Pneumatic pull downs
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  1. #1
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    Default Pneumatic pull downs

    Anybody ever use these or something similar?
    Pull Clamp - Fixtureworks
    We have a range of parts that get a final operation in a mill. It's a quick profile, hole pattern drilled, and a front/backside edge break, two parts at a time. We use an impact and a 1/2" bolt to clamp a custom cap onto the part and sandwich it in place to a locating fixture. The current system is nice because it is flexible and fast to change up for different parts, and easy to update when a brand new part gets added to the catalogue. The downside is it takes operators a minute or two to unbolt, remove cap and finished part, replace cap and new part, and rebolt. Do that 100 times a day while they're also running the other machines and it means the spindle on time is down to maybe 30%.
    I'd like to replace bolts with something like this that is A) faster and B) repeatable. Originally looked at pneumatic chucks but we have too many different sizes, something like this allows us to use pretty much our same flavor of fixturing but hopefully it increases our throughput, or at least cuts down on slipping parts.
    Downside I see to this particular item is it needs constant air pressure otherwise it will unclamp, but is that really even a downside? Also not really sure is the 562lb "clamping force" is a lot or not much at all...

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    Did some Googling (should have done my homework ) and a 1/2-13 bolt torqued to 50 ftlbs yields 4000lbs of "axial clamp force" so those aren't gonna cut it. Is there another clamp system out there that would be ideal for replacing a traditional fastener? We have a range of thicknesses on the feature that gets clamped from .216 to .669, so an adjustable length stud, or something with a range of clamping depths would be ideal.

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    A couple things to consider:

    I don't know what you're cutting, feedrates, material. How heavily you're hogging at it. But you don't likely need 4000lbs of downforce. What you more need is something that keeps the part from sliding around.

    I know NOTHING of the pulldowns you linked. But if you can secure them nicely, and you can make locating "pullstuds" that fit in your parts and these locators precisely so there isn't a lot of play, you'll probably need far less downforce than you think. As long as generally you can get it to not move around.


    Now, the downside? you said you 562lbs of downforce. LOL no. That site has all the dimensions in metric, including the air pressure. I'm pretty sure that downforce spec is in Newtons. and 562 newtons is 126lbs of force. And that is at .5mpa (about 72psi)

    If you can run the max air pressure (1mpa; 145psi) you can double the force to 250lbs.

    If you had 3 or 4 of those on a part, and you're cutting aluminum or not doing a ton of stuff to steel, maybe that'd work. as long as you can keep it from wiggling around (can't have .030 clearance for the locating pin, for example)

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    If you have the space, you could also combo those pull downs with one of these.

    ID / OD clamps for machining - Form Holding Clamps | IMAO

    Gives you the lateral positioning Dan mentions above. You might be able to find a pneumatic version that you could tie in.

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    Missed the unit conversion, my bad.
    Tried to post a picture earlier but I couldn't get it to work, would have made this a lot easier to understand.
    op3.jpg
    Part of the problem is there isn't really a good way to lock the part in place. There's 50+ different hole pattern configurations we have to work around so we can't really add a feature to fix one because it will interfere with the next part. I see systems like Jergens or Gerardi that could probably work with a custom made adjustable length pull stud, was just looking for something a little more "off the shelf."

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    Bolt the fixture to some sort of zero-point pallet and hot swap pallets.

    What kind of repeatability are you seeking? Rigidity requirements? Budget?

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    Clamps & Accessories | Carr Lane

    I've built fixtures with the hydraulic clamps. Also check out Mitee Bite, they make a variety of clamps.

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    We are leaning towards a Midaco APC for the machine and duplicating our fixtures which will help with the spindle on time.
    Each part is probed in the cycle for some engraving so locating isn't thaaat critical.
    Not sure on the budget, but it doesn't take a lot of scrapped parts to add up to a new fixture. Just doing research right now.

    Maybe I'm not explaining this well... essentially just trying to replace the bolt with something like a drawbar and pullstud so there's less room for operator error, dead or lost drill, slipped drill gouges the part, etc.
    And hopefully its faster too.

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    Quote Originally Posted by GiroDyno View Post
    We are leaning towards a Midaco APC for the machine and duplicating our fixtures which will help with the spindle on time.
    Each part is probed in the cycle for some engraving so locating isn't thaaat critical.
    Not sure on the budget, but it doesn't take a lot of scrapped parts to add up to a new fixture. Just doing research right now.

