Two other holders, Photograph 4, have a facility for changing the angle by the addition
of shims, this I think is a later development. The photograph shows the left holder
with its shim removed and in front whilst that on the right has it fitted. The shims,
which are tapered on their thickness, are available to cover a range of helix values,
typically -2° to 4°.
These two holders, as purchased, are suitable for 1° the angle being provided by
a slope in the holder itself, as with the first holder discussed. The shims provided
therefore have parallel sides. For other angles the shim is removed and one fitted
that has a taper between its sides. Do take note, the seating in the right hand tool
slopes down towards the lathe mandrel but the left hand holder down towards the tailstock,
for cutting left hand threads.
You will see though that the holders in the photograph are of different hands. This
can be better seen in Photograph 5, but as I do not have any left hand tips at present
only the shim can be seen in that one. The terminology used for defining the hand
of these tools is that a right hand tool (that shown on the left) is one that normally
cuts from right to left and is the one most likely to be required in the home workshop.
Do not be fooled by the fact that the thread form tip is on the left of the holder.
Conversely, a left hand tool normally cuts from left to right. I have used the word,
normally, as it is possible, if fitted with the appropriate shim, to use either holder
in either direction.
I am sorry for having taken photographs 4 and 5 with the holders arranged differently.
To avoid any confusion please refer to Sk. 7 to ensure that you are fully aware
of the situation when purchasing both holders and tips, being expensive you certainly
do not want to end up with the wrong holder and tip.
With regard to accommodating helixes beyond that provided by the 1° value provided
as standard with the holder when purchased, I believe a possible option, rather than
to purchase and change the shim. is to use a strip of tapered packing under the holder
itself. See my later comments.
Making your own holder
As I think the cost will be for some a deterrent making one's own holder may be a
way round the situation as the cost of the tips themselves would be within most peoples
budget. However, many readers will I think also find this idea rather daunting in
view of the various angles involved.