A large part of any automotive metalworking project involves cutting and shaping the component parts. Sometimes cutting and shaping is the whole project, but more often the initial formation is followed by welding, brazing, or other techniques to create the final product. This chapter looks at the use of standard tools for cutting and shaping metal, and offers some useful projects for practice.
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People choose metal as a working material because it can be reshaped and strongly joined far more easily than wood, and is stronger than wood or plastics. You can cut metal into pieces, then weld the pieces back together and grind them smooth so that the cuts are afterwards invisible. And just as important, the piece is as strong or even stronger than it was before you started.
Most metal is sold in basic forms and quantities. Sheetmetal comes in large sheets, tubing and angle iron comes in long sticks, and plates come in a variety of sizes. These forms are almost never exactly right for what you’re making, so they have to be cut and shaped. In the past, a blacksmith used a variety of chisels, files, and hammers to separate bulk metal into the required sizes and shapes. Today we have a variety of tools to help us, and we can cut many of our pieces out of cold metal. Still, there’s no substitute for cutting iron by melting it, and we have tools for that, too.
Using Abrasive Cutting Tools
For the automotive metalworker on a budget, abrasive cutting tools are the default. You can purchase abrasive blades for any power saw on the market, and a carpenter’s table saw is good for straight cuts in metal up to 1/4-inch thick. You can even put an abrasive blade in your 7.25-inch circular saw and get the job done. However, a small investment in a dedicated metal-cutting chop saw makes things substantially easier and safer. The table saw and, especially, the circular saw fling chips and dust all over your shop— and all the hot metal chips seem to find their way to your skin. Plus, when you’re moving metal through the table saw or passing the circular saw through the metal, it can get hung up and kick back on you, or the disc can disintegrate, with potentially disastrous consequences.
A chop saw works by lowering the spinning blade onto the metal being cut. Because you’re not moving the metal through as with a table saw, or holding the saw by hand as with a circular saw, a chop saw gives you better and more accurate cuts with a better margin of safety. As with any saw, you have to be careful and observe all manufacturer’s safety precautions. Accidents happen all the time with saws, and you don’t want them to happen to you.
You can buy a saw designed for conventional abrasive blades or for cold cut carbide metal blades. Conventional abrasive blades are made of a composite material that is designed to be consumed rather quickly when cutting. These blades are typically black in color and made from metal oxides, epoxy, and a mesh fabric. They’re the same material as a cutoff wheel blade. These blades are generally inexpensive and work well enough that many fabricators need nothing else.
Metal blades for cold-cutting metal are typically designed to run at about 1,300 rpm, which is much lower than the 4,000 rpm used with abrasive blades. The advantage to this kind of saw is primarily a more accurate cut and much less dust and grit released in your shop. But while abrasive blades cost about $6 to $8 apiece, you’ll pay over $100 for a 14-inch cold-cutting metal blade. Some saws have adjustable running speeds, so you don’t necessarily have to buy two saws to use both kinds of blade. Check the documentation on your saw, or any saw you’re considering, and see if it runs at the correct speed for the blades you want to use.
Using a Chop Saw
1: Always follow manufacturer’s safety instructions and wear eye protection when using any saw.
2: Make sure the material you’re cutting is held firm in the clamp provided with the saw, and if it’s long material, make sure your piece is well-supported at either end.
3: When you measure your material, be sure to account for the width of the saw blade when making your cut. Mark your cut line precisely and then cut on the far side of the line for precise results.
4: Let the chop saw work its way through the material. Don’t press down on it with great force, especially with a consumable abrasive blade. You can damage your piece with excess heat, and in extreme cases you can break the blade, sending pieces everywhere.
5: When the cut is made, you may need to dress it up on the belt grinder before welding.
A cutoff wheel is another name for the type of blade used in a chop saw, but the name is generally used to refer to a smaller-diameter wheel that is used in a handheld tool. The blade may be mounted in-line with the tool body (such as a circular saw) or mounted on a body grinder, or mounted perpendicular to the saw body, as is typical with air-powered cutoff wheels.
While chop saws are used to cut long pieces to length, a handheld cutoff wheel is generally used for dress-up work or to remove material from an item too large to fit into a chop saw. For example, you would use a handheld cutoff wheel to remove excess length from a part that is already welded to an automobile body, or from the auto body itself.
