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  1. #41
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    25% compression would be a lot for foamed cord stock, for solid .005" is what I would use for your application. When you pull a vacuum with a plate in place does it rest on the aluminum fixture or is it held up by the o-rings? How wide are your o-ring slots? They need to be wide enough for the cord stock to compress into them. If you are super glueing the cord stock into the slots that would be a GIANT fuckup and could easily be your leakage problem. The o-rings need room to compress. If you ever start dovetailing your cord slots you will never go back, sure it is more $$ for the tool and a little more time to cut them but they work sooooo much better. As I said earlier same goes for foamed cord stock, compared to solid the shit is magic. If you haven't already download Parker-Hanifins guide to o-rings, their engineered groove sizes work much better than anything I have ever come up with, don't reinvent the wheel. Proper o-ring grooves are engineered tight tolerance features. Follow the guidelines and they work much better than making shit up on the fly. I have done both and no longer make shit up on the fly when using o-rings.

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    Quote Originally Posted by Delw View Post
    just thought of one other thing.
    you bolted it down in the center? and it looks like you took the plate off the vices put cord on then put back one vices, then bolted the center bolt down?
    you might be bowing your plate
    I made a spacer from some 2" round 6061 bar between the table and the fixture so when I tighten the bolt it snugs the whole thing to the table and doesn't allow the vises to bow it in the middle this bolt was in place when the fixture was made and when I use it.

  3. #43
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    Quote Originally Posted by DavidScott View Post
    If you ever start dovetailing your cord slots you will never go back, sure it is more $$ for the tool and a little more time to cut them but they work sooooo much better.
    Ive heard that before as well, never tried it yet, might have to one of these days.

  4. #44
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    Quote Originally Posted by DavidScott View Post
    25% compression would be a lot for foamed cord stock, for solid .005" is what I would use for your application. When you pull a vacuum with a plate in place does it rest on the aluminum fixture or is it held up by the o-rings? How wide are your o-ring slots? They need to be wide enough for the cord stock to compress into them. If you are super glueing the cord stock into the slots that would be a GIANT fuckup and could easily be your leakage problem. The o-rings need room to compress. If you ever start dovetailing your cord slots you will never go back, sure it is more $$ for the tool and a little more time to cut them but they work sooooo much better. As I said earlier same goes for foamed cord stock, compared to solid the shit is magic. If you haven't already download Parker-Hanifins guide to o-rings, their engineered groove sizes work much better than anything I have ever come up with, don't reinvent the wheel. Proper o-ring grooves are engineered tight tolerance features. Follow the guidelines and they work much better than making shit up on the fly. I have done both and no longer make shit up on the fly when using o-rings.
    After thinking this all over I am considering leaving the fixture as is since it works as far as hold down. Instead of fixing the fixture deal with the coolant by constructing a clear reservoir with a large drain in the bottom that after the part runs I can open a ball valve and drain it back into the machine. I need to start making parts soon I am out of this part.

    My old fixture was a bolt down design, I held the 4 corners and drilled all the interior holes, then added screws through those drilled holes to hold the part while I machined the outside profile. I am wanting to speed things up that is why I went to vacuum if I add steps to deburr the blanks I start trading time from bolting to more work then going to vacuum and it starts losing the advantage in cycle time.

  5. #45
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    Quote Originally Posted by gundog View Post
    I made a spacer from some 2" round 6061 bar between the table and the fixture so when I tighten the bolt it snugs the whole thing to the table and doesn't allow the vises to bow it in the middle this bolt was in place when the fixture was made and when I use it.
    But the main question is did you indicate the top of the fixture AFTER you put it back in?
    that plate is what 11-12" wide? your running 5/8" thick vacumm plate and holding it in a vise. I highly doubt its flat. I am betting .015 out of flat easy in some spots
    that one you might want to bolt directly to the table.

    wide stock you need to go thicker or bolt directly to the table as a vise will bow it.

