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Milling machine – making – dovetails – as used on quick change toolposts
Most quickchange toolholders as used on lathes utilise dovetails to hold the toolholder onto the tailpost. In this case the dovetail does not slide. It is either loose or is firmly clamped. But, of course, what it essential is that each time a particular toolholder is fitted the cutting edge must be in exactly the same position the last time it was fitted.
What is interesting about these is the different ways the male part is clamped onto the female part. In all cases the male part of the dovetail is on the toolpost.
There are at least four ways of doing this:
One side of the male part moves outwards so locking the female part,
colchester – pre Dickson
The problem with this design is it can only work with a toolholder on one side of the toolpost. This work properly with most turning tools that are aligned across the bed of the lathe. But when the tool has to be aligned along the bed of the lathe it leads to a rather gruesome arrangement.
fig colchester toolholder for boring
This is clearly not very rigid along the length of the boring tool. It is possible to use an ordinary toolholder with the toolpost tunred round as shown:
fig Colchester toolholder used to hold boring bar.
These seemed to have been standard issue till about 1965. After this Colchester seem to have used Dickson type toolholders.
One side of the male part moves upwards but as it is tapered it also moves outwards
A round boss on the toolpost pushes out against the inside of the female part of the toolholder.