What they are

High-precision cast-iron T-slotted plates are rigid fixture bases made from gray cast iron (commonly EN-GJL-250 / GG25 / HT250). The working face is precision-machined (often fine-milled, ground and/or hand-scraped) and contains T-slots to DIN 650 (or JIS) so standard T-nuts, studs, step blocks and clamps can be used anywhere on the surface.

Why cast iron

• Vibration damping: graphite flakes in gray iron dissipate cutting forces better than steel, improving surface finish and tool life during setups on the plate.
• Dimensional stability: after stress relieving (thermal aging) and a ribbed underside, the plate resists creep and bending under heavy clamping loads.
• Machinability / wear: typical hardness ~170–220 HB with good bearing properties for scraping.

What they’re used for (metalworking)

• Flexible workholding/fixturing: build modular jigs for odd-shaped parts, large weldments, dies, molds, gearboxes, engine blocks, etc.
• Assembly & layout: square, mark out, and assemble sub-systems to tight datums referenced to the plate’s flat face and slot lines.
• Process and test benches: bases for drilling units, line-boring bars, rotary tables, or endurance/pressure test rigs.
• Inspection & rework: when you must clamp the part (unlike granite plates), you can still perform height-gauge checks, runouts, and straightening.

Key technical features

• Flatness class: top face finished to a specified DIN 876 grade (e.g., Grade 1 or 0 for “high-precision” plates).
• Slot standard & accuracy: T-slots to DIN 650 (common nominal widths 14/18/22/28 mm) with controlled parallelism/position to the datum edges.
• Structure: thick deck with boxed ribs below; leveling pads or jack-screws at defined support points; lifting holes/eyes for safe handling.
• Edges & protection: chamfered edges, coolant/drip grooves, non-working faces painted; rust protection on the working face.
• Scalability: supplied as single plates or floor plates that bolt together and can be grouted into a foundation for large installations.
• Variants: T-slotted angle plates, box cubes, and bridge risers to fixture vertical faces.

Typical manufacturing route

1. Patterned casting → natural/thermal stress relief.
2. Rough machining → secondary stress relief.
3. Finish milling/grinding; optional hand scraping to reach final flatness and bearing pattern.
4. T-slot machining to standard; inspection for flatness, parallelism, and straightness; preservation.

When to choose them vs. granite surface plates

• Choose cast-iron T-slotted when you must clamp and apply load (machining, straightening, assembly).
• Choose granite when you need the highest metrology stability with no clamping (pure inspection).

Installation & care (brief)

• Support only at specified leveling points to avoid distortion; if used as floor plates, grout after alignment.
• Keep oiled and clean; deburr parts before clamping; cap unused T-slots to keep chips out.
• Periodically verify flatness and re-scrape when needed.

In short: these plates are the modular, vibration-damping “ground truth” and clampable datum for building, machining, and checking heavy or complex workpieces across the metalworking shop.