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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Linear Motion to Push Metal Parts Into Grinding Wheel
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  1. #1

    Linear Motion to Push Metal Parts Into Grinding Wheel

    I am looking to build a semi-automated grinder for our foundry. We are currently using an anchored pneumatic piston to push some production pieces into a 14"x3" grinding wheel. FYI, we mainly deal with steels and stainless steels. Grinding is generally a 2"x1" square about 0.5" deep, varies quite often. I can draw a sketch if need be. It would be a horizontal motion into the 'side' of a belt grinder, the grinding surface would be vertical.

    I am leaning towards using a ball screw accompanied by a closed loop stepper.

    Relative Information:
    14" wheel with a 3" abrasive belt
    Force used to push production part into grinding wheel is unknow but grinding has typically been done by hand
    Consideration for spark "dust"
    Speed of linear motion has to be fairly quick, I can come up with a definite number if needed

    I have been looking into prebuild linear slides/ guide rails, they're on amazon. This is a mock up so I'm trying to keep costs relatively low, under $1,000 in parts for the motor, screw and rails.
    For the slide I have been looking at, I can link, the specs are 200mm Stroke, 1605 ball screw (16mm dia. screw, 5mm lead), square/ profiled linear bearings (unsure of size).
    For the motor, a hybrid Nema34 12nm, because I assume the bigger the better... don't want to be limited by the motor size.

    An enclosure can be made to 'seal' system from debris.

    Keep in mind I have yet to do a deep dive into learning, I am doing that but figured I would post this to gain some input or advice.

    Linear rail:
    https://www.amazon.com/dp/B0899JVBDP...ding=UTF8&th=1

  2. #2
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    Re: Linear Motion to Push Metal Parts Into Grinding Wheel

    Hi,
    aside from trying to prevent grinding dust from buggering everything up I think that's highly do-able.

    The only critical part is control of the ram/linear actuator so that the part is held in contact with the wheel enough to promote rapid grinding and yet not so hard
    it tries, or worse, succeeds in stalling the wheel.

    Two possibilities occur to me.
    1) Using an AC servo that has torque mode. In torque mode an analogue voltage from potentiometer or other control device determines the torque the motor
    produces. If you stall the motor it produces the same torque, and it suffers no ill effect. If you hooked such a servo to a ballscrew or rack & pinion or crank and
    conrod etc you'd get a constant force which is adjustable at need at yet would stop at its programmed end-stroke.

    2) Hydraulic servo/ pneumatic servo. I don't know if you are familiar with hydraulics but a power steering rack in a car is both simple and clever and is in effect
    a hydraulic servo. The force that it exerts is obviously dependent on hydraulic pressure (adjustable) and it will exert constant force until it reaches its set end stroke (adjustable).
    I haven't encountered one but imagine pneumatic servo cylinders are available also.

    Either of these devices would allow you to preset the grinding force and also the end stroke.

    Craig

  3. #3

    Re: Linear Motion to Push Metal Parts Into Grinding Wheel

    Craig, thank you for the advice; I will look into both. My assumption is the servo would provide a higher level of precision (my assumption could be wrong...), so I may lean in that direction.

  4. #4

    Re: Linear Motion to Push Metal Parts Into Grinding Wheel

    This morning I had found a program, Yaskawa SigmaSelect, to estimate servo size. I believe a 750W ebay servo would do (pending a bit more research), linked below.

    https://www.ebay.com/itm/ToAuto-750W...kAAOSw0~de6G2b

    I will dive a bit deeper into controls to determine the best rout. I'm aiming to have simple controls because it will eventually be used by our shop employees, if all goes well.

    Controls:
    Simple to use
    In the most basic form, 3 user defined locations.
    - (1) point farthest from belt, for part loading
    - (2) point right before part is introduced to the belt
    - (3) stop point, furthest point into belt
    The intention is to have a push button or pedal to initiate movement
    - Fast travel from point 1 to point 2
    - Slow travel from point 2 to point 3, grinding
    - fast travel from 3 to 1, finished piece

    My original idea was to just use an Arduino to control everything but I'm not sure if that's the best option.

  5. #5
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    Re: Linear Motion to Push Metal Parts Into Grinding Wheel

    Hi,
    that servo you linked to, ToAuto, is a cheap entry level Chinese made servo. Don't go there. I have no reason to doubt its quality but its
    documentation is Chinglish at best, un-decipherable at worst, it has no set-up software, you have to program it by pushing button like programming a microwave, avoid like
    the plague!

    I would recommend Delta (Taiwanese made in China) or DMM (Canadian made in China) as two quality brands with good backup, good documentation and most
    importantly set-up and tuning software at, if not bargain basement prices, fair prices.

    https://www.fasttobuy.com/flange-80m...er_p28084.html

    Craig

  6. #6
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    Re: Linear Motion to Push Metal Parts Into Grinding Wheel

    Hi,
    I think the control can be fairly simple, an Arduino certainly, but even that may be overkill.

    With a servo in torque mode it will travel as fast as it can until it encounters a load whereon it will push as hard as necessary to maintain
    the torque its is commanded to produce. It doesn't really need a fast zone and a slow zone, it will travel fast until the workpiece engages
    and thereafter travel fast enough only to maintain pressure on the workpiece.

    You will need a switch or detector (adjustable) to set the end stroke.

    I envisage something like this:
    1) a device with approx 2 inches of travel, each end of travel defined by a switch.
    2) with the device 'open' it recieves a new workpiece placed there by the operator.
    3) a button is pressed which starts the cycle
    4) the servo in torque mode advances at its max speed until the workpiece engages the wheel which resists the device from closing any further
    5) the servo now maintains steady torque which in turn means steady pressure of the workpiece against the wheel.
    6) the workpiece grinds down to final dimension as determined by the end of stroke switch (adjustable for different workpieces)
    7) the control voltage reverses going from positive (advancing to the wheel) to negative (driving away from the wheel)
    8) the device opens until it reaches it stop where it can be unloaded
    9) the servo could sit there stalled in the opening/fully opened direction until a new workpiece is loaded although turning it self off so that no current flows through the servo
    may prevent it getting warm.

    My idea for the control is one switch, with the switch in one position it advances to the wheel, with the switch is to other position the device retracts.
    The control would have a potentiometer that allows you to increase/decrease the torque of the servo, ie regulate the applied grinding pressure.

    Craig

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