An Alternative to the Four Jaw Chuck. Page 1.
Workshop Projects
The following lists what I consider to be its plus and minus points
Minus points
On the minus side I can only suggest that in a few cases it takes a little more time to initially set up.
Plus points.
1. Can use a mix of jaws and workpiece clamps
2. Has deeper jaws than a comparable sized chuck, *35mm compared to 20mm
3. With the jaws still within the perimeter of the body it takes much larger diameters , *83mm compared to 58mm
4. Total projection from the lathe's mandrel mounting surface is less, *65mm compared to 73mm
5. Much more adaptable for complex shaped workpieces
6. Reversing the jaws, which is a slow process, is not required.
7. Much easier to keep the mechanisms clean.
8. With two clamp screws in each jaw it is possible to set a long length of bar true, both next to the jaws and at its end .
9. Without any jaws fitted there is a very robust faceplate having the advantage that, with tee slots, there is no need to access nuts or screw heads at the rear using a spanner. This leaves the second hand free to assist with placing the workpiece on the front of the faceplate.
*Comparisons with a four jaw chuck and are with my 6” four jaw chuck.
Page 2 includes some brief notes regarding its manufacture together with photographs of a few of the processes, links to the drawings are also included. However, if a more detailed explanation is required a detailed constructional article was published in the Model Engineers’ Workshop Magazine Issues 157/8.
Page 2
When considering the chuck's manufacture only the body presents a problem the remaining parts are very straight forward, I am not therefore including any suggestions as to how they should be made.
The main problem with the body is getting the tee slots accurately placed, even here, if a suitable rotary table is available, the task should be a relatively easy one. However, as a sufficiently large rotary table is unlikely to be available in most workshops, I am proposing an alternative method that should be as easy, if not easier than using a rotary table.
First drill and tap four holes M6 x 12mm deep on one face and on a PCD to suit the faceplate on which it is to be held. Hold it on the faceplate, using some spacers so that the boring tool can break through, machine the bore and make the thread for the mandrel nose, also surface the main face and the outer diameter. Remove from the faceplate and mount on the lathe using the bore and thread just made and face the second side, skim the outer diameter also. Incidentally, it is intended that the machining of the tee slots will machine away the M6 holes as they will have served their purpose.
It is now necessary to mark the outer face at its periphery so that the body can be rotated for each slot. Rather than explain here how this can be done it is fully detailed on drawing 2.
Next make a locating disk, a close fit in the parallel bore and mount this onto the milling machine table. With that done place the body over the disk when it can then be rotated into position for each slot using the lines made on the body and a reference line mounted on the machine table. This process is best understood by reference to the photographs. As I suggested earlier, if you want a more detailed explanation of the process do obtain issues 157&8 of MEW.
