I had a problem with Robarts binding that I traced to the four pieces of threaded barstock that space and support the side frames. They were not all the same length. Micrometer or calipers required to measure the difference. I had dissassembled and did not get them back in exactly the same position. This caused the cross bar on the end of the cylinder rod to bind up in the side frames. I don't remember if I shimmed them or just matched them for reassembly, but They worked fine after that.