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#1
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"...but I don't have a lathe."
"...but I don't have a lathe."
Sound familiar? The truth is, you probably have any number of things around your shop that can serve as a lathe. In a lathe, the work rotates against the cutting tool. ( In a milling machine, it's the cutting tool that rotates against the work.) The main purpose of a lathe is to produce a circular part, which is achieved by pressing the cutting tool against the work-piece as it rotates. Anything that achieves that goal with sufficient accuracy for the task at hand will allow you to do the job. The most common thing used to rotate the work is the ubiquitous quarter-inch drill-motor. A drill press works even better. And the cutting tool may be anything from a hand-held file to an angle-head grinder fitted with a flapper wheel; even a portable belt sander can be your 'cutting tool.' "Tried that," they usually say. "Didn't work." Odds are, they didn't try hard enough :-) The trick to holding the work-piece in a drill-chuck is to use a coupling nut. Put the coupling nut into the chuck and tighten it evenly, taking the slack out of all three jaws. (Just put the chuck key in each hole in turn, taking out any slack. If you tighten a Jacob's chuck at only one point there will always be some slack in the other two positions, usually enough so that whatever is chucked will not run true.) The centroid of the work-piece is then drilled to accommodate a bolt that matches the coupling nut. The standard 1/4-20 will serve for most work but coupling nuts come in all sizes. To keep the work-piece from spinning on the bolt you may use a lock washer. When using a hand-held tool as your cutter, be it a file or even a belt-sander, the trick to producing a true edge is to use your eye to align the OPPOSITE edge of the work with a known-true reference, such as the string of a plumb-bob. Or the blade of a protractor, if you're creating an angle. Any deviation is instantly apparent and just as quickly corrected. In most drill presses the chuck is attached to the quill with a simple taper. A taper has the advantage of providing a virtually error-free alignment but has the disadvantage of not being able to withstand much of a side-load. Even a 3M fiber-wheel (used for dressing aluminum edges) may cause the chuck to leap off those cheap Chinese drill presses. To prevent that from happening when using the drill press as a lathe, the head of the bolt you use to secure the work-piece to the coupling nut should be drilled in a cone large enough to accept a small ball bearing. Simply trapping the ball between the drill-table and the bolt will provide enough axial pressure to prevent the chuck from coming adrift. - - - - - - - - - - - There are endless elaborations to this theme but the basic idea is that you DO have a lathe, if you put a bit of thought into it. Although crude in appearance such jury-rigged tools are accurate enough to allow turning down a piece of 4130 tubing to fit a standard bearing, make circular flanging dies of any diameter and even create the plug for a 10 x 12 inch spinner for your propeller hub. -R.S.Hoover |
#2
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.. Put the coupling nut into the chuck and tighten it
evenly, taking the slack out of all three jaws. (Just put the chuck key in each hole in turn, taking out any slack. If you tighten a Jacob's chuck at only one point there will always be some slack in the other two positions, usually enough so that whatever is chucked will not run true.) The hole you choose to tighten a chuck has no bearing on the centering of the jaws. They're all on the same screw. |
#3
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It is indeed the same screw, but the mating surfaces of the chuck are
not perfect and tightening only one hole will cause some off centering. Tightening all three holes reduces any such tendency. Ask any machinist they will tell you "tighten at all holes". |
#4
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Tightening all three holes reduces any such tendency. Ask any machinist
they will tell you "tighten at all holes". I've been a Tool and Die maker for over 20 years and I disagree with your statement. A drill chuck isn't meant to be accurate, nor is it meant to be a three jaw lathe chuck. I'm not saying you can't do some cheating here and there, but expect the accuracy of your equipment to take a beating. I do understand that you can't always have the perfect tool for every job that needs to be done, but you gotta be careful when you improvise. Remember, a drill press isn't designed to take side loads, and neither is a drill chuck. With that being said, I'll admit that before I bought my first CNC lathe, I used one of my CNC mills as a lathe to make simple plastic parts. Perhaps the difference is the quality of my equipment. The drill chucks I use are completely rebuildable, and cost almost as much as some people spend on their whole drill press. Perhaps that's why I've never had an accuracy issue when tightening only one hole. Or, maybe it's because if I really need it to be accurate, I use collets instead. I think your ideas are very reasonable if the craftsman doesn't get in a hurry and chooses his cutting tools carefully. Avoid clamping things to the table, and feeding in with cross slides if you have that capability. As long as you're using hand held tools, it would be difficult to overload your bearings, and with your mounting idea, you'll be less likely to have the part go flying across your shop. Especially if you back up the end of the part like you suggested. |
#5
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LCT Paintball wrote:
Tightening all three holes reduces any such tendency. Ask any machinist they will tell you "tighten at all holes". I think your ideas are very reasonable if the craftsman doesn't get in a hurry and chooses his cutting tools carefully. Avoid clamping things to the Mr. Paintball, I think the giveaway was when Veedubber mentioned "cheap chinese drillpress". In my mind this is one of the $30 Harbor Freight models. It takes about two of those to complete a Dyke Delta. (the first one wears out halfway through). Combining precision in the same sentence with one of these is a great injustice to the english language. Now not every piece on an airplane requires millionth of an inch accuracy. Will an airplane crash if the plug used to make lightening holes is slightly oblong? -- This is by far the hardest lesson about freedom. It goes against instinct, and morality, to just sit back and watch people make mistakes. We want to help them, which means control them and their decisions, but in doing so we actually hurt them (and ourselves)." |
#6
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You can get an import mini lathe for under $400. I got one for building
my home built making many valuable custom precision parts and do not regret the investment. There is no way you can reach the versitility or precission with a drill chuck. There is a 7x12 mini lather for sale on eBay now for $360 with no bids http://cgi.ebay.com/NEW-METAL-LATHE-...c mdZViewItem -------------------------------------------------------------- SQ2000 canard: http://www.abri.com/sq2000 |
#7
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Thanks again veeduber!
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#8
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Thanks again veeduber!
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#9
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"...but I don't have a lathe."
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