Trailer frame rebuild - Ep4

Carried an extra two 4m lengths of steel stock to the boatyard on the ute racks. (A 3x2" RHS for a draw bar and a 3x1.5" 4mm walled rolled galvanized channel)

Studied the Orcon steel product catalog for the weights per meter. The main aim is to keep the trailers weight similar to the original   This is so it's not any heavier than before so my existing back-wheel drive 2.7 litre light ute can haul the whole rig up a steep boat ramp and along the highway.

(3x2") RHS 75x50x3mm = 5.42kg/m - this is the standard building material of Teria's old style trailer.

 75x40mm "heavy" channel = 5.92 kg/m - For the lead keel bearing cross beams, realized this was lighter than i first imagined, it has 4mm side wall, 6mm parallel flanges and square corners.

75x40mm "light" galvanized channel = 4.07kg/m.-  4mm walls, parallel flanges and rounded rolled corners. For the forward cross beams which should bear the less heavy load of the boats bow.

Tacked the outside beams onto the base jig

First job was to tack weld the rear RHS beams to the old frame (building jig) and remove the holding clamps. Getting the A frame RHS leveled aligned, joins prepared and tacked.

RHS join is fabricated with square ends, then bevels are added - for good weld penetration.

RHS join - tack welded

Temporary bar tacked on to hold front end

Keel cross beams

Teria's trailer has the most difficult keel cross beams to make - 3 piece with a horizontal middle segment for the keel base. (Other trailers cross beams are easier - 2 piece V-beams, even one piece straight beams). But the advantage of the 3 piece beam is the keel is at the lowest level of all relative to the road surface, in conjunction with a drop-axle).

Template for the keel bearing cross beams.

Found an old sheet steel box (kept from an old double flouro light, it eventually did have a use!) which happened to be nearly the right size and cut one end to fit between the RHS side beams aft. Pencil traced the profile of the old aft cross beam onto it. Then measured it up and scribed (sharpened round steel file end) the beam shape into the surface. For the joins, used a protractor to bisect the angle and get the half way angle required to join the 3 pieces of the beam evenly.

Made a template for the keel bearing cross beams

The material I used was the plain "black" 3"x1.5" heavy channel.  For the aft  beam, It's concave side was faced forward so an aft roller can be later fitted to guide the boats keel up onto it. (this may catch a bit of road mud in use but it can be easily hosed off)

The first beam is the hardest to fit up correctly.working off the template, laid flat on the ground makes the process easier. I cut the pieces off square a few cm longer than needed, then had a workable length. to scribe the correct join angle on. Also marked with white engineering chalk, easy to see on plain steel.

The 9" grinder with a cutting wheel sliced through it. A 5" grinder with grind disc did the final trim back to the scribe line. Builder's squares and adjustable angle helped. The parallel flanges on the channel make it easier (tapered flanges would be very hard). Safety gear was poly-carbonate face shield, ear plugs, weld glove, weld apron, weld spats (boot covers).

A steel cut-off wheel machine on a long work bench would be the ultimate, to set the angles and cut squarely every time - allot faster and accurate at first pass. but the good brands cost over $300.

Test fit the first two pieces (NB Wheels and drop-axle rolled out to measure the dimensions to fit new RHS frame)

Aft keel frame - aligned on template, butt joins tolerance good.

A steel plate over hanging the bench frame makes it easy to clamp work piece for cutting/grinding end.

Joins beveled then, tacked together, no distortion seen against template.

Fitting, beveling, tack welding and full welding the pieces together reminded me of building the frames for my wylo2 yacht, but that was back in 1989! Been a long while, old brain cells vaguely remembered that distortion which bends the frame out of  design shape must be stopped.

The first steps are in the weld preparation, the butt joins must meet accurately. Next the join edges are beveled to allow good weld penetration, used a 45 degree angle but it may have been too wide, it's probably a bit tighter about 30-40 degrees. 

 Tacked at opposite points on the join first, which kept the frames in shape on template.

 Then the first fitting, it worked.

The aft keel frame fitting. 

Angled cross beam cut on angle is 12mm wider than 3" (75mm) RHS box section beam

However discovered that the cross beams vertical join to the RHS is a bit wider than the RHS, about 6 mm sticks above and 6 mm below, should weld up OK. 65 mm wide steel stock would be ideal but may not exist, the next steel size down was 50 mm (2") , some trailers used this in square box section form, 2" channel may not be strong enough.