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  1. #25
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    Default Re: freejoth turret mill to cnc

    I can now give info on the cnc technics break out board - that is, don't buy it. The board might be ok, but the documentation is atrocious. Unless they fix that up, steer clear.



  2. #26
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    Default Re: freejoth turret mill to cnc

    Quote Originally Posted by Pearo View Post
    I can now give info on the cnc technics break out board - that is, don't buy it. The board might be ok, but the documentation is atrocious. Unless they fix that up, steer clear.
    Are you going to persist or 'bail out' and buy something else?



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    Default Re: freejoth turret mill to cnc

    Quote Originally Posted by Sterob View Post
    Are you going to persist or 'bail out' and buy something else?
    I'll persist for now since I own it. I have managed to get it working, but anyone with out a solid experience in electronics I think would struggle.



  4. #28
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    Default Re: freejoth turret mill to cnc

    Thanks for the advice pearo

    After spending a lot of time reading on this forum i am amazed at what is possible, and after i convert my mill i would then like to use it to build a cnc router plasma combo, which brings me to my next question ? is there such a thing as a working reliable combo or would you have to build a dedicated one for each for the best performance.

    regards wayne



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    Default Re: freejoth turret mill to cnc

    Hi,
    a router and a CNC plasma table are similar, essentially 2.5 D mills.

    The difference comes in the required rigidity and accuracy. A router has to contend with cutting forces that a plasma does not.
    Plasma tables often have to travel fast but accuracy smaller than 0.1 mm is seldom required.

    By the time you've built an accurate (0.01mm) router with the rigidity to withstand cutting forces using exotic and expensive components I doubt
    you will want to spray the whole thing with cutting dross of a plasma!

    Craig



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    Default Re: freejoth turret mill to cnc

    My next build is going to be a combined router and plasma, but I wont be chasing accuracy better than what is required for a plasma. I cant see myself doing it for a little while yet, but I am currently researching how I am going to do it. Plan is to be able to cut full 1200*2400 sheets of timber.

    CNC Router parts do a combo which is worth a look at.



  7. #31
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    Default Re: freejoth turret mill to cnc

    i can see what you mean craig ,i was thinking of making one end the router end and the other the plasma with the router part higher,
    craig would it be less messy if i made a water bath.

    like pearo i would make it 3 meters 3 meters so i could cut a 2400x1200 sheet of timber one end and the other end a sheet of steel 2400x1200 would be awesome

    thanks wayne



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    Default Re: freejoth turret mill to cnc

    Hi,
    that makes it worse not better. The bigger the table then to achieve a given level of rigidity the cross sections of materials
    you have to use go up exponentially and weight likewise. With increased weight comes increased horsepower from your servos
    and on it goes.

    If your table had 1200 mm travel in X then you could use a longish rolled ballscrew, maybe $200 or so. At 3m you'll have to use
    rack and pinion, with backlash adjustments $500 or more.

    When it comes to CNC big means very VERY expensive.

    I would guess that you could build two 1200 X 2400 tables for less than you could build one 3m X 3m.

    Craig



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    Default Re: freejoth turret mill to cnc

    Yes.
    No.

    ALL posts re weight and mass grossly overestimate the effect of very heavy tables and beams.
    They are practically immaterial for hobby use.
    "10x heavier" in steel is usually just about right.

    A tiny 40$ 3Nm nema 23 stepper effortlessly moves my old 1600x500 mm steel milling machine table with 100, 200, or 300 kg of stuff on it.
    The table is 200 kg in mass and 3 cm thick tool steel.

    The commercial guys, I used to be one, have to use bigger servos to get silly rapids (never used to effect) - due to advertising and competitors propaganda.
    So the same 1000 kg mill table, 15 cm thick cast iron honeycomb, today has 2 kW servos instead of 1 kW like 5-10 years ago.

    3m screws and linear guides are std stock items and not at all expensive.
    I am happy to sell and source original hiwin equipment in europe, if someone needs some.
    Just use about 25mm++ guides and 32 mm screws.
    I use 32 mm screws on my lathe and VMC (35 mm guides).

    The VMC z mount without the assy is == 150 kg and has == 8kg stiction and under 1kg friction.
    Strength is theoretically about 16 metric tons.
    The tiny stepper moves it fine, I switched to 400W ac servos, 290€ all-in, for better accuracy and publicity.

    Quote Originally Posted by joeavaerage View Post
    Hi,
    that makes it worse not better. The bigger the table then to achieve a given level of rigidity the cross sections of materials
    you have to use go up exponentially and weight likewise. With increased weight comes increased horsepower from your servos
    and on it goes.

    If your table had 1200 mm travel in X then you could use a longish rolled ballscrew, maybe $200 or so. At 3m you'll have to use
    rack and pinion, with backlash adjustments $500 or more.

    When it comes to CNC big means very VERY expensive.

    I would guess that you could build two 1200 X 2400 tables for less than you could build one 3m X 3m.

    Craig




  10. #34
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    Default Re: freejoth turret mill to cnc

    I would guess that you could build two 1200 X 2400 tables for less than you could build one 3m X 3m.

    That is probably correct craig ,so you think keep the size down and use ball screws rather than rack and pinion on both x and y and drive ball screws directly with servo motors,what would be the maximum length of a ball screw without getting whip and obviously the dia of the screw changes that.
    You don't seem to be a fan of rack and pinion,another thing i would like to know is how good are the linear rails and carriages or are there some poor quality ones that i should stay away

    thanks wayne



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    Default Re: freejoth turret mill to cnc

    Hi,

    You don't seem to be a fan of rack and pinion,
    No thats not quite correct. Rack and pinion are good and the only option beyond 2m-3m because a ballscrew will whip.
    The problem is that all rack and pinions have backlash. There are some very clever (and expensive) pinion drives that can
    improve or eliminate backlash.

    The cost of the rack and pinions aren't bad but when you add the low-lash reduction box....that gets expensive.

    I use C5 ground ballscrews on my mill, they are short, only 500mm overall and I got them second hand, they are way too expensive
    for me to buy new. They are preloaded...so no backlash and have a manufacturer guaranteed 18um per 300 mm accuracy and 8um within
    one turn. In short they are very good, with such ballscrews you can make parts to 0.01mm with confidence.

    You will not achieve that with rack and pinion.

    I deal with plasma tables at work and even with water tables everything ends up with black gritty grime over everything. If you want to pay
    big dollars for nice components like rails and ballscrews and then use them in a plasma table where they WILL get covered in rubbish that's your
    call.

    Craig



  12. #36
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    Default Re: freejoth turret mill to cnc

    Hi craig thanks for the advice.

    What dia ball screw would be needed at 3 meters to get no whip, and because i want to drive the ball screws 1,1 what pitch ball screw would i be looking at needing 10 mm pitch or 20mm pitch,
    you said that you use ground ball screws does this mean that rolled ball screws are not great but are they useable.

    If i used ball screws is it any advantage using double ball nuts.

    thanks wayne



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