Oldham couplings


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Thread: Oldham couplings

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    Default Oldham couplings

    Hello all,

    I'm new here and am seeking some advice. I'm installing a CNC Fusion kit on a Sieg X2D mini mill. I found an old thread here where the topic of discussion was couplings...and the majority seemed to be in favor of Oldham style couplings. I just ordered some from McMaster but now am wondering if I jumped the gun.

    My concern is the x-axis ballscrew setup. The thrust bearing is on the right side of the table and the motor goes on the left side. The ballscrew is unsupported on the motor end and relies on the coupling to keep it in line with the motor shaft.

    I've never seen an Oldham coupler aside from in pictures, but it sure looks like they would like to have the shaft supported, else they could slide way out of alignment and bind up when the motor turns again.

    Any thoughts re this?

    Thanks!
    Scot

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    Default Re: Oldham couplings

    It is always better to ensure a ballscrew is supported by bearings on both ends. If you do what you are suggesting the bearings in the motor are carrying the ballscrew load and the coupling would really need to be rigid to it can move in any direction.

    Russ



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    Default Re: Oldham couplings

    Unfortunately, I don't have the resources to modify the CNC Fusion kit at this time. I actually don't think a bearing can be added without sourcing a longer ballscrew or sacrificing x-axis travel.

    If the Oldham couplers don't work, what should I use? I want to try Clearpath servos so don't want to introduce slop if it can be avoided. Part of the challenge is finding a coupling with 2 different bore sizes. The ballscrews are 5/16" and the motors are 3/8".

    Thanks!



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    Default Re: Oldham couplings

    That is an extremely poor set up, a ball screw should definitely be supported both ends and proper bearings to prevent end float, Couplings are never intended to do the job, What is the reason for not fitting the bearings at the motor end? Room?
    One excellent source of hardware is Misumi USA.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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    Default Re: Oldham couplings

    I have no idea why there's no bearing on the motor side. I honestly didn't study their website too much prior to purchase as there are not very many options for ready made kits. The machining looks really nice and the ballscrews are also very nice.

    If the ballscrew were longer and the motor mount thicker, bearings could be added to the motor side. That's basically a redesign of the entire x-axis at that point.

    The kit is available for purchase with Lovejoy couplers or, as an upgrade, beam type couplings. I have the Lovejoy type but they won't fit the motors I want to use...wrong shaft size. Both the Lovejoy and beam type are not really what I want to use anyway.

    It's funny, the Clearpath manual recommends bellows type couplings but most coupling manufacturers seems to indicate bellows type are not meant for higher torque applications. At least that's what it seemed like to me. Bellows couplings are quite expensive, in any case, and difficult to source with different bore sizes on each end.

    I guess I have no option for now but to try the Oldham couplings and see if they're going to work. The ballscrew is somewhat supported by the nut in the table and thrust bearing on the far end.



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    Default Re: Oldham couplings

    If you do use bellows type for servo drive, they have to be stainless, not aluminum, these are for encoder drive etc.
    Oldham is not a type of coupler per-se, they are actually spider couplings, Oldham sells, or did, many different types of couplings, their are a few that are zero back lash, but they cost more, suppliers such as Misumi, sell spider couplers that are close to zero backlash due to the spider material used, in place of soft rubber.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Oldham couplings

    Probably hundreds if not thousands of these Fusion Kits have been sold and are in use and NO-ONE has ever complained about the 'un-supported' shaft end!
    I think the Oldhams are a pretty good engineered / economic solution and quite capable for these machines - you'll stall the steppers before overloading the couplings. Trying to add a motor end bearing will more than likely result in binding within the shaft as its unlikely you'll get the shaft both parallel and square to the ways without a lot of effort which doesn't really achieve anything that an unsupported screw does IMO!



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    Default Re: Oldham couplings

    The problem is that the description Oldham is a used (mistakenly) for a particular design coupling, and you can buy all degrees of quality of these spider couplings from non-backlash CNC possible quality. to ones only suited to motor-pump driving
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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    Default Re: Oldham couplings

    Just to clarify, the Oldham couplings I ordered are the kind with the delrin coupler thing...not exactly sure what it's called. These are not the spider type of coupling. With the spider type, the two ends are somewhat captive due to the shape of the spider. The Oldham style couplers can "disengage," for lack of a better descriptor when, say, the motor stops moving at just the right angle and if the unsupported screw were to droop. When the motor starts up again, I'd imagine the screw would whip as it moves back into alignment. Hope that makes sense?



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    Default Re: Oldham couplings



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    Default Re: Oldham couplings

    Well, a quick initial test of the Oldham couplings is promising. The ballscrew seems to be supported enough so that the coupling stays engaged enough and, so far, it seems to be quite usable. The McMaster couplings are a Ruland product and quite spendy. I ordered the clamp-on type which are about $20 for a single coupling, i.e. you need 2 plus the delrin insert to make one usable coupling so about $45 for one complete set. A setscrew type would be about $30 for one set. They are very nice though and seem to indeed have zero slop. Inserts are available in delrin or nylon. I ordered both. I'll have to place another order because I didn't realize you needed 2 to make a set so I came up short 3 pieces! :-)



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    Default Re: Oldham couplings

    The Oldham's are really easy to make with a mill, especially with set screws. McMaster is fast but expensive on most everything. I bought the inserts from them but made my own couplers on the manual mill. Just needed the right reamer and some set-screws and taps.

    Once the motor is mounted up, what you are effectively doing is supporting that end of the screw using the motor's bearings rather than bearings in the table end-caps. The Oldhams allow huge mis-alignment without stressing the shaft, so that keeps you from putting a lot of axial load on the motor bearing. The thrust load is handled on the other end so you should be in good shape.

    Personally I'd want at least a slip-fit bronze bushing on the motor end to limit the wobble possible if just to limit vibration possibilities but it may not be a real issue for you.

    CNC: Making incorrect parts and breaking stuff, faster and with greater precision.


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