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View Full Version : General Metalworking Bending Aluminum - An Improved Rifle Rack for Offhand Stands



Bob Smalser
03-26-2014, 9:32 PM
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As an ex-Army competitive shooter who is now a volunteer coach for a large junior program teaching Olympic small-bore, I’m constantly looking for ways to reduce the distractions and inefficiencies of match preparation, and getting the rifle off the ground to speed buttplate and sight adjustments is an excellent example. While there is at least one commercial model of these “antler” rifle racks available, it is unpopular with our advanced shooters and coaches because its design allows the rifle to spill out of the rack should the arm screws come loose, and is considered too flimsy in construction, making the offhand stand easy to tip over and easy to damage the stand’s shaft by over-tightening the set screws. As a boatbuilder by training who often has to fabricate custom hardware, I designed and made another that’s a bit heavier and shorter, grips the much stand better, and is totally spill-proof. It’s been surprisingly well-received, so I prepared this tutorial on making one in a modestly-equipped home shop, as there are far too many operations required to make this a profitable venture for any but fully-equipped commercial machine shops with forging and casting capabilities.

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To improve gripping the offhand stand’s easily-dented aluminum shaft, I increased the surface area in contact by using thicker stock for the base, and shown are 1”-thick aluminum plate scrap acquired locally. Three-quarter inch thick would also work well. Also shown are the remaining materials necessary to make these - half-inch aluminum rod stock, thick-walled latex surgical tubing of half-inch inside diameter for padding, and a handful of assorted-length ¼ X 20 thumb screws through one-inch. (Aluminum doesn’t like fine threads.) Alaska Copper in Seattle or McMaster Carr in Baltimore can supply new plate, Tacoma Screw or Home Depot the rods and hardware, and eBay has a good selection of latex tubing. Local scrap yards can also be excellent sources of materials, especially for the heavier stock that can be expensive to buy new and ship. Finding one near a shipyard or other major manufacturer can be very rewarding, even if you have to do business via telephone and UPS.

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I cut the plate into rectangles of 2 X 5 3/8 inches on a power band saw with a bimetal blade. You could also cut the stock by hand using a hack saw or take it to your local metal fabricator and pay to have it cut to your specifications. Length isn’t critical plus or minus a half inch – I selected 5 3/8 based on the capacity of my drill press. Lubrication isn’t absolutely necessary when cutting soft aluminum, but can speed things up and extend blade life.

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I clean up the bandsaw marks by taking multiple, 1/32” trimming crosscuts using the miter gage and a carbide-tipped blade in my table saw. Care is required, as are adequate safety glasses. Don’t expose any more blade above the saw table than necessary, because like in any table saw work, it’s only the carbide teeth that do the cutting. Feed the workpiece sufficiently fast or misaligned so that the stock you are cutting comes in contact with the steel saw plate instead of the teeth, and the workpiece will be thrown with great force. And don’t even think about making this crosscut soley on the table saw, as you can’t feed material this hard into a table saw by hand with sufficient consistency to avoid it being thrown.

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Next, I lay out my stock for drilling for the arms, allowing a quarter - inch thickness remaining in the walls so they can take holes and threads sufficiently strong for set screws to hold without stripping.

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I drill the half-inch holes for the arms in three incremental passes of increasing size, flipping the workpiece to drill from both ends. This is based on the depth and power limitations of my radial-arm woodworker’s drill press, but incremental drilling of long holes generally allows for a more accurate hole, as the larger drill sizes act as reamers, following the original pilot hole.

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I’m very careful to use low speeds and not to take more bite with the drill bit than the bit’s flutes will clear the waste from, plus I clean the chips from the workpiece and flutes as I go. This usually means quarter-inch bites to begin with and eighth-inch bites as the hole deepens, covering and filling the clearance flutes with chips. In this job, as the arms are inserted into the base from each end, perfectly-concentric holes aren’t absolutely necessary.

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After drilling for the arms, I center-punch dead center of my base stock for the 1 1/8” shaft hole necessary to fit the offhand stand, a hole that will be drilled with the arms mounted.

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Next, I begin the process of bending the half-inch aluminum arms using an oxy-acetylene torch. This requires some practice, as aluminum’s temperature increment between being sufficiently hot for easy bending and crumbling from too much heat is small compared to bronze, brass or steel (which are adequate but significantly heavier alternatives for those who have trouble getting the hang of aluminum.) The technique here is to use an acetylene-rich flame to smoke the rod, followed by adding oxygen so as to heat the rod slowly with a neutral flame to the point where the flame burns off the soot. By moving the flame gradually up and down the rod to clean it, the rod becomes uniformly heated to the correct bending temperature when all the soot is removed. For those without an acetylene setup, MAPP (or probably even propane) gas can also be used if you first soot the rod using an alcohol lamp burning mineral spirits like in fitting the swamped barrel during the antique stock repair shown below:

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When the rod is at the correct temperature, it is simply placed in the jig and bent. As the rod tends to slide along the fence as it’s bent, the pencil marks where I place the end of the rod in the jig. I find half-inch rod likes to be slightly hotter than the soot burn-off point for optimum bending of perfect curves, but as overdoing the heat will result in failure, usually it’s better not to risk overheating. Any unfairness in the resulting curves can be corrected later by cold-bending over a mandrel with the aid of a mallet. Better jigs can be made from other materials, but wood is cheap and easy, although because it chars and gouges, a metal fence is required for multiple bends. Here I use two diameters depending on the rifle I’m making these for – 2 ½” and 3”, the three-inch being the more versatile.

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The rod it reheated using the soot technique, and the next bend is made in a simple, 90-degree bending jig made from square stock and drill rod, the blind holes silver-brazed for strength and spaced to tightly fit the rod or flat stock.

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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.

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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.

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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.

Continued...

Bob Smalser
03-26-2014, 9:32 PM
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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.

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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.

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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.

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

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…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.

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Next I lay out the base to its final shape…

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

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The holes for the shaft set screws are laid out…

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

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The base is cleaned up by drawfiling to any level of finish desired, all edges and corners eased using files…

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…and a simple brush finish applied.

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Last, the rods are cleaned up using files, the sections to take the latex tubing are buffed to a high shine using an 8-inch power buffer and green rouge…

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…and the tubing sections worked on using Armorall liberally as a lube. This can be the most difficult task in the project, so don’t omit the polishing, even if you have to do it using Brasso by hand.

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Final test assembly on the bench reveals a snug hole that will grip the shaft snugly with minimal torque on the set screws, yet will also slide easily when the screws are loosened.

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Double checking it at home on an Annie 1613 in the high position shows it to be a good fit to the rifle and fully functional. To gage sizes, this particular stand was made with 2 ½-inch diameter arms covered with 8th-inch thick latex tubing, and fits the rifle snugly.

Regards,

Bob Smalser
Seabeck, Washington
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ray hampton
03-27-2014, 10:05 PM
thank you for this post

Brian W Smith
03-28-2014, 5:55 AM
+1.thanks for posting.

Just an observation,and may spark an idea?....but those "arms",in their scale and appearance,look like handlebars on roadbikes.So you might look into studying and possibly adapting their(bike)style of holding.Not being critical...just looking at it from a different viewpoint.