Month: January 2007

Making bullet sizing dies

Posted by on January 22, 2007

Making sizing dies is not difficult, just slow and painstaking. Richard Bowman and I have made a few, partly for the hell of it, partly because it seems silly to pay for such things if you’ve got a lathe, and partly because it’s a good idea to develop the skill for making things. Who knows what one might need to make ?I’m not going to delve into the finer nitty gritty at this stage, I’ll just explain the bare bones of it. Basically it is a simple lathe job in which a piece of suitable steel is turned to outside dimensions and the bore drilled, bored and polished, or is you can afford the reamer drilled reamed and polished.Reaming is the easiest, quickest and most accurate method. But reamers are not made exactly to bullet size. An adjustable reamer is best. I have found that they can be adjusted very finely to ream out exactly to size. The hole must be drilled 0.20mm smaller to leave enough meat for the reamer to remove without leaving the tool marks of the drill. The reamer will leave a mirror finish. I have made dies at least as smoth or smoother than factory dies. There’s no harm in polishing the reamed bore with 1000 or 1500 grit, which will leave a finish best described as optical.But expanding reamers are about R500 each. Machine reamers are about one third of that and available in 0.01mm increments. That makes possible a reamed hole only a few microns smaller than desired, which can be brought to size by polishing.To avoid even that cost I recently made a die by drilling to about 0.50mm under size and machining with a boring tool almost to size, and finishing by polishing. The reason for boring is that a properly sharpened boring tool will leave a finer finish that a twist drill and therefore requires less polishing. The danger with polishing is that it is easy to end up with a hole that is tapered or oval or both. In the even I bored too big and ended up with a die too big. But the exercise proved the practicality of the method. Polishing removed three thousandths of diameter ( 1.50 thousandths all round = about 40 microns ). I went through all the grits from 220 to 1500. I used wet or dry paper attached with masking tape to a wood dowel. The circumferential polishing was done with an electric drill, the lengthwise polishing by hand.Tests with a small hole gauge showed that the bore was parallel and concentric within very close limits and the finish was optical.The only real difficulty with this simple method is that one must start three or four thou under for polishing, but there’s no reliable way to predetermine how much metal is being removed. It has to be regularly tested with a small hole gauge, and you don’t want to get to final size with 320 grit. On the other hand you don’t want to end up one thou small after the 1500 grit. So there’s a lot of feel and cut and try about it. And in the worst case you might make two or even three before you get it right.But the point is that it works. And each success in making such an item adds to experience gained when it comes to the next.[Originally posted to SATalkGuns -- Admin]

Home Gunsmithing

Posted by on January 5, 2007

Further to the matter of home workshop activities, let me make it clear that I am not a pro, I am an amateur with a good bit of practical gunsmithing experience. There are others who know a lot more than I about gunsmithing, machining and toolmaking. But until they come forward I’ll continue to offer bits and pieces occasionally. Although my methods may not be the best they are all tested and proven to work.There are all sorts of little devices that are not too expensive and can be useful out of all proportion to their cost. It is useful to know which those are because we amateurs don’t usually have the bucks particularly for machine tools and expensive accessories so we must get good bang for each buck we spend.A very useful and versatile item is the micrometer head, which is a micrometer thimble and spindle with no caliper and opposite anvil. It is intended for holding in a fixture for controlling the movement of the work or a tool. Possible uses would fill a book. It can be used as a comparator, which is a simple table and column that usually holds a plunger type dial gauge. The purpose is to measure the thickness of a workpiece on the table. It is a small item, the table usually being only a few centimetres each way. A respectable one can easily be made, and a mike head used instead of a dial gauge.A mike head can be mounted on a bracket on a lathe bed for precise control of carriage movement. I use one mounted on the cross slide of my Myford for controlling compound slide travel for threading, especially for small threads. I bring the tool up to the point where a feeler gauge will fit between the tool and the work. Why not bring the tool into contact with the work ? Because feed screw pressure and a sharp tool make it difficult to judge, ie the tool can dig in without my realising it. Hence the feeler gauge trick. Then I bring the micrometer anvil into contact with the corner of the compound slide which is set to 29.50 degrees for metric threads. The mike then controls the depth of cut. More accurate than the lathe feed dials or visual judgement.I also use it for getting finishing cuts very close to size before final checking with a conventional mike. Yes I know that can be done with the lathe dials but this baby does it better and more accurately. With a lathe turned collar it can serve as a depth mike.As I have mentioned screw cutting, not much real nitty gritty has been published. Most lathe users are scared of it, but it’s easy once you know how. There are two little books that give chapter and verse. “Screw Cutting in the Lathe” by Martin Cleeve is the most complete and detailed exposition I have seen. I found it invaluable. “Drills Taps and Dies” by Tubal Cain is about thread cutting with hand tools and covers it in extreme detail. This particular book explains the various British, US an Metric threads, and has a very useful set of charts of drill sizes.It should be understood that the drill diameter usually given on the box of a tap set is not the only size that can be used and often may not be the best choice. It has to do with thread engagement. A nut and bolt or a screw and it’s tapped hole seldom if ever need 100% engagement. In most cases 60% engagement provides 90% of pull out strength and much easier cutting. Tapping a hole for 100% engagement needs three or four times as much torque as 60 or 75% engagement and is a common cause of tap breakage in small sizes below 4mm or so. Tubal Cain’s book provides the engagement % for various drill sizes for each thread diameter.Although a close running fit of screw and hole are seldom necessary it is sometimes nice if only for the satisfaction of that nice “close fit” feel especially if it is an operating screw in a jig or tool one has made. The best way to achieve that is by tapping a hole in a piece of scrap to use as a gauge for the male thread if it is being lathe turned. When you approach finished size the tapped hole becomes the gauge and the job is done when the gauge screws freely but not loosely on to the male thread. I have made some very nice screws this way.Note that drill size is more critical for small holes. That’s because the thread “teeth” are smaller on smaller diameter threads. Drills come in 0.10mm increments. 0.10 makes a much bigger difference in thread engagement in a 3mm thread than a 6mm. On a standard 3mm metric thread the thread is only 0.30mm deep. A difference of 0.10mm drill dia is one sixth of thread depth. With the metric fine threads it is worse. On the very small threads it might sometimes be necessary to resort to a drill in the 0.05 increment class because two drills only 0.10mm apart might cause insufficient engagement one way or so tight as to risk tap breakage the other way. 0.10mm Increments are not usually available at hardware stores but are usually available at engineering supply shops. 0.05 drills are usually a special order item.I have not mentioned dies because I seldom use them. Almost never in fact. Dies are expensive and a different one is needed for each thread. A lathe on the other hand can cut any pitch thread any diameter. Well, not all lathes can, some will thread only in their primary language ie metric or imperial. My Myford will cut both without special gearing.[Originally posted to SATalkGuns -- Admin]

