New Small Flat Bottom Level/Prism/Parallel Casting Design - Page 2
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  1. #21
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    Well, Cole2534, I really appreciate your vote of confidence and kind words. You are now on the list! If all goes well, I will be casting two or three tomorrow. I think two people have already expressed interest. IF the castings are perfect (less than perfect castings suffer the fires of the melting pot again!), They will be stress relieved on Tuesday and I could ship a raw casting on Wed. They will ship in a Priority Envelope for just under eight dollars. I am starting out selling the first five castings at 50 dollars plus shipping per casting. Please contact me at Denis g foster at
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    for more information.

    PM's are OK (barely) but I do much better with emails.
    Denis

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    Denis I’m definitely interested in one. Nice work!
    Keith


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  4. #23
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    A few days ago I said I would put up a drawing of a possible flexure mechanism that could be used to adjust a vial mounted in the new small level/parallel/ prism/ SE. Well here is a rather crude napkin drawing of what I have been daydreaming about.

    Because my drawing skills are so poor I felt I needed to color some of the components so that anyone trying to decipher the sketch might have a better chance.

    flexure-mechanism-8-inch-level..jpg


    The heart of the system is a shallow (1 degree) taper that deflects a flexure whose arms rock in a 10:1 ratio. In green is a 1/4-40 threaded pin that pushes a 1 degree taper smooth sleeve to force open the long end of the flexure. The sleeve is a fairly loose fit on the end of the screw so that eccentricity of the screw does not deflect the flexure end. The sleeve is pushed and pulled by the screw which has a pin fitting inside the sleeve but loosely peened over so that the sleeve can be retracted and pushed but the sleeve is free to not follow any radial deflection of the pin. The face of the screw that rides on the sleeve should be polished smooth as should the bearing of the sleeve that contacts the screw. The tapered sleeve and the socket in the flexure should also be polished smooth and be gently rounded on the crown of the pin. The set pin shown near the flexure would be .001 undersize for the corresponding hole in the flexure plug to allow for slight pivoting.

    As drawn a full rotation of the screw moves its end 25 thou and causes the flexure end to open (sin 1 deg) x 25 thou = .017 X .025 = .0004
    If the vial end of the flexure moves 1/10th as much as the screw end, it will elevate .00004"

    One might debate if this is too fine or too coarse. Adjustment of socket taper can make larger or smaller deflections.

    The mechanism has to be secured in the level without flopping around. I envision this being done with small o-rings strategically placed. They would allow deflection and provide an adequately snug fit.

    The level would be bored 21/32 to accommodate the 5/8" diameter vial which is itself 3.75" long. I am referring to a Geier and Bluhm 4-3080 10 sec tubular brass-mounted level. ($62.50)

    I don't think this is necessarily the "perfect" design, but I do think it is a workable one that requires minimal disruption of the level scraped surfaces. If a similar but non-deflecting plug were made for the other end of the level, only a few setscrew holes in the unmachined top rail grip are needed to mount the flexure plug and the support plug. I think that "clean" design is a good feature.

    I'd like to hear suggestions for improvement or criticisms of the proposal so that it can be improved.

    Denis

    Added: Not shown on the sketch is that the 1/4-40 screw would either be slotted or have a hex recess (preferred by me).
    Last edited by dgfoster; 02-05-2020 at 07:50 PM.

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  6. #24
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    I like it.

    You mention the adjustment range, and possibly adjusting this by changing the taper of the socket taper.

    There is another option to consider. Place the 1/4-40 thread off center so you can rotate the yellow piece to provide a coarse adjustment. The yellow piece is then secured with a set screw, and the screw thread and taper provide the fine adjustment. The adjustment screw taper would contact a pin transecting a bored recess. For the flexure pivot Use a drilled and reamed hole with a pin. Drilling and reaming the two pins at the same time should make them parallel.

  7. #25
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    Quote Originally Posted by J_R_Thiele View Post
    I like it.

    You mention the adjustment range, and possibly adjusting this by changing the taper of the socket taper.

    There is another option to consider. Place the 1/4-40 thread off center so you can rotate the yellow piece to provide a coarse adjustment. The yellow piece is then secured with a set screw, and the screw thread and taper provide the fine adjustment. The adjustment screw taper would contact a pin transecting a bored recess. For the flexure pivot Use a drilled and reamed hole with a pin. Drilling and reaming the two pins at the same time should make them parallel.
    Doh! Would not have thought of that, but might have done it (accidentally) anyway. That is a good idea. Only a very few thou eccentricity would do the trick. Easy to do in the 4-jaw or even just shimming my 3-jaw.
    Thanks you!

    Denis

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    I always like to see flexures in precision instruments. I'm worried that 1 degree is a self-locking taper, unless you make your tapered sleeve from something like PTFE (Teflon). Could make it difficult to adjust in the "pull out taper" direction due to stick-slip.

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  10. #27
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    Quote Originally Posted by sfriedberg View Post
    I always like to see flexures in precision instruments. I'm worried that 1 degree is a self-locking taper, unless you make your tapered sleeve from something like PTFE (Teflon). Could make it difficult to adjust in the "pull out taper" direction due to stick-slip.
    You bring up a good point. You MIGHT be right. But, my intuition is that because the "socket" that the tapered pin enters is split, that locking will not occur. And the socket should probably not be a fully a tapered conical recess with just a partial split. Rather it could be a simply straight-walled cylinder with a smooth round chamfer at its opening. The slit could be sized to remove maybe a cross section consisting of the central 1/3 of the cylinder so that contact with the chamfered lip of the cylinder would not be full circle, but would still be practical to act as a wedge. This would be especially true if the cylinder's diameter were equal to a little more than the full depth of expected insertion.

