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Thread: Eichenberger Gewinde Speedy lead screws?

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    Default Eichenberger Gewinde Speedy lead screws?

    I am working on a mid size CNC router for wood (parts such as patterns for iron casting, some small furniture etc). I have a proper machine shop so other than perhaps a little aluminum machining with loose tolerances, this machine is for wood and plastic only.

    This is a more or less conventional moving gantry design and I am going to have double screws on the long axis (X). I will be using the Igus W system for the linear motion.

    What I am trying to decide is if given my allergy to Chinese parts should I go with lead screws or ball screws. I don't mean some crap threaded rod from the hardware store but swiss made high helix leadscrew (say 18x16mm Standard thread with flange nut | Eichenberger Gewinde AG) with self lubricating nuts. Lengths are in the 1200mm range. I will use a ball screw for the Z but need to decide on the other three screws I need (two for X and one for Y). I can run numbers until the cows come home but that doesn't tell me much about the day to day application. So has anyone used these things for a wood routing CNC?

    pros for lead screws are:
    quieter (but then router spindles are freaking loud so not sure this matters)
    self lubricating
    have better dust tolerance (no need for sealed nuts etc)
    soft spindles are a bit easier to machine than case hardened ballscrews
    somewhat less expensive (the nuts are the only difference in price and the bottom end of the ballscrew range overlaps with the top of the leadscrew nut prices)
    more choices in pitches, diameters etc.

    the negatives:
    lower efficiency (although not terrible for high helix)
    lower force capability
    more backlash
    I could use rotating (driven) nuts with ball screws but I don't think it would work with lead screws. That said with the short length this is probably not worth the trouble.

    common:
    With larger pitches such as these both are non-locking (can be back-driven)
    similar pitch accuracy (independant of backlash)

    I am looking at Eichenberger, Isel, Igus etc not chinese stuff if for no other reason than it is nicer to work with the European made parts. I have both types onhand and there is no chance of confusing the source. Also at the end of the day rolled screws from Europe are not that much more expensive than the better of the chinese options (unlike many things in the manufacturing space where it is a 10x difference)

    Thanks

    Luke

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    Default Re: Eichenberger Gewinde Speedy lead screws?

    This is hard choice to make. Frankly you can get fooled ball screws and nuts that are very competitive with common lead screws. They might not be the highest quality when it comes to lead accuracy but they are very capable for many machine applications. You imply that you are already running a shop with plenty of machine tools, this leads me to suspect that you might have higher expectations than many for this machine, which leads to more expensive or accurate parts for the drives.

    Personally I'd go with ball screws and use an automatic lube system to help keep the ball races flushed out. As you note dust is a real problem with ball screws so you would want to address that. In this sort of application I don't see ball screws as being remarkably better but simply have a preference for them over ACME or similar lead screws. Part of the reasoning here is that I see you getting better high speed performance which starts to be a real issue when machine stroke lengths are beyond about a half meter. In other words rapids can be very important with the longer axises and as such ball screws should perform better.

    One thing to watch out for is nut heating with synthetic lead screw nuts. Take this advice with a bit of salt as there are many new materials available that we didn't have when I first saw this problem on machines. What we ran into with was heating of the nut & screw, causing tolerances to close up and thus leading to high torque on the leadscrew shaft. This was in a high production environment trying to hold very tight tolerances on repeatability (1 to 2 microns) in a precision lathe. So getting things adjusted just right was a challenge.

    Of course everything heats up once the machine starts running but generally you don't have ball screws heating up to the point that the motor/servo drive faults due to following error. For a light duty, small router you likely could flip a coin and get good results either way, that is ball screws or lead screws.



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    Default Re: Eichenberger Gewinde Speedy lead screws?

    Just my 2 cents.
    The main difference that you'll see is the efficiency. Other than that, they'll work fine. I've been using multistart acme screws and plastic nuts for years.
    And if you are going to use them for the X and Y axis, you might as well use them for the Z axis as well. They will perform better with lubrication, though.

    Gerry

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    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

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    Default Re: Eichenberger Gewinde Speedy lead screws?

    Thanks for the replies, I have sent an enquiry to one of the producers of both ballscrews and high helix leadscrews to see what they have to say about the choice. This is another really nice thing about working with western suppliers, they are surprisingly helpful with technical questions, after sale support etc.

    As for my expectations, it is true I have high expectations of quality etc but the also an understanding that this type of machine is not intended for precision work. A part such as a casting pattern is usually made by hand so if a router can quickly make a part that is within a few 10ths of a mm then I think it will be more than acceptable. Even if it is within a mm of the designed envelope it probably wouldn't actually matter so long as the finish is good.

    From what I have seen in the home built router world there is a tendency to spend money on parts that do not enhance actual performance while using poor designs or weak links that are the actual limitations. I am trying to combine components in the most consistent and logical manner. I think modern leadscrews should be the most appropriate choice but as I have never worked with them I am a bit wary.

    These modern leadscrews are far removed from conventional acme/trapezoidal screws, they have efficiencies that are not quite as high as ballscrews but are not so far off (over 70% anyway) and can have very high helix angles although I need to balance force and speed so I wouldn't be looking at the more extreme end of that spectrum. A helix of around 45 degrees should work well I think (with or without balls in the nut). The plastic bearing materials can handle extraordinarily high surface speeds far beyond what are possible with a router (over 3m/sec) so I think heat will not be a huge issue although running highly loaded anti-backlash nuts might make this more of an issue.

    L



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Eichenberger Gewinde Speedy lead screws?

Eichenberger Gewinde Speedy lead screws?