    Maybe I'm not explaining this well... essentially just trying to replace the bolt with something like a drawbar and pullstud so there's less room for operator error, dead or lost drill, slipped drill gouges the part, etc.
    And hopefully its faster too.
    Cylinder underneath, swing washer and nut on top.
    No need to unscrew the nut.

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    A pneumatic table might be an option. We had Bregnard in this country, patented in the fifties. You would only need a set of stops to the floating part of the table.

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    Quote Originally Posted by digger doug View Post
    Cylinder underneath, swing washer and nut on top.
    No need to unscrew the nut.
    That sounds just right!
    IIRC Midaco even has a hydraulic attachment for the APC that comes with everything sans actuators, should do the trick.

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    FWIW I designed a fixture using OTC threaded body hollow pull cylinders in the base plate. Qty (9) of them in a row.

    Top "cage" was custom made for the product, had simple "keyhole" cut outs for the nut to pass thru.

    Simply drop cage down with large hole, past the nut, and then sideways to the
    smaller dia.
    Actuate cylinder to pull down.

    No need of a swing washer.

    Powered with a simple air powered "shoe box" pump.

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    If we cut a slot into our caps we wouldn't need a swing washer. Set the part on the locating fixture over the cylinder, slide the cap over the part and under a flange on the ram, and press the button to suck it all down.
    Knew there had to be a better solution out there just needed to get some fresh input.
    slotted-cap.jpg

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    My last contribution was stupid. Looking at the part more intensely I see an internal cylindrical surface. Am I right? Expanding mandrel chucks would then be the best and quickest mounts.

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    Quote Originally Posted by GiroDyno View Post
    We are leaning towards a Midaco APC for the machine and duplicating our fixtures which will help with the spindle on time.
    Each part is probed in the cycle for some engraving so locating isn't thaaat critical.
    Not sure on the budget, but it doesn't take a lot of scrapped parts to add up to a new fixture. Just doing research right now.

    Maybe I'm not explaining this well... essentially just trying to replace the bolt with something like a drawbar and pullstud so there's less room for operator error, dead or lost drill, slipped drill gouges the part, etc.
    And hopefully its faster too.
    Nooo idea if it fits, but we did everything we COULD do with manual eccentric cam pressure, often acting against a back-stiffener / pressure distributor thence pushing a form-fitting shoe.

    Get's worn, swapping-in a new cam was dead-quick because we always made the first spare when we made the initial fixture.

    Cheap. Fast. No fasteners to fumble about with, neither air nor hydraulic needed.. but one COULD integrate either of those, too ,and many HAVE done, and they are even SOLD that way as well as with the all-manual lever.

    Our trigger? Store-bought Heinrich camlock vises of the 1950's that didn't actually FIT very many of our needs well at the time, but were not all that bad an idea.

    Must have helped SOMEBODY. They were not "new" even then and are still made over 70 years on ... and counting?

    Heinrich Company - Camlock Vise - Racine, Wisconsin

    And they have always had power-operated choices as well!

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    Quote Originally Posted by GiroDyno View Post
    Knew there had to be a better solution out there just needed to get some fresh input.
    There will be other challenges.

    We all benefit when we share!

    "PM at work, doing what PM does best!"


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    How about air hose hooked up raises a pull stud up air off equals spring loaded draw bar pulling down part
    Don


    Sent from my iPhone using Tapatalk Pro

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    Quote Originally Posted by D Nelson View Post
    How about air hose hooked up raises a pull stud up air off equals spring loaded draw bar pulling down part
    Don


    Sent from my iPhone using Tapatalk Pro
    Springs strong enough to match air pressure of any reasonable pressure, and no F(ine) Way hydraulics, do not generally come in zero cubic volume sizes!
    Stacked Bellevilles, maybe?

    But re-config flexibility would be degraded, not enhanced.

    INDIRECT cams and sliding wedges have the advantage that they do not need all THAT much travel to multiply the point force off rather modest actuator strength. Then also be somewhat "self locking" so as to not be easily shaken loose as cutting-tool forces ramp-up.

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    Just like a spindle upside down


    Sent from my iPhone using Tapatalk Pro

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    Quote Originally Posted by D Nelson View Post
    Just like a spindle upside down
    Folks put internal-expander 5C into spin-indexers all the time.

    Not that I'd try to mill off one! But the concept is sound enough!


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