Revising the toolchanger to hold a 2.2kw milling spindle

Discussion in 'Tool heads & ToolChanger' started by Alex Dattilio, Jan 15, 2020.

  1. Alex Dattilio

    Alex Dattilio Member

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    Hi all. New user here in the forum. I am building a fully automated multi-use cnc machine (possibly with 5 axes) The machine will use hemera extruders for 3d printing on a glass bed, and when milling (i will be milling things such as aluminum, and wood and i might consider adding a plasma cutter down the road for steel), I will be using a 2.2kw chinese spindle. I've worked out just about everything at this point except for getting the spindle to work with the toolchanger. The E3D support team told me that the toolchanger can only hold 500 grams (about 1.1 pounds) and my spindle is 4989 grams ( 11 pounds). Ive attached a photo of the setup for my spindle attachment, but ignore the second spindle on the tool wall on the left as that is just for the spindle's placement in storage (spindle is in green, tool changer parts are in red, and x-axis armature/carriage plate is blue) Also, since the toolchanger is not wrapped around a gantry, the reason i dont have all the toolchanger parts modeled is that i have to redesign it to make it more compact. Now, in my setup seen in the attached photo, the x-axis is a gantry made out of aluminum, with an aluminum housing armature (for the additional axes) attached to the x-axis carriage. What I am calling the 4th axis is located at the bottom of the armature and is a rotating disk powered by a nema 23. This disc is what will hold the toolchanger. Now, since the tool changer is attached to a heavy duty gantry and armature, and the spindle is connected horizontally to the toolchanger, what kind of improvements would I need to make to the toolchanger to ensure it can hold my spindle? I'm guessing that the carrying weight E3D provided me was, in part, due to the limits of their motion system x-axis, and the servo that is used to control the toolchanger. If this is the case, would a using a stepper instead of a servo be the solution to my problem? Any help would be appreciated as im extremely close to finishing my multi-use cnc design! I will be glad to share my designs and videos of it being built and/or fully operational :)
     

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    #1 Alex Dattilio, Jan 15, 2020
    Last edited: Jan 15, 2020
  2. Joe Pomo

    Joe Pomo Active Member

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    I have a Hemera tool on my TC. When it is locked to the X-Axis and fully drawn into the kinematic assembly, it does not take much force to separate the plates at the top VEE/Ball Bearing. I think this is mostly a function of the spring tension on the tool changing "bayonet" rod that grabs each tool. The rod itself is mostly free to slide fore and aft, and when it attaches to a tool, the spring tension is what holds the tool in place. And for what it's worth, the tool-changing mechanism already uses a small stepper motor in lieu of a hobby servo.
    (My Hemera tool is probably close to 500g.)

    The three major hurdles I see:
    1) Your spindle's mass would far exceed the tool-changer's ability to even 'grab' and draw the tool in.
    2) The TC's x-axis rail will noticeably deflect in its middle of travel with the spindle attached. (It is easy to make the rail bend and twist by hand)
    3) The motion system uses NEMA 17 steppers and 6mm wide fiberglass belts. You would want NEMA 23 steppers and wider or multiple belts for a moving mass that large

    I'm also researching TC-compatible spindle tools, and I think our best bet is to find a way to keep the tool's mass low. Maybe something like a handpiece connected to a flex-driveshaft and remote motor combo would work, like the one used on this kickstarter mill:
    https://www.kickstarter.com/projects/rp3d/the-micromill-a-desktop-cnc-milling-machine

    It's an admittedly less robust spindle set-up, but it might save you the hassle of doing a major redesign of the TC.
     
  3. Alex Dattilio

    Alex Dattilio Member

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    Hi joe. Im not using the E3D's motion system, as i mentioned in my post and you can view in my picture. Im using nema 23 and ballscrews for all axes. My gantry for the x-axis is going to be all aluminum plating, about 6.35 mm for the gantry beam. Unless proven otherwise, I don't think my frame or motion system will be an issue with the toolchanger. My primary concern would be the parts of the toolchanger, like the rotating shaft and the servo motor. Im not exactly sure what conditions E3D were quoting the 500 gram weight limit, but i would guess that they were taking their motion system x-axis into consideration for that calculation. If i can make some small modifications to reinforce the toolchanger and, if necessary, my gantry design, then their might be a way to make it work with the spindle.
     
  4. Joe Pomo

    Joe Pomo Active Member

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    Sorry, I should have read more carefully.

    For the 500g maximum E3D told you, yes, I would say the stock X-axis rail would play a roll. But the toolchanger toolhead (the part that grabs your tools) will be a problem, based on my experience. The kinematic interface works well for light tools, but you may need a different design for your spindle. Using a servo vs a stepper is probably not as important as using a more robust spring on the drawbar to keep the tool in place. Here's a toolchanger design on an MPCNC:



    You can see that it uses two "draw bars" to attach the tool and 8 alignment pins (compared to the 3 on the E3D design).
     
  5. Alex Dattilio

    Alex Dattilio Member

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    Ah. Thanks for the suggestions, Joe. I was already considering adding another draw bar on the toolchanger as i figured one just wouldn't be enough. I actually wasn't aware that those 3 thing on the toolchanger were for alignment ;) In my revision, I was going to make the toolchanger plates square anyways, so I could use that extra surface area to include more alignment points. In doing so, of course, I'll need to shift the mounting plate pins for toolhead storage to allow the toolchanger face plate to slide between the mounting pins to pick up the toolhead. In regards to the spring, does anyone have a video of how the spring is loosened/tightened in the toolchanger? I've been scouring the internet for pictures and video of the internal mechanisms of the toolchanger, but have yet to find anything that shows how the spring works.

