Harold Hall

Workshop Projects

Workpiece Positioning Fixture for the Rotary Table, Harold Hall

I developed the subject of this project when making my Lathe Milling Head and using  the head to make the steam engine “Tina”. I have made reference to the fixture elsewhere on this site and both in my magazine articles and books, but only with a sketch showing the basic idea, I decided therefore that dimensioned drawings for the parts would be worthwhile.  Even if the dimension do not suit the rotary table that the viewer possesses it will be easy to modify  them to suit, though as almost all rotary tables have four tee slots the dimensions given should do for all but the largest tables.


I have described the main features of using a rotary table elsewhere on this web site, which the viewer should read if its use is not fully understood, but will very briefly mention here the basic requirements.


First, it will be necessary to mount the rotary table onto the milling machine table so that it is concentric with machine's spindle. With that done it is then very often the need to mount the workpiece with a particular aspect of it concentric with the rotary table. With a large part it can be located onto a central locater and clamped to the table with clamps around the workpiece's periphery.


Often though a part is very small and needs to be secured using a screw through the  hole located on the central locater. Unfortunately, there is nowhere solid that the screw can be screwed into. Providing a secure tapped hole to take the fixing screw is the main feature of the device in this project. Photograph 1 shows the parts that make up the assembly with two or more of some parts to cope with different workpiece diameters. The photograph was taken using a mirror to show the rear of the Upper Plate (B)


However, the hole in the workpiece will vary from part to part and some will only have relatively light work being done on it whilst for others it will be a much heavier task. Also, the hole in the workpiece will vary from a few millimetre to very much larger. It is necessary therefore to provide for differing sizes of clamp screws in the Rotary Table and Upper Plate Locator (A) and  Workpiece Locaters (C). Whilst two sizes of clamp screws will probably suffice, certainly no more than three, there will be a need for very many more workpiece locaters. The design has therefore been produced so as to make it possible to make additional locaters with the minimum of work.


Photograph 2 shows it in use with a very small part and having to use an M3 workpiece securing screw, whilst the part is much bigger in Photograph 3 and uses an M6 screw. Obviously, the workpiece locaters were also quite different diameters.



The main requirement is concentricity between diameters and for parts to fit with minimal clearance so not to effect the accuracy of the final assembly in terms of concentricity. The drawings have more details relating to these requirements .

Rotary table workpiece locater
Rotary table workpiece locater
Rotary table workpiece locater








All pictures can be clicked on to provide a larger view