What's inside
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A circle guide turns a plasma cutter’s torch into a pivoting tool: a center point holds the radius, while the torch travels around it. It can make a cleaner, more repeatable circle than freehand cutting, but only if the guide fits your torch, the work is secured, and the torch stays square to the plate.
Choose a guide that fits your cutter
Check your plasma cutter’s manual before buying or making an attachment. Circle guides usually connect to a torch stand, a magnetic base, or a pivot arm. The torch must sit securely in the holder without blocking the trigger, airflow, or consumables. Also confirm the guide’s radius range covers the circles you need; advertised diameter ranges can be misleading if the pivot-to-torch distance is what the manufacturer actually specifies.
A basic compass-style guide is often enough for occasional circles in mild steel. A magnetic guide is quick to reposition on clean, flat plate, but can slip on rusty, painted, curved, or thin material. A stand or track gives more support for repeated cuts, though it costs more and takes longer to set up. Compare the mounting style and size range before choosing:
| Guide type | Best use | Main trade-off |
|---|---|---|
| Simple pivot arm | Occasional circles on a flat, secured plate | Low cost; fit and rigidity vary |
| Magnetic base | Quick setup on clean, flat steel | Can shift on rough or thin stock |
| Track or supported stand | Frequent cuts or larger circles | More stable, but bulkier and pricier |
If your cutter’s torch is not compatible with a guide, a plasma cutter circle guide search can help you compare adjustable attachments. Do not assume a universal clamp is safe just because it fits around the torch body.
Prepare the plate and set the radius
Wear the PPE specified by your cutter’s manual: a suitable welding helmet or plasma-cutting face shield, gloves, flame-resistant clothing, and hearing protection. Plasma cutting throws hot metal and sparks; keep flammables away, use appropriate ventilation, and follow local fire-safety rules. Check the work clamp, torch consumables, air supply, and electrical connections before starting.
Lay the plate flat on a stable cutting table with space beneath it for the arc and slag. Secure it so it cannot shift when the torch is pulled around the pivot. Measure the desired finished diameter, then mark the center. The radius is half the diameter: a 150 mm circle needs a 75 mm radius from the center point to the torch’s cutting path.
Account for the kerf—the material removed by the arc. If the inside edge of the cut must finish at a particular diameter, the torch travels slightly outside that edge by roughly half the kerf width. Kerf varies with cutter settings, material thickness, speed, and consumable condition, so make a test cut in scrap of similar thickness when accuracy matters.
Set the guide’s center-to-torch distance, then measure it directly rather than trusting a stamped scale. Keep the center point secure without letting it penetrate a table or interfere with anything below the plate. On thin sheet, a sharp center pin may distort the work; a small center mark or suitable non-slip pivot can be better.
Make the cut smoothly
Position the torch at the circle’s start point and check that it is perpendicular to the plate. The guide should rotate freely, without wobble or binding, and the torch lead should not tug on the arm. Confirm the full circle is clear of clamps, table edges, and nearby objects.
Use the cutter’s recommended amperage, air pressure, and cutting speed for the material thickness. Pierce inside the waste area if the cutter’s instructions call for it, then follow the circle in one steady rotation. Keep a consistent torch-to-work distance if the torch is not designed for contact cutting. Avoid stopping mid-cut: a pause can leave a divot, widen the kerf, or create a hard-to-restart section. If you must stop, follow the manual’s restart procedure and expect to dress the joint afterward.
Do not force the guide faster than the arc can cut through the plate. Excessive speed leaves a heavy, angled dross or an incomplete cut; moving too slowly can widen the kerf and increase heat distortion. Watch the underside when it is safe to do so, and adjust speed based on the cut quality rather than trying to finish in one pass at any cost.
Common problems and fixes
If the circle is out of round, check for a slipping pivot, loose torch clamp, wobbling arm, or a plate that moved. A magnetic base needs clean contact; grinding off scale where it sits can help, but do not use a magnet where it could attract hot debris or interfere with the setup. If the torch leans, the cut may be beveled. Re-square the holder and make sure the torch is not being pulled sideways by its lead.
Heavy dross usually points to incorrect travel speed, poor air quality or pressure, worn consumables, or settings that do not suit the thickness. Check the manual and consumables before compensating by changing several settings at once. If the circle is consistently too large or small, measure the actual kerf on a test coupon and adjust the guide radius for the intended edge.
For occasional work, a modest torch guide compass is often the sensible choice. If you cut circles frequently or need repeatable dimensions, spend more on a rigid, well-supported guide and verify its setup with a test cut. A cheap guide is fine when it holds the torch square and the pivot stays put; accuracy depends just as much on setup and technique as on price.