I have some large castors I want to fit onto a hen house. The floor of the hen house is 12mm plywood and there is an edging of 50x25mm timber round the edge below the floor.
The castors are on metal plates with four 10mm holes for fixing.
I could simply put bolts through the floor but I'd really prefer not to as I'd like to preserve the smoothness of the floor as far as possible to make it easy to clean etc. I'd also prefer to keep the henhouse as low as possible on the wheels, thus I'd like to minimise the thickness of anything I put below the floor to fix the castors onto.
Countersunk bolts through the floor would be OK but, 1) I don't have any and 2) I'm not really sure the 12mm ply would be string enough with the countersinking as you wouldn't be able to use washers to spread the load.
At present the best plan I can come up with is substantial chunks of (say) 18mm plywood fixed under the corners of the floor (the surrounding 25x50 will help) with 10mm bolts through in the right positions to fit the castors. The heads of the bolts would be buried in the 18mm ply (counterbore them) and you just use nuts to fix the castors. The 18mm ply will spread the load and can be screwed/glued to the 12mm floor.
However I fear the heads will turn when I one day want to remove the castors.
Can anyone come up with any better ideas for fixing these castors?