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  1. #37
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    Default Re: freejoth turret mill to cnc

    Hi,
    hanermo previously responded that 32mm diameter screws would be adequate at that length. I have no experience with long screws, in
    fact I can't find any screws over 2.5m in 32mm size. As to the pitch.....I would take what I can get. The high pitch types allow high axis
    speeds at low rotational speeds, ie good for avoiding whip, but then require high torque servos or gear reductions to get the required torque.
    5mm pitch screws will provide greater thrust with direct coupled servos but you may be speed limited before the screw starts to whip.

    Rolled screws are commonly C7 grade, 50um per 300mm accuracy but up to 30um in one turn. They are adequate but not for highly accurate
    machines. You should avoid the 'T' grades, they are for transport purposes and not accurate enough for CNC axes.

    A 1200mm X 20mm C7 rolled screw with preload ballnut without bearing blocks might cost around $75. A ground C5 of the same dimensions
    might cost $1500. Unless you want to spend mega-bucks rolled C7's are your choice.

    Double nutted ballscrews are the original backlash elimination technique. The flexibility with which they can be applied makes them still a good choice
    despite the extra expense and loss of travel.

    Craig



  2. #38
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    Default Re: freejoth turret mill to cnc

    Hi craig since your last post i have been looking for ball screws that are 25 mm or bigger they are very few and far between and costly
    a 32 mm ball screw and nut 3000 long are about $600 each 2 for the y axis and 1 shorter one for the x axis,now i can see if you want it to be very accurate and at a lower cost make it smaller and stronger,but i would be kicking myself if i was limited by size at what i can do after i built it i think i will make it 3000 x 1500 which will give me room around a full sheet and because i will be making most of the parts in the build myself i can afford to put good components in the rest, even with the cost of the ball nuts linear guides and rails ac servo motors and drives i recond i can build a 3000x1500 super strong table for $5000au or less which is still a lot cheaper than buying one of the same quality, i have never been one to do a half a job it's not me.

    are machined ball screws any good and do you rate them is it (ground > machined and then rolled

    regards wayne



  3. #39
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    Default Re: freejoth turret mill to cnc

    Hi,
    yes long ballscews are expensive. I would not go less than 32mm at that length or the rotational speed of the screw will be limited
    by its potential to whip.

    For your budget, assuming you use ball screws at all, then rolled screws are your only choice. You could spend your entire budget
    on one ground ballscrew alone.

    I would rate rolled screws as suitable for machines with accuracy of 0.05mm to 0.1mm whereas ground screws are required for
    0.01mm accuracy.

    You should consider rack and pinion:
    discounted automation products: Motion Control, Rack and Pinion
    Cost effective depending on the sophistication of the pinion drive.

    Craig



  4. #40
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    Default Re: freejoth turret mill to cnc

    I think i could save a bit by making the y axis 1200 and the x axis 2400 that way that way the two ball screws for the y axis will be cheaper and use on long screw on the x.

    i did want to machine aluminium parts for engines with high precision, but after what i have read and been told i think it might be a good idea to build a plasma table than i can learn from that build and it will make me much more aware of things that might need changing in the router build.

    I think i need to rethink the size of the router build because any reduction in size is going to be a lot cheaper to build, and i also have to ask myself how much more work am i going to get by machining objects larger than a meter x meter which would be a lot cheaper to build and you could make it precise and strong.

    !!! lots to think about

    regards wayne



  5. #41
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    Default Re: freejoth turret mill to cnc

    Hi,

    i did want to machine aluminium parts for engines with high precision
    now your off on a whole different tangent. A Router is design that can be made rigid enough for plastics and
    wood. Sufficiently strongly built machines will do a fair job in aluminum but not with the high accuracy of
    bed mill.

    The cutting forces of cutting metals is way WAY higher than wood or plastic and to be accurate the rigidity of the
    machine needs to be that much higher also. An insufficiently rigid machine will vibrate in a manner that makes getting
    a good surface finish impossible.

    Craig



  6. #42
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    Default Re: freejoth turret mill to cnc

    I am a shade confused here. One minute we seem to be discussing a budget-build of a door-sized router, then we are discussing seriously over-sized servos, then we are discussing machining precision aluminium engine parts, still on that low-budget build.
    Ambition is great, but there is a serious lack of engineering reality in all this.

    Cheers
    Roger



  7. #43
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    Default Re: freejoth turret mill to cnc

    No that is not right the reason i asked about servos was for my turret mill which has a broken feed worm gear and the mill does not feed anymore so hence the reason i wanted to convert it to a 3 axis cnc ,but i just found out recently about 3 weeks ago who sold my mill in australia in the first place which is a mfi quantum but i could not find anyone in australia that has had anything to do with them, i now find out that they changed business name to cnc machines australia i rang them up and they sold the machine to the first owner and they contacted the mill manufacture freejoth and i can now get anything for it so i ordered all the parts to fix it ,the parts arrived from taiwan to cnc machines in melbourne late this week and i will have them next week.

    before i got on here i new nothing about cnc just wanted to fix my mill,i always needed a plasma cutter but before i got on here i didn't think i could build one or afford one,the reason i need one is i work for myself mine specing plant and machinery for mine sites and this nearly always involves building guarding for exhaust manifolds or fan guarding both need to have slots in them which i could cut out on plasma table and then fold them in my folder.at the moment i am using perforated sheet which is very expensive and time consuming nut serting all the pieces together,
    the reason i would of liked it to be a router as well is because i would like to play with wood at some point but metal is my thing.
    but clearly it is not great trying to make one machine do two jobs.



    regards wayne



  8. #44
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    Default Re: freejoth turret mill to cnc

    clearly it is not great trying to make one machine do two jobs.
    You have got it.

    Cheers
    Roger



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