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Is there a nice trick to setting a boring head to match the radius of a receiver when machining scope bases? Beyond making a cut and adjusting and making another cut and adjusting? Scoty | ||
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You can set it "mathematically" but that won't do you much good, because your finished cut will likely not match the math and you'll still be adjusting. I never liked using a boring head and quickly found other ways to do it. Nathaniel Myers Myers Arms LLC nathaniel@myersarms.com www.myersarms.com Follow us on Instagram and YouTube I buy Mauser actions, parts, micrometers, tools, calipers, etc. Specifically looking for pre-WWII Mauser tools. | |||
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You can get pretty close, and I generally use a slightly under-size radius on bases so that the base touches on the outside edges first. Stick something vertical in the vise, like a 1-2-3 block. Put the cutter in the spindle and turn the spindle so that the cutting edge lines up with the block. Adjust the table until the cutter just touches the block (0.001" shim stock feeler, etc.). Then spin the cutter 180 and measure from the block to the cutter with calipers. Adjust from there. | |||
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Sometimes its adjust cut adjust and cut again as you go. I have several Enfield receivers that Tom Burgess surface ground. I would truly love to ask Tom B what he ground them for but that is hard as he left for the Happy Hunting Grounds years ago Had two of the bases to machine last week The rear bridge looks like a Rem M700 BUT. When I set up for the larger 3.937 dia cut to match the M700 we are way off. So kept adjusting and do a cut and adjust, seemed like forever. At last I got the base to match at 2.875 dia cut. So now have that written down as I still have 4 more bases to machine for the other receivers one of these days. And this was all done in a special vise jaw I made years ago. It has a cut out on one end to hold the new scope base in vertical, so I can find the center, and repeat the set up and then use the DRO to move the boring head in so the next cut. J Wisner | |||
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Every gunsmith in this day and age should have a CNC Knee Mill. They are cheap, plentiful, and simple to program. While I 100% support the old fashion way of doing things, I don’t know how you guys find customers that are willing to pay for the time you take cutting bases this way. I made several sets of scope bases with a boring head and realized I couldn’t charge my customers enough and feel good about the cost. At the time I couldn’t afford a CNC Knee Mill, so I bought a Kearney and Trecker 2D, which will do everything a 2 axis CNC will do and more. I still cut most scope bases on this machine, and I have tried lots of different methods. Nathaniel Myers Myers Arms LLC nathaniel@myersarms.com www.myersarms.com Follow us on Instagram and YouTube I buy Mauser actions, parts, micrometers, tools, calipers, etc. Specifically looking for pre-WWII Mauser tools. | |||
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What I do is first measure the radius I need. Then I use an edge finder to center the spindle on edge of my mill vise. I install the boring bar and crank the table and vise away from spindle center the measured distance (radius); having a DRO makes this easy. I then adjust the boring bar so it just touches the vise as I turn the spindle by hand. Now I’ve got the boring bar set and ready to cut my bases. John Farner If you haven't, please join the NRA! | |||
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I wonder if anyone could explain the reasons you do this work. Is it just to make a more-seamless mating with the receiver or to fix elevation problems without shims or excessive turret clicking? | |||
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Hello Sambarman: I do it for two reasons. 1, to get a better fit to the receiver and, 2, to ensure there is no stress on a high-dollar scope when the bases are screwed to the receiver. Rather than a boring head, I use a surface grinder, a radius dresser and precision machinist's vise. The receiver radius (front and rear) at the base-mounting holes is first determined and this figure is dressed on a 3/4" or 1"-wide wheel. The bases to be fitted are levelled to .001" TIR--bottom-side-up--in a machinist's vise, with their centerlines located under the center of the wheel. The underside of each base is then ground until the radius extends to both edges. Note that the radius is often not the same, front and rear. After both bases have been radiused, the scope to be mounted is fitted to the rings and the front(or rear) base is screwed to the receiver; the other base is clamped in the ring on the opposite end of the scope, but not screwed to the receiver. At this point, clamp the empty ring to the base on the receiver and note if there is daylight under the base at the other end of the scope. If there is, measure the gap with feeler gauges or multiple thin sheets of shim stock. They need to be thin so you'll get an accurate measurement of the gap. If the gap is, say, .015", remove the base screwed to the receiver, relocate it in the machinist's vise and grind that amount (.015")off its underside. Mount the re-ground base to the receiver and check the gap of the other base--as described above. If done properly, the unsecured base should sit on the receiver with no gap or upwards tension. If there is no gap between the unsecured base and the receiver when first checking for fit, the unsecured base must be screwed to the receiver, with the other base unscrewed and clamped in its ring. If you're very lucky, there will be no gap on this base either. Usually there will be a gap, which simply means that the base you just screwed to the receiver is the high one that needs grinding on its underside. Hope this helps. Dave Manson | |||
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Thank you all for the replies. You have given me a lot of ideas to think on. Scoty | |||
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If anyone cares, I do it like John Farmer does. One thing though, the radius on the rear bridge on a few actions can be difficult to measure accurately. There is a formula for this in the "Machinists Handbook" Jim Kobe 10841 Oxborough Ave So Bloomington MN 55437 952.884.6031 Professional member American Custom Gunmakers Guild | |||
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Could I use a modified version of the "Machinist's Handbook" technique, using an edge finder and the DRO? | |||
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Don't know what that is but I use the edge finder and my DRO to locate and then the boring head. I mount the base stock vertically in the mill vise. Jim Kobe 10841 Oxborough Ave So Bloomington MN 55437 952.884.6031 Professional member American Custom Gunmakers Guild | |||
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Thanks Dave for that detailed explanation. What is your opinion of the plastic inserts in Burris Signature rings as a way to avoid stressing the scope and the eccentric inserts to fix elevation problems? | |||
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Dave, Thank you for making those special order reamers for me. Got them last week, and I hope once I have some free time will work on them. Appreciate you help. | |||
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This may be redundant on this thread. The average gun owner mounting a scope should check the bases with a straight edge and shim if needed. Dave | |||
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If you have any tooling aligned math skills you can cut any radius you want with a mill and any cutter that has a smaller radius using as small of a stepover as you care to poke into a scientific I make radius cuts, angle cuts and combos of the two daily with nothing more then a Bridgport or any machine you care to toss in. All with calculator and scratch paper. ________________________________________________ Maker of The Frankenstud Sling Keeper Proudly made in the USA Acepting all forms of payment | |||
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