Basic gunsmithing skills: Lathe setup, tapping, grinding: these basic metalworking skills will put you in position to take on most of the home gunsmithing chores you'll encounter.
One of the first big expensive tools hobbyist gunsmiths obtain is a metal cutting lathe. Having a lathe opens up a whole new area of gunsmithing. They are, however, somewhat complicated to operate for novices and thick books can be needed to fully understand capabilities and uses.
The first problem the novice lathe user has is getting it to cut right. The first thing needed is sharp tooling (lathe bits). Tool shaping and sharpening is a skill in itself, so I recommend novices purchase pre-sharpened tool bits. An inexpensive set (about $30 for 36 pieces from tool suppliers such as Wholesale Tool Co.) of import tool bits is best to begin with.
They are not the highest quality, but considering that a novice may break them on a regular basis, they are better than breaking $15 bits all the time. Once you learn lathe use, then you can buy the good bits.
These carbide-tipped bit sets usually come with an assortment of shapes suitable for most common lathe jobs. No matter what shape of tool bit you are using, it needs to be set on the centerline of the work piece to cut right. A center point in your tailstock can be a good alignment tool for getting the cutting edge right at the centerline of your work.
If you set your tool too high, the cutting edge will miss the work and the unsharpened bottom of the tool will rub your work. If you set it too low, it will not contact the work at a good angle for proper cutting. The bit must also be set so that the front cutting edge is engaging the work not its rear edge.
Once the cutting tool is aligned right, the workpiece must be rotated at the right speed and the tool fed into the work at the correct rate. These speeds and feed rates vary depending on the size of the part and material composition.
There are books and charts that give specific information for this, but most casual lathe users just guess. The most common mistake novice lathe users do is run the lathe too fast and try to take off too much material all at once.
Spindle speeds for beginners should only be a few hundred rpm. Take off a few thousandths (.005-.025") per pass. It's not like a wood lathe where you may take off 1/4" at a time. In general, soft materials such as aluminum can be worked at higher speeds and feed rates than hard materials such as steel.
Be aware, though, that all steels are not capable of machining. Harder types can only be lathe-turned with special tooling, and if hard enough may not be lathe turned at all. When learning to operate a lathe, experiment on scrap material to get a feel of how things work.
Start by moving the carriage and tools with the hand wheels only until you get a good feel for the machine. Once you have a good idea, you can move on to the power feed functions. Remember when using power feeds that the machine is dumb; it doesn't know to stop when it's gone too far, that's your job. Failure to pay attention can result in a crashed lathe and severe damage to equipment and parts.
Another common problem novice lathe users have is when cutting long parts, both ends are not the same size/ diameter, even though the cutting tool wasn't moved. This is especially common when the novice tries to turn a long barrel blank.
The muzzle end may be much larger or smaller than the breech. This is because the cutting was done at a slight taper. The tailstock that was supporting the end of the work was not aligned perfectly with the center of the chuck. Most metal lathe tailstocks are adjustable. While trial and error tailstock adjusting can be done, an easy-to-make tool will ease the process.
Obtain a piece of 3/4" precision drill rod sized to fit the length of your lathe. Center it in the chuck and use a center drill to counterbore the end. Be sure to center the rod precisely if using a four jaw chuck. Remove the rod and place the un-drilled end in the chuck and the drilled end on a tailstock center.
Set a dial indicator up on the carriage and zero it on the side of the rod at the chuck end. Run the indicator on the carriage down to the tailstock end and observe its reading. If the indicator is no longer zeroed, it indicates the tailstock is off center and needs to be adjusted.
Ignore the dial indicator readings in the center of the bar, since it may be slightly warped; all that matters is the ends. When making adjustments, be sure to check alignment only while everything is tightened in place, since the tightening may move the tailstock slightly. This procedure should get the tailstock centered to within a couple thousandths or less.
One of the most common gunsmithing chores is tapping (threading) a hole. Taps are available in many configurations. The most common types found in gunsmith-ing are known as taper, plug and bottom taps. A taper tap features a long tapered cutting edge that allows the tap to easily enter the hole and cut the threads.
A bottom tap features almost no taper at all, and is intended to cut threads almost all the way to the bottom of a blind hole. A plug tap splits the difference between the two and has some taper to the cutting edges. If you're tapping a hole with no closed bottom, a taper tap would be the best choice. If you're tapping a hole with a closed bottom and want threads most of the way (4-6 threads from bottom) to the bottom, a plug tap would be the choice.
If you want threads almost all the way to the bottom, a bottom tap would be used after a plug tap cut as many threads as it could.
Taps are sized by their diameter and thread pitch. English or fractional taps are specified by their fractional size (or number size in small taps) and the number of threads per inch. Metric taps are specified by their metric diameter and the number of threads per millimeter.
There are hundreds of tap sizes available to metalworkers. The most common tap thread pitch sizes in fractional taps are known as coarse thread, fine thread and extra fine threads. Fine and extra fine are the most common ones found in gunsmithing but be aware that manufacturers can and do use whatever thread pitches they want in their products.
If you are going to tap a hole for an existing screw, measure its diameter and check it with a thread pitch gauge to verify its exact size. Guessing wrong by only a thread or two can result in ruined holes and screws. Metric and fractional sizes are not interchangeable, so don't try, even if they do look close to the eye.
Before a hole can be tapped, it must be sized correctly. A drill and tap chart is used to determine the correct size hole for a tap. Most generic tap and drill charts only cover coarse and fine thread pitches, so if you are using an odd size you will have to find the size elsewhere. Some taps come with a hole size printed on the tap, other times the info may have to be looked up in a machinist book.
