Thursday, 1 March 2012

Draw-bar Recovery (2)

In the last article dealing with the water ingress and carp-related damage to the rear draw-bar's cushion cavity, I got as far as getting some paint slapped on to protect it from further corrosion. Now I had to get to grips again with the steel plate rolling machine that I'd used on the ashpan walls.

This time, I did remember to use my camera a little more effectively!

The old cover plate measured 33 inches long and 11.5 inches wide. As continual footfalls had dented it, this time the plate was going to be thicker at 2mm (which is about 2/3 of an 1/8th of an inch!) and will possibly have some angle bracket welded underneath to make it even stronger. K M Steel Fabrications Ltd of Haydon, Radstock kindly supplied the sheet steel and cut it to size.

The rolling machine with sheet inserted ready to roll!
Great care has to be taken to ensure that the sheet enters the rollers at right angles to avoid a twist which would make the sheet unusable. There is no photo evidence of my accurate tri-square used to set the sheet in place (I haven't got enough hands to hold a square, move a metal sheet and use a camera simultaneously even with a tripod!). It pays to take one's time to set things up accurately to avoid regretting it later.
Lines were drawn for the folds and the start and finish of the curvature
I had a problem in that I could not see my lines for the start and finish of the curve as they had to be trapped at the rollers' pinch point.

By moving the start of curve line to be directly below the right side of the roller and making a mark directly below the left side of the roller, I could then make the 'HERE' mark half-way between the two roller side lines. Thus, putting the 'HERE' line to the left of the roller then made sure the line for the start of the curve was at the pinch point of the rollers. Same for the end of curve line only the other way round.

Put the 'HERE' line to the left of the roller...
...then raise the rear roller and wind the sheet through...
...then a bit more...
...until finally!
Ok, so I went a bit too far and had to do some unbending which is not as easy as it seems; it's supposed to be a smooth curve, not one with a gradual curve in places and something tighter in others. Again some patient, manual adjustment got it there in the end.

This is how it happens in practice (also on YouTube).

A flange was then required at each end of the sheet for the mounting holes. This was the first time I'd used a sheet metal bending machine since about 1972 but it wasn't difficult.

Sheet metal bending machine
The lever without the counter-weight raises and lowers the clamping mechanism that hold the sheet in place. The lever with the counter-weight does the work.

So, having clamped the sheet in place at right angles to where you want the bend, it's simply a matter of raising the handle at the front like this (also on YouTube):

Note that, owing to only having two hands, the plate was already bent and the video is for illustrative purposes only!

And the final result:

The new cover plate with template; the old cover plate is above!
Now just some paint, drill a few holes, fix it in place and try standing on it. Then consider welding an angle iron reinforcement below the top for strength (and preferably before painting it!).

My thanks are due to Lackham College, Lacock, Wiltshire, for letting me skive-off my Monday evening welding class to do metal forming instead. It's all part of the fabrication process, honest!


  1. I always read this blog on the Google reader but never know what to say - today is little different - it's all so alien to me; quite fascinating in its way though.

  2. Via the blog, I'm keen to show how it's done and what lies beneath the surface. Being described as 'alien' probably means I am actually succeeding in showing things that are no longer familiar to people.

    Now what is Google Reader for?

  3. Link to K M Steel Fabrications updated as requested.


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