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Old 02-19-2014, 09:00 PM
Bob Smalser Bob Smalser is offline
 
Join Date: Apr 2013
Posts: 32
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Note that the 90-degree bend is made in opposite directions to produce fore and aft rods, and depending on the rifle, I like to put a little more depth of curve in the forearm rods so when the rifle rests in the stand, the buttplate is slightly elevated, as that’s where most of the adjustments are made. This isn’t necessary, as it makes the racks right and left-handed, but I can easily make a new arm to accommodate a specific rifle or shooter. The length of the arms is tailored to the rifle, based on its balance point, which should be perfectly centered on the offhand stand. Most Anschutz rifles, for example, balance at the front of the receiver ring, and the distance between the balance point and the front of the pistol grip is 6 ½ inches, which as the arms meet in the center of the base, is generally the length I cut them at. If you are making a large run of these to interchange with a variety of club rifles, then shorter is better than longer plus or minus a half-inch, as when the stand is bumped, the rifle tends to rock in short arms rather than the entire stand tip with long arms.



Next I fair any irregular curves on a mandrel using a soft mallet. If you don’t have an anvil, short lengths of PVC pipe filled with Quickcrete are even better, as they are kinder to inside surfaces that need to be slick to cover with latex tubing later.




I double check all my hole fits, as half-inch aluminum rod can vary significantly in diameter based on manufacturer and length, and while my holes are all .50, my rod aquired from several sources varies from .49 to .51. Fortunately, I have a .52 clearance bit, in the photo above have marked the holes I’ll have to ream to this dimension, and have also numbered all my pieces to avoid mismatches.



Once I have a good rod fit, I mount the arms to the base by drilling, tapping and fastening using thumb screws. How you do this isn’t critical, but these are blind holes that only penetrate to around ¾ depth of the arms. What is critical is that the arm ends touch each other and meet in the exact center of the long hole, and that’s why I laid out and marked them using masking tape.



Once I have my base holes tapped for the thumb screws locking the arms, I ream the holes in the arms made by the tap drill to half depth using a quarter-inch clearance bit. The resulting stepped hole provides me some “squish” to overtighten the thumb screws if necessary to clear the rifle when mounted in the stand, without damaging the threads.



There are a couple of options for boring large holes in aluminum, brass and bronze in small shops. One of the best is a carbide-tipped hole saw designed to bore steel, but these cost around 50 dollars if you only expect to perform this job once. Another is boring a clearance hole followed by a heavy-duty 3/8” or larger router using a carbide-tipped straight bit, using multiple tiny passes of around 1/32” against a scribed circle. Either way, it’s useful to have both, as like aluminum rod, hole saws and offhand stand shafts vary slightly in size by manufacturer, and the router is an efficient method to ream an undersize hole.



So with the arms firmly locked into their final positions, the 1 1/8” shaft hole is bored…



…the result being the arms are locked in place by the shaft and not merely by the set screws, making the rifle rack totally spill proof. On the bench you see the stand’s shaft and the router with a straight carbide bit. Here I’ve already cleaned up the hole using the router and fitted the shaft so it is snug but can slide without binding. If your arm holes are sloppy, you’ll have trouble with the hole saw catching and stalling trying to drill through loose arms. The solution is to drill the base hole without the arms, and then mount the arms to finish the hole and cut the arm-end profiles using the router.



Next I lay out the base to its final shape…



…drill holes in the inside corners to ease the task of making clean, interesecting sawcuts, and cut the base to its final shape.



The holes for the shaft set screws are laid out…



…and drilled and tapped using a level when necessary to insure all holes are centered and plumb.

Continued...
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