  6. #46
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    Quote Originally Posted by Delw View Post
    Ive heard that before as well, never tried it yet, might have to one of these days.
    I actually have a dovetail "o" ring cutter made by Harvey Tools. That was how I originally planned to make this fixture and I had some "o" ring cord stock but changed that plan after suggestions to use the EPDM foam cord stock. The cutter I have is for .139 cord stock but the EPDM I found from McMaster Carr was .125" and I decided not to use it but I still could. I did not use a ball mill for the cord channel I used a carbide 2 flute .125" EM. But the cord stock does not fit tight enough to stay put without gluing it in.

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    Quote Originally Posted by gundog View Post
    I am wanting to speed things up that is why I went to vacuum if I add steps to deburr the blanks I start trading time from bolting to more work then going to vacuum and it starts losing the advantage in cycle time.
    if you dont debur the blanks youll never be able to hold on a vacuum fixture EVER UNLESS your part is bigger than the vacuum plate and the material over hangs.
    you just take a deburr tool and run it around the cut edges takes a whopping 30 seconds.
    a vacuum plate works fast, BUT you have to do things right from the beginning. Just like any fixture, if you micky mouse it and dont pay attention to details you'll have issues. (not saying that in a bad way)
    its just going to take some practice as your new to this.
    just remember a vacuum plate must be FLAT , you dont glue the cord in and your parts in, and your blanks cant have burrs on them unless they over hang on your fixture.

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  9. #48
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    Quote Originally Posted by gundog View Post
    I actually have a dovetail "o" ring cutter made by Harvey Tools. That was how I originally planned to make this fixture and I had some "o" ring cord stock but changed that plan after suggestions to use the EPDM foam cord stock. The cutter I have is for .139 cord stock but the EPDM I found from McMaster Carr was .125" and I decided not to use it but I still could. I did not use a ball mill for the cord channel I used a carbide 2 flute .125" EM. But the cord stock does not fit tight enough to stay put without gluing it in.
    did you use that cord stock I sent the part number for? that stuff is called .125 but is over sized, is your grooves actually .125 or did they cut over sized?
    if the foam stuff doesnt work for you go with the rubber surgical stuff. that stuff is better for thicker material, the foam I use for thin stuff only to keep the part from bending.

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    heres the foam stock I use on the thinner parts 8605K41

    the one I use on thicker parts 5234K931

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    I thought you had solid cord, foamed is different! Then the PH o-ring instructions don't work, nevermind. Have you measured, fun to do, the diameter of the foamed cord stock? Those dovetail o-ring cutters are wonderful, you need to use it next time. Try removing the glue and just use clean new cord stock, I don't even glue the ends together, just cut them long. I would bet this is why you are leaking so much coolant. Try holding the cord stock in your grooves by peening the edges with a ball, just a thought, don't hold me to it.

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    Vac pump connects to a reservoir tank with sight glass. But reservoir is for sucked in coolant. Valve from tank to chuck to activate the chuck. No wait for tank to evacuate. 3CFM is a seriously good volume so every few parts drain tank back to sump. Make a rotary airlock drain if you feel ambitious.
    You have leaks in your system with that much coolant collection. Put a piece of Plexiglas over the chuck and flood the edges and watch for leaks.
    The fit of epdm in a straight groove should have the round gasket protrude high enough to make easy contact with the part, but not so much as to get pinched or squashed at the edges as it gets compressed in the groove. If your groove path is complex and has intersecting lines then you are best with using a ball endmill. If you really need high projection then you run a second, much larger BEM over the same tool path to "chamfer" the corners giving the excess epdm somewhere to go.

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    Quote Originally Posted by Scruffy887 View Post
    Vac pump connects to a reservoir tank with sight glass. But reservoir is for sucked in coolant. Valve from tank to chuck to activate the chuck. No wait for tank to evacuate. 3CFM is a seriously good volume so every few parts drain tank back to sump. Make a rotary airlock drain if you feel ambitious.
    You have leaks in your system with that much coolant collection. Put a piece of Plexiglas over the chuck and flood the edges and watch for leaks.
    The fit of epdm in a straight groove should have the round gasket protrude high enough to make easy contact with the part, but not so much as to get pinched or squashed at the edges as it gets compressed in the groove. If your groove path is complex and has intersecting lines then you are best with using a ball endmill. If you really need high projection then you run a second, much larger BEM over the same tool path to "chamfer" the corners giving the excess epdm somewhere to go.
    I really like that idea to check where it is leaking and I have some clear lexan or polycarbonate laying around.

