Using a plasma cutter to cut straight lines on a sheet of steel is very easy if you have the right accessories and approach. Cutting up a 4′ x 8′ sheet of steel can be done in fifteen minutes with perfect cuts as long as you take the time to setup your cuts correctly. This includes using some cheap accessories like a straight edge, stand off torch guide and a slow steady cutting speed. Don’t be fooled in thinking you need to buy expensive roller guides or fancy clamp on cutting hardware.
Step 1: Draw A Straight Cut Line
Drawing a straight cut line on steel plate is easy using a large “T Square.” Simply place the T-Square on the the edge of the steel snug and it will provide you with a straight edge to draw your line. T squares usually come in 4 foot lengths, so if you have to draw an 8 foot line you will need to use the T square on both sides of the steel. We recommend you use a sharpie to draw your line. While sharpies can be harder to see, we find them better than soap stone as it will provide you with a sharper line. This means that your cuts will be more precise.
Note: If you’re making smaller cuts less than four feet in length you can also use a carpenters “L square.” These are smaller in size and can be useful when marking out smaller cuts.
GreatNeck 48″ T Square
T Squares are awesome for a lot of different applications and we believe every shop should have one on hand. Most T squares are fixed in length, but they also offer some that can adjust in size. Personally I don’t see much utility in the variable adjustment so I stick with the fixed length.
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Step 2: Clamp A Straight Edge To Your Sheet Of Steel
After your line is drawn you will need to attach a straight piece of steel along your drawn line with vice grips (C-clamps). A long piece of angle iron works best, but you can also use a piece of flat bar or square tubing. This straight edge will give you something to guide your plasma torch along while you cut. It is crucial that your plasma torch stays in contact with this straight edge to insure you’re staying on your cut line perfectly. Make sure you clamp both sides of your straight edge so it does not move under pressure.
IRWIN Vise-Grip (C-Clamp Pliers)
These are a must have for anyone doing metal fabrication. They will work great for holding down your straight edge tightly to your sheet of steel and are quick to adjust. We usually carry 8-10 of these on our welding/plasma carts.
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Step 3: Install Your Stand Off Guide On Your Plasma Torch
Installing a stand off guide on your plasma torch will allow you to drag the torch along the sheet metal without having to worry about the tip of the torch touching the metal. A stand off guide will give you the most consistent results as it will stop your plasma torch from rotating while you cut. Certain companies make specific stand off guides for their torches, but we also find that pretty much any stand off guide will work with any torch. You may have to do a bit of an adjustment with a pair of pliers to get it to fit snug, but it is easy to do.
Two Point Stand Off Guide For Plasma Cutter Torch
This stand off guide will work well and is adjustable to fit just about any torch. You can bend the circle larger or smaller to change the height at which it will hold your torch to the metal. These are very cheap and it’s always good to have a couple on hand. We find that these work better than the roller style stand off guides that many companies sell.
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Step 4: Adjust Your Straight Edge To Your Plasma Torch
Now that you have you straight edge on the table with the clamps set snug you can place your torch against the straight edge and make final adjustments. Be sure the very tip of your plasma torch is directly over your drawn line. Run the torch up and down your straight edge to make sure it stays on the line the entire time. If it doesn’t, that means one of the sides of your straight edge needs to be moved slightly. Once it looks good tighten your clamps nice and tight.
Step 5: Make Your Cut
Once everything is lined up correctly it’s time to make your cut. Start with you torch at the top edge of the plate and pull the torch toward you slowly. You want to make sure the plasma cutter is fully penetrating the steel as you move.
Be sure to pull your torch at an angle towards your straight edge to ensure that your torch stays in contact with he straight edge the entire time. If you lose contact with the straight edge your line will not be straight.
If for any reason you have to stop cutting you can resume your cut easily by starting 2-3 inches into the area you have already cut and continuing back into the uncut area.
Pay close attention to where the cut piece of metal will fall and be sure you are away from it. For larger pieces it’s best to have them held up by saw horses so they don’t fall to the ground.
Additional Resources
If you have never used a plasma cutter before be sure to read our comprehensive beginner’s plasma cutting guide. This will help walk you through the entire process of getting your machine hooked up correctly and making cuts safely.
If you are looking for help finding a new machine be sure to check out our list of the best plasma cutters that we recommend. If you need a plasma cutter with a built in air compressor you can view the machines that we recommend here.