Workpiece Clamping on the Machint Table 3

Harold Hall


An advantage of making ones own is that they can be economically made in a wide range of widths and lengths. Photograph 3 shows some typical clamps and would suggest a minimum of 4 of each size made. Also shown are some T nuts, also shop made. Of particular interest are those on the extreme left and right, front row. These it will be seen are tapped off centre and provide some flexibility in the positioning of the stud providing greater reach or spacing. This I find gets me out of an otherwise difficult situation where the limited size of the average Mill/Drill table can sometimes make mounting the workpiece, or larger machine vice, more difficult than anticipated, occasionally, even impossible.


I am not including dimensions but obviously the thickness should be greater the longer the clamp. As a rough rule, up to 50 mm long 25 x 6 mm section, 75 mm long 32 x 8 mm and over 75 mm long 35 x 10 mm.


Studs will be required in a range of lengths but suggest you standardise on a thread size of M8, or say M10 if you have a large size machine. When I purchased my machine and making my own T nuts, I equipped it with both M8 and M10 sizes, the latter now rarely used.


Studs are one area where I consider it worthwhile you purchasing your requirements as they are not overly expensive and would suggest at least four of each length, normally 63 mm, 100 mm and 160 mm.  Alternatively, a length of studding could be purchased and cut into lengths. In this case, take a pin punch and distort the threads on the underside of your T nuts. This will prevent the stud passing through and hitting the base of the T slot. The commercial studs have a short length of thread at one end and a plain portion then a longer thread at the other. This prevents the stud passing through the T nut.


The rules

Much has been written regarding the principles of workpiece clamping and I am therefore going to keep my comments very brief.

1. The packing must be slightly higher than the workpiece.

2. Arrange the clamping stud nearer to the workpiece than to the packing wherever possible.

3. Do not use a single clamp unless the task is a light duty one and that the workpiece is further restrained by supporting pieces. At least two and preferably three clamps should be aimed at.

4. The clamp must be thick enough to prevent it noticeably bending.

5. Do not use an unstable pile of odd size pieces of material as packing.

6. When using slotted clamp bars do support the nut with a heavy duty washer, say 25mm diameter by 3mm thick for an 8mm stud, rather than standard washers. This equally applies to fixings in angle or face plates.

Clamps for the milling machine table



Workshop Processes