As always, to use a cutoff wheel safely, keep the blade shields mounted on the tool and always wear proper safety clothing.
Sometimes a more traditional saw is the right answer for a cutting problem. This is especially true when you’re cutting panels out of a car. If you don’t own a plasma cutter, consider a reciprocating saw such as a Sawzall brand for big work, or a basic saber saw such as a Skilsaw for fine control. Both styles of saw offer blades specifically for cutting metals.
To use a reciprocating saw safely and with good results, you need to work slowly and carefully. Especially with a Sawzall-type machine, it’s easy to overshoot your mark or get off track. Auto bodies typically have layers of metal, and the in-out motion of a reciprocating saw sometimes hits a hidden interior panel and diverts the saw or worse, bends the blade inside the cut panel.
When you’re working with thin sheetmetal (18 gauge or thinner, or aluminum up to about 1/4-inch thick) you can use a traditional general purpose bandsaw for curved cuts. You need a specific metalcutting blade, available at most hardware stores and all metalworking supply stores, but no other specialized equipment is required.
A general purpose bandsaw is a good all-around tool to have in a metal shop. Blades are not prohibitively expensive and you can do good work conveniently. Even a novice can cut out complex shapes as long as the design does not require an internal cut. In a pinch, you can weld up the access cut to the internal cut, but this situation is where a tool like a plasma cutter really simplifies matters.
For straight cuts in larger pieces, consider a metal-cutting bandsaw. These saws are generally oriented horizontally and designed to use the weight of the saw to work through the metal. They usually come with clamps and have the adjustability to make angled cuts. Some of them use a water attachment to keep the saw blade and the work piece cool.
Another useful tool option is a handheld bandsaw. These generally have an opening of about 4 inches and are useful for cutting lengths of box section or tube that you cannot maneuver into a conventional bandsaw. Using this tool, you can cut any length of 4×4 box steel quickly and easily.
Hacksaw or Coping Saw
At the bottom of the technology pyramid is the basic hacksaw and coping saw. Although they are inexpensive and labor-intensive, no metalshop should be without these fundamental tools. There are often times when no other tool will do, and this is especially true of the coping saw. You can make delicate internal cuts using a drill to open a hole, and then thread the coping saw blade through the hole to begin your cut. It’ll take a bit longer than using a plasma torch, but if you don’t own that tool, a coping saw is affordable on every budget.
Always use a blade with at least 32 teeth per inch to cut metal. Also, invest in the best, most solid saw bodies you can find. A weak saw body allows the blade to twist as you cut, giving you an angled cut that must then be ground down. Keep your saw blades tight in the body and work slowly for a clean, straight cut.
Using Shearing Tools
Along with grinding tools, there are many low-cost tools available for shearing sheetmetal and light-gauge plate. Some of these tools are benchmounted and useful for cutting heavier stock, some are free-standing and used to cut large pieces of sheetmetal. But by far the most common tools are hand shears, and every shop should have a selection. Hand shears allow you to do small cuts and fine adjustment cutting quickly and easily.
Also in the category of shearing tools is the nibbler. These tools are typically pneumatic-powered, but are also available in electric varieties. The nibbler operates by taking a series of small bites out of a piece of sheetmetal. You can use a nibbler to cut many complex shapes from sheetmetal, but the primary tradeoff is the width of the cut. A nibbler makes a wider cut than a traditional shear. A nibbler is also harder to use to achieve square corners.
The other challenge of using a nibbler is that you have to hold it carefully, or it will “eat” off in its own direction. There’s quite a bit of vibration as it works, so it can take practice and a steady hand to get precise results with a nibbler.
Cutting a Sheetmetal Gauge Surround with a Nibbler
If you have a nibbler, here’s a practice project to create a simple round-cornered under-dashboard gauge panel using a nibbler. Use a hole saw to cut the gauge holes and a brake or basic bench vise to make the single bend, but the overall shape is good and convenient to make with a nibbler.
1: You can lay out an under-dash hanging gauge panel easily by hand. To fit two standard 21⁄16-inch gauges you need a piece of sheet aluminum that is 5 inches wide by 4 inches tall. Use a soda can to trace 90 degrees of curve on the lower end of the mounting plate and a straightedge to mark an inch from the top for a 90-degree bend.
2: Use your nibbler to trim the rounded edges of the plate. As you cut, note how difficult it would be to get a nice square corner with the nibbler. For that, you need a shear.
