About the year 1797 Maudslay commenced business on his own account in Wells Street, Oxford Street, removing a few years afterwards to Margaret Street, Cavendish Square. Here he matured and carried out many improvements in tools connected with the mechanical arts, bringing into general notice and use planing machines and the slide rest. So great was the prejudice felt against this last named important adjunct of a lathe, that on the first introduction of the slide rest to the engineers of the period, it was received with great disfavour, and called by one in derision the 'Go Cart.' Maudslay also directed his attention to the subject of screw cutting. Previous to his time the tools used for making screws were of the most rude and inexact kind: each manufacturing establishment made them after their own fashion, and no system was observed as to the pitch. Every bolt and nut was a speciality in itself; and to such an extent was this carried that all bolts and their corresponding nuts had to be marked, any mixing of them together causing endless trouble and confusion. Maudslay changed all this--he brought screw-cutting into a proper system, and laid the foundation of all that has since been done in this important branch of machine-construction, and many of those who afterwards became eminent in this particular branch of manufacture, acquired their first knowledge of the subject in his employ.[25] While residing in Margaret Street he became acquainted with Sir Isambard (then Mr.) Brunel, who was in the habit of bringing drawings of small pieces of machinery for him to construct: this attracted Maudslay's attention, and at last he one day exclaimed to Sir Isambard, "Ah! I see what you are thinking of--you want machinery for making blocks:" this so pleased Brunei, that he became more open of communication, and in the subsequent completion of the beautiful block machinery afterwards erected at Portsmouth Dockyard, Mr. Brunel derived great advantage from the sound mechanical knowledge of Maudslay. The friendship commenced thus was never afterwards shaken, and when Brunel began the Thames Tunnel, he consulted his old friend relative to the construction of the shield, as it was termed, under shelter of which the excavation beneath the bed of the river, and the brickwork for forming the Tunnel were proceeded with.