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Cut the drawbar to length, and predrill for the coupling, safety chain shackle and light cable outlet as per the drawing below.
Cut the drawbar brace and mark its centre to allow easy lining up of the drawbar. Square the drawbar brace with the drawbar, and tack weld together.
Once all components have been cut, lay them out in position on a flat surface, upside down.
Tack weld the crossmembers to the side chassis rails and square the frame by measuring from one corner to the other on both sides at identical positions. Once both measurements are the exactly the same, clamp or sand bag the frame securely. weld a couple of good strong tacks around the frame, checking regularly that the frame is still square,
Tack weld the front chassis rails to the frame with the drawbar and brace in position.
Tie a string line to the centre of the rear crossmember and run it under the centre of the front crossmember up to the end of the drawbar.
Using a square, align the centre of the drawbar with the string line. Check the drawbar alignment along its length. Double check the alignment by measuring from the front of the drawbar to a point on the chassis at identical points on both sides of the trailer.
When all measurements are identical, tack weld securely.
Check again for chassis and drawbar squareness and alignment, clamp or sandbag to secure and fully weld all components.
Once welded, grind off any excess raised weld on the outside corner of the chassis rails and fit the corner plates.
Weld the tiedown braces in position at the rear of the trailer.
Australian Trailer Builders -
Now is a good time to fit the safety chain to the trailer - the safety chain must be permanently attached to the trailer (welded) and the weld must extend around 50% of the circumference of the welded link and the adjoining link must have free movement.
Weld the safety chain as near as practicable to the coupling.