3: Dress up the edges of the sheet with your deburring tool, sandpaper, or your belt grinder until they’re smooth.
4: Drill two or three mounting holes about 1/2 inch from the top edge. Then place the top inch or so in a sheetmetal brake and give it a 90-degree bend.
5: Now mark your gauge locations on the surface of the plate. If you use the actual gauges as your template, be sure you’re not using the outer rim of the bezel. The actual gauge body is smaller.
6: Use your hole saw to cut the holes for your gauges. Alternately, you can drill a hole and use a Use your hole saw to cut the holes for your gauges. Alternately, you can drill a hole and use a coping saw, but this is time-consuming and the result won’t be better than a hole saw cut. For the best fit, use a slightly smaller hole saw than the finish size of the hole. For example, choose a 2-inch hole saw for a 21⁄16- inch finish size and then finish the holes with your deburring tool. Be sure to use the slowest possible speed on your drill press when you’re using hole saws, and also be sure to have a stout piece of wood behind the sheetmetal you’re cutting. Clamp your sheetmetal to the wood block for best results.
As an alternate process, if you don’t have a brake you can still get good results bending a piece of this size in an ordinary bench vise. Carefully insert your piece in the vise with the short end clamped in the jaws. Make sure the bend line is lined up at the lip of the jaws and the piece is all the way to one side or another. Using both hands, and with your thumbs right at the brake point, carefully bend the top about 15 to 20 degrees. Don’t go too far! Now loosen the vise jaws and move the piece to the other end. The width of the vise jaws should overlap the previously-bent area. Again, line up the piece carefully along the brake line and bend the part about 20 degrees with your thumbs along the base. Then move the piece back and repeat this process until you’ve got a nice 90-degree bend all along the brake line. You should end up with a reasonably sharp bend. A couple light blows with a rubber mallet or other dead-blow hammer can tighten up your angle if it’s not sharp.
As another alternate project, you can lay out a custom-fit gauge panel with a template. Because this panel should be made for your particular car, take a sheet of thin single-layer cardboard and cut it to fit the available space in your dash. Be sure to make some provision for attaching the panel to the dash! For example, older air-cooled Volkswagen Beetles have a panel just to the left of the speedometer that can be removed and replaced with a sheetmetal panel that fits two small 21⁄16-inch gauges for oil pressure and temperature.
Hand and Bench-Mounted Shear
For straight-line cuts, you can’t beat a shear. Virtually every metal shop working with sheet uses hand shears of some kind. The most basic are tin snips, and these are just large heavy-duty scissors. You can get good results with a basic set of aircraft style hand shears. Remember that they come in straight-cutting and left/right-biased styles, and it’s good to have all three types. This is not to say that you can’t cut left or right curves with a straight-cut shear, but it’s easier and yields better results to use the right tool for the cut. If you have only left- or right-cut shears, remember that a left cut is a right cut if you start at the other end, or flip the piece over!
The biggest free-standing units handle up to an 8-foot sheet of metal, but limit you to straight-line cuts. More common are the benchmounted varieties, which can be purchased for as little as $100. The largest of these “throatless” models can handle mild steel up to 3/16-inch thick and with a little practice you can use them to make steady curves in thick sheet metal. Throatless shears work like a very heavy set of hand shears, and work with replaceable blades. The body of the shear also curves upward toward the back to accommodate rotating the sheet metal as you make your cut—this is what allows the throatless shear to cut curves. If you plan to work with heavier sheet and cut curves, this tool is a good investment.
Making a Removable Sheetmetal Panel with a Hand Shear
This is a simple project that can be done in minutes with a set of aircraft shears. If you like, you can use a bead roller to add some fancy touches to your product, or just leave it plain.
1: Make a template of the panel you need. You can draw it right on your sheetmetal, or make a cardboard template and transfer the design to your sheetmetal. Note any bends you might need to make and be sure to leave plenty of overlap (about an inch in every dimension) if you plan to use Dzus fasteners.
2: Working as much as possible with the existing edges of the sheetmetal, cut out your panel shape with your shears. Take your time the benefit of aircraft shears is that you can get a good look at your work while you’re cutting.
3: Clean up your edges with sandpaper or your belt grinder.
