Model Engineers’ Workshop – July 2019

40 http://www.model-engineer.co.uk Model Engineers’ Workshop

T

o achieve anything with a lathe it

is necessary to fit a suitable tool

and present it to the work. For the

vast majority of turning work this means

fitting a tool of some sort to the topslide,

and virtually all lathes come supplied with

some form of toolholder to facilitate this.

The requirements of a toolpost are:

Rigidity – the more securely tools are

held then the less vibration, improving

finish and enabling deeper cuts and faster

metal removal.

Adjustment – at the very least it is

important to be able to adjust the angle

of the tool to allow different operations

such as turning and facing and ensuring

parting tools are represented exactly

perpendicular to the work. Toolposts can

be height adjustable to remove the need

to use packing strips under tools.

Ease of use – some older toolpost

designs are very fiddly to use, requiring

the tool to be accurately reset at every

change. At the other extreme, quick

change toolposts allow tools to be

swapped over in seconds with no need to

check their adjustment.

Traditional Toolposts

The traditional tool holder for British lathes

is shown in photo 1, a simple L-shaped

clamp that is tightened down onto the tool

by a nut on the toolpost. The tool height

is set using packing. This style of toolpost,

although fl exible and rigid, is fi ddly to set

up and off ers no help with aligning tools

and it has long been rare aside from still

being standard on a few ‘heritage’ designs

whose owners almost always replace them.

The American counterpart is the ‘lantern’

tool post. This is a more complex hollow

toolpost with a ‘boat’ shaped insert that

is used to angle the tool to set the height

of its cutting edge. The downside being

that changing the tool height also changes

its geometry. It leaves the tool with more

overhang than the British style and also

limits the lathe to tools that can fi t through

the toolpost slot.

1

Lathework for

Beginners

Part 12 - TOOLHOLDING

This ongoing series will build into a complete guide to using an engineering

lathe. This month Neil Wyatt looks at toolholding and setting in more detail.

The traditional-style toolholder of a Super Adept lathe

The large four-way toolpost of an SC4 lathe Using packing strips to set a tool at centre height

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