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  1. #2061
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    Default Re: Milli a new composite mill kit

    Hi All - I'm tending to think the shape optimiser is the go vs generative or automated. We know the outside maximum dims of each part (bounding box of each part) and this is the starting point as this is maximum geometric inertia. Then the optimiser removes non stressed areas. I'll keep playing with generative as well. Peter

    The nominal design is all steel, weighs 1486kg and has a static stiffness of 67N/um. The optimiser has removed around 50% of the material and has dropped the stiffness from 75 to 67N/um. The process has been quite smooth.

    Its X = 660mm Y= 330mm and Z=300mm

    So Fusion has automated modelling that can join "required" geometry - it has Generative design which can connect required geometry (both of these work on stress minimisation and may not give a max stiffness geometry) - it has the optimiser which works with loadpaths which is better for machine design... I now think my earlier thoughts of building a 50N/um benchtop machine was a pipe dream... Now to build one closer to reality including bolt access and drives that meets the original Milli intent. Only 4.5 years I must be a slow learner...

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    Last edited by peteeng; 03-17-2024 at 04:42 PM.


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    Default Re: Milli a new composite mill kit

    Morning all - I'm going to call this last model Milli-24OPT1. 24OPT-1 does not meet the Milli objective in a couple of places. 1) its not a benchtop machine; at 1.5 tonnes of steel its not small 2) it has a high speed spindle and the configuration makes it difficult to achieve a slow speed one for steel 3) This also applies to my favoured high rail design. So this means I need to move to the Mori 200 type of config which has an outreach providing real estate for a motor and pulley/spindle.

    In another thread we spent time on spindles for steel. It comes down (for me) to a 750 or 1000W AC servo with an upspeed pulley to give 0-6000rpm or 0-9000rpm or use a high speed spindle with downspeed pulley to give 6000-12000rpm say or even 4000-9000rpm....

    The other aspect is that 24OPT1 was designed from the spindle backwards and arrived at 600x300mm envelope. This is driven by the 80mm dia clamp and 20mm flanged bearings. Each bearing patch sort of grows as it goes from Z axis to the column. So the next version needs to use 15mm square bearings to minimise the bearing patches...

    I did more reading on shape optimisation in Fusion and it definitely is the better approach then generative for machine parts until I become better at generative. GD is a tool and all tools you need to get competent with. I do like the M1 config so will model the motor/pulley/spindle and see if I can package it into the 24OPT1 or 2 Z axis....

    So onward to Milli-24OPT-2 Peter

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    Default Re: Milli a new composite mill kit

    Hi all - Milli is also a materials thread. So if I built it from aluminium it would be 3x softer then 24OPT1 but a lot lighter. (2700/7800= 2.9 ~1/3 lighter) Since I removed material that did not help stiffness it would not be worthwhile putting some back to try to recover the stiffness. if I made it from concrete It would be less stiff then aluminium and then there's EG less again... See what OPT-2 brings Peter



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    Default Re: Milli a new composite mill kit

    Hi peteeng,

    In another thread we spent time on spindles for steel. It comes down (for me) to a 750 or 1000W AC servo with an upspeed pulley to give 0-6000rpm or 0-9000rpm or use a high speed spindle with downspeed pulley to give 6000-12000rpm say or even 4000-9000rpm....
    I strongly agree. For a mill such as you envisage being able to cut steel is the goal, and in which case high torque at low(ish) speeds are required from your spindle.
    An AC servo, with an upspeed pulley is viable, as is a high speed AC motor with a downspeed pulley. While both lack the top speed of the 24000rpm asynchronous spindles
    so favoured by hobbyists, they are a better match for larger tools in steel....no matter the cost or inconvenience.

    You know already I have an AC servo driven spindle for steel. It is direct coupled so the spindle is capped at 3500rpm of the servo, but is none the less very useful, and it requires
    no more real estate than a 24000rpm asynchronous spindle. I swap back and forth between my highspeed (24000rpm) spindle and this low speed (3500rpm). Takes a few minutes
    so is not too bad.

    Just had notification that NZ Customs are going to release my new 3.5kW HSK35 ATC spindle to me.....after quite some correspondence. Bottom line is do not BS Customs....
    you'll regret it!!!!

    Craig

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    Default Re: Milli a new composite mill kit

    Hi Craig - What is the torque of your AC and what would the biggest dia tool you'd run in it? rpm?

    1000W 3000rpm 4Nm with 2x up gives 0-6000rpm at 2Nm
    2.2kW 24000rpm (0.8Nm) at 3x down gives 2000-6000rpm at 2.4Nm a 12mm tool at 6000rpm has a surface speed of 226m/min so probably don't want to go faster then that...

    servo probably gives more options...

    Peter



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    Default Re: Milli a new composite mill kit

    Hi peteeng,

    What is the torque of your AC and what would the biggest dia tool you'd run in it? rpm?
    The specs say the rated torque of my new spindle is 3.4Nm. I would guess that I could run a 12mm four flute tool in steel at 2500rpm or 94m/min surface speed.
    This is a guess based on what I know from my servo driven spindle. What I am looking forward to is that my new spindle is rated at 10,000rpm so I expect to easily get
    down to 5000rpm, and possibly as low as 2500rpm with good spindle security.......but will have to wait and see.

    Really this new spindle is about ATC, it has an HSK32 tool interface. While its rated at 10,000rpm its max is 40,000rpm. I'm thinking that I have a useful range of 25000rpm to
    40000rpm.......and ATC.

    It is a moderately expensive purchase for me, $4000NZD, so I'm hoping that the overall increase in capability justifies the cost. You can well imagine my sigh of relief when Customs
    released the spindle, I was a hairs breadth from losing it altogether with zero compensation. That would have hurt!.

    I still have to buy a VFD for it, and it requires a high frequency model, so that in itself is likely to set me back another $1000NZD.

    servo probably gives more options...
    I agree. Modern AC servos have so much overload capacity, you'd swear they are rather more powerful than the nameplate suggests.
    Should you encounter a brief moment where the tool experiences a very great increase in torque demand (toolpath anomaly or a sudden unanticipated plunge) a servo will 'man up'
    and deliver whereas AC asynchronous motors tend to stall.

    I would urge you consider:

    https://www.fasttobuy.com/delta-2kw-...nc_p33936.html

    It is 2kw, 6.4Nm @3000 rpm cont. , 19.1Nm peak and 5000rpm max. You have a viable speed range of 0 rpm to 5000rpm, which I think you'll agree is pretty damned good. Cost $895USD plus shipping.
    (At 5000rpm is in field weakening mode so torque is 6.4 x 3000/5000 =3.84Nm)

    My Allen Bradley servo, previously pictured, is 1.8kW 6.1Nm @3500rpm cont. 18Nm peak. Personal experience is that 6.1Nm is highly useful.....you'll always find the need for more, especially for rigid tapping, but nonetheless 6.1Nm
    does a power or work. I have run 16mm four flute carbide tools in med tensile steel quite happily, if cautiously, with it. 16mm is about as big as the ER25 toolholder can manage.

    Is there a need to upspeed?. If anything I'd be tempted to downspeed so I could use 3 and 4 inch face mils and really start removing material! Be great for rigid tapping as well.

    Craig

    Last edited by joeavaerage; Today at 12:22 AM.


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