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IndustryArena Forum > Metalworking Machines > Benchtop Machines > Double ball nut worth it for long C7 grade rolled ball screw?
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  1. #1
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    Double ball nut worth it for long C7 grade rolled ball screw?

    So I've been a little recently frustrated with an abrupt lack of response from these "TEN-HIGH" vendor on Amazon (before CNY- which I realize is now but this was before they had an excuse) regarding my X axis screw which I have saved for last on my machine retrofit. Still, I'm eager to get that done after my Z and Y axes turned out unexpectedly well.
    I use this machine for occasional prototypes in the course of product design, not any heavy or industrial use - I frequently also use it as a manual machine.. That said, my X screw is going to be around 900mm (including end machining, and the last 4" of thread on either end won't need to engage because of the large carriage/motors/etc.

    I was all settled on my purchase and upcoming challenge of installing it, when I discovered double ball nuts. In this application I have plenty of room for one without any real consequence, but it seems to be a rare offering from the manufacturers in China. I worry about the length of the screw and the additional load it will have to carry compared to the other axes and so I'm thinking if I can find a double ball it might help alleviate some of these anticipated issues. The threads I've found here seem to validate them at least in concept- I don't mind doing some extra modifications to tighten them up, as I will have to modify nearly every other part anyway in one way or the other.

    Similarly, although they provide the kits with bearing blocks, I was looking into maybe spending a few more $ on a bearing upgrade as I'm sure they use the cheapest option. Has anyone tried that and do you think any of this would be worth it? In some ways I feel like its lipstick on a pig, and I'm not shooting for a world class machine- just a substantial improvement over the lead screws that were originally supplied. From another perspective though, for a few extra bucks now, if I could increase my reliability and precision I can probably convince myself its worthwhile. Just looking for a good balanced bang for the buck. Thanks for any opinions, figured I may as well use this delay as an opportunity to do more research.

  2. #2
    Gold Member
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Double ball nuts will be better than single nuts hands down.


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  3. #3
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    In general, double ball nuts are great, but without knowing what kind of machine, what kind of materials and purpose, it is impossible to say if it is "worth it".

  4. #4
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Trouble is its also impossible to say what it's purpose is other than prototyping- that prototyping involves cuts with nearly every material and tool type you can imagine (and some you probably can't! haha). For example, I've used this machine to plasma cut, to laser cut, to etch with a laser, to cut steel, aluminum, plastic, and to cure resin. I've cut & blown glass on this machine also. The machine started life as a Tri-power "Eldorado" bridgemill from Shopmaster but has been pretty drastically modified since then. This isn't my machine, but it is the same model (as an example). I think your general statement is probably the best answer I could hope for- thanks! I was curious more because it seems pretty uncommon to find a double ball nut. I'd expect them to be more commonly available if the advantages were more readily known.

  5. #5
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    The double nut is usually for reducing/eliminating backlash. If you're worried about too much load, go to a bigger screw. If it's the type of double nuts I'm thinking of, they don't get you anything in terms of extra load capacity.

  6. #6
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    From your description, and looking at the video of the type machine, I would say that double ball nuts would be the way I would go.

  7. #7
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Ok, cool. I'm going to go with the double then- thanks for the input. I'll have to order from another vendor- I hope they are comparable. The "TEN-HIGH" units worked out really well. The new vendor is off ebay. 20mm is a bit larger than the lead screw diameter that came with the machine. The Z was the smallest at 16mm, but the Y is also a 20. There would be clearance issues elsewhere if I went larger, and 20mm seems conveniently standardized, so I'll go with it. I'm not super worried about loading, probably just being a little OCD. In a perfect world, each screw would be precisely proportional to its load, but I think this should work. Still could upgrade the bearing spec in that block, but we'll at least give these a try.

  8. #8
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Just like to mention.
    I bought some double 1605 size ballscrews/nuts for a PM25 type conversion.
    Haven't got them fitted yet but the quality difference is CLEARLY visible:

    These are good:
    https://www.ebay.co.uk/itm/2-set-DFU...jRE:rk:12:pf:0
    Properly machined tab slot almost perfectly spaced.

    These are crap:
    https://www.ebay.co.uk/itm/ballscrew...s3uu:rk:2:pf:0
    Slot is pretty hacked and no spacer fitted at all!

    I found on my smaller mill that thrust bearings don't seat that well on these pre-machined screws. If you go even a fraction too tight it forces a bend on the screw as they slip into the area where there is no flat spot (roll thread end).
    For this new machine I'm going to use AC bearings of size 12x32x10mm on x,y and making bearing blocks using my small mill.
    These bearings seem to seat really nice on the end when I checked.

    Z will be using the crap screw and thrust bearings for now as I'm looking at replacing it a later date with 2005 DFU from the same seller that sent the good 1605's. Cost more but so be it.

  9. #9
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Thanks for the feedback! I have to admit I have the same worry but there's not a whole lot I can do about it until I get my hands on the delivered assembly to assess. The original Z & Y single nut assemblies turned out to be really good. The Z in particular is maintaining .001" repeatability with almost no backlash- of course it's not carrying a heavy load or a long range but still. I wish TEN-HIGH would respond but I don't think they offer a double ball nut anyway. I'm trying a new vendor for the big X axis here, and as a bonus they can customize with some mill operations (I requested a slot on the end so that I can lock the axis to the mechanical drive and still do manual threading operations when desired). TEN high was unable to do that. They also have 100% positive feedback so that's nice. Also, they can deliver these in about 2 weeks in spite of CNY, so that's nice too.
    I'll try to come back with some info after I receive them! Even if I do have to make some of my own customizations I'm hoping this offers a pretty good head start on the process.

  10. #10
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    Also I hate to add to this, but based on my research (and not experience) you might want a c6 screw for an almost 1 meter span.

  11. #11
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    Re: Double ball nut worth it for long C7 grade rolled ball screw?

    In spite of that long screw, my X axis actually has around 25.5" of actual real movement, so hopefully we'll be ok. It'll be about 2 weeks until I can receive this assembly.

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