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Type: Posts; User: joeavaerage

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  1. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi peteeng,



    You are correct, any instantaneous change in velocity would imply an infinite acceleration.....but that is NOT what a trapozoidal planner, also called a second order planner does....
  2. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi peteeng,


    You've obviously forgotten your calculus over the years.

    Trapezoidal velocity means just that. A machine travelling at speed V0. It is then commanded to accelerate at max...
  3. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    my training is in Physics and Engineering, and I would agree that the max thrust is acceleration plus cutting thrust plus friction.......and that's fine until you are standing in front of the...
  4. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    found it, BK17 are the standard size for 25mm screws, a DF pair of 7003 bearings at 125N/um.

    Craig

    PS: Have seen a typo in the previous post, I claimed 190N/um for FK20's, they are in...
  5. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    depends on size.

    A BK15,FK15 or EK15 are the standard size for 20mm diameter ballscrews. They use a DF pair of 7002 bearings for a stiffness of 100N/um
    A FK20 or EK20 are standard size for...
  6. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    consider also that a 400w servo (1.27Nm@3000rpm) or a 750W servo (2.4Nm@3000rpm) will exhibit a great deal more thrust than the acceleration alone.

    A 5mm pitch ballscrew exerts 125kg (1250N)...
  7. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    that calculation predicts the axial compression/extension of the screw but does not accommodate the fixed mount.

    Elements that are logically in series, for instance the ballscrew, the fixed...
  8. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    this is from the THK catalog:

    A 2005 BNFN (20mm diameter, 5mm pitch, double nut 2 circuits of 2.5 turns/circuit) is 760N/um
    A 2505 BNFN (25mm diameter, 5mm pitch, double nut 2 circuits of...
  9. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,



    Yes they do. Firstly the section is thicker therefore more force to cause a given extension/compression. Secondly larger ballscrews have larger fixed mounts with
    larger, axially more...
  10. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    you are correct, the screws need to be rigid axially as the thrust of the screw is transmitted that way. The radial rigidity is really only so the screw does not flex under
    rotation.

    When my...
  11. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    my own machine (pictured above) has travels of 350mm x 350mm x 350mm (13.7" x 13.7" x 13.7") and is very similar to your design.

    I have 32mm C5 ballscrews which are great, very stiff. It did...
  12. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    these may be very useful as well:

    https://www.ebay.com/itm/196245983675?itmmeta=01HSY3S6A80JSRYXQBYM89YBJD&hash=item2db12c11bb:g:V1MAAOSwAaRlzfhX

    They are 25mm diameter and 10mm pitch. I...
  13. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    see a mistake in my earlier post. The threaded length of the 20mm screw I linked to is actually 528mm with a spanner flat ground into one end, making the usable threaded portion 510mm and with...
  14. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,

    This may be useful:

    https://www.ebay.com/itm/224036123406?itmmeta=01HSVSY2BYX00K737PJJ5DQJJX&hash=item342997f30e:g:w7sAAOSw2lBe2yu0

    A C5 THK screw complete with fixed and floating...
  15. Replies
    6
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    79

    Re: Mach4 autoload Gcode on startup

    Hi,
    no you don't want to put it in the screen load script. The script loads little chunks at a time. What happens if the bit they you want to load requires some other bit that has
    not yet...
  16. Re: 14x8x14" Mill Build, Advice Appreciated

    Hi,
    that is a good size. There is no doubt that the larger the machine the costs go through the roof.

    Of all the parts that you need the costliest and most difficult to get are the ballscrews. If...
  17. Replies
    6
    Views
    79

    Re: Mach4 autoload Gcode on startup

    Hi,
    you could put some code in the PLC script.

    The Screen Load script loads first when Mach4 fires up. At the conclusion of that script loading then the PLC runs. There is a counter so that you...
  18. Replies
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    1,160

    Re: BST automation vs dy-global eBay

    Hi,
    like Bosch Rexroth the screws are rolled and then finish ground. TBI claim C5 and C3 grades, Bosch Rexroth claim close to C5...but not quite.
    The argument has always been that rolled then...
  19. Replies
    151
    Views
    1,160

    Re: BST automation vs dy-global eBay

    Hi Jackjr,


    BS, TBI roll their ballscrews, always have.



    ????? The real killer is cyclic variation, also called 2PI error. That is near impossible to map and short of ultra high bandwidth...
  20. Replies
    151
    Views
    1,160

    Re: BST automation vs dy-global eBay

    Hi

    TBI are not ground, they are precision rolled and supposedly are to JIS C5 standard, but they are not ground....good for the price but they are not ground.



    You are correct, its near...
  21. Replies
    151
    Views
    1,160

    Re: BST automation vs dy-global eBay

    Hi Lars,



    Thats rubbish!!!! If you have a 40mm gutter that means there is 60mm undisturbed steel underneath.....surely that is enough!!!! The rail idea works but inevitably they'll rock...
  22. Replies
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    204

    Re: How to Set Microstepping

    Hi,
    there is no magic number.

    Microstepping came about because astronomers wanted increased resolution. As it turns out beyond 1/2 stepping that does not work, nice to imagine it does but in...
  23. Re: Reducing Diameter of Aluminum Rod for Linear Bearing

    Hi,
    aluminum is 70GPa whereas steel is 210GPa, ie steel is three times stiffer than the same size aluminum.

    Aluminum rods will be as stiff as limp noodles, they are not right for the job....
  24. Replies
    2,095
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    132,590

    Re: Milli a new composite mill kit

    Hi peteeng,
    yes, looks great, but looks can be deceptive. Does it have tuning software? If not walk away, in fact don't walk....run away.

    Craig
  25. Replies
    2
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    88

    Re: Rotary converter 20hp ST20

    Hi,
    yes, you can but the cost will be huge. Entirely probably you'd have to install a high current single phase supply just to run the phase converter.....might be cheaper
    just to get three phase...
  26. Re: Specing and sourcing motors for Supermax retrofit

    Hi,
    I use Delta B2 servos. They are broadly equivalent to DMM. They certainly have a velocity mode, and I have used velocity mode for various projects which require a free running
    motor. The B2 has...
  27. Replies
    4
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    Re: What is Tinned Copper Wire?

    Hi,
    tinned copper wire, proper tinned copper wire that is, is expensive.

    In New Zealand, and I guess other jurisdictions, double insulated tinned copper wire is mandatory in any ship that is...
  28. Replies
    3
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    137

    Re: Epoxy resin machining

    Hi,
    casting is OK but nothing beats machining for dimensional accuracy.

    If you try it make sure you use a casting resin, ordinary laminating resins exotherm in even small volume and you must...
  29. Replies
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    Re: Don't BS NZ Customs

    Hi,
    it all comes down to the numbers. Mostly it cost me 15% to import parts and materials, and I think that is pretty reasonable.

    I imported a gear reducer from the US a while back. It cost...
  30. Replies
    2,095
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    132,590

    Re: Milli a new composite mill kit

    Hi peteeng,
    jackjr is right, do not buy el-cheapo Chinese servos. Its not because they don't work but they typically have atrocious documentation, even worse technical support and no set up and...
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