    On a side note, I hope that other people, particularly the E3D toolchanger team, provide some input to my design so that others can use it for similar needs. Thanks.
     
  6. elmoret

    elmoret Administrator

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    Very possible I'm interpreting things wrong, but assuming by "6.35mm beam" you mean a square beam measuring 6.35mm on each side, I think you are underestimating deflection just a bit.

    [​IMG]
     
  7. Alex Dattilio

    Alex Dattilio Member

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    The gantry beam is going to be an approximately 6.35mm thick, 1285mm long, 100mm wide aluminum plate. I'll be honest, I have no experience with calculating deflection, inertia, etc. This is my first cnc mill build but I need a larger milling area (3x3 ft). Im consulting with a friend who has some experience in such calculations, but I would absolutely appreciate any improvement suggestions to my motion system and toolchanger designs to make this work. I'll provide any info as needed.
     
  8. elmoret

    elmoret Administrator

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    1285mm - that's longer (worse!) than I'd assumed.
    100mm is better, but only makes it significantly stronger in one direction.

    Which direction is "wide", here? Lets say the beam is oriented vertically, so the 100mm dimension is parallel to the gravity vector. In that case, your 5kg spindle will cause a deflection of ~0.1mm, still not very good in terms of CNCing, but OK.

    But if you orient it that way, and start cutting some metal, things look bad in a hurry. I calculate around 150lbs of tangential cutting force for feeds and speeds that use about half your spindle's power. With 150lbs of force, I calculate around 200mm of deflection.

    Probably not ideal for CNCing parts.

    So orient it the other way. Now you get 0.9mm deflection from cutting force (still bad) and 18mm of deflection from gravity (very bad).

    The design work you're looking for is not something people can do quickly or the type of thing one would expect to get for free on a message board. It is the type of thing people pay consulting engineers $100/hr+ for.

    Disclaimer: All of the above is back of the envelope, have not double checked my work, but the general idea is correct. There's a reason no one uses 6mm by 100mm aluminum plate in CNC gantries that are 1300mm long...
     
  9. Alex Dattilio

    Alex Dattilio Member

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    I see. Well look, I don't need the fastest speeds possible on the spindle at this moment, but I am still wanting to go forward with the build. I do have a 80x 160 piece of aluminum extrusion that could be used, but that was bought for my original 4x4 ft design. I understand that the design can be difficult to figure out, but those in the openbuild community have created many aluminum milling machines, especially using aluminum extrusion framing. The gantry is the only thing that isn't designed to work well for my purposes right now. I do appreciate you pointing out the deflection for me so I can rule that option out. Would you consider an aluminum extrusion gantry beam strong enough for these purposes in regards to deflection? That's one design that I see through professional and diy machines
     
    #9 Alex Dattilio, Jan 16, 2020
    Last edited: Jan 16, 2020
  10. mhe

    mhe Well-Known Member

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    I dont' believe it is a good idea to change tools that way, especially not with a spindle like that - you can easily cut aluminium with it, however the cutting forces that such a spindle will generate easily overpower the holding force of the TC plate system (as it is spring loaded). I fully understand the desire for a modular CNC/printer machine, but I think it would make more sense to get some inspiration from stuff like the 5axis maker.

    However, bear in mind that 3d printers are comparably flimsy to CNCs that you can do proper machining with. So the all-in-one center doing CNC, printing and lasering simply won't work that well as it always will be a compromise between very polar opposite requirements - a laser for example wants to move fast, which warrants very lightweight assemblies and belt-driven systems, CNC machining needs stability and mass a lot more than speed. In printing you can get away with slow (but it will make it very time consuming and also a lot more power-inefficient as you'll have to keep beds heated for longer etc), but with lasers, slow will get you burn marks etc. The only thing you could do is PWM-modulate the beam and hence use only a fraction of the power. And that is with diode lasers, once you go CO2, you have to somehow get mirror assemblies into that design - and those will be very unhappy with the dust a CNC generates etc.

    Whatever you do, it will either suck as a CNC or it will suck as a printer/laser. You can't have it all in one machine, to make that happen - even if it were technically possible - would be veeeeeery cost inefficient. The only scenario where I can see that making sense is when you simply don't have any workshop space. And building a do-it-all wonder machine is probably even then more costly than just getting a bigger space to work in.
     
  11. Alex Dattilio

    Alex Dattilio Member

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    Sorry for the delayed reply, but considering the above issues, I've decided to go a different route on my cnc mill design. I am designing a 6 axis robotic arm suspended from the top of my enclosure that will be able to hold my spindle and other tools as needed. Obviously the mechanical engineering required to make it is intense, which is why my friend who has experience with such is guiding me through the steps to calculate the necessary speed and torque for each joint to withstand my milling speed and feed. I've been spending a few weeks doing these calculations, so its coming along fairly well. While im not sure how well it would operate for 3d printer purposes, I am going to make certain that it is designed to account for the many forces involved with milling, using gearboxes to dramatically improve torque. I certainly hope it will end up being sufficient for multi use purposes, like robotic welding, 3d printing, laser etching, etc. Tool changing would likely be done with screwed-in metal holding clamps for each tool, with an automated system at each tool storage dock to screw the tool into or unscrew the tool from the robotic arm. But, that system is still up for debate until i get the arm working for milling. While the e3d toolchanger is not useful for larger purposes such as mine, it certainly has given me great design inspirations ;) I shall update you all if and/or when i get the arm operational, which could certainly take a few months or longer. Thanks for your assistance!
     
  12. elmoret

    elmoret Administrator

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    A 6 axis robotic arm that can handle 150lbs of force and maintain accuracy relevant to CNC machining costs upwards of $150k and is roughly the size of a horse.

    I have some doubts about your friend's expertise.
     
    Jason Chodakowski likes this.

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