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  1. #73
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    Default Re: What Part To Start ?

    Em..
    You are extremely talented and at the top-end of industrial designers if you are participating in the design of carbon-fiber yacht hulls.
    These tend to be pre-preg today for manufacturing and custom ovens/baking for the bigger ones racing.
    All use vacuum infusion.
    Pre-preg is frozen cf substrates with epoxy that the customer bakes into shape in their facility.
    I cast no aspersions and make no snide comments.

    But CF yacht hulls for 15 years have a dismal record.
    They break, fail, don´t last, despite 50M$ budgets for a single yacht (americas cup, fastnet, others).
    Yacht loads are not well understood, today, and no current FEA sw and design practice has done well with them.
    I believe 1.5 years ago one of the maxi hulls broke apart in testing, no storm, australia maybe.

    Imo, the problem is that yacht loads are 5x bigger in torsion than expected and 100x higher in common impact loads due to waves/wind/speed/mass acting against each other.
    The dashews website setsail had data on 3-5g loads acting on their alu hulls, of 28 metric tons, 24 m, FPB Wind Horse.

    A modern VMC, 1 m table, VF3//, 1.5 kW servo, 1000 kg table, will react in 1 ms.
    So will my shop built vmc, with 200 kg table and 200 kg of stuff on it.

    The inertial load is huge, but that does not mean the machine frame has anything to do with it.
    Modern VMCs are bolted to the floor, but not tight.
    They are bolted loose/light to achieve a flat table/machine frame.
    According to haas manuals, training, and the 4 millwrights I had working while selling 65 machines.

    And most-all other brands, where the (industrial engineer) millwrights had worked at least 10 years.
    And the extensive training I/we got at the factory and our shop, as the biggest/best haas hfo in the world.
    Trained by the best guys in the world, who designed the new (ST series) machines (Hi Miltons!).

    ---
    Example.
    Milling machine, cheap tech.
    400 kg mass for my old mill table was absolutely nothing with Nema 23 steppers, 48V, 3Nm, 1:3 HTD belts.
    Push force approx 600 kgf, 6000 N.
    More than 1G acceleration, and mills need less (quite a bit less).

    It juddered and had extreme response speed, quite similar or better to a HAAS, at 1 ms response, with a 100€ pokeys controller, 125 kHz.
    And an MPG, 100 counts.

    I switched to 400W ac servos for commercial reasons.
    1.3 Nm cont, 3.9 Nm peak, 3000 rpm, 5000 count, 400 kHz+.

    And I may go to direct-drive, again for commercial reasons only.
    The stuff needs to look-good on paper, thus it must use modern commercial-type stuff.

    The belt drives got 1 micron resolution, and direct drive might struggle with that at 5 mm screw rise, on new 32/5 screws.
    I expect actual resolution to be 1-2-4 microns, with 1 micron repeatability being achievable via clever programming or fixtures and hard stops and external digital 1 micron readouts read back into programs.
    My goal is 1 micron feature accuracy on small work cubes.

    I did not say "accuracy" overall of 1 um or general resolution of 1 um.
    The lathe has 1 um resolution, using 750W servos of 10.000 counts.

    When I get a spare 3k, the VMC might get the upgraded servos as well.

    I try to explain my reasoning, not be "better".


    Quote Originally Posted by peteeng View Post
    Hi Hanermo
    From 500g bicycle frames, carbon fibre yachts to 50 tonne trailers carrying 900T trucks they all ask me to remove weight yet achieve their performance criteria. That's the workspace I live in. I'm happy you agree with some things and happy to keep you entertained and it's great your participating.
    Peter




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    Default Re: What Part To Start ?

    But CF yacht hulls for 15 years have a dismal record.
    They break, fail, don´t last, despite 50M$ budgets for a single yacht (americas cup, fastnet, others).
    Yacht loads are not well understood, today, and no current FEA sw and design practice has done well with them.
    I believe 1.5 years ago one of the maxi hulls broke apart in testing, no storm, australia maybe.

    Imo, the problem is that yacht loads are 5x bigger in torsion than expected and 100x higher in common impact loads due to waves/wind/speed/mass acting against each other.
    The dashews website setsail had data on 3-5g loads acting on their alu hulls, of 28 metric tons, 24 m, FPB Wind Horse.

    Hi Hanermo - Thankfully my work in car parts, bicycles, hulls, masts and rigging has not had any failures that I know of in the 30 years I have been playing around with CF. Yacht loadings have been underestimated for decades. Its a battle to create objects that are the required weight yet be strong enough in any racing machine. Plus in the decades past composite materials have not been understood well or made well. This has changed in the last 10 years however. Happy to set up a thread to discuss these if asked. FE can and does a good job of modelling composites I do it alot. A friend has just given me a stack of CF offcuts so may make some CF parts for maximus... but do remember that aluminium, steel and timber racing boats also did fail, it's the nature of the game. Peter



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    Default Re: What Part To Start ?