No matter what size the hole is going to be tapped, the tapping must be done square to the hole. Some can determine reasonable squareness by eye, while others can't get anywhere near square. If you turn the tap into the hole crooked, it will create a crooked hole; the tap will not straighten out as it enters the hole.
Off-square tapping can also lead to taps breaking off in the hole, a real "oh crap!" moment. If you cannot determine approximate squareness by eye, use a tapping guide. These can be purchased but are also easily made in the workshop.
To make a simple tapping guide, just squarely drill a tap-sized hole into a piece of rod. Be sure the ends are perfectly square. Lay the guide over the hole being tapped and allow the guide to support the tap as it enters the hole. Once you get the tap in several threads, the guide can be removed.
When tapping, always use lubricants. There are dozens of tapping/cutting oils on the market, and each one says it's the best; use whatever works best for you.
When turning the tap into the hole, turn it in one turn or so and then back it up to clear the chips. Harder steels may require backing up for chip removal every quarter turn or so. This turning and backing will help form smaller chips that are easier to work with than long strings of chips.
Depending on the material and size of hole, you may have to remove the tap completely from the hole every so often to clean caked-up chips from the flutes of the tap. Trying to force a packed up tap through a hole is inviting tap breakage.
Disc Sander Use
One of the most useful tools for the hobbyist gunsmith or metalworker is the disc sander. These may be 6 to 12-inch bench models or small hand-held electric or air-powered models. I use both types on a daily basis. These tools can do in minutes what could take hours to do with files. They can be used to shape any number of parts made from wood, plastic and metals. They also work great for tool sharpening. Material removal rates can be adjusted by how hard you push the work into the disc and by the coarseness of the abrasive disc.
Most bench models feature adjustable tables so angles can be cut, but most often you will have it set for 90[degrees]. Simply square the table to the disc with a square. An adjustable guide on the table will also allow for sanding at an angle or 900 .
Unless you have excellent dexterity, this guide should be used for all sanding to prevent sanding off at unintended angles.
Although the table extends all the way across the disc, the sander is designed to primanly work from only one side. Use the side that pushes the workpiece down against the table. This will result in the sparks and dust being propelled away from you and not into your face. Using the down side will also prevent the part froin being flipped up into you if the disc would tear and grab the part being sanded.
The other small disc sander I use almost constantly is an air-powered angled hand grinder. These can be fitted with small sanding disc, grinding stones or abrasive cutoff wheels. This air powered tool is best for general purpose sanding, deburring, and parts shaping.
An alternative to an air-powered grinder is a electric Dremel Moto-Tool. This type Of tool is especially suited for fine grinding or polishing. No hobbyist gunsinith should be Without one. There are hundreds of accessories for them. For polishing a feed ramp, for example, this is the tool to use.
Whichever type of tool you use, be cautious in its use. Coarse grit discs or wheels can be very aggressive in material removal. Remember you can always take more material off if needed, but you can't put it back on once it's gone.
If you're gunsmithing, you're gOing to be using files. I probably have more than 100 files in my toolbox, just to give you an idea of how important they are.
Files are available in hundreds of shapes, sizes and cutting patterns. Smaller files with fine cuts are the most common types found in gunsmithing. Very small files known as Swiss pattern files are used more often than large general-purpose files. Whatever type of file you are going to use, be sure to install handles.
While small files may have handles formed into the end, larger files simply have a pointed tang on the bottom. This tang is designed to fit into a hard file handle, not into your soft palm. It shouldn't take you to long to figure this out while you're digging a sharp handle out that is embedded in your hand! File handles are almost as cheap as bandages, so use them.
When flung, pay particular attention to keeping the file square to your work. It is very easy to be filing at a slight angle that could ruin a part. Files are designed to cut in one direction only. Dragging the file backward over the work after the forward cut does nothing but wear the teeth faster. I know everyone does it (myself included sometimes), but you really should train yourself to lift the file on the backstroke.
One thing I see novice filers do is try to file with a dirty, plugged-upfile. This just makes the job harder and makes for a poor cut. Files should be cleaned with a file card (not the 3x5 kind!). A file card is a very short wire brush. These short wires will get into the file teeth and remove the built up shavings.
Use the card every few strokes. One trick to minimize buildup on the file is to rub a piece of blackboard chalk on the face of the file every so often
Many home workshops are equipped with a small bench grinder. They can be used to shape steel parts and also for tool sharpening. They can also be dangerous if not used correctly. When using a bench grinder, be sure the rest is always close to the wheel. If you have an excessive gap, the workpiece may get wedged down between the rest and wheel and be thrown with a fair amount of velocity. Also never grind without the rest installed and your work against it. If not lying against the rest the part will be difficult to control making careful grinding difficult.
The most important thing to remember about grinders is this: grinding wheels can and do explode or disintegrate. When wheels fail, they throw large, chunks of rock hard wheel out at great speed and force. Failure to operate them correctly and observe safety rules can lead to serious injury.
In the last 20 years I worked in industry I saw a half-dozen wheels fly apart during use. Some of these were 18x2-inch wheels that could have severely injured the operators if they hadn't been following safety rules.
Never operate a grinder with the wheel guard removed. Never run a grinder with a cracked wheel. Never stand directly in line with the wheel. When wheels let go, they tend to fly apart in line with the wheel due to the great centrifugal forces involved. Never apply excessive force to the side of the wheel. Very light side grinding is commonly done but its best to avoid it if possible.
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|Date:||Apr 1, 2014|
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