August 2019 63
8tpi Screwcutting
of a 127 tooth wheel matching the pitch
of the others in the set-up and will be,
comparatively, rather large. If obtainable,
a 127 tooth 14DP gear would be 9.21”
(234mm) diameter. Oft en it is diffi cult or
impossible in practice to accommodate it
into the calculated gear combinations due
to the great diff erence in diameters.
“My” method.
Remember my 1.0 module 125 & 127 tooth
double wonderful gear?
I thought that if I could find a suitable
mating gear with a sensible number of
teeth I could come up with a system of
integrating this pair of gears in with the
normal 14DP Drummond gears to give a
totally practical set-up for producing true
metric pitches.
The only proviso is that the two 1.0
module gears must always be meshed
together with the smaller one keyed to
a standard Drummond gear with the
127 gear attached to the lead screw. See
photos 3, 4 & 5.
Being a magpie, I had obtained a
number of 1.0 module gears from a
scrapped-off special purpose machine
rescued from the skip of a local company.
In this collection was a 48 tooth gear.
Other mod 1.0 pitched gears could also be
used but the 48 tooth one was the best of
the “rescued” ones for my purpose.
A session with the pocket calculator
and some trial set-ups showed that the
48 tooth gear (divisible by 8 compatible
with the lead screw pitch) gave a good
practical match.
Both gears were bored or bushed to
give a 5/8” bore and side connecting holes
were drilled to match the Drummond
gears. (Drummond gears do not have
keyways).
I decided to use the 127 tooth gear on the
leadscrew for all set-ups.
Table 2 shows the change wheel
arrangements using gears that I had
available.Postscript
Some years ago I reluctantly sold theflatbed Drummond lathe due to lack of
workshop space. It was a very nice lathe
to use being very smooth and almost
totally silent in operation. I retained
the wonderful 125 /127 gear for future
use as the purchaser of the lathe had
no interest in cutting metric threads. I
never considered motorising the 100
+ year old Drummond lathe with its
flimsy headstock bearing arrangements
designed for human power only.
I enjoyed every minute of owning the
old Drummond lathe and used it to make
several model engines including James
Coombes. Stuart V4 variant, V10, H10 and
S50. I also made many items of workshop
equipment, made spare parts for some
obsolete shoe repairer’s stitching
machines belonging to my brother in law.
When our Grandson, Archie, was
very small I made him a toy milk float
from a Hobbies plan. Construction was
very straightforward but there was a
requirement for some crates of milk
bottles 24 in each crate. I made the
dummy bottles from 3/8” dowel rod on
the trusty Drummond using a suitable
form tool. This was a rather boring job
but after I had made two dozen or so, my
wife Susan took over production when
I convinced her that the Drummond
was a very good “exercise machine”.
Photograph 6 shows the finished milk
float complete with milk bottles.
I was very sorry to part with this
wonderful old lathe but happily it went to
a very good home. ■REFERENCES
- Chester Machine Tools for the 125 /127
toothed gear (for 910 lathe) - HPC Unit 14, Foxwood Industrial Park,
Chesterfi eld.S41 9RN Tel 01246 268080
for 1.0 Mod gears. Other suppliers
available.
5
Archie’s milk fl oat with milk bottles.