4: Decide where you need to mount your Dzus fasteners. For an ordinary rectangle shape, you can use two or four fasteners. If you use two, position them at diagonally opposite corners of the plate. Drill holes to accommodate the fastener. Generally this means a 5/8- inch hole for the main body of the fastener and two smaller holes for the rivets that mount the fastener to the plate. Drill the main hole first and insert the fastener, then mark and drill the rivet holes. Pop-rivet the fasteners in place.
5: Next, go to the receiving panel and overlay the cover panel. Mark the location of the Dzus fasteners. You can drill a smaller hole in the receiving panel to receive the shaft of the Dzus fastener.
6: Working from the back side of the receiving panel, drill smaller holes for the pop rivets to hold the Dzus wires to the panel. Pop rivet the wires into place from the front, however, for a flat, clean, and professional-looking installation. The Dzus wire is generally made of springy material and it stands back from the panel a bit, so the Dzus fastener makes a snug connection.
7: Test fit your panel. The most common mistake is to use a Dzus fastener that is too long, so it fails to get a secure grip on the wire. If that happens, drill out the rivets and get a shorter Dzus fastener or put some gasket material between the cover panel and the receiving panel.
Dzus-fit panels can be any shape or size, and they’re easy to remove and replace for ready access to any part of your car. Dzus-fit panels are accepted as bulkheads by virtually all racing organizations.
Using Grinding Tools
No matter how precise your cutting tools may be, you also need metal grinding tools to produce finished products. Every edge cut with a torch or a shear requires sanding or grinding to become smooth and look good.
There is a huge variety of filing, grinding, sanding, and other abrasive tools on the market. We’ll cover the most common tools and their uses.
Beyond the usual basic safety precautions such as wearing eye protection, there are specific habits that should be avoided with grinding tools. Chief among them is the practice of using any part of the abrasive other than the designed grinding face, for example, grinding on the side of a grindstone wheel on a bench grinder. Many bench grinders have lost their protective side covers over time, but grinding on the side of a commercial grindstone can cause it to shatter and that is dangerous at high RPM when you’re standing in the way.
If your body grinder is set up with a grinding face, do not use its edge as a cut off wheel, and don’t try to grind with the face of a cut off wheel. They’re not made for it. Another common safety problem with body grinders is allowing the cord to get in the way of the work. A metal grinder eats through a power cord in no time at all, creating an electrical shock hazard.
As always, follow the manufacturer’s safety instructions with all grinding tools.
Body Grinder and Grindstone
Most body grinders are set up so that the grinding surface faces away from the user. To effectively use a body grinder, use a light touch. If you lean or press into the work, you can gouge the metal more than you intend it happens in an instant and then you have to fill the hole with weld or body filler. Keep the grinder moving in long, smooth motions and let the grinding face wear down the high spots.
Be aware that using a grindstone, disc, or belt imparts heat to your work, and you can generate enough heat to warp light materials simply with grinding. You can also take the temper out of tool steel and other hardened materials with grinding. In fact, you can get a good look at heat colors by simply holding a bolt against a grindstone. Try it, and you can see the blue, brown, and straw colors that indicate temperature effects on steel.
But you can also produce many useful tools and parts using only a standard bench grinder with a rough stone and a smooth stone. Change one stone to a wire wheel and you can smooth out most of your work. Change the other stone for a buffing wheel and you can polish your work to a mirror finish. The key is patience using a grinding tool always takes time.
A belt sander with an additional flat grinding face is a key tool in any metalshop. You can quickly dress up or shape any piece with a strong belt grinder. The rounded end produces almost any kind of curve you need, while the flat part of the belt gives you a reliable straight edge. If your grinder includes a round disc, you can also use that face for straight edges. Straight lines are much harder to create with a bench grinder or a body grinder.
Get a variety of belts to go with your grinder. You can get extremely rough grits for removing lots of material quickly and fine belts down to 400 or 600 grit for polish work. The other secret to good results is to replace your belts frequently. Also, keep separate belts for working with aluminum and steel. You don’t want to introduce flecks of either metal into a piece made from another— especially if you’re dressing up an edge prior to welding.
A belt grinder is especially useful for creating welding bevels and precise angles such as fishmouth joints in tube steel. As with all grinding tools, bring your patience and use a light touch when grinding.