    Just one further comment on FEA and boat design if I may;in about 1980 Ron Holland published a screenshot of one of his IOR boats as a mesh to demonstrate the use of FEA as an aid to efficient boat design and it was the first reference I recall.I suspect more recent failures have been because of a desire to go light and to underestimate shock loads.

    To divert back to router design.I asked a bit earlier about resonance and ballscrews with reference to the resonance changing with respect to the position.To clarify a little further I was interested in knowing whether the position of the ball screw changed the resonance of the structure in much the same way that moving one's fingers on a guitar changes the frequency of the note produced.I appreciate that the natural frequency of the portion of the screw on either side of the nut will change,but does it infuence the whole structure?I suppose the nature of the cutter itself has an impact as we might be using a single flute,twin flute or even four flute tool with the consequent change in the frequency of edges entering and leaving the workpiece.Probably not something that will have too much impact on hobby machines but I expect it would increase in significance as the machine grows-say to the size where full size boat hulls are being machined.



  4. #76
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    Default Re: What Part To Start ?

    Hi Routalot - In all racing type activities failures are expected but all reasonable efforts are taken to prevent them. We also have aircraft accidents that kill a lot of people and we investigate and learn from them yet air travel is the safest travel we have. The yacht industry tends to bury these things vs investigating them and letting the industry benefit from the events. Accidents and failures are complex events and we will continue to have them.

    Machine resonance - The whole machine is a big guitar with each bit prone to vibration at its natural frequencies. If it gets excited by some input at that freq it will vibrate then it will dampen according to its material properties and its surrounding contact conditions (visco elastic conditions) same as a guitar sound board and back vibrate differently. All structures vibrate. Bridges vibrate, some have fallen down in the past due to aerodynamic loads and uncontrolled vibration. Airplanes have issues with "flutter" and fall out of the sky, routers have issues with tool loadings and machine movement. Its all a symphony or a cacophony!! All of these are well known and understood events. We have the tools and the resources to solve and answer all of these things. I'm sure Mazak, HAAS and all the other machine makers have engineers like myself slaving away at each problem current and future. We are entering a new paradigm of machine design and build. Cast iron will be replaced by printed parts that are internally honeycombed and will be 50% the weight of current machines yet are faster, damper and stiffer. Titanium printed parts are showing up all over the place and its ideal for machine tool parts. By 3D printing we can control the loadpath in a part and how it is damped at the same time. You heard it here first? Lecture ends here. Peter

    By the way a company has just released a desktop 3D metal printer very exciting...

    https://www.titomic.com

    Last edited by peteeng; 04-11-2019 at 06:50 AM.


  5. #77
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    Default Re: What Part To Start ?

    Quote Originally Posted by peteeng View Post
    Hi Routalot - In all racing type activities failures are expected but all reasonable efforts are taken to prevent them. We also have aircraft accidents that kill a lot of people and we investigate and learn from them yet air travel is the safest travel we have. The yacht industry tends to bury these things vs investigating them and letting the industry benefit from the events. Accidents and failures are complex events and we will continue to have them.

    Machine resonance - The whole machine is a big guitar with each bit prone to vibration at its natural frequencies. If it gets excited by some input at that freq it will vibrate then it will dampen according to its material properties and its surrounding contact conditions (visco elastic conditions) same as a guitar sound board and back vibrate differently. All structures vibrate. Bridges vibrate, some have fallen down in the past due to aerodynamic loads and uncontrolled vibration. Airplanes have issues with "flutter" and fall out of the sky, routers have issues with tool loadings and machine movement. Its all a symphony or a cacophony!! All of these are well known and understood events. We have the tools and the resources to solve and answer all of these things. I'm sure Mazak, HAAS and all the other machine makers have engineers like myself slaving away at each problem current and future. We are entering a new paradigm of machine design and build. Cast iron will be replaced by printed parts that are internally honeycombed and will be 50% the weight of current machines yet are faster, damper and stiffer. Titanium printed parts are showing up all over the place and its ideal for machine tool parts. By 3D printing we can control the loadpath in a part and how it is damped at the same time. You heard it here first? Lecture ends here. Peter

    By the way a company has just released a desktop 3D metal printer very exciting...

    https://www.titomic.com
    Just so you can catch up they have had 3D metal printers for more than 20 years and not much has changed with there design, laser sintering has been used for a long time the use of Titanium is not new, even Hobby 3D printers can use materials such as carbide Inconel titanium just to name a few

    Stick to what this thread is about

    Mactec54


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