I am just building mine now and have a big issue with the centre shaft. When I put it in its right on the edge of the holders and when I turn the spur it comes out. If its positioned perfectly central it stays in but as soon as I turn the spur it moves one way or the other slightly and drops out. I have already put the holder at the front end right on the edge of the cut out on the shaft so can't move it any nearer to the edge. What can I do as its useless at the moment?