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  1. #21
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    On Friday, I received some supplies and tried out version-1.0 of some "new & improved" grippers. These are pre-cut rubber strips with aluminum backing by Fixture Works/Fairlane. Drilled/counterbored for mounting bolts. Then machined a 5* angle on the contact faces to match the draft-angle on the parts. Lastly, a strip of anti-slip traction tape across the gripping face. Arranged now so that they're parallel with the parting line of the parts, to give more & better contact as well.


    gripper-2.jpg



    Initial thoughts are that they seem to hold well, although I couldn't test them with the problem-child painted parts yet.

    I'll report back with updates to let you all know how they perform. I appreciate everyone's input thus far - Thank you.

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  3. #22
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    If emery cloth solves your friction problem and is durable enough, you can laminate emery cloth to the smooth elastomer faces with 3m VHB tape. VHB tape is pricey but worth it if it solves your problem. I've done this with wet dry shop roll fabric backed sandpaper and 1" wide VHB. Laminate one surface of the tape to the sanding strip, apply pressure between thick plates in an arbor press then cut into circles with a punch. Last step is to laminate those circles onto the gripper face with a press again. VHB tape requires a certain pressure to activate the adhesive and we used a press to reliably apply that pressure. Someone can do a batch of these at a time with less work than molding your own. The vhb tape adds some conformance and does not come off if applied correctly. the tape and cloth backed sandpaper can be had in sheet form as well and with flat gripper faces, you can laminate both sides of the tape in one shot. I made the dots for curved grippers so we pressed in two steps.

    If the textured neoprene from mcmaster works well for friction and durability, loctite 380 and a vacuum bag or clamping plates works well to laminate that material to aluminum. Both faces need to be roughed up with ~120 grit sandpaper and cleaned with a strong solvent like acetone. We've used textured neoprene on aluminum with good results for a different gripper project. Full coverage of the flexible adhesive was key to prevent edge peeling.

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  5. #23
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    In marine use for extreme service aka cruising boats, epoxy and a sand (washed, graded) thrown on has worked well for decades.

    Not suggesting to throw sand on the glued grippers -- although it might work well.
    (Until or if the sanding wears).

    But something like plastidip with a sprinkled coating of suitable steel powder or grit might be a good idea.
    Perhaps stainless grit for less contamination.
    The plastidip can provide minimal yield and conformal contact.

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  7. #24
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    Confused on abrasive use.
    VHB or other to attach emery cloth a good/great idea but?
    Aren't these painted parts? Even if no slip is there not pinholes in the paint if the grit too course or dispersion not fine enough?
    We had this problem with painted axles going though the robots. Still looked okay by eye but under corrosion tests those tiny spots became a bad thing as we had violated the paint.
    Grit size, concentration and grip pressure play a roll.
    Making it work one thing, making it not hurt the part counts too.

    I do not know your parts so this could be just bullcrap but I just thought to mention it as a concern.
    Bob

  8. #25
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    Quote Originally Posted by CarbideBob View Post
    Confused on abrasive use.
    VHB or other to attach emery cloth a good/great idea but?
    Aren't these painted parts? Even if no slip is there not pinholes in the paint if the grit too course or dispersion not fine enough?
    We had this problem with painted axles going though the robots. Still looked okay by eye but under corrosion tests those tiny spots became a bad thing as we had violated the paint.
    Grit size, concentration and grip pressure play a roll.
    Making it work one thing, making it not hurt the part counts too.

    I do not know your parts so this could be just bullcrap but I just thought to mention it as a concern.
    Bob
    Bob (and others,) the concern about damage and/or contamination of the paint are valid concerns, but fortunately for us, these 'painted' surfaces are not final show surfaces. The forgings are dipped in paint for general rust-prevention during international shipping. I'd say more than 50% of the part's surface gets machined - including the surfaces where the grippers hold the part. So, simply put, in a later operation, we mill/drill away the painted surface where the robot grips those parts, therefore, no worry about paint damage on these surfaces.

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  10. #26
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    I have a Norton diamond abrasive roll that I use on a certain grinding job. It is a very fine grit so likely would not harm a painted surface as long as it did not slip on that surface. It is a 1" width and about ,010 thick so would be easy to attach to your device. It is plastic backed so very strong.

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    Perhaps somewhat OT, but PM's display of topics, at least on my screen, has this thread labeled "Need help with a rubber..."

    Like driving past a car accident I finally had to open it...

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  13. #28
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    Quote Originally Posted by Oldwrench View Post
    Perhaps somewhat OT, but PM's display of topics, at least on my screen, has this thread labeled "Need help with a rubber..."
    Like driving past a car accident I finally had to open it...
    And that classifies you as rubbernecker, I don't want to know the drive behind it. .

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  15. #29
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    Quote Originally Posted by CarbideBob View Post
    And that classifies you as rubbernecker, I don't want to know the drive behind it. .
    No drive, just resisted opening that thread about two hundred times. I couldn't imagine needing help, most women are familiar with installation techniques and some can do it no-hands.

  16. #30
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    This is probably a bit too obvious, but could you throw an assist spring between the fingers? Most grippers can grip on closing or opening. It's an easy way to get 50-100% more force out of the same gripper, depending on which way the gripper is stronger.

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    Quote Originally Posted by Comatose View Post
    This is probably a bit too obvious, but could you throw an assist spring between the fingers? Most grippers can grip on closing or opening. It's an easy way to get 50-100% more force out of the same gripper, depending on which way the gripper is stronger.
    That's not a bad idea. The only trouble in this application is that we grip the parts in both the OPEN & CLOSED orientations. We grip the part in the gripper OPEN orientation as pictured, then set the part on a re-grip stand, let go, re-orient, then grip the part on another geometric feature in the gripper CLOSED orientation.

    The abrasive gripping surface has shown the most promise so far. I'm having trouble finding a durable solution as my first attempt (second gripper pictured) failed pretty quickly on the durability front. But, I'm still working on constructing some kind of metal/rubber/abrasive gripper pad that's more durable.

    Also, to whoever suggested the 3M VHB tape - AMAZING stuff!
    McMaster-Carr

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    Came across these cheapo diamond wheels (below) for a dremel. There are lots of cheap plated abrasives out there for masonry cutting, search the bowels of amazon/ebay/alibaba for a bulk pack of them.
    you could stick an array of these diamond abrasive disks on an aluminum plate with VHB tape. VHB is definitely amazing stuff.
    Amazon.com: 5 Diamond Wheels Lapidary Discs Cutting Saw fits Dremel


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