Frequently the rear of an angle plate being used on the milling machine will be left
by the manufacturer in its as-cast condition. If the rear is very rough, Sk.3 A,
then ere on the side of caution and find another method of clamping the part. If
however the rear is relatively flat then with care it may provide a suitable face
on which the clamp can sit, see Sk. 3 B. Actually, a thin piece of soft copper under
the jaw, say 0.5mm to 1.0mm thick, will help to accommodate very small discrepancies.
Clamping onto a curved surface can be acceptable, but again only in carefully chosen
cases. Sk.4 shows one definite no (A) and two possible's (B and C). Of course, being
suitable or not suitable will depend on the applications and the number of clamps
being used. For example, attempting to mill a flat on the round bar in Sk.4 A would
without doubt be a foolish task to undertake. If though you were only marking out
the position of the flat using a height gauge on the surface plate then there should
be no problem if the clamp was carefully set. You do need to consider the application
Used for Milling
I remember reading a letter from a magazine reader who considered it was bad practice
to use toolmakers clamps on a machine tool, particularly a milling machine, and that
such a situation should not have been shown in the magazine. Whilst I do not agree
with the comment I do agree that there is considerable potential for disaster if
not used with care and in accordance with the above described setting methods.
Photograph 3 shows a casting being lightly surfaced whilst being held using two toolmakers
clamps between two angle plates. Both angle plates are machined on their inside and
outside faces providing a perfect face for the clamp to mate with. However, the left
hand clamp is mating with the rough face of the casting as should be apparent. The
casting was acceptably flat at this point so there was nothing to be concerned about.
Also, almost the whole length of the jaw is in contact with the casting, worth attempting
in any set-up.
The right hand end of the casting has a steel plate attached, being part of the final
assembly, and the smaller clamp is clamping this to the right hand angle plate. I
think the reader will appreciate that this set-up using toolmakers clamps was much
easier to establish than one using other forms of workpiece clamp. Admittedly, the
casting was only being lightly surfaced but I see no reason why the set-up would
not be acceptable for heavier cuts. In any case, there was room for a second clamp
at each end and as I often say with all forms of clamping, one too many will not
cause a problem, one too few most certainly will.