Activity 001: Joint Preparation & Fit-Up Practice¶
Activity ID: U6M1-ACT-001 Duration: 40 minutes Objective: Students will prepare metal coupons for welding by grinding, cleaning, fitting, and tack welding the five basic joint types. Group Size: 2 students
Overview¶
Before welding, proper joint preparation determines 80% of weld quality. Students will practice cutting, grinding, cleaning, and fitting mild steel coupons into butt, lap, T-joint, corner, and edge configurations, then tack weld each to hold the assembly for future welding practice.
Materials & Equipment Needed¶
- 10 mild steel coupons: 3" Γ 6" Γ β " (2 per joint type)
- Angle grinder with flap disc (80 grit) and cutoff wheel
- Wire brush (hand) and/or wire wheel for grinder
- Acetone or degreaser and shop rags
- Welding clamps and magnets (90Β° magnetic squares)
- MIG or TIG welder (for tack welds only)
- Gap gauge or feeler gauges
- Combination square
- Soapstone or marker
- PPE: Safety glasses, face shield (grinding), leather gloves, welding helmet (for tacking)
Instructions & Procedure¶
Phase 1: Material Preparation (10 minutes) 1. Inspect all 10 coupons for excessive rust, mill scale, paint, or oil 2. Use the angle grinder with flap disc to remove mill scale from 1" on each side of all joint edges β grind to bright, shiny metal 3. Use acetone and a clean rag to degrease all joint surfaces 4. Wire brush all joint edges to remove any remaining surface contamination 5. Inspect edges β they should be bright silver with no discoloration
Phase 2: Joint Assembly (20 minutes) Assemble each joint type using clamps and magnetic squares:
Butt Joint 1. Place two coupons edge-to-edge on a flat surface 2. Set a gap of 1/16" (use a feeler gauge or thin nail) 3. Ensure the pieces are level and aligned β check with a straightedge 4. Tack weld at both ends and center (3 tacks total, ~ΒΌ" long each)
Lap Joint 1. Overlap two coupons by 1" β measure and mark 2. Ensure the overlap is consistent along the entire length 3. Clamp or hold flat 4. Tack weld at both ends on one side
T-Joint 1. Stand one coupon vertically on the center of another (horizontal) 2. Use a 90Β° magnetic square to hold perpendicular 3. Check 90Β° with a combination square on both ends 4. Tack weld at both ends on one side
Corner Joint 1. Place two coupons at 90Β° forming an open corner 2. Use magnetic square to maintain angle 3. Ensure edges are flush 4. Tack weld at both ends
Edge Joint 1. Place two coupons parallel, edges aligned and touching 2. Clamp together 3. Tack weld at both ends along the top edge
Phase 3: Inspection & Assessment (10 minutes) 1. For each assembled joint, verify: - Gap is consistent (butt joint) - Overlap is consistent (lap joint) - Angles are correct (T-joint: 90Β°, corner: 90Β°) - Tack welds are secure β gently tap each assembly; nothing should move - Edges are clean and free of grinding debris near the joint 2. Label each assembly with joint type and your name 3. Store for use in subsequent welding activities
Discussion Points¶
- Why is it important to remove mill scale before welding?
- What happens if the butt joint gap is too wide? Too narrow?
- How does the 90Β° angle on a T-joint affect the final weld strength?
- Why are tack welds placed at the ends rather than the middle?
Expected Outcomes¶
- Students can prepare metal surfaces to welding-ready condition
- Students can assemble and tack all 5 joint types with proper fit-up
- Students understand that preparation quality directly affects weld quality
Assessment Rubric¶
| Criteria | Excellent (4) | Proficient (3) | Developing (2) | Beginning (1) |
|---|---|---|---|---|
| Surface Preparation | Bright metal, no contamination, consistent grinding | Good preparation with minor areas missed | Adequate but inconsistent | Poor preparation, contamination remaining |
| Fit-Up Accuracy | All gaps, overlaps, and angles within tolerance | Minor deviations in 1-2 joints | Several joints out of specification | Cannot achieve proper fit-up |
| Tack Weld Quality | Secure, correctly sized, properly placed | Mostly secure with minor placement issues | Some tacks too large/small or misplaced | Tack welds fail to hold assembly |
| Safety Compliance | All PPE, proper grinder technique, clean workspace | Minor safety reminders needed | Multiple safety corrections | Significant safety concerns |
Safety Considerations¶
- Face shield AND safety glasses required during all grinding operations
- Leather gloves required when handling hot or sharp metal
- Secure workpiece in a vise or with clamps before grinding β never hold small pieces by hand
- Angle grinder guard must be in place at all times
- Remove all combustibles from the grinding area (sparks travel 10+ feet)
- Welding helmet required for all tack welding
Last Updated: 2026-03-19