    I am thinking of using a round tapered wedge and a cylindrical receptacle primarily for ease of fabrication and for the fact that the round wedge and cylinder tend to maintain self-centering. Alternatively, I think a true flat wedge could be used and attached to the 1/4-40 screw with a post either peened over as drawn or the post inserted into the drilled screw and fixed with Loctite.

    Tomorrow perhaps I will test out the locking idea with a simple mock-up.

    Denis

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    I'm also of the opinion that having a split means it can't hold like a wedged taper. And it'a a good point about the receiving socket perhaps not being an exactly matching taper. I had one application of an expanding arbor that just didn't work well. I finally figured that with a matched taper, as soon as the outer started to expand, my contact point was now at the small end and I'd lost all the leverage. Once I made sure that the taper of the plug was a little steeper, everything worked as intended.

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    Denis,
    Personally, I would cut the taper significantly steeper than 1°. Consider that, with a 40 TPI screw it is fairly easy to adjust to 0.0001" (i.e. micrometers). A ten fold improvement on that would be more than enough, without sacrificing too much in terms of range of adjustments.
    And, as you have pointed out, you do not need mating tapers in screw and flexure. The tip of the screw could be rounded or even ball shaped to minimize friction and it will act well in spreading apart the walls of the taper.

    Paolo

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  15. #30
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    Thanks for the suggestions Sfriedberg, TGT, and Paolo. It is very helpful to get various points of view. It really helps refine design considerations. Putting all the ideas together, the idea of using a tapered recess on the flexure and a blunt broadly radiused spreading plunger may be the best amalgamation of ideas so far. I chose the 1 degree taper more or less as the extreme low angle that would provide the finest possible adjustment which may not necessarily be the most practical adjustment as Paolo points out.

    Denis

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    Here is another idea to consider.

    Given the limited access, mount the vial housing and adjusting mechanism in a thin walled tube, which is then inserted into the casting and held in place with setscrews, after adjusting for rotation.

    In the drawing below the tube allows a vertical pin to locate the vial housing, with a horizontal pin securing the lever, and a spring to tension the housing against the lever.

    I did not do a drawing showing that the threaded adjusting taper could be eccentric to the bore for coarse adjustment.
    Attached Thumbnails Attached Thumbnails adjusting-lever_20200206_0001.jpg  

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  18. #32
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    I see affordable going out the window
    Keith


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    Quote Originally Posted by ripperj View Post
    I see affordable going out the window
    Keith


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    Not at all. What we are discussing is the question of the "ultimate" way of inserting a vial into the simple cheap (the charge is to help reimburse the expenses involved in building and maintaining the furnace, flasks, crucible, fuel, pattern, muller, and molding equipment involved in making these simple and inexpensive) castings. I doubt many folks will actually go to the trouble of through-boring the casting and making a precise flexure mount for the vial. Most folks will simply buy either a mounted or loose vial and mill a pocket in the casting top rail and drop it in using tiny o-rings under the mount tabs and fine thread screws for adjustment. And that simple approach will work just fine. And then there are some folks who enjoy the challenge of making a clever elegant mechanism. Those folks will spend ten to twenty times the shop hours inserting the vial and they will end up with a level that functionally is a little better but also gives them pleasure of accomplishment. And then there will be a fair number who won't care about a vial at all and simply want to use the tool as a parallel, prism and straight edge. To each his own.

    For those who want it I will likely provide basic milling of all reference surfaces and through-boring of the casting. It will be up to users to do their own scraping and vial mounting.

    Denis

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    Nice work on the casting! Email sent to add me to the list!
    Thanks,
    Turnmtl

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    Denis- I hope you don’t think I was finding fault with your work.. the post was in jest


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    Quote Originally Posted by ripperj View Post
    Denis- I hope you don’t think I was finding fault with your work.. the post was in jest


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    No worries, Keith. I thought you were kidding too. But, it gave a chance to point out a few things that maybe needed clarification (or not) anyway.

    Denis

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  25. #37
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    Well, after much work and frustration I have finally gotten good results from this casting that seemed like it should be a simple pattern to cast correctly and I have added test and a logo to the casting. Success came when I decided to flip the pattern orientation in the flask. I had been trying to cast it pointy side up several times with various riser configurations and gating options. Nothing was working as the prism surface insisted on collapsing as the metal shrank and hardened. Then, I flipped the pattern over and rammed it up on Tuesday. Success.

    I also wanted to put my name and logo on the SE but did not want to use standard foundry letters as the logical location was on the convex surface of the top rail as other areas could potentially call for machining later. Standard foundry letters I felt would be to high and too sharp when grasping the SE. So, I used two layers of adhesive vinyl and had letter cut from it using a CNC knife. The logo had to be done free-hand.

    I have a fairly long list of people lined up to buy these SE's. So, I will work down the list as I cast more. Initially that progress may be somewhat slow as my furnace requires some significant maintenance---iron temperatures are hard on small furnaces. Here is a pic as a pair came out of the sand.
    img_6377-1-.jpg


    I'll also be working on machining a couple for delivery as well. thank you all for your patience.

    I will be in touch with a few folks in the next couple days.

    Denis

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    For those folks who have expressed an interest but have not yet been in contact to actually set up a purchase, I am currently sold out of 8” levels. But, I expect to cast some more within the next ten to 14 days —- as soon as I finish rebuilding my furnace lid. Casting iron is hard on equipment. Bronze and aluminum not so much.

    For those folks I have committed to sell 8’s, those orders will be finished in the next couple days and some have already shipped.


    Denis

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    The (proverbial) check is in the mail. Thanks again.

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    Sorry I think I missed it but how much are these going for. I have a piece of durabar I was gonna make something similar from but would buy this depending on the price.


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