Cutting with an Oxy-Acetylene Torch
An oxy-acetylene torch is a very familiar sight and a basic symbol of welding. Many movies begin an automotive construction montage sequence with the lighting of a cutting torch. Yet it’s important to know that a cutting torch and a welding torch are very different tools even though they both use the same bottle of oxygen and acetylene.
A welding torch uses the basic valves on the oxy-acetylene torch handle to control the mixture and flow of gases. A welding torch produces a comparatively small flame, and is used to gently melt the welding rod and surrounding metal into a small puddle for joining parts together. A cutting torch is a larger tool that includes a lever and an extra valve for additional oxygen flow. When you’ve got a puddle of molten steel from the basic flame, pressing the lever actuates the increased oxygen flow and literally blows the molten metal out the other side of your piece. If your piece is too thick, you might not be able to cut it all the way through, but thin materials cut very easily.
Note that you cannot use oxyacetylene to cut very hard stainless steel alloys, and gas cutting generally melts aluminum into a big puddle of slag. Use your oxy-acetylene cutting torch for mild steel and tool steel only. If you need to cut other materials, get a plasma torch. You’ll be glad you did. The best way to learn gas cutting is to try it and practice, so let’s get right to the projects.
Cutting Practice with an Oxy-Acetylene Torch
This is a basic project to get you used to cutting with an oxyacetylene torch. You need your torch kit and some scrap steel. Ideally, you should clamp your scrap metal into a vise on your welding table or workbench. Make sure you’ve got your gloves and all your safety gear together, and that there’s nothing around that’s flammable. A fire extinguisher and a bucket of water are good to have close at hand.
Note that the best position for oxy-acetylene cutting is always to lay your piece out flat so you’re cutting through from above. This allows the molten metal to drain out the bottom of the cut rather than running down the side of your piece. Obviously, you should never cut from below, or you’ll have molten steel raining down on you! Follow these steps:
1: First, close all the valves on your welding torch. You don’t want gas leaking out while you’re setting things up. Get a piece of scrap steel and put it in your bench vise. It gets hot, so put on your gloves. Select your cutting tip size to match the thickness of the metal you’re cutting. Choose a #0 tip for all steel up to .25-inch, #1 for .25 up to .50-inch, #2 for metal up to 1 inch thick. Larger number tips can be used for cutting thicker materials, but are almost never used in automotive applications. In general, select the lowest number (smallest) tip suitable for the metal you’re cutting. Your cuts will be more precise and you’ll use less gas.
2: Next, set the correct pressures at the regulators attached to your welding bottles. Open the main valves on the top of your bottles. Your regulators have two gauges each. The gauge nearest each bottle shows the pressure in the bottle. You should see at least hundreds of pounds of pressure in each bottle. The gauge on the other side of each regulator shows the gas pressure going to the torch. You adjust the gas pressure at the torch by turning the valves on the regulators. Start out by dialing in about 20 pounds of oxygen and 7 pounds of acetylene pressure for cutting. If you are using a large cutting torch, you might need more pressure.
3: Now find the acetylene valve on your torch. You can tell the acetylene valve because the hose leading to it is red. The hose leading to the oxygen bottle is green. Equipment makers make acetylene bottles with reverse (lefthand) threads so it’s hard to get these mixed up if the hoses are already attached to your regulators. Get your torch lighter ready and open the acetylene valve just a little. You can usually hear the gas start to flow. Light it immediately, because you don’t want unburned gas to accumulate around you.
4: The fire you get from the torch should be yellow, and it’s likely to be smoky. If the first isn’t smoky, slowly close the acetylene valve until it starts to produce a little smoke. Then open the oxygen valve on the side of the torch a little bit, and notice that there is no change in the flame. You have to open the valve down by the hose and the valve that is up on the side of the torch in order to flow oxygen into the flame.
5: When oxygen joins the acetylene, the core of the flame turns blue, and there’s a set of bright blue flames right at the tip. By adjusting the knob up on the side of the cutting torch, you adjust the constant flow of oxygen into the flame. When the set of blue flames is small and consistent, try pressing the lever on the torch. The center of your flame should jump out and you should hear the flame increase. If it doesn’t do this, open the oxygen valve down by the hose a little more. Pressing the lever releases more oxygen directly from the hose to the center of your flame, and this is crucial for cutting.
