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Thread: Jig for cutting ejector pins?

  1. #1
    ADFToolmaker is offline Cast Iron
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    Default Jig for cutting ejector pins?

    We are a small mold tool shop. We cut our ejector pins on a t&c grinder using a 0.8mm thick abrasive wheel, holding the pins in vee block. I have been sketching some ideas for a system with stops to hold the pins at a specific length to be cut. I have made similar setups at previous companies, some worked better than others. Also I can see the same jig if well made being useful to end grind on a surface grinder.

    I am asking is anyone has ideas or pics they eould like to share? We cut pins from 1mm dia to 25mm dia, and would like to be able to cut short core pins also.

    I have looked at one of the dedicated pin cutting machines with cutting & facing wheel, but the length stop has to be re calibrated each time is it moved, and they do not offer the versatility we would like, eg angle and step cutting.

  2. #2
    Modelman is offline Stainless
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    I bought one of these years ago, and really like it:

    Choice Mold Components, Inc.

    I don't remember the Choice name... Burger Engineering sticks in my mind, but maybe they sold the design. For short core pins, I clamp a "wee block" in the V block. The dresser on top is handy, and I tend to use it just as a dresser whenever I need one six or seven inches above the chuck.

    Dennis

  3. #3
    implmex is online now Stainless
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    Hi ADFToolmaker:
    I found my personal joy around ejector pin cutoff with the wire EDM instead of the grinder.
    I hate the smoke and the stink and the shit all over the shop when you cut them off with an abrasive cutoff wheel.
    I also hate it when you cut a big expensive pin and the wheel wanders and scarfs a big divot in the top of the pin.
    I hate even more, standing up a big pin and grinding forever to bring it to length only to find it's grown from the heat and you have to scrap it or grind the parallels down and redo all the other pins.
    I really really really hate sidewheeling a big pin and gnawing away on it half of forever to get it kind of, sort of, to length.

    So, if you have a wire at your disposal, it will make your life joyful to the point where you can't hardly stand it.

    Here's how I do it:

    I made a hardened bar, ground nice and flat that I can bolt to the front table and clock in to the X axis.
    It's got a pair of wired holes for a snug running fit on a pair of rods (1/2" ejector pin cutoffs).
    At the other end of these rods is another bar with ten vees wired into it, and I've got ten knurled clamps to hold all my pins in the vees so they're laying down in the tank, each one butted up against the ground bar.
    The vee rail is adjusted to be around 0.100" short of the shortest pin.
    I stone all my pin heads and mount the first 10 pins in the vees butted up against the rail.
    I make the pin in station #1 a return pin.

    To determine my ejector pin lengths, I bolt the cold side together and shove in my ejector plate, and either clamp it to the bottom plate or jack it onto the bottom plate with studs from my milling clamp kit, so I know the plate's down hard.
    Then I depth mike through a return pin bore to give me my return pin height.
    All other pin lengths are referenced from the return pin length as plus or minus values from the parting plane and I usually find these lengths with a drop gauge or by referencing the CAD model.

    I wrote a program for the wire EDM that calls variables I can input and will calculate what to do from those variables.
    All the variables are grouped at the head of the program so I can edit them.
    I input all the pin diameters and their lengths relative to the return pin length which is called Zero.

    Now I cut a return pin and make it approximately 0.100" too long.
    I do a roughing cut and a couple of skim cuts, then measure the pin as accurately as I care about.
    I make the appropriate adjustment and cut the return pin again to final length.
    I set that as zero in my work coordinate system.
    Now I can call up my pin cutting program again and just hit the green button and walk away.
    I've never had a bad surprise this way; I can get all my pins easily better than 0.0005" of what I intended and I come back after an hour and load the next lot, then go away again and do some other toolbreaking.

    It's a really simple way to do it once the program is written and the jig built.
    Each pin is a bit slower to cut this way, but the machine is doing all the work, and I don't have to blow all that black crap out of my nose holes at the end of the day; very civilized indeed!!