Accurate drilling

Posted by on January 2, 2007

We hobbyists have to make do with the equipment we have, which is often limited in capability. So methods sometimes need to be devised that will get more accuracy from a machine than it is theoretically capable of. What follows will not be new to many, but it may provide a glimpse of what can be done with simple equipment for those who are just starting into this hobby.I make sprue cutters for Lee six cavity bullet moulds because the factory sprue cutters don’t work. Not many will want to make sprue cutters but the method can be used for lots of other things. I refer to drilling holes in a dead straight line and accurately spaced on a cheap hardware store drill press. How accurate ? Within two thousandths easily ( 50 microns ) and within one thou ( 25 microns ) with a lot of care.Why does it need special methods ? Because cheap drill presses usually have considerable spindle run out. Mine can be seen and felt and it is quite impossible to drill a hole accurately to position. It doesn’t matter for most home workshop purposes because 99% of holes don’t need to be closer than half a millimetre.There are two requirements to get good accuracy. First the spindle run out must be eliminated ie the drill bit must not wander even slightly. That is accomplished by a drill guide bushing which is a little precision made item that costs about R25. Mine fits a 4mm twist drill and is such a close fit that there is no run out. It is carried in an easily made bracket. The second requirement is a means of positioning the work and shifting it’s position by a measured amount.Here’s how it is done. My drill press is small. Stands on the bench and is small and light enough to carry around. A similar press costs no more than R300. It’s table is about 150 x 150mm. Take a piece of bright drawn flat, size not critical, try 6 x 25 x 250mm long. Drill a series of holes so it can be bolted to the drill table in whatever position needed. This is a “fence” against which the work is positioned and slid back and forth as required. Somewhere near the middle you need a tapped hole to attach the guide bushing bracket. The bracket is a simple arm that carries the guide bushing just a bit higher than the work, and must have some adjustment of “reach” to accomodate work of different sizes. Various lengths of arm can be made as needed. It is bolted to the fence with the bushing positioned over the hole in the middle of the table and directly under the chuck.Any hole drilled in a piece of flat stock held against the fence will be exactly the same distance from the edge of the work, for the reason that the fence and the bushing will not move. Consequently a series of holes will be in a perfect straight line. Spacing the holes where you want them is done by vernier caliper. After the first hole is drilled and the work is still clamped to the table, measure the distance from the end of the workpiece to the end of the fence. The work can then be moved a measured distance to the next hole by altering the vernier reading by the required amount.Any errors are not cumulative because hole number six is measured from hole number one not hole number five.This is much simpler in a picture than a written explanation. It is so simple to make and to use that it is almost a joke.This is just one way in which great accuracy can be accomplished with simple equipment. There are many others.[Originally posted to SATalkGuns -- Admin]