6: When your flame is set correctly, go to your piece of scrap steel and hold the flame against it. As the steel heats up, it starts to glow and eventually start to spit sparks like a fireworks sparkler. That happens when the steel is at the melting point, and you’ll get a puddle of molten steel. Now press your oxygen lever and begin cutting.
7: In a smooth motion, push your puddle forward very slowly. You can gauge how fast you can cut by how fast the metal melts in the path of your flame. If you go too fast, you’ll lose your cut. Too slow and you’ll melt more than you want to and your cut will be a mess.
Practice your cutting technique on scrap steel until you are comfortable cutting steel of different shapes and sizes. Be very careful about your ventilation whenever you use gas welding. Not only does the flame generate carbon monoxide, but sometimes there are impurities in paint, grease, and other substances on your materials that generate poisonous gases. Galvanized metals and tin in general produce poisonous vapors when heated to welding torch temperatures, and you don’t want to breathe any of that.
Making an Anvil from Railroad Track
A good piece of practice with a cutting torch that also makes a useful tool for your shop is to create a small anvil from a piece of scrap railroad track. This low-cost project can be completed in an afternoon with a cutting torch, body grinder, flat mill files, and perhaps a drill.
When done, you have a small anvil suitable for chiseling, light forming, and many other workshop uses. Note that this railroad track is not a hardened steel surface, so you won’t be able to beat on it with a 16-pound sledge, but it serves for small work adjustments and light duty forging.
First, you need a length of railroad track. Any piece of track about 12 to 24 inches in length will work. You can use light gauge or full size rail, depending on the size of anvil you want. You can get a piece of track at many iron scrapyards it’s not hard to find. But resist the temptation to go prowling for a chunk of track in a railyard or along train tracks. That’s always dangerous and usually illegal.
The thickest cut needed is up to 2 to 3 inches through the bulk of the rail-top to rough out the anvil horn, so you’ll need a #4 or #5 tip for those cuts, and a #2 tip for the cuts through thinner portions of the rail. Make sure both your oxygen and acetylene tanks are full before you start, because you’re going to use a lot of gas to get this project done.
When you have your piece of railroad track, follow these steps:
1: Design your anvil and mark the design on the metal with a welding marker, soapstone, or paint pen. You probably will not have enough space to plan hardy or pritchel holes. About the only thing you can do is plan a horn or other rounded shape at either end of the piece. Think about the kind of work you plan to do and you can decide on a rounded or flat top, one or two horns (or no horn), and how deep to cut out the throats.
2: Brace up your piece of track on your welding table or some other good surface where you can cut from above. Never cut or weld directly on a concrete floor, because water in the concrete can flash into steam and cause part of the concrete to explode. If you have a vise large enough to hold your piece of track, that works best. Clear all flammable materials away. Pay special attention to what’s directly underneath the area you plan to cut.
3: Get out your gas torch and #2 tip and first cut out the throats from the base area. Start with about 3 pounds of acetylene pressure and about 40 pounds of oxygen available when cutting. Take your time and make your cuts as clean as possible. Follow your marked line carefully and try to keep your cuts straight through the material. Note that the whole anvil gets very hot before you’re done cutting. Leave the base of the anvil in place all the way out to the ends of the working surface; it’s better for stability.
4: Next, rough out the horn (or horns) you designed. Use the #4 or #5 tip, based on the thickness of the material you’re cutting. You want 4 to 5 pounds of acetylene and 45 to 50 pounds of oxygen pressure available. If you want a flat-topped horn, you can just cut straight down from the sides. If you want a round-topped horn, you can try to cut again at an angle to remove a lot of material fast, but unless you’re very good at cutting, this is likely to take more work than simply grinding away what you don’t need.
5: Now your anvil has its basic shape. The rest of the process requires harder work. Start by grinding your cuts smooth with an electric body grinder. This takes some time, and if you made any deep mistakes with the torch, you might consider filling them with weld from your MIG welder and then smoothing over with the body grinder. At this time, you should also use the grinder to flatten the top of your anvil if you want it so. If your anvil is long enough, you might consider flattening some of the face and leave some of it curved. If you’ve got a friend with a machinist’s mill, you can also flatten the face easily using that tool.
6: After a couple hours with the body grinder, you probably used up a couple of grinder discs and made a big pile of grinding grit on the floor. But your anvil’s looking pretty good by now. You can finish up the detail work with files for the areas you couldn’t reach with the grinder. Mill files are also good for checking flatness. If the file wants to rock back and forth on the face, it isn’t flat yet. Some people polish their anvils up to a mirror-bright finish, but you can take yours to whatever level you like. It’s your tool, after all.
