The JGRO design achieves linear motion using bearings running along pipes. The bearings are made from standard skateboard bearings bolted to aluminium angle. There are 3 pairs of bearings, a pair for each axis of motion, and each pair a different size. These bearings run along metal pipes, 0.84 inch diameter gas pipes for the Z (up and down) axis and the X (side to side) axis. I can't find these gas pipes in the UK so I am using cold rolled steel tube for the time being. The Y axis uses thicker 1.3 inch diameter gas pipe, which is not easily available in the UK. I am going to use 1.5 inch diameter chrome plated steel handrail for this axis, but if this proves unsuccessful I will modify the bearings and use square cold rolled steel tube.
The pipes are supported at either end by adjustment blocks. The plans call for MDF for these blocks but some forum members at cnczone have had better success with HDPE (high density polyethylene) a plastic that is easy to machine and will hold a thread well. I used HDPE from kitchen chopping boards: these were 0.5 inches thick rather than the 0.75 inches in the plans so I will need to use some spacers to get the correct clearance.
The plans are drawn up with American hardware stores in mind and use imperial measurements in all cases. Unfortunately UK hardware stores use metric sizes so it has been impossible to replicate the plans exactly. In most cases the UK stock is thinner, for example the available aluminium angle is much weedier than the American equivalent (value engineering I think!) and the 0.75 inch MDF is actually 18mm in the UK! All the nuts, bolts and machine screws have to be substituted for the closest metric size. It has also been difficult to find threaded rod in lengths greater than a metre, and ordering long lengths by mail runs the risk of them bending in the post. Having said this the plans are excellent and if you proceed carefully, making sure things will fit as you go along (before drilling etc.), it is not too difficult to work with metric stock.