In article ,
"DoN. Nichols" wrote:

On 2008-02-10, Joseph Gwinn wrote:
In article ,
David Billington wrote:

[ ... ]

Sounds like you're not doing the nut down tight enough to hold the
Dickson toolpost in place or the base is not sitting on the compound but
maybe being held off it by something. I have never had an issue with my
Dickson toolpost moving even when the locating pin was not in use.

I did crank it down pretty hard, using a 15/16" box wrench a foot long.
Under ordinary cuts (with tool close to the axis for the threaded rod),
no problem. With the cutoff blade (with tool an inch farther from the
center), slow rotation. The mating surfaces on toolpost bottom and
cross-slide top are pretty smooth, and properly oily.

The bottom of my Dickson style is ground too smooth.

Sounds the same as mine.


I assume that originally the toolpost came with a big cylindrical post
nut with a ball-headed arm, for rapid clamping and release, so one could
rotate any of the three holders into position.

Nope! You don't rotate the holder -- you set it up with one
side parallel to the face of the chuck, and the second parallel to the
axis. The third is towards the tailstock end of the lathe, and is used
when you need to work closely to a live center in the tailstock, or to
produce a step facing towards the headstock. I don't have that one, but
I would like to have it as part of the collection.

Is this approach universal? A toolpost maker will be trying to
accommdate all customers, even the misguided.


You select the angle by selecting the tool which you drop onto
the post. I keep (for my 12x24" Clausing) insert tools set for a square
face when turning and facing, plus a pair (one in turning position, the
other in facing position) with triangular inserts which present edges at
a 30 degree angle to the shank of the tool. These I use most often for
chamfering after turning and facing.

But the main reason for keeping the faces of the toolpost
parallel to the axis and face of the chuck is so that insert threading
tooling is presented at the proper angle to cut proper threads instead
of giving you buttress threads when you don't want them.

The only time you should have to unclamp the toolpost and change
its angle is when you loosen the compound and set it to a new angle, at
which point you should reset the toolpost so its faces are parallel to
the references surfaces again.

This is entirely unlike the usual operation with a lantern style
toolpost where you are constantly adjusting the tool angle.

And turret style toolposts often had a spring-loaded index pin
mating with a series of radial grooves on the bottom at 15 degree angles
so you could easily restore them to proper position when rotating to the
selected tool.

What I would suggest is that once you have your pin in service,
set the compound to the various common angles (29-1/2 degrees left and
right for normal threading, 60 degrees left and right for chamfering,
and perhaps 14 degrees left and right for acme threading) and drill
holes for the pin matching each of these, so you can more quickly set
the toolpost to the proper angle when changing the compound setting.

Sounds like a good idea, although the angles cannot be too close
together or the pin holes will overlap. The pin center is 1.000" from
the pivot axis, and the pin hole is 0.272" in diameter, which subtends
an angle of 15.22 degrees. So, 29.5 degrees ought to work.



BTW I took a look at the underside of my EMCO (Dickson style) toolpost
today and find the taper was a lot smaller than I had
remembered. It looks something like this (set font selection to
a fixed-pitch font like Courier to avoid distortion of the
image):

+------------+ +-----------+
| | | |
| | | |
| | | |
| | | |
| | | |
| __| |__ |
| / \ |
+--------+ +-------+

and the washer at the top has a step to drop into the bore size and keep
the screw (a big metric Allen screw) fairly centered.

Obviously, I've left out the details like the V-ways and the T-studs
operated by internal cams, as they are not necessary for what I was
showing.

I've got to bring that toolpost and the bevel protractor up here
where it is warm to try measuring the angle of the taper so i can
duplicate it.

I'm not visualizing this above. Is the recess all taper, or is there a
cylindrical part?



On my toolpost, there is a similar recess on the bottom, centered on the
hole that accepts the 5/8-18 clamp rod. This recess is tapered, and
then cylindrical, and the cylindrical part accepts a 1.5" diameter
collar. The recess is not ground to precise shape. In any event, the
collar I just made will go between this recess and a similar one to be
machined into the ridged plate.

Joe Gwinn