Key Selection Points for Granite Machine Bed Lifting Tools

Granite machine beds (marble bases) are highly brittle, sensitive to impact and local compressive stress, and strictly prohibited from being squeezed by single-point hard clamping. The lifting methods for cast iron beds cannot be directly applied. The core principles are: uniform force distribution, flexible contact, avoidance of edge stress concentration, and prevention of slipping or bumping.

Risk Warning: Granite is brittle. Improper lifting can easily cause invisible internal cracks, leading to cracking and scrapping during later processing and use. Prioritize safety protection.

I. Confirm Basic Parameters First (Prerequisite for Selection)

1. Weight: Net weight of the bed including accessories, with a reserved safety factor of 1.2–1.5;
2. External Structure: Presence of pre-cast lifting bolt holes or lifting slots; whether it is a plain solid granite block; whether edges are chamfered; thickness, length, and width;
3. Permissible Loading Positions: Granite only allows loading at designated lifting points; arbitrary binding on sides or edges is prohibited;
4. Surface Protection: Working surfaces and reference surfaces must not be damaged or scratched by lifting tools.

II. Comparison of Lifting Tools and Applicable Scenarios

1. Lifting Bolts Eye Bolts (Preferred choice for beds with pre-embedded bolt holes)

Suitable for: Granite machine beds / granite platform bases with factory-prefabricated threaded lifting holes

• Selection: High-strength eye bolts (alloy steel), strictly matching thread specifications and screw-in depth, must be tightened completely to the bottom;
• Ключевые моменты:
• The force direction of the eye bolt should be as vertical as possible; lateral diagonal pulling is prohibited. Diagonal pulling significantly reduces the eye bolt’s load capacity and introduces splitting stress to the granite around the bolt hole;
• There must be no chipping or cracks in the granite around the bolt hole;
• Use shackles synthetic fiber slings; do not hang the eye bolt directly with steel wire ropes.
  Note: The embedded threaded sleeve in granite is not cast iron; do not overload the eye bolt to prevent the threaded sleeve from being pulled out.

2. Synthetic Fiber Flat Slings (Most commonly used, flexible lifting)

Suitable for: Plain granite without lifting bolt holes, bottom-support lifting
✅ Advantages: Flexible, will not chip edges, and does not scratch the granite reference surface
❌ Prohibited: Do not bind granite directly with ordinary steel wire ropes. The sharp edges of steel wire ropes will crush the stone edges and create hidden cracks.
Selection:

1. Load: Rated load of the sling ≥ bed weight × 1.5 safety factor;
2. Prefer wide flat slings to widen and disperse pressure. Narrow slings create line pressure that can crack the granite;
3. Corner positions must be equipped with corner protectors (rubber / polyurethane corner sleeves). When the sling wraps around a right angle, corner protectors must be used to prevent the edge from cutting the sling and crushing the stone simultaneously;
4. For bottom-support lifting, the sling angle is recommended to be 60°–90°. The larger the angle, the load on the sling increases exponentially; angles > 120° are strictly prohibited.
   ❗ It is not recommended to lift by directly cradling the short side, as it is prone to slipping and tipping over. Prioritize four-point bottom support.

III. Recommended Lifting Solutions for Different Bed Structures

1. Bed with Pre-embedded Lifting Screw Holes

Best Solution: Eye bolts shackles flat synthetic fiber slings, four-point lifting.

2. Solid Smooth Granite Bed without Lifting Holes

Solution: Four-point bottom support with wide flat slings, all corners fitted with rubber corner protectors, soft pads placed underneath, confirm slings will not slip before lifting; lift as horizontally as possible, dragging at an angle is strictly prohibited.

3. Thin Granite Base (Small Thickness)
   Two-point lifting is strictly prohibited as it is extremely prone to breaking in the middle; multi-point bottom support must be used to increase the contact area and reduce bending stress.

IV. Critical Prohibitions (Common Pitfalls)

1. ❌ Directly binding granite edges with steel wire ropes will cause internal hidden cracks;
2. ❌ Using ordinary steel plate lifting clamps to hard-grip granite sides;
3. ❌ Pulling pre-embedded screw holes at an angle with eye bolts;
4. ❌ Using slings without corner protectors directly against granite right angles;
5. ❌ Single-point or two-point lifting of large-sized thin beds, causing bending stress cracks;
6. ❌ Dragging, bumping, or hard impact upon landing; rubber mats and wooden blocks must be placed underneath the landing area, direct hard contact with the ground is prohibited.

V. Supporting Auxiliary Tools

1. Rubber corner protectors, thickened rubber mats;
2. Shackles (alloy steel, load-matched);
3. Wooden blocks / rubber buffer pads (for landing support);
4. Secondary safety backup slings to prevent accidental slipping.

VI. Simple Selection and Judgment Steps

1. Check if the bed has pre-reserved lifting screw holes → If yes, use eye bolts slings;
2. No lifting holes → Select wide flat synthetic fiber slings for bottom support, with a full set of corner protectors;
3. Calculate weight, ensure the rated load of lifting gear is ≥ 1.5 times the workpiece weight;
4. Confirm lifting point positions to ensure the workpiece remains horizontal after lifting;
5. Protect all edges and corners, direct metal contact with the granite body is prohibited.