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  1. #37
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    Default Re: Designing new Router called Maximus

    Hi Peter,

    IMO, this is going to be your biggest challenge regardless of the Z-slide shape.

    Designing new Router called Maximus-capture-jpg



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    Default Re: Designing new Router called Maximus

    Excellent post, I can see I will learn a lot from this, thanks.



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    Activation process peteeng's Avatar
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    Default Re: Designing new Router called Maximus

    Quote Originally Posted by davida1234 View Post
    Hi Peter,

    IMO, this is going to be your biggest challenge regardless of the Z-slide shape.

    Designing new Router called Maximus-capture-jpg
    I presume you mean the small distance between the bearings? If so there is no recommended spacing for these. All you can do is stay within the manufacturers recommended loads. Obviously the further apart the better but there are limits on this to the size of the machine being designed. So this distance is considered in two ways 1) That the bearings have a satisfactory static load and life loading 2) it provides maximum stability in the geometry available. ie they are as far apart as possible. In routers and mills it is recommended to use heavy preloaded bearings. My experience with std light preloaded bearings is that some time down the track they turn into clearance bearings. This is with medium quality and priced units. Peter



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    Default Re: Designing new Router called Maximus

    Its a very interesting thread so far and the depth of engineering continues to impress me greatly.On the topic of resonance,will the ballscrews and their mountings have a differing effect on the resonance as the travel varies?



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    Default Re: Designing new Router called Maximus

    Yes the screw being of different length has a different frequency. Peter



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    Default Re: Designing new Router called Maximus

    My counterpoint was/is that cutting plywood efficiently, needs a great deal of rigidity.

    You are building a tool to cut 2.4 m sheets, of presumably some thickness like 12-15 mm++.
    There is no doubt your design will work - to some extent.

    But if your gantry bends 0.3 mm, theoretical, I think it might not handle carbide router bits efficiently in sizes 8 mm+ at efficient speeds.
    So the cutting will progress at 4x slower speeds using 6 mm cutters, again 2x slower in MRR / work done.
    == 8x slower work than it should be, for a semi-work advanced hobby design of some cost.

    E:
    Look at cutting times for 16 passes (4 shapes, back-forth), 2.4 M long sheets, say 4 m cut length (not rectangles nor artwork).
    A single pass might take 12-15 minutes, say 192 minutes total.

    This might be ok commercially, if the value you get from the sheet is high, you only need a few sheets per project, assy/design/finishing is the critical path etc.

    But if You could increase the frame rigidity (linears),
    drive rigidity (ballscrews),
    spindle quality,
    gantry rigidity (much bigger sections),
    the 192 minutes of cut time should go down to about maybe 45 minutes.
    (Still 2-5x slower than modern commercial routers at 700 ipm cut speeds at 40k rpm+--16 mins).

    Biz (imho):
    The router(cnc) commercial-guys sales pitch of cost/part in faster cycle times is mostly wrong.
    Your goal here is right - so is the approach.
    Do "something", do "better", for "your" market.

    biz-case.
    Even if you could cut the sheet in 1 minute using a uber-router (500k),
    automated sheet loading/unloading,
    unlimited power,
    no issues with vast quantities of waste and dust,
    unlimited space,
    free materials racks (40k$),
    and logistics equipment like stackers (4k$), cranes (10k$),
    loading docks, etc.,
    free financing for 200k in sheet goods,
    free financing for the cnc uber tool,
    You could/would probably sell more/less the same number of your products to your marketplace.

    And selling other products to other customers, competing with those who already have all above, mostly paid off, is a fast way to ruin.

    But..
    If it costs You 40$ to make 1 sheet in 3.2 hours, just in your living allowance at half minimum wage,
    then your bos or balance-system should be well profitable to make it reasonable, and very much depend on your needing to have total control of the process.
    Otherwise, for 40$ you get your stuff cut in 30 mins at the other place.
    And there may be a big value in clients seeing "your" industrial-sized cnc machines.

    And slow may not matter if you do other stuff meanwhile.



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    Default Re: Designing new Router called Maximus

    Some good points by Hanermo, there are many occasions when I wish I had a small router spare. Running a 10hp vac pump, 10hp dust extraction and 15hp spindle is overkill most of the time, not forgetting the noise and dust produced by 20mm tools. Sadly I only have room for one router at present, but plans are being made.



  8. #44
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    Default Re: Designing new Router called Maximus

    I presume you mean the small distance between the bearings?
    No, I think he's referring the the Z axis and spindle mount hanging so far below the bearings.

    Gerry

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

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

    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Designing new Router called Maximus

    Quote Originally Posted by peteeng View Post
    I presume you mean the small distance between the bearings?
    Quote Originally Posted by ger21 View Post
    No, I think he's referring the the Z axis and spindle mount hanging so far below the bearings.
    Both of them. They, IMO, have to be considered together.

    The small spacing between the bearings AND the spindle being so far
    below the bearings. It looks like you have a cantilever four or five times the
    spacing between the bearings by the time you add the bit to the spindle.

    IMO, this will result in quite a bit of deflection of the bit regardless of the
    preload of bearings or any other reasonable measures.



  10. #46
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    Default Re: Designing new Router called Maximus

    Hi All -Thats a design issue and needs to be resolved in Round 2. Hopefully Hanermo can clarify a target stiffness. A cantilever has the highest deflection so that's why we do FEA to understand and achieve the design requirements. Deflection is a function of the support structures not the bearings per se. So the support structures need to be dimensioned correctly. Peter



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    Default Re: Designing new Router called Maximus

    So I reread Mr Bambergs thesis and he quotes some machine stiffness requirements. So I've picked a round figure target of 10N/um (or 0.001mm deflection per 10N force) as a start. I then changed the loadcase in my current model to a load of 100N which should deflect less then 0.01mm and we are at 0.02mm. So now I can start working through the parts again and get to the target stiffness. Getting closer to starting Round 2. I reran the model with the Z axis plate set to rigid ie its infinitely stiff. This reduced the deflection to 0.01mm. This infers that half the deflection is the Z plate and half the deflection is the rest. So I need to make the Z Plate much stiffer. Plus I need to include the bearing compliance soon.

    We are in what's called the "Fuzzy Front End" or FFE of the project. But we are nearly ready to nail down a few things so R2 will be better specified and targeted.

    Peter

    Attached Thumbnails Attached Thumbnails Designing new Router called Maximus-capture-jpg   Designing new Router called Maximus-stiffness-jpg   Designing new Router called Maximus-stiffness-1-jpg  
    Last edited by peteeng; 04-11-2019 at 09:45 PM.


  12. #48
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    Default Re: Designing new Router called Maximus

    Hi All - Now we have a stiffness spec to chase (10N/um) I looked back at Scoot. Scoot was not designed to a stiffness spec. It was designed as a MVP (minimum viable product) to test various functional things and commercial arrangements. The philosophy was to build it to a minimum function (vs stiffness) and work it then solve the issues as they came up. Scoot is now at its development end.

    I reran the solver with 100N longitudinal and 100N transverse loads. Its long stiffness was 0.25N/um and its transverse is 0.5N/um. Scoot cuts plywood, plastic and soft materials quite well holds better than 0.1mm as far as I can see. But now it's time to up the stiffness. So Maximus will be 40x stiffer than Scoot maybe more if we can. I may measure Scoots actual stiffness next week to see how it goes against the model. Peter

    Last edited by peteeng; 04-12-2019 at 03:17 AM.


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