    Of course, if you don't have a wire, you'll have to suffer the old fashioned way; but if you do, and you want my program, email me and I'll email back to you with the file attached when I get back into the shop tomorrow.
    My email address is easy to find on my implant-mechanix site.
    The program is written for a Sodick A320 but you should be easily able to edit it to run on whatever machine you have (assuming you've got one).
    Cheers

    Marcus
    Implant Mechanix – Design & Innovation - home
    Vancouver Wire EDM -- Wire EDM Machining
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  4. #4
    Zahnrad Kopf's Avatar
    Zahnrad Kopf is offline Titanium
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    +1 how Marcus describes. It's exactly how I do it. Variables and all. In fact, I've become very fond of variables in the last 6 months. You can do some really neat stuff in a wire with them.

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    ADFToolmaker is offline Cast Iron
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    Dennis:

    Thanks, great link, I may well buy one. I guy that works for me has a homemade one similar, we use it a lot. The one in the link is better though. I still may have to make one since we often do pins twice that long. I have been considering an indexable stop, say every 25mm or so to speed setups. I would also like to avoid a screw to clamp, as I suspect at times the screw has pushed the pin off the stop for me, making an undersized length.

    Marcus:

    Thanks for taking so much time to reply, but alas we do not have a wire available to cut pins. It goes on the list as a smart way of doing it though. We do a lot of grinding so the mess is not considered too much of a nuisance.

  6. #6
    implmex is online now Stainless
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    Hi ADFToolmaker:
    If you're committed to grinding pins rather than wire cutting them, here's a way I used to use (in the days before wire for me)
    I built a rough and dirty cutoff machine from a pedestal grinder, and put a swing arm on it basically like a Deckel single lip cutter grinder but without the fancy collet system.
    I welded a pair of vise grips onto a bracket I could slide along the arm, aligned so the pins could be clamped parallel to the swing arm axis (give or take a smidge).
    I made no attempt to build a rocket science device; it was just for cutoff, not for finish grinding.
    I made the swing arm long, almost down to the floor, so a cutoff movement was a big arc; almost linear over the distance needed to cut a one inch pin.
    I got a cheap throwaway digital scale and bolted it to an end stop bracket so I could move the end stop predictably and set my zero wherever I wanted it.
    I made a fine adjust mechanism for the end stop just like you see on simple height gauges.
    All was made to be used; not to be a work of art.
    It took a weekend to make, and I used a cheap shitty Taiwanese bench grinder to power it

    This cutoff system worked like a hot damn.
    The beauty of it was that it was very fast; the vise grips, crude as they were, were perfect for this application.
    You could adjust them so a skinny pin could be grabbed without locking them and then driven past the wheel by swinging the swing arm, then swinging it back and releasing the pin.
    I could whang through a gazillion pins really fast, maybe 2 seconds per pin for a 1/8" pin.
    Big pins could be clamped very securely just by adjusting the vise grips to lock on the pin.
    That way a big pin could be cut by bouncing the pin into and out of the wheel to keep it from overheating.
    I could control the pressure easily; in fact the whole affair was something like a chop saw except I moved the pin instead of the motor and wheel.
    Even though I'm right handed, I mounted the affair on the left side of the grinder; that way I could put all my pins on a little table on my left side and grab them without even looking at them. (I'd sort them first, obviously, so all of the same size and length would be cut as a batch).
    I could also hold them against the stop with my left hand while I squeezed the vise grips with my right hand, and then release the pin into my left hand without burning my fingers.
    The beauty of this wonky contraption over a chop saw was its blazing speed; the clamping, cutoff and unclamping motion is all done with the same hand and it never leaves the vise grip handle.
    You can set up a bucket with water underneath your cutoff station and just drop the pins in as you cut them.
    You can cut bolts, dowel pins, barstock; all kinds of useful stuff (come to think of it, I'm kinda nostalgic for it now!!)