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    My plan is to make a water trap reservoir out of polycarbonate tube and machine some ends for it out of plastic I have on hand. I am going to do a time measurement of just how long it takes to fill the water separator I have now and measure how many ounces it is to see how big a reservoir I need to contain the coolant plus a safety factor. I will plumb a drain back into the VMC so while I am changing parts I can open it to drain for the next run. I will use a 3/4" drain so it empty's fast. I need to install a bleeder valve anyway because it took it a long time to lose vacuum to remove the part. I plan to bypass the current vacuum reservoir the pump currently has it is 17.5" x 12" x 3" it is in 2 chambers under the unit and is the base for the unit. The new reservoir will take the place of the steel base reservoir now for vacuum storage. Right now the pump will pull the vacuum in just a few seconds using the current reservoir. I may do some tests to see if I can leave the current reservoir in the circuit but if it takes too long to pull a vacuum I will eliminate it to use the new one.

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    I built a water separator today and it worked great not one drop made it to the small separator. I ran about 20 parts so far and it is working great 6 minutes and 52 seconds. The new separator has a 3/4" drain hose with a ball valve plumbed back into the cabinet. I measured how much coolant was leaking for 1 cycle and it is about 16 ounces. The new separator holds 160 ounces and it only takes about 10 seconds to pull enough vacuum to start the next part. I left the stock reservoir in the circuit as a test and since it pulls the vacuum so fast I am going to leave it in the system. Here are some pictures.

    This is an overall picture 24" of 4" ABS pipe with PVC cap and fittings I used ABS because I already had it and did not want to buy a full length of PVC. I used glue that is designed to glue PVC to ABS. I wanted the cap PVC so I could glue in a piece of 1/2" PVC pipe into it for the inlet on the inside.

    20190402_155317.jpg
    Attached Thumbnails Attached Thumbnails 20190402_110837.jpg   20190402_110846.jpg   20190402_155327.jpg   20190402_155923.jpg  
    Last edited by gundog; 04-03-2019 at 10:29 AM.

  18. #55
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    A few more pictures.
    Attached Thumbnails Attached Thumbnails 20190402_155322.jpg   20190402_155947.jpg   20190402_160109.jpg  

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    Quote Originally Posted by Delw View Post
    heres the foam stock I use on the thinner parts 8605K41
    That is the one I used. How deep do you usually go with the groove that holds the cord?

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    The CNC router we have at work has a giant blower that is used for vacuum hold down. no oil required. 10HP electric motor and a tight tolerance centrifugal blower/fan. I'm not sure how it would behave with coolant getting in there. I've seen some companies that use a whole house vacuum cleaner as their vacuum pump. I'm not sure if this would be strong enough on small parts, though. I Imagine that the smaller the surface area, the higher the vacuum needs to be to hold.

    I'm only getting about 12" of vacuum, maybe a little more with that 10HP blower, but it holds a 4x8 piece of plywood or MDF snug to the point where you could never move it.

    ours is basically one of these, same company, different model name: Samos - Busch Vacuum Pumps and Systems United States

    the newer machines seem to be sold with these: Mink - Busch Vacuum Pumps and Systems United States

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    A deadhead rotary vane pump that pulls about 7.5 CFM. I used these for years if light cutting is done you can get away with out seals if you have a clean fixture surface and flat of compliant material. With your project in mind and what you intent to do I would use seals.

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    Quote Originally Posted by Delw View Post
    heres the foam stock I use on the thinner parts 8605K41

    the one I use on thicker parts 5234K931
    Bumping this one to say thanks for that. Before I was always ordering from pierson... spent way too much money on cord stock.

    From mcmaster, 100' of Ø1/8" is about 1/5th the cost.

    I ordered some a while ago to try. Used this just recently and seems to be working good. Thanks

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    Look on the picture. This is what you need. Regards Libor
    im004274.jpgim004273.jpg


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