7: Finally, turn your anvil over and drill some holes at the four corners of the base. You can also burn these holes through with your gas torch and the #2 tip. This allows you to bolt the anvil to your workbench or your welding table. Track anvils have also been bolted to truck bumpers, mounted on stumps, and placed on custom-made stands. If you plan to hammer on your anvil, it’s best to mount it on a solid piece of wood like a workbench or a section of a log. Hammering on a steel anvil bolted (or welded) to a steel table is extremely noisy!
Optional: If you have access to appropriate equipment or if there’s a heat-treating company in your area, you can harden your track anvil somewhat by heating the entire piece to red-hot and placing it in an oil quench. Do not use a water quench or the piece may break. You can also buy some hardfacing rods for your stick welder and build up the top and machine it flat again. But for automotive work, hardening a railroad track anvil is generally not necessary.
Cutting with a Plasma Cutter
Plasma cutters are relatively new tools that use superheated compressed air (or other common arc welding gases) to cut metal. Without getting too much into the physics, gas plasma is what stars are made of. Plasma is also present in the arc of your electric welder, and that’s how the plasma cutter works. A plasma cutter (or torch) is an arc welder with a supply of filtered, compressed air. When you actuate the plasma cutter, it creates an arc strong enough to puddle the metal you’re cutting. Then the compressed air blows through the arc, which turns it to plasma. The superheated plasma then blows the molten metal out of the cut you’re making and melts the metal in its path. A second jet of air or gas does not pass through the arc, and this is used as a shielding gas in the same way that a MIG or TIG welder uses gas.
Modern plasma cutters can be purchased new for less than $1,000. Larger models can cut through steel up to an inch thick, and a plasma cutter can also work stainless steel, aluminum, and other non-ferrous metals easily. The precision and quality of a plasma cut is nothing short of amazing.
There are several plans for plasma cutting tables with waste receptacle trays available on the Internet. These tables feature a grid plan to support your work. The bars of the grid take some abuse from the plasma cutter, but are designed to be replaceable when they become too damaged for further service. Many of these tables also include a chute or tray to catch the slag, dust, and other waste materials from the plasma cutting process. Some of these waste trays are designed to be filled with water, which reduces fire danger and simultaneously helps limit dust distribution.
Plasma is the perfect tool for repairing rusty automotive bodywork because of the narrow cut and the precision of the cut. With a plasma cutters, there is very little oxidization of the surrounding steel in the cutting process. Gas torches especially in the hands of amateurs, leave a great deal of burned steel behind. The plasma torch passes along the metal so quickly that the heat does not disperse. Thus, there’s little or no weakened area left behind. You can cut painted metal without ruining the finish much beyond the place where you cut. Then you can cut out your replacement parts with identical accuracy. If you plan to do automotive bodywork repair, a plasma cutter is almost a requirement in a modern shop. It’s a great investment in your work.
Cutting Stencil Designs with Plasma
Follow these steps to get started cutting with plasma. Automotive painting stencils such as flames are a good source for practice designs, but if you want to start with an easier cut, consider a basic Chevy bow-tie logo. You can trace virtually any design on thin plate or sheet of steel or aluminum.
1: Make sure you’re cutting in a clean, safe environment. Cutting plasma reaches temperatures of about 30,000 degrees, and you can cut right through your welding table or light your workbench on fire very easily. Never use a plasma cutter on concrete, because water that has soaked into the concrete can flash into steam and cause the concrete to explode.
2: Because a plasma cutter is a modified arc welder, there’s a ground clamp you need to attach to your workpiece or your welding table, just like an arc welder.
3: Position your piece of plate or sheetmetal and draw or trace a complex shape on it with a felt-tip pen or welding marker. You can use purchased stencils or make your own. For flames, try it yourself. Draw some flames on a sheet of thin cardboard. If you don’t like your results, start over with a different color pen or just turn the cardboard over.
4: When you like your design on the template, cut it out with a craft knife or razor and you’ve got your stencil. Position it on your metal and trace around it to transfer your design to the metal.
