Sigma J-PRO Jolly Edge — Perfect 45° Tile Miters From Your Own Grinder

Mitered tile edges are the mark of a high-end job: two tiles meeting at a crisp 45° corner with no raw edge showing, wrapping a curb, a niche, or a countertop like the tile was poured around it. Cutting those miters freehand with a grinder is slow and uneven. The Sigma J-PRO turns your angle grinder into a precise, repeatable miter machine.

Mount the J-PRO on your grinder, fit a diamond cutting disc, and its guide plate rides along the edge of the tile as you go. That's the key: because it follows the tile's actual edge, it copies the real contour of the slab — even the slight curves a big porcelain slab has — for a miter that stays uniform the entire length. A machine on a rigid rail can't do that; it cuts dead straight while the slab isn't, and the miter goes thick and thin. The J-PRO comes preset at 46° (the ideal tile miter angle), so setup is minimal — you just set how far the disc sits from the edge and go.

It handles tile from 5 to 20mm thick and from 12" to unlimited length in a single pass, so it covers everything from standard tile to big slabs. A dust-extraction port keeps dry cutting clean, and with the Sigma Water-Kit it runs wet for an even finer finish and longer disc life. The universal spindle thread fits standard angle grinders (grinder and disc sold separately). For decorative eased or chamfered edges rather than full miters, pair it with the Sigma Simple Bevel.

Why Tile Pros Choose It

• Perfect 45° miters: Clean, professional mitered tile edges
• Follows the slab: The guide rides the real edge for a uniform miter full-length
• Preset at 46°: Minimal setup — just set the disc distance from the edge
• Big capacity: 5–20mm thick, 12" to unlimited length, single pass
• Wet or dry: Dust port for dry cutting; Water-Kit for wet finishing
• Uses your grinder: Universal spindle thread fits standard grinders
• Bench-mountable: For machining small pieces
• The difference between "tiled" and "custom": Is usually a clean miter

Pro tip: Let the disc do the work at a steady feed and keep the guide plate flat and firm against the tile edge the whole pass — consistent contact is what keeps the miter even. Run it wet with the Water-Kit on hard porcelain to save your disc, and leave the very tip of the miter slightly back so the two faces meet tight and chip-free at the finished corner.