    For grinding pins, I ALWAYS stood them up instead of sidewheeling them.
    I'd grind them all to +.005" in one increment, using the grinder as if it was a shaper, and toss them in a water bucket.
    They'd usually expand just enough from the heat that I'd have maybe 0.002" left for a finish pass by the time they cooled again.
    Then I'd re-dress the wheel and finish grind them to length, putting the pin heads on the mag chuck so I always knew exactly where I was.
    The pin grinding fixture was a pair of angle plates mounted back to back with a pair of keys between them so I could slide them up and down.
    The upper angle plate had a vee ground into the end of the short leg (the horizontal one) and a Destaco over center toggle clamp bolted on.
    I'd leave the mag chuck always on, pop a pin into the vee with the head a bit above the mag chuck and put a smidge of pressure on the clamp; enough to align the pin in the vee, but loose enough so I could still slide the pin up and down.
    I'd give the chuck right under the pin head a quick wipe with my fingers and push the pin down until it sucked itself onto the magnet, then clamp the Destaco.
    I found it best to load the pin before I did the wipe; that way the pin blocked all the shit on the fixture from falling onto the mag chuck when I pushed the pin down.
    For shortie pins, I'd either use a mag block or I'd clamp a mag base from a dial indicator onto the upper angle plate at the proper height.
    (I surface ground the top of the mag base to make it parallel to the bottom, and just blocked it up to the right height with 123 blocks and parallels).
    Again it was simple and fast to set up on the surface grinder, and it was fast to use and very accurate, making nice smooth pin faces that were dead nuts square and dirt simple to control the length.
    Then I got the wire EDM, and promptly abandoned the setup, so unfortunately I don't have pictures.

    On a last note; a couple of points from my experience.
    Some of my toolmaker buddies built enormously elaborate multi pin cutoff fixtures over the years.
    All were slow and difficult to use; hard to load, hard to get all the pins down on their stops, hard to maintain with all the shit and corruption around grinders.
    I also tried a DME pin grinder once; I was not super impressed even though I'd had a big boner for one before I got to try it for real.
    Slow, not that accurate; just nothing to write home about. (besides did I mention I hate sidewheeling pins)

    Cheers

    Marcus
    Implant Mechanix – Design & Innovation - home
    Vancouver Wire EDM -- Wire EDM Machining
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  7. #7
    Modelman is offline Stainless
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    Quote Originally Posted by ADFToolmaker View Post
    Dennis:

    Thanks, great link, I may well buy one. I guy that works for me has a homemade one similar, we use it a lot. The one in the link is better though. I still may have to make one since we often do pins twice that long. I have been considering an indexable stop, say every 25mm or so to speed setups. I would also like to avoid a screw to clamp, as I suspect at times the screw has pushed the pin off the stop for me, making an undersized length.
    I've never had a problem with the screw pushing the pin up, but it may be technique. The clamp for the V has a good bit of clearance; when I clamp a pin I push down on the pin (assuming the pin is standing vertical) while concurrently raising the thumb screw on the clamp a little above perpendicular to the pin. As the screw tightens it slides downward to perpendicular, forcing the pin downward in the process. You could, I suppose, substitute a screw with an integral pivoting rest pad, but in my case, I needed to grind a taper on the end of the screw to reach the smaller diameter pins I use a lot.

    There are a couple design features that are not evident and worth mentioning:

    The V block clamp and the depth stop are both cast bronze, non magnetic, so if you lay them down on the chuck you can pick them up again.Likewise the thumbscrew is nonmagnetic stainless.

    The depth stop is cast with a crowned upper surface, so no mater what angle it is tightened at, it only presents one high point to the pin. Likewise, the pin always indexes off a point near the center of the head; even if it is slightly bowed, it won't stand on the edge of the head and get ground too short because of the angular error.

    The base has screw holes. It should be rather easy to grind a riser block that continues the track for the stop so the stop can be mounted below the original base for those long pins.

    And, I agree with Marcus. I hate sidewheeling. I typically rough grind a bunch of pins oversize, then go back after they've cooled and grind to finish length.

