisy and needs much more maintenance and protection from chips etc.

    Ball-screws give a silky smooth action where has R&P is in comparison a clunky action so this does translate back into the cutter at some level.!!. . . For general wood working then this is fine and doesn't get noticed but if your wanting high quality finish or high detail then you will see a enough difference compared to ball-screw machine.

    Again just My opinion and you choose to take my advise or not.? . . . . But let me just say go try to find some one who has experience of Both and ask which they would choose for a machine this size, weight and with your requirements.?? . . . . I know the answer because I've give it you.!!
    Last edited by JAZZCNC; 22-08-2013 at 08:10 PM.

  5. #5
    OK,
    I get it. I appreciate the help.

    Then what would be your exact recommendation?

    Drivers, breakout board, nema 23 motors , PSU combination in combination with which ball screws?

  6. #6
    Quote Originally Posted by silyavski View Post
    OK,
    I get it. I appreciate the help.

    Then what would be your exact recommendation?

    Drivers, breakout board, nema 23 motors , PSU combination in combination with which ball screws?
    Ok for this size and with Gantry upto 70-80KG.

    80V Digital drives and recommend Leadshine AM882
    3Nm nema 23 motors like these SY60STH88-3008BF
    70Vdc PSU preferably unregulated toroidal with correct amperage for all motors.

    BOB recommendation is difficult because the one I'd recommend and think is by far the best is PMDX 126 but it's expensive. PMDX.COM - Products for CNC and motion control applications
    The next I'd recommend and use often so know are OK boards is this one. OPPB but it's not in the same league has PMDX.

    Ball-screws would be 10mm pitch and 16mm Dia for X & Y axis with 5m pitch 16mm dia. Motors would connect to them using 15mm HTD timing belts and pulleys with 1:1 ratio. This lessens resonance which helps on a steel framed machine and it's much more flexible if you ever want better resolution or higher speed has it's easy to apply a ratio with simple pulley change.
    20mm Dia 10mm pitch could be used but really not required at this length and would be over kill, would also restrict performance not increase due to extra inertia of larger screw and ballnut.

    All the above I've used on several steel framed machines with gantry's approaching 80Kg so know they work.!!

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  8. #7
    Talking about the frame or any other frame for that matter,
    If it's to be painted, which would be a good idea, do the rails sit on top of the paint ?
    If epoxy is to be used under the rails or part of the associated support structure is the epoxy under the paint or on top of the paint ?

    I'm asking because paint has thickness and is not rigid.

  9. #8
    Quote Originally Posted by EddyCurrent View Post
    Talking about the frame or any other frame for that matter,
    If it's to be painted, which would be a good idea, do the rails sit on top of the paint ?
    If epoxy is to be used under the rails or part of the associated support structure is the epoxy under the paint or on top of the paint ?

    I'm asking because paint has thickness and is not rigid.
    I am still waiting for a friend to bring me around new year the laser cut parts. Will solder, epoxy, mount rails and paint. In that order.

    Let me explain. This machine exactly i am making for a friend who is pro model maker / yachts/ . First i suggested him to spray with gun Henkel machine paint/ anti oxide and paint directly on metal/, which i use and is very good. But the guy is a maniac, and honestly i felt ashamed when i saw his perfect yacht models which any watch maker will envy. So lazy me, i pretended i don't know how to paint a car :-) and he will come to help me with the painting. It would be painted the way the cars are painted- perfectly with glossy double component car paint and all the stuff that comes before that. Will document with pictures the process.

    At the end i thought that it is good that somebody raise my bar, when perfection is expected. I will do so with the other machine i am building. Yes, 2 days job but imagine the hours i will be happy looking at it.

    Basically the plan is to base paint the metal, polish, thin base, polish, 3-4 hands, laquer 2-5 hands and polish after a week or so when dry. I will use Standox car paint or Duracoat. At the end, looking at all the time and money that will go there, why not make it beautifull.
    Last edited by Boyan Silyavski; 16-12-2013 at 07:41 PM. Reason: i meant Standox car paint, not Sikkens

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  11. #9
    Forgot to say that the epoxy can be colored black for example, a smallish bottle of like 20ml will color 1l. I doubt it will affect its viscosity, the small bottle i have at home looks quite liquid, like water. Its special epoxy color though, not general type. That would be great if its difficult or not possible to paint it later, or the frame is painted beforehand.

  12. #10
    Well, the laser cut parts came. So, i finished soldering the parts to the frame. That includes the ball screw mounts. What i did was mount the ballscrews to the supports/in the middle so there is place left for adjustmennt/ and that greatly helped the correct placing. Carefully made some tacks with the Mig and waited all to cool, so checked again if the screws move smoothly. Have to note that the machine was welded with precision <1mm greatly helped.

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    Now its epoxy time. Several mistakes here. Just to fulfill my worries.

    I used some aluminum angles, hot glue from outside, instant glue below, silicone at the angle inside.

    the mistakes:

    -the channels connecting both sides should be wider, say at least 3cm, not like mine-8mm :-). Epoxy has difficulty to flow in so narrow channels
    -i am epoxy greedy, calculated the just amount. had to mix second time to fill the channels
    -scratched the base below the epoxy, with the idea of better contact. Now i can see the scratches. nevertheless i would paint the machine, but is good to know that the epoxy is quite transparent yellowish color

    The clever stuff:
    -the epoxy sides will be 40mm wide, works great for leveling.
    -it seems the way i fixed the channels holds pretty well , cust came from the garage, no pour for now, one hour later we will see.
    -used bolts on the legs to level the machine perfectly
    -as i wanted 5mm epoxy thickness, i found some magnets which together made 4.5mm and put then at the corners. This was extremely clever as right from the beginning i could see how much epoxy and where to pour. In fact i believe i poured it perfectly and did not need the channels, as there was a moment when the epoxy just covered the magnets.
    -used small torch to help leveling and take away the bubbles.

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    Other clever stuff was that i welded 2 wheels at the back and fixed 2 handles at the front. That helps me greatly maneuver the 100kg around.
    Last edited by Boyan Silyavski; 25-01-2014 at 08:06 PM.

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