Started work on the other pair of legs. Installed the crush tubes and welded in the cross piece.
Drilled and welded two bits of box that will hold the lifting bar in place then cut the lifting bar and crossed drilled it. For cross drilling I used a trick I got from the internet to check if the drill was on the centre line. I used a small rule that I held in place with the drill bit, when its level your on the centre line. Funny thing is I've used this method to set lathe tools to centre but never thought about using it for cross drilling.
Cut a piece of box section to go over the lifting bar and that was pretty much job done for the lifting mechanism.
Here it is assembled
I threw everything together to see how it looked (metal for the crush tube hasn't arrived so everything is a bit sloppy at this stage).
I'm slightly disapointed by the max height available using the cheap jack I have which is why I've lifted it up on planks in the picture above. I might experiment with moving the lifting mechanism (or rather having a couple of positions I can have it).