Model Engineers’ Workshop – August 2019

July 2019 19

Readers’ Letters

Lathe Identifi cation

Knurling

Dear Neil, The attached photos are of a lathe my mechanic purchased a few years back. It is still serviceable, but has been abandoned in

favour of a newer (safer!) machine.

There are no identifying marks, labels etc and so we cannot identify the manufacturer.

Do you think it can be identifi ed from the photos? It could be of interest to a collector or museum.

Brian Sala, Piggoreet, Australia

Dear Neil, In response to Mr Lill’s correspondence regarding knurling
(‘Scribe a line’, MEW issue 282) I can only suggest what works for me - a
method taught to me when I fi rst started using a lathe in 1969:

1. Use a low spindle speed (my lathe at home is an old Drummond and
   has a choice of three speeds plus back gears - I use the lowest normal
   speed, which is around 200 RPM).


2. Use plenty of cutting fl uid (to wash away the tiny fragments of swarf
   produced) - fl ood coolant if possible.


3. Go in ‘hard and fast’ with the knurls to prevent a double pattern
   (if using a scissor type knurling tool, a couple of quick twists of the
   clamping screw will set the tool to full depth in a second or so).


4. If using a scissor type knurling tool, ensure the wheels are truly
   above and below the work axis - if they are not, there is a risk that the
   work will be ‘squeezed out’. If using a ‘bump’ type tool, make sure the
   tool is set vertically so the force on the work piece is at centre height to
   avoid excess stresses on the tool and the work piece, and if diamond
   knurling the two halves of the pattern will be cut with diff erent depths


5. Keep the knurls moving - do not ‘dwell’ in one place.


6. Complete the knurl in a single pass - do not attempt to go over a

piece a second time to cure an initial cut that was too shallow.

6) Feed along the work piece at a rate of about 1/4 inch (5mm or

so) per second.

I feed the tool by hand, but feeding under power is equally good

Regarding the issue of knurl pitch and its relationship to work piece

circumference, I was not taught to ‘match’ the circumference of the

work to the knurl pitch and I have never done so. The knurling pattern

seems to adapt to any circumference without any problems.

I got involved in a discussion on an engineering forum on this

point and as I had never heard of this idea of matching work size to

pattern pitch I decided to investigate. I produced a brief write-up of

my investigation and I attach a copy which Mr Lill may fi nd interesting.

Please will you be kind enough to forward the document to him.

Ian Newman, by email

Thanks Ian, I have passed on your document and by now you will

know I have invited you to write up your fi ndings as an article

for MEW – Neil.