5: Before you work on your real project, take a piece of the same material and get your plasma torch set up with the correct power. Use the least power consistent with making smooth cuts when working with aluminum. For sheet-gauge aluminum, this is the minimum power setting on your torch. Ensure that the workspace is clear and that the material is sitting at a comfortable height. In short, make your mistakes here and be ready for smooth work when you cut for keeps.
6: You can start plasma cutting anywhere—the plasma will quickly penetrate aluminum or steel and start your cut. Start in a waste portion of the metal and bring your cut over to your desired cutting line. This prevents you from leaving a large starting hole in the finished piece.
7: Start your cuts at one edge of the piece and cut out your design by alternating sides. This limits the amount of heat transferred into the metal at one time in one area. Sheet aluminum is very prone to warping with just a little heat, so be extra careful with that material. Cuts should begin and end in natural locations and be as smooth as possible. If you need to rest or you’re running out of reach, angle your cut into waste material before you stop the torch. You can pick up the line again from another point in the waste material.
8: Try to get a feel for how quickly you can cut the material and still maintain a smooth, clean edge. For best results, hold your cutting tip at the manufacturer’s recommended distance from the material and do not exceed the tool’s recommended speed as you cut. Your cutter’s manual will have this information for you. Master plasma cutters move through their work with smooth, sure motions in long cuts.
9: Work your way through the pattern, discarding waste as you go. You do this by making several cuts so that as much of the leftover metal falls away as soon as possible. This prevents a large weight of hanging scrap metal from moving your piece or making the cutting process more difficult. It also gives your plasma cutter a rest from its duty cycle and allows the tip to cool.
10: Notice how much dust and slag and scrap the cutting process generates. Plasma dust and slag is renowned for getting all over the place, so fabricators have designed special tables strictly for use when cutting with plasma or gas.
Plasma Cutting Roll Bar Mounting Plates
In Chapter 7 we learn how to make a custom roll bar or roll cage for a car. Your plasma cutter is a good tool for cutting out odd-shaped base mounting plates and gussets you might need to use when mounting a roll structure to a unibody chassis. This procedure is also good for cutting plates to make custom engine or transmission mounts or suspension attachment tabs. However, if your plates or tabs are basic rectangles, choose your chop saw to make those cuts. Note that most sanctioning bodies require roll bar mounting plates to be at least 36 square inches of .125 (1/8 inch) mild steel.
Follow these steps to cut out plates, gussets and other custom shapes from steel plate:
1: Create a model for your part in cardboard, or trace an existing piece onto the steel using a felt-tip marker or welding pen. Use existing edges on the material whenever possible.
2: Steel for mounting plates is likely to be thicker and harder to cut than aluminum, so set your plasma cutter correspondingly higher—at least halfway through the range for 3/16- or 1/4-inch mild steel plate. Also, make sure there’s nothing flammable under your cutting area, as molten steel will be falling from the plasma cutting process.
3: Make some test cuts in similar materials to make sure your settings and environment are correct before you commit cuts to your real work.
4: It’s less critical with most construction parts, but start your cuts at the edge of the material or in a waste section of metal to get the best, cleanest results. Cut as quickly as possible in smooth, long motions. If you’re cutting straight lines, consider clamping a piece of angle iron to your work as a torch guide.
5: Molten steel tends to flow and rejoin itself easily, especially if your gas plasma pressure is lower than it should be. You should set the machine with enough power to melt through the material and enough pressure to blow the molten steel out decisively. Still, you might have to run over some small spots twice to free up your pieces as you cut.
6: Knock each piece out as you cut it free. Set it aside or let it drop to cool before you handle it. Dress your cuts up with a grinder, at least at first. Plasma cutting masters can make a cut so smooth that it hardly needs extra work. You can also angle the torch slightly to create your own welding bevels rather than grinding them in later.
One benefit of plasma cutters over gas torches is that there is very little oxidization of the surrounding steel in the cutting process. Gas torches especially in the hands of amateurs, leave a great deal of burned steel behind. Because the heat is so intense and brief during plasma cutting, oxidization is limited even though the shielding gas is usually just normal air. Thus, there’s little or no weakened area left behind.
The bottom line on cutting and grinding is that if you have a body grinder, a belt sander and grinder, a chop saw, and a plasma cutter, there’s very little you can’t do.
Written by Russell Nyberg & Jeffery Zurschmeide and Posted with Permission of CarTechBooks