Shaping Frames in Metal Construction
What steps does a metalworker undertake to form a frame from a section angle iron (L-section)?
What tools, equipment and machinery does he require for this?
It is assumed that a “spits” type of boat is being newly built. The yard has the lines plan and already has experience of building these types of boats. The tools required are present in the workshops. The office instructs the workshop to produce the frames required. The bottom is riveted together first and then serves as the basis for fitting the frames.
The photograph shows a boat (on the left) with the frames already in place on the bottom. For the “spits” on the right (bottom) in the photograph the bottom is placed and frames are stacked ready for fixing to the bottom.
First we will look at the tools, equipment and machinery required and in the second part we explain the successive steps to form a frame.
Tools, equipment and machinery required for turning an L-section into a useable frame
1.Clamp 2.Frame 3.Jig
These are used to hold the frame in position next to the jig
This buckling is hammered flat using the hammer
The frame that is now ready for fitting after it has already undergone the necessary processes
The workshop must have basic equipment consisting of a forge and a draw bench.
Various jigs on which the frames will be formed. The jigs are numbered according to the lines plan.
Which are used to position the jig on the draw bench.
The clamp is used to clamp the frame to the jig.
These are used to hold the frame in position next to the jig.
This tool is used to apply the curvature to the heated frame.
When bending the frame the metal will buckle. This buckling is hammered flat using the hammer.
Wedges are used where the setting pins or the clamp offer insufficient connection with the jig.
Successive processes that an L-profile is subjected to in order to create a frame suitable for fitting
- Selection of the iron or steel by length and thickness
This depends on the location at which the frame is to be fitted. For a “spits” lengths of 3 metres are used for the centre section. This thickness can vary according to the location of the frame in the boat, or the boat’s sailing area, or the individual wishes of the shipping firm/owner-skipper. The majority used a frame thickness of 6 mm.
- People know from experience what curvature a specific frame requires. The frames are numbered on the lines plan.
The jigs to be used for forming the L-section are also numbered. For the next processes we will assume a frame that has to be bent 90°. Frames with a 90° bend are used for the centre section of the boat that takes up approximately 32 of the total length of 39 metres.
- Place the selected jig onto the workbench (draw bench) and secure it using the locking pins. These locking pins are tightened against the underside of the draw bench using a nut.
- Heat the L-section at the correct location. This is the location where the bend is to be made. The L-sections for a “spits” were cut into 3-metre lengths, with the bend being made approximately 65 cm from one end. The heating is undertaken in a forge. Once the metal is white hot it is placed on the draw bench and secured at one end to the jig using a clamp.
- Forge with L-section. The greatest heat is achieved in the centre using a blower system. The forge was mainly used for forming L-sections. Cut-outs have therefore been made in the edge of the forge into which the L-section drops. This gives purchase and makes the work a lot easier.
- First of all the L-section has to be secured on the jig.
The jig with the L-section on two of the three free sides. The L-section is held against the jig using a clamp and, if necessary, extra wedges. To keep everything together the clamp is hammered down using a sledgehammer.
- Draw the L-section to the correct curvature.
The L-section is bent to the right by using body weight (leg push) and by operating the gaff using the left hand. The buckling occurring during this process is hammered flat at the same time using the forge hammer. You have to work fairly quickly to achieve a 90° bend. The L-section is only heated once. Two people are required for bending. The shaper who operates the gaff and draws the L-section over the jig until the required angle is achieved, and a helper who uses the forge hammer to hammer out the buckling in the heated metal.
Jig with a 90° bend
Plan with numbered frames
Jig with locking pins