48” Featherweight Camelback Straightedge Pattern is Taking Shape. - Page 4
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  1. #61
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    Quote Originally Posted by CBlair View Post
    This has been a lot of work, thanks for sharing.

    Charles
    Thank you, Charles, but not so fast. I’m not done yet!

    There was still the logo to make and I just finished that last night I made it from a piece of .125” aluminum which probably is too thick for the actual final logo itself but I’ll mill it down a little bit to make it thinner.
    img_e0149.jpg

    As always start out with a blueprint, of course, and here is a picture of the blueprint (I guess I didn’t have any yellow Post-its. )



    It it was just a matter of using a jeweler’s piercing saw to roughly cutout the general profile and then gluing the bit to a piece of wood (called a pin by jewelry makers I believe though I claim no jewelry skills).
    Then I used my Foredom and a miniature bit to refine the profile and cut in the notches in the feather. I used a couple of shop-made bent knives to pare away the excess wood under the piece so that there is easy access to the side of the piece.


    img_0150.jpg


    Then fine Swiss files were used to to smooth and fair the sides.



    As a final step, I will heat the piece a bit to soften the cyano glue and then glue it to a small metal backing piece and mill it down 50 thou or so until it is about as thick as the letters used elsewhere on the pattern.

    And still to come is a hydraulic pattern-lift-assist device that I think may be of some interest and is, so far as I know, an original design and use. You see, lifting this long, somewhat detailed, and deep pattern perfectly level and vertical is a tricky business which can easily damage the sand. The hydraulic lifter should solve that.

    Denis

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  3. #62
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    Quote Originally Posted by dgfoster View Post
    And still to come is a hydraulic pattern-lift-assist device that I think may be of some interest and is, so far as I know, an original design and use. You see, lifting this long, somewhat detailed, and deep pattern perfectly level and vertical is a tricky business which can easily damage the sand. The hydraulic lifter should solve that.

    Denis
    LOL! "old genius never fries, it just slowly creates new sources of amusement."

    Bit o' fun, ain't it?

    Enjoy!

    Bill

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  5. #63
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    Here’s a pic of the new logo glued into place on the pattern. I simply carefully position the logo (or letter as the case may be) and use a syringe to place a single drop of thin cyano glue right next to the letter or logo. The glue wicks under the item and then I use a paper towel edge to absorb the excess glue. The result is a nice neat, firmly attached letter or logo with no excess glue obscuring details or making a general mess. I do sand the application area first to get a clean surface wtih "tooth." The pattern looks a bit grey now as I also use graphite along with talc as a parting agent to get the green sand to separate cleanly from the pattern.

    I wish it came through so nice and shiny on a casting. Maybe I should carve one for each casting and rivet them in place rather than casting them into the SE! ;-). Ummm, maybe not...

    img_6046-2-.jpg


    Not done cleanly enough for jewelry but will cast just fine:

    logo1.jpg


    Denis
    Last edited by dgfoster; 09-28-2019 at 03:37 PM. Reason: typo!

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  7. #64
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    A couple of posts ago I mentioned I would be working on an hydraulic pattern lifting setup to make lifting a longish pattern out of the sand easier and more precise. Well, that system will be put to the test in the next couple of days.

    So, I learned a couple things about this setup today. (Working at 1/3 efficiency due to a cold---uggh). First off, using the foot pedal to operate the driving cylinders results in an action that is extremely smooth and easy to precisely control. That is, as long as there is NO air in the system. As I was putting the cylinders together originally I thought it would make little difference if a small amount of air were in the lines since the lifting forces were small and compression of said air should be very slight. However the difference between the static coefficient of friction in the cylinders and their dynamic coefficients does cause trouble. The resulting stiction causes just what you don't want---some initial hesitation followed by the driven cylinder breaking free from stiction and then springing forward. Yes, the deviation from smooth movement is slight, but definitely noticeable.

    Here are the cylinders (the system will consist of 3 pairs of cylinders with 3 driving cylinders (maybe four if needed) paired with 3 lifting cylinders. The construction of each cylinder is: 2" diameter by 1" thick 12L14 bored to accommodate a 0.875" OD SS tube and drilled and tapped for a typical 1/4" pipe threaded barb. The tube is glued into the base. PEX tubing connects the driving cylinder to the lifting cylinder for each pair. All of the driving cylinders will be mounted in a foot-pedal unit that will allows hands-free perfectly simultaneous excursion of the driving cylinders. See video below. The rams are all made of 6061 aluminum with 1/16" o-rings in grooves sized per Parker Handbook recommendation for dynamic o-ring installation. All rams are also drilled and tapped 1.5 inches deep for 3/8-18 fine adjustment screws to be placed on the top of the cylinders. I am using plated carriage bolts as the round top mates well with the foot pedal. (I turned the emnbossed letters off the round cap and polished them for easy smooth sliding on the pedal.

    img_e6055.jpg

    img_e6054.jpg

    img_6051.jpg
    img_6052-2-.jpg


    The solution was to through drill one of the cylinders in each pair and place a o-ring-sealed SHCS in the through hole to allow bleeding of the air post-assembly. As mentioned above, there was already a 3/8-18 hole 1.5 inches deep in the top of all the cylinders to accommodate a height adjustment screw. So, I just drilled that hole all the way through with a tap-sized hole for an 8-32 screw. The bottom of the 3/8-18 hole was flattened with an end mill. The through hole was tapped for half an inch 8-32 from the top of the cylinder. A tiny o-ring was pushed onto a short 8-32 SHCS and then the two-cylinder system was filled with oil after connecting the cylinders with the PEX tubing. The rams were inserted and the 8-32 screw allowed bleeding of the system so that no air remained.