    Dennis

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    ADFToolmaker is offline Cast Iron
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    Thanks Dennis and Marcus for your detailed replies. I certainly agree, side wheeling pins is not the way forward, and is one of the reasons I have not bought one of the proprietry cutoff machines. I have included many of your suggestions in my design, I will post pics when it the unit is complete. But for now I have been pulled away to other more pressing process improvement, such as splitting molds on the bench, (new thread).

  9. #9
    ADFToolmaker is offline Cast Iron
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    So I finally got something made, and I am pleased with how it works for how simple it is. The height gage sets the length to be cut straight off the display. The vee block holds pins from 1mm to 30mm in diameter. The hand operated lever clamps the pin in the block with spring pressure, swapping pins is fast and easy. Unlike most dedicated pin cutting machines, this will also cut angles by unclamping one screw and rotating the fixture ont he table. There are two dowels that locate the fixture to the table tee slot to regain the square cutting position. It does not have the second cup wheel spindle to grind to length, but we usually end grind when it counts anyway.
    Attached Thumbnails Attached Thumbnails right.jpg   left.jpg  
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  10. #10
    sable's Avatar
    sable is online now Stainless
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    Quote Originally Posted by ADFToolmaker View Post
    So I finally got something made, and I am pleased with how it works for how simple it is. The height gage sets the length to be cut straight off the display. The vee block holds pins from 1mm to 30mm in diameter. The hand operated lever clamps the pin in the block with spring pressure, swapping pins is fast and easy. Unlike most dedicated pin cutting machines, this will also cut angles by unclamping one screw and rotating the fixture ont he table. There are two dowels that locate the fixture to the table tee slot to regain the square cutting position. It does not have the second cup wheel spindle to grind to length, but we usually end grind when it counts anyway.
    Thanks for that ,I've been thinking about a similar setup for general cutting up of bits of metal too small( or too hard) to put in the cold saw

  11. #11
    ADFToolmaker is offline Cast Iron
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    Quote Originally Posted by sable View Post
    Thanks for that ,I've been thinking about a similar setup for general cutting up of bits of metal too small( or too hard) to put in the cold saw
    Yep, it works great for bolts and screws too.

  12. #12
    implmex is online now Stainless
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    Hi ADFToolmaker:
    That rig looks pretty darn nice I have to say.
    Of course if you leave the wheel unguarded, the NZ safety Nazis are going to jump right down your throat if they're anything like ours up here in Canada.

    I was always too timid to cut a pin bigger than about 8mm without clamping it securely.
    Does your spring clamp hold adequately for bigger pins?
    Also, are you able to leave the machine set up like that permanently, or does it routinely get commandeered for other work?
    Having a dedicated machine was one of the big reasons I used a bench grinder instead of a cutter grinder: I like to just be able to walk up to the machine and start cutting instead of having to tear down a setup, drag out the new bits set it all up and then cut one or two pins. (of course I have to do that now on the wire EDM, so I did make the compromise there)

    Cheers

    Marcus
    Implant Mechanix Design & Innovation - home
    Vancouver Wire EDM -- Wire EDM Machining

  13. #13
    ADFToolmaker is offline Cast Iron
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    Hi Marcus,

    Yes the unguarded wheel may cause problems with osh (or version of ohsa). There is a theory than an inspector will always want to have found something before they leave, an unguarded wheel is a bone for them to stop looking too hard elswhere. I can say sorry, refit the guard and we are all good. In reality an inspection normally only happens after a serious incident, which I would be pretty unlucky to have 0.8mm wheel cause. I've broken my share, like being hit by a high speed feather. Whenever we fit any other wheel, the guard goes right back on. I have worked in enough shops and seen enough injuries to never use a wheel of any reasonable proportion unguarded.

    The spring clamp works well up to 16mm diameter, after that it needs the operator to pull up on the lever to clamp fully, no biggie. We leave the machine set up for this work 95% of the time, when we do other work the fixture can be left in place most of the time anyway. To re-set the length it is just a matter of zeroing the height gauge, and winding the table until the stop rod just touches the wheel.

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