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Thread: Making your rest track perfectly when making a vertical adjustment from the rear leg

  1. #1
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    Making your rest track perfectly when making a vertical adjustment from the rear leg

    Perfect vertical movement (no reticle wiggles on target) from rear leg adjustment of unmodified Hart rest. Interest? More tomorrow.
    Last edited by Boyd Allen; 03-14-2012 at 01:34 AM.

  2. #2
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    Good Morning all.

    The first thing that we need to understand is that when we adjust one or more of the leg points, we change the distance between them. If all three points have equal traction on the bench top, there is no sure way to tell how the rest will shift because of a new point to point distance. This shows up as a lack of linearity of the reticle's movement on target, when vertical adjustments are made using the rear leg point, and the rest squirms to find its new interface with the bench, because of the change in point to point distance.
    The answer is to let the rear leg slip.

    This all started (this time) because the time before last that I was at the range, my rest placement had the points in the pock marks left by one of a number hammering ins, and when I turned the rear leg adjustment knob on my Hart rest, the cross hair would initially move diagonally, before going up or down.This did not make for great confidence when making very small adjustments. I made a note to bring a set of point disks that my friend Ed Hellam had given me the next time that I came to the range, and something else that I vaguely remembered might be lurking in a tool chest drawer.

    First, I should explain that the disks, unlike the ones that Dave Dohrmann sold, are made of single pieces of 1/8" thick aluminum, and are flat on their tops. I have modified the traction material removing the full undercoating of overly bouncy ( a guess), waffle style non skid shelf liner with three evenly spaced pieces of thinner harder rubber sheeting, each the size of a nickel. The traction is good and there is little evidence of potential bounce. In the center of each 3" diameter disc is a hole that is chamfered for a better fit with rest leg points. So far so good, but we still have a squirm issue.

    The last, and key piece is a delrin disc, about the diameter of a silver dollar, that has a radiused raised rim that sticks up on its bottom, and a non piercing, tapered hole centered on its flat top. I don't remember where I got it. Perhaps someone reading this will know who the likely maker is. In any case, after adjusting my rest so that I was on target, I picked up one of the front disks (with leg point in place, momentarily tilting the rest) and set it back down, so that both front points would be more securely centered in their disks, and then I picked up the rear leg and placed the plastic disk under its adjustment point with the raised rim against the top of the disk, and the leg point in the tapered hole on its top. (I should mention that my targets had been placed on their frame with their tops leveled with a torpedo level that I keep in my range kit.)

    After that, when I made a vertical adjustment, large or small, it was a perfectly straight movement, because the rear point would slide, and the front two were secure in the centers of their disks. This is a great product that anyone with a lathe should be able to make. I think that anyone that uses the rear leg on his rest to make aiming adjustments would benefit from having one.
    Last edited by Boyd Allen; 03-14-2012 at 11:49 AM.

  3. #3
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    Boyd a picture of what you are describing would be very helpful in my making the device. I have been experiencing the same issues as yourself and have not found the means and methods to correct it. It sounds like you the answer to my problem and I would truly enjoy making one and giving it a try.

    J.Louis

  4. #4
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    First some measurements, pictures to follow. As it turns out, my memory is imperfect (beg surprise). The point disks are 3.5" in diameter, and 1/8" thick. The rubber on their bottoms is roughly .95 in diameter and with the superglue, about .038" thick. It was originally part of one of those give away things that you can use to get a grip on a tight jar lid. The delrin disk is a little over an inch and a quarter in diameter, and counting the rim, a little over .3 thick. The rim is about .075 wide, and protrudes around .06". The edge is flat, not radiused (again the memory). The hole in the top does not pierce the disk and looks to have been made with a center drill that was sunk slightly deeper than the conic section.

  5. #5
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    A penny and a center punch mark placed in the middle is a simplistic solution to the rear leg problem you describe.

  6. #6
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    I am a big "if it works, that is all that is required" fan. I used what I had, and boy did it work slick. I will have to try a penny next time. All suggestions are appreciated.
    Last edited by Boyd Allen; 03-14-2012 at 03:38 PM.

  7. #7
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    Actually, the penny (or nickel, or dime, or silver dollar [express yourself!]) works great. The next step up the technology ladder, which works great is to take a washer and ream the center hole so that a router bit bearing is just a press fit ...


    Click image for larger version. 

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  8. #8
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    Slick,
    I presume that the bottom of the disk was left smooth to be able to move on the bench.

  9. #9
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    Quote Originally Posted by ReedG View Post
    Actually, the penny (or nickel, or dime, or silver dollar [express yourself!]) works great. The next step up the technology ladder, which works great is to take a washer and ream the center hole so that a router bit bearing is just a press fit ...


    Click image for larger version. 

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    The "Pumpkin" has made one with a bearing years ago. I have one. His flags also have bearings.........

  10. #10
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    Rear leg feet

    I've been using this one for a long time. It was made by James Pappas,a Rim fire shooter/Rest builder. James made these before the "Super feet" were made available. Works great. My aggs have not improved since I've been using it,but that has nothing to do with the product design.











    Glenn
    Last edited by Chism G; 03-14-2012 at 06:12 PM.

  11. #11
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    Pictures, as requested:





  12. #12
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    Yes, Boyd, flat and flush on the bottom to allow movement. Very smooth.

    And, Joe, my rebuilt wind flags (cast-offs from Mickey Coleman) are mounted in Delrin tubes which are reamed to a press-fit for these same bearings, which then slip over metal rods in the stands. A sweet set-up, though it hasn't done a thing to help me understand what the darn things are saying to me.

  13. #13
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    The rear or adjustable leg does not need a point. Give it a radius and use anything flat under it. This will bridge the
    divots in the bench top and easily adopt whatever change there is in point distance. I use an 1/8" piece of delrin.
    There will be no surprises.

  14. #14
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    I would certainly enjoy seeing a new rule in place whereby using a hammer to sink in the points of your front rest on a newly refinished concrete bench, would be reason enough to make you sit out a match.
    These people haven't a clue what it takes to spend days to set up a form to fit said benches, and refinish them with new concrete.
    A w/e performing that task by the guilty parties would cure them....

  15. #15
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    Joe I agree but we both know thats not going to happen.
    However it could be done by the individual range/club.

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