    Once that is done there is still some stiction in the system but the "spring" of air is gone so the movement is very predictable and smooth. No herky-jerky stuff.



    The reason for the wood rim all around the foot pedal top is to make it easy to push around on the floor with my foot should I need to reposition it while I am moving the pattern. I noticed such a ridge on my tig foot pedal is very useful in that regard and copied that idea here.

    MAYBE tomorrow I'll get a chance to try it in real working conditions. The cold seems to have eased considerably, so, more should be accomplished tomorrow.

    Denis

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  9. #65
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    That looks good and I hope it works as well as intended. I have a question in my mind about synchronization of cylinders. Hydraulically, if they're all attached to a manifold at the same pressure, they're not constrained to work together. That is, of one encounters resistance and stops moving, the others can continue until pressure overcomes the resistance of the slow cylinder. If there are guides to mechanically constrain the physical parts, the cylinders will have to follow even if they see differing pressures or forces internally. There are some hydraulic tricks to synchronize movement but it gets more complicated.

    This isn't intended to throw sand in your process there, but more a theoretical consideration. I'm expecting and hoping that this will do just what you want if your thought and craftsmanship in patternmaking and casting is any indication.

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    Quote Originally Posted by TGTool View Post
    That looks good and I hope it works as well as intended. I have a question in my mind about synchronization of cylinders. Hydraulically, if they're all attached to a manifold at the same pressure, they're not constrained to work together. That is, of one encounters resistance and stops moving, the others can continue until pressure overcomes the resistance of the slow cylinder. If there are guides to mechanically constrain the physical parts, the cylinders will have to follow even if they see differing pressures or forces internally. There are some hydraulic tricks to synchronize movement but it gets more complicated.

    This isn't intended to throw sand in your process there, but more a theoretical consideration. I'm expecting and hoping that this will do just what you want if your thought and craftsmanship in patternmaking and casting is any indication.
    No manifold involved. Each pair of cylinders is a single closed independent circuit for the reason you outlined regarding a manifold. More pics in a couple hours

    Denis

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    Here are a few pics and a video that shows a bit more about the operation of the "Featherweight Levitator"

    This is just an exploded view of the bleed screw and adjusting screw setup.
    img_6064.jpg


    Bleeding the circuit is a messy job.
    img_6066.jpg






    Denis

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    Quote Originally Posted by dgfoster View Post
    No manifold involved. Each pair of cylinders is a single closed independent circuit for the reason you outlined regarding a manifold. More pics in a couple hours

    Denis
    Great! Well you've got that question licked. That has some parallels (no pun intended) to other synchronization schemes.

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    Quote Originally Posted by TGTool View Post
    Great! Well you've got that question licked. That has some parallels (no pun intended) to other synchronization schemes.
    The brick Cape Hatteras lighthouse was lifted with a large number of hydraulic jacks and moved 800 feet. To make that lift a similar-in-principle system was used to ensure a simultaneous and equal lift from all the jacks. So,this is not an original idea, obviously, but, so far as I know, it is an original application of the principle to sand casting.

    I am going out to drag myself out to the foundry this afternoon to mull some sand in preparation for a melt in a couple or three days.

    Denis
    Last edited by dgfoster; 10-03-2019 at 08:49 PM. Reason: typo

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    Quote Originally Posted by dgfoster View Post

    I am going out to drag myself out to the foundry this afternoon to mull some sand in preparation for a melt in a couple or three days.

    Denis
    And recovering from the cold, yet. Glad you could DRAG out but how do you COPE?

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    The hydraulic levitator worked!! The draw is so much more controlled with this system.

    Sorry for the poor viewpoint of the video. Was working alone and failed to realize my big rear end would occupy much of the screen.



    Here is a "tour" of the pulled pattern.



    Lessons learned: I need to place the lifting sticks I attach to the pattern further toward the ends. Having them so close to center allows the pattern to rock too easily as seen in the very early part of the lift.
    Overall I am pretty pleased with the first try. I will make a few slight refinements for next time. I think I will have a much higher pattern draw success rate using this system on largish, deepish patterns.

    Added: It looks like the new logo pulled cleanly as well:

    img_6074.jpg


    I am glad to see the notches in the feather logo will print just fine.

    Denis



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