Model Engineers’ Workshop – July 2019

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

1.

15.

(16.00 on construction) (132.75 on construction)

(204.50 on construction)

40.50 129.

Leadscrew

200.

Fillet 0.25r

60°

chamfer

45° chamfer

45° chamfer 25° chamfer

2.

5.

5.

Metric trapezoidal thread 12mm x 2mm pitch

Metric trapezoidal thread 12mm x 2mm pitch

2.

Ø8.77 Ø9.98Ø9.35Ø9.

Ø16.

4.

1.

10mm

x 1mm

10mm

x 1mm

20.

A Second Cross-

Slide Leadscrew

T

his article is the second of a series

of articles exploring the techniques

used when making a copy of an

existing item such as the cross-slide

leadscrew and associated components.

There is no intention to provide a blow-

by-blow account of these items, merely

to use them to demonstrate the thinking

and procedures involved in such a project.

However, in this particular article, I shall be

looking at the leadscrew which is such a

complex item that detailed information will

be given. The leadscrew is shown in photo

1 and fi g. 1.

Initial considerations

As shown on the drawing, there a number

of unusual values such as 16.08mm for the

diameter of the fl ange and 9.98mm for the

diameter of the plain section. Some of these

may be put down to poor measurement

technique whilst others may be due to

tolerancing by the original designer. It

seems to me that, for example, the fl ange

diameter of 16.08mm probably should have

been 16.00mm, there being no obvious

reason for the extra 0.08mm. The diameter

of the plain section at 9.98mm may well be

correct for the original device, but for the

copy, as the matching hole will be made

by reaming, and a 10mm reamer has a

tolerance of -0 to +0.012mm then perhaps

the diameter should be best described as a

nominal 10mm.

Another consideration is that I decided to

make the trapezoidal thread slightly longer,

to gain a few millimetres of extra travel.

What this means is that when

constructing a new lead screw, making

the fl ange diameter 16mm means that the

complete leadscrew may be made from

an as bought 16mm diameter bar of BMS

with a resultant saving in material being

removed. However the 8.77mm diameter at

the right hand end of the 10 x 1mm thread

and the 9.30mm at the left hand end of

the trapezoidal thread are used as thread

runout grooves, and as such should be

adhered to as closely as possible; the

9.98mm plain section I decided to make

as near to 10.00mm as I could achieve;

whilst the other dimensions are not that

critical and hence it will not matter if they

are not exact.

Constructional Notes

The leadscrew requires that two threads

Peter Shaw returns to the story of his cross-slide odyssey

1

Fig.

(Part 2).

Leadscrew.