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  1. #49
    Activation process peteeng's Avatar
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    Default Re: Designing new Router called Maximus

    Hi All - I have been doing some part sensitivity analysis on the current model. Whats showing up is a relationship between the tool plate stiffness and the gantry stiffness. I call the tool plate the part that carries the machine tool, its usually a flat thick piece of aluminium or steel. If the tool plate is not stiff and bends a bit this distorts the bearings and local area on the gantry and the gantry twists and bends. If the tool plate is over a certain stiffness the load pushes the toolplate directly backward and does not twist the gantry it only bends. Which is ideal as the tool stays vertical. So now I have to design a suitable tool plate that is Uber stiff. Currently I'm looking at a tubular sort of design or a deep U shape.

    This process is also called a "form finding" process or exercise. We are finding the best form or shape for the task the part has to do. Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-beam-jpg  
    Last edited by peteeng; 04-12-2019 at 04:24 AM.


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    Default Re: Designing new Router called Maximus

    Hi All - So after some tooing and froing from CAD to simulation, back and forth here's where we are. I've got to the target of 0.01mm for 100N load. There are two areas to address in the structure to make it better. See image attached I have balanced the gantry vs tool plate deflection and I'm happy with the general design trajectory of the structure. To get the inertia up on the tool plate it will have a bolt on front section. The next model will include bolts and compliant bearings so our machine stiffness will drop and we will figure out how to get it back. Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-target-jpg  


  3. #51
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    Default Re: Designing new Router called Maximus

    Hi All - Getting ready to start Round 2. I have rebuilt the bearing into 3 pieces. I have modified the manufacturers STEP model of the bearing. The red ends will be set to a plastic or zero stiffness. They are there only as a geometric reference so I can check clearances to things like bolt holes and stops. The grey top will be steel like the real part and the maroon part will be tuned to deflect like the bearings. This will be a figure of around 5000MPa. I'll look at the bearing catalogue and run a test model to check this out next. Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-15mm-car-jpg  


  4. #52
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    Default Re: Designing new Router called Maximus

    Ok I have built and tested the bearing model. I looked through the PMI and WON catalogues, couldn't find a stiffness figure. So I've picked some numbers from the Bamburg thesis and Star brand. 600N/um (0,001mm) is about right. So I built the model and used ABS (tried other plastics but too stiff or too soft, can set up a custom material) plastic data for the guide. I applied 60,000N which should compress 0.1mm and it compressed 0.07mm close enough for now. Easy to change in the future now its set up.

    So Round 2
    Cutting Envelope to be 2500-3000mm x700xZ200mm plus
    Target tool stiffness 10N/um
    Bearing stiffness 600N/um
    Parts to be laser cut and bent
    High Rail design, timber bed
    Anything else I've missed? maybe target acceleration 0.1g (9800/10=980mm/s/s)

    Round 2 shall start by rebuilding assemblies from scratch and adding motion parts. Moving right along... Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-bearing-tuning-jpg  


  5. #53
    Community Moderator ger21's Avatar
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    Default Re: Designing new Router called Maximus

    How often will you need 300mm of Z axis travel?

    The long lever of the Z axis require considerably more stiffness than if the Z axis was only 150mm.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  6. #54
    Activation process peteeng's Avatar
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    Default Re: Designing new Router called Maximus

    Hi Ger - The last post specs Z200mm plus. I build moulds and cavities by the time I have vacuum clamps and bolsters and thick blanks I'll need 200mm. If I want to make Carbon Fibre gantry parts or Z axis parts I'll need more. Of course a long cantilever needs more support then a short one. If I was doing car body panels which is on the list I'll need 1000mm or 1500mm down the track and 5 axes. Now we have a 10N/um spec its an engineering exercise to achieve that whatever the Z axis length is. Everytime I open CNCZONE I get a blue elephant ad. That machine has much more than 150mm... This is a concept design exercise there's no use in achieving the usual or aiming at the ordinary. It will take a couple of hundred hours to work through this and unless I learn lots or achieve something different I may as well go and learn to play golf.

    My machines also have an apron so people can do edge work like dowelling and dovetails and boxwork. This means ideally the tool has to be able to go under the bed height. Attached is a picture of Scoot fixing a bee frame using the apron.

    Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-frame-12-jpg   Designing new Router called Maximus-blue-elephant-jpg  
    Last edited by peteeng; 04-12-2019 at 05:32 PM.


