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non-cylindrical internal polishing?

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  • non-cylindrical internal polishing?

    I have recently learned how to lap a cylindrical hole, straight, to whatever size I decide. How basic is THAT! (I am pleased with myself) I want to tackle a point forming bullet swage die. It's bullet shaped with a small hole for the ejection pin. It has to come up to proper diameter at the same time it comes up to proper finish. I can't visualize an expandable lap that would do the chore correctly. If multiple laps are used, how do you get them the right size? Anybody have any tips, or a reference, for this chore? He'p me!

  • #2
    Swage dies are tougher to make because of the work involved. You will need to profile a cutter and copper laps to the bullet dimensions (slightly undersized). Cut the die out, harden it, and then lap to size and final polish. Diamond pastes work well with copper laps - you charge the lap by rolling it or a hard surface over the diamond paste it embed it in the copper lap. A ball bearing on a handle works well. You need a separate lap for each grit used. The diamond cuts the hardened steel extremely fast - a little goes a long way. Use water (best for non-metals) or kerosene (best for metal) for lubricant/coolant. You could even make the dies out of carbide this way (soft steel shell - carbide insert brazed in). You can get the Diamond pastes at lapidary stores cheaper than from tool suppliers in most cases. You can also use SiC, Jewelers Rouge, and Tripoli but it will take much longer to finish.

    You should not lap this by hand unless you build a jig that insures the lap is concentric with the bore of the die. Tilting the lap in any direction will change the shape of the die from the designed shape. This will result in a bullet with a tendency to tumble or wobble in trajectory to the detrement of accuracy.

    The bottom punch that pushes the slug and jacket into the die should also be polished very well. It has been shown with cast bullets that the base is far more critical than the nose. The extruded tit (if any) of lead is best cut or milled off to give a flat meplat (very tip of the bullet nose).

    Once you have the dies completed and they work to your satifaction they can be TiN, TiCN, or TiAlCN coated to reduce wear and friction. It is not required at all, but if you come up with a great performing bullet you can have the punch & die profiled in a CMM so it can be duplicated again.

    [This message has been edited by Thrud (edited 05-28-2002).]