Revolving tailstock centres
The problem with most revolving centres is that they are bulky and often this can restrict access to the workpiece. This is because the revolving centre must contain at least two ball bearings within the housing. I came across a different type of revolving centre in a book called Lathe Accessories by E.T.Westbury.The centre described in the book required only one ball and it was extremely compact.
I made one of these centres and it worked well. At a later date I needed a cone centre to support some tube so I made a new revolving head. As time has gone on I have made more heads for different jobs as shown above. The set shown comprises, from left to right, the MT2 shaft, a 60 degree male centre, a 60 degree female centre, a revolving chuck, and a 60 degree cone centre that has a maximum diameter of 50 mm.
I made one of these centres and it worked well. At a later date I needed a cone centre to support some tube so I made a new revolving head. As time has gone on I have made more heads for different jobs as shown above. The set shown comprises, from left to right, the MT2 shaft, a 60 degree male centre, a 60 degree female centre, a revolving chuck, and a 60 degree cone centre that has a maximum diameter of 50 mm.
This photo shows the shaft and ball. The shaft was machined from a piece of 3/4" round bar. First the taper was cut and drilled and tapped 10 mm for a draw bar. The taper was then fitted into the headstock using a MT3-MT2 adaptor. The end of the bar was then turned down to be a close revolving fit in a 10 mm drilled hole. The tip of the bar was then centre drilled to form a 60 degree female cone to accept the ball. The ball should sit in the cone so that approximately half the ball diameter protrudes. The ball was salvaged from an old bicycle pedal shaft and was 6 mm in diameter.
This shows the 60 degree male centre. This was made from 3/4" round bar. This was chucked in the lathe and a 10 mm hole drilled in the end to accommodate the shaft. The shaft, complete with ball, should enter such that there is a 3 mm gap between the end of the bar and the shoulder of the MT2 taper. The bar is then cut off to a suitable length. The cut off piece was secured to the shaft using cyanoacrylate adhesive. The MT2 taper was put in the head stock using an MT2-MT3 adaptor and secured with a draw bar. The tip was then cut using the top slide to a 60 degree angle and the outer diameter skimmed. Remove the assembly from the headstock and warm up the conical head to soften the adhesive and pull it off. Clean the shaft and the conical head with acetone to remove any traces of adhesive. This method ensures tht the cone is accurately concentric with the shaft. Note the small 1 mm hole near the top of the conical head. This is drilled so that the drill penetrates into the conical cavity inside the piece left by the tip of the 10 mm drill. This hole is to provide an exit hole for the grease that is placed inside the piece when it is assembled onto the shaft.
This shows the assembled unit. The shaft is well greased before use and the ball placed in the tip of the shaft. A little grease is placed inside the conical head and this is placed on the shaft and it is ready to use. The head is much smaller in diameter than a conventional revolving centre.
The other centres were made in the same way. The conical hole for the female centre was formed using a centre drill. In this case there is no need to drill a grease escape hole because the centre dril pilot can penetrate into the cavity inside the head. For the large 60 degree cone centre a centre drill was again used to make a grease exit hole in the tip. The chuck centre was made from a 1/2" chuck salvaged from an old power tool. This had a 1/2" UNF female mounting thread. A piece was machined from 16 mm round steel bar that was bored out 10 mm to fit the revolving centre shaft. This was then stuck to the shaft with cyanoacrylate and mounted in the headstock. The outside was turned down and screw cut on the lathe to fit the chuck.
These centres have proved very useful for a number of jobs. They are very easy to make and the principle can be adapted to any other revolving centres likely to be needed in the future. In use they run quite cool although there is obviously a little more drag than with a conventional revolving centre. The male centre has been used quite often and the others less frequently and despite only being made from mild steel there is little evidence of wear on either the ball or the inside of the heads. I use Castrol MS3 grease for lubrication and this is loaded with molybdenum disulphide.
These centres have proved very useful for a number of jobs. They are very easy to make and the principle can be adapted to any other revolving centres likely to be needed in the future. In use they run quite cool although there is obviously a little more drag than with a conventional revolving centre. The male centre has been used quite often and the others less frequently and despite only being made from mild steel there is little evidence of wear on either the ball or the inside of the heads. I use Castrol MS3 grease for lubrication and this is loaded with molybdenum disulphide.