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    Default Re: Designing new Router called Maximus

    Hi All - Been looking at the z axis assembly and deciding whether the gutter design is the go. It's really stiff so is a good benchmark. The tube type design is complicated but should be much much stiffer yet it's only about 30% stiffer for double the weight. Seems the bottom edge of the plate is deflecting more then the global deflection. So its a local issue. So looks like the gutter is in and I'll add a cap to it as well to make it tubular. I'd like to spend a little time sorting the gantry foundations before I formally start Round 2. I'v up'ed the nominal load to 10000N so I get the difference in 0.01mm's Being a linear model this doesn't mean much. I do run non linear occasionally to check no NL effects are present. Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-gutter-jpg  


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    Default Re: Designing new Router called Maximus

    Hi All - Been looking at the gantry foundations and the Z Axis bearings. I've sent off a request about some crossed linears that will save some parts (maybe). I have also consolidated the 3 parts for the foundations into one part which I'm happy about. I'll get this from my sketch book into CAD asap. If I use the crossed linears I still have to have a bearing plate to attach the Z axis drive to. But it will be more compact then using the current arrangement. Plus the load path is direct from the Z axis to the gantry vs through some other parts. Comes down to cost and availability. Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-cross-linears-jpg   Designing new Router called Maximus-foundation-jpg  
    Last edited by peteeng; 04-13-2019 at 01:13 PM.


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    Default Re: Designing new Router called Maximus

    Hi All - Did a little work on the gantry foundations or columns. I consolidated the 3 original parts into one. Still close to 0.1mm at 1000N deflection so all good. Would be good to use the bottom flange of the gantry to tie into the bearings somehow but no inspiration yet. The intent is to have the fwd bearing in line with the tool so there is no tool overhang. But the FE shows that the foundation plate bends a little in the middle so I should bring the bearing back a little. Then it overhangs.... Hmmm maybe a small overhang is the compromise. Peter

    Hi Gerry - to revisit the Question on 300mm Z. If I wanted to make this gantry as a CF part I'd need 300mm plus Z to cut the cavity. I'd need a tool+collet 157mm long. Plus the mould would be 20mm thick so perhaps even more Z is needed. Or I have to split the mould and do it in two halves on 45degs or do them as flats, assemble hand detail and finish which is not the game. Peter

    I have also asked the forum admin if they can allow MP4 movies to be uploaded. Videos are much better for this sort of thing.

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-gantry-end-jpg   Designing new Router called Maximus-gantry-foundation-jpg   Designing new Router called Maximus-overhang-jpg   Designing new Router called Maximus-gantry-mould-jpg  

    Designing new Router called Maximus-bend-jpg  
    Last edited by peteeng; 04-13-2019 at 01:15 PM.


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    Default Re: Designing new Router called Maximus

    I've also made plugs for dagger boards and rudders, from MDF, and I'm intending to do something similar again, hence my interest in this thread and your informative blog. The biggest problem I found when making the plugs ( on a 3 axis Multicam stepper motor machine at the time ) was that the job took many hours because of the small stepover and tight radius surfaces around the perimeter.

    As most plug / mould making materials are quite easy to cut have you considered sacrificing some stiffness for speed and better access ?



  11. #59
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    Default Re: Designing new Router called Maximus

    Hi Zorbit - Scoot was designed for speed and making foil plugs. It runs at 20m/min and can run faster but I usually don't. I don't see the need to relate stiffness with speed as such. You design & build what is needed. People ask me two things a lot 1) can I get a bigger Z please than 150mm which is sort of a std and 2) can it cut aluminium? Maximus is trying to answer those questions at a kit machine level. First thing is to design a structure that has the required stiffness then we move onto the drive system to get the required speed and accelerations. Thanks for watching. I think it's time to draw up a bench so the Round 1 structural picture will be complete.

    In regard to foils a 4 axis machine (prefer 5 axis on the ToDo list) and use a flat bottomed bit is the next step vs a small stepover and say a 1/2" veining tool which is a good choice. I've attached an image of MDF wing plugs made on Scoot. Sting 600 is a 22ft flying trimaran being built by a friend. Cheers Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-sting-600-wings-jpg  


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    Default Re: Designing new Router called Maximus

    There are many things I'd like to ask, but I don't want to clutter up this thread which is so useful as an insight into the design process. Would you consider starting a more "general purpose" thread to cover broader design issues and some of the topics on your website ? If your time allows it of course, I quite understand if one thread is enough to keep up with.



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