Fit, Clamp, and Tack Weld a Small Steel Assembly

A. Finished-Project Specification

Outcome: one small, noncritical mild-steel frame or bracket assembly, fit up from parts on the approved shop drawing and cut list, squared within the drawing tolerance, held with balanced sound tack welds, and released through a signed pre-weld fit-up acceptance record. No final welding is performed as part of this chapter's finished work; final welding is Chapter 17's scope.

B. Component Schedule

Component	Quantity	Source	Condition Before Fit-Up
Frame or bracket members	Per approved cut list	Cut, deburred, and cleaned in Chapters 4–6	Verified against cut list, identified, weld zones clean
Temporary strongbacks or spacers	As specified by the shop drawing, if any	Shop stock	Clean, undamaged, matching the specified size

This chapter does not introduce new parts beyond those already produced in Chapters 4 through 6. Do not substitute an unlisted part, a different thickness, or a different joint configuration for the approved cut list.

C. Material Takeoff

• Steel parts: the full set of identified mild-steel parts already produced and inspected in Chapters 4 through 6, matching the approved cut list in quantity, size, and condition.
• Tack-weld consumable: the same SMAW electrode or GMAW/FCAW wire classification and diameter recorded for this material and thickness in the applicable process chapter.
• Temporary fixturing stock: strongbacks, spacers, or stops only where the shop drawing approves their use; none invented beyond the drawing's specification.
• Consumables beyond tacking: none. This chapter does not perform final welding, grinding, or finishing.

D. Acceptance Standards

Check	Standard
Part verification	Every part matches the approved cut list in identifier, material, size, and condition before layout begins
Reference edge and origin	A single reference edge and assembly origin is used for every layout measurement
Overall dimensions	Length and width match the drawing within the stated tolerance
Diagonals	Both diagonals are equal within the drawing tolerance before and after every tack sequence
Flatness	The assembly lies flat against the layout table within the drawing tolerance
Clamping	Every joint is clamped without lifting parts from the table and without blocking weld or inspection access
Tack quality	Every tack is free of cracking, porosity, poor fusion, and excessive size, and falls within the approved location and length range
Tack sequence	Tacks are placed in the planned balanced order recorded on the traveler or drawing
Release condition	Pre-weld fit-up inspection record is complete and signed before any final welding is authorized

E. Preparation — Drawing Review and Part Verification

1. Review the approved shop drawing, dimensions, tolerances, material, joint type, process, tack plan, and final weld sequence. Confirm the drawing revision matches the parts on hand.
2. Verify every part against the cut list. Check each part's identifier, quantity, material, and size against the approved cut list before continuing.
3. Inspect part length, angle, squareness, bevel, burrs, cleanliness, and identification. Confirm each part meets the acceptance standard set in Chapters 4 through 6.
4. Reject or correct parts outside tolerance before assembly. Return an out-of-tolerance part to the cutting or grinding process rather than fitting around the error.
5. Clean the table, fixtures, squares, clamps, magnets, stops, and contact surfaces. Remove oil, scale, and debris that could affect layout accuracy or clamp contact.

F. Layout, Squaring, and Clamping

1. Establish a primary reference edge and assembly origin. Mark the origin on the table and confirm it will remain fixed for the full fit-up sequence.
2. Lay out the first two parts against stops or layout lines. Position each part from the reference edge, not from the previously placed part.
3. Verify orientation, inside and outside faces, and joint location. Confirm each part is installed in the orientation shown on the drawing.
4. Set the specified gap or contact condition. Use a gauge, spacer, or shim to hold the approved gap rather than estimating it by eye.
5. Clamp the first joint without lifting parts from the table. Confirm the clamp holds full contact with the table or fixture surface.
6. Add remaining parts in the specified order. Follow the drawing's assembly sequence rather than an order of convenience.
7. Use a square to check corners. Check every corner the drawing identifies as a right angle or specified angle.
8. Measure overall length and width. Record both measurements against the drawing tolerance.
9. Measure both diagonals on rectangular assemblies. Record both diagonal measurements before any tack is placed.
10. Adjust the assembly until dimensions and diagonals meet tolerance. Reposition parts, not clamps alone, to correct an out-of-tolerance reading.
11. Verify flatness against the table. Use a straightedge across the assembly to confirm it lies flat within the drawing tolerance.
12. Add temporary strongbacks, spacers, or stops only as approved. Do not introduce a fixturing method the drawing does not call for.
13. Confirm clamps will not block torch, gun, electrode, or inspection access. Reposition any clamp that would require the tack to be placed blind or at an unsafe angle.

G. Tack-Weld Planning and Placement

1. Plan tack locations to balance shrinkage. Identify a sequence that alternates sides and corners rather than tacking around the assembly in one direction.
2. Attach the work clamp to clean sound metal on the assembly or fixture as approved. Confirm the clamp location matches the drawing or fixture instructions.
3. Set and record the approved welding parameters. Use the machine, consumable, polarity, and setting recorded in the applicable process chapter for this material and thickness.
4. Place the first tack at the specified location. Confirm the tack falls within the approved location and length range before proceeding.
5. Allow brief cooling as required. Do not proceed to the next tack while the previous tack area remains too hot to inspect safely.
6. Place opposing or balanced tacks in the planned order. Follow the recorded sequence rather than tacking the nearest untacked joint.
7. Keep tack size and length within the approved range. Confirm each tack matches the size specified for this material thickness and joint.
8. Do not place unnecessary oversized tacks. An oversized tack increases shrinkage and is harder to incorporate cleanly into the final weld.

H. Tack Inspection, Dimensional Recheck, and Release

1. Inspect each tack for crack, porosity, poor fusion, crater, and contamination. Clean the tack before inspecting it if slag or spatter obscures the surface.
2. Remove defective tacks using the approved method. Do not weld over a cracked, porous, or poorly fused tack.
3. Recheck dimensions, diagonals, squareness, gap, and flatness after each tack sequence. Compare every reading against the drawing tolerance before continuing.
4. Correct movement before adding more weld metal. Reposition and reclamp the affected part rather than tacking around an out-of-tolerance condition.
5. Do not force a severely distorted tack-welded assembly into position. Remove and replace the tacks causing the distortion instead.
6. Add required intermediate tacks. Complete the planned tack sequence once dimensions and diagonals are confirmed in tolerance.
7. Clean tack welds if they will be incorporated into final welds. Remove slag and spatter from tacks that Chapter 17 will weld over.
8. Blend tack ends where the procedure requires it. Taper the tack ends only when the approved procedure calls for it.
9. Mark the planned final welding sequence on the drawing or traveler. Record the order Chapter 17 will follow to balance heat input.
10. Release selected clamps gradually and observe movement. Watch for spring-back or shift as each clamp is released.
11. Reclamp only through the approved correction method. Do not reclamp by forcing a part that has already moved out of tolerance.
12. Complete the pre-weld fit-up inspection. Verify every item in Section D against the physical assembly.
13. Record part dimensions, gaps, diagonals, tacks, distortion, corrections, and accepted fit-up. Complete the fit-up and tack record established at the start of this chapter.
14. Do not begin final welding until the assembly is signed off. Hold the assembly for Chapter 17 only after the responsible person signs the pre-weld fit-up acceptance record.