On 2009-06-14, Michael Koblic wrote:
DoN. Nichols wrote:
[ ... ]
The post which you have is capable of having two holders
installed and tightened equally, as there are separate screws to lock
up each station -- just as there is for the Dickinson style toolposts
used on Myfords, and on my Compact-5/CNC. Actually, the one for the
Compact-5/CNC would probably be very good for the Taig as well. It is
way too small for my 12" Clausing. :-)
This would only be possible by cutting a 7/64 hex key very short and
tightening the screws 1/8 turn at a time and then only for tools directly
opposite each other - you cannot fit two holders on at right angles.
You can if they are short enough -- or have 45 degree beveled ends.
There is no reasonable need for two on opposite sides of the
post.
I
venture it is quicker to use only one tool at a time as one can access the
screw head through the hole opposite. Doing it the other way would probably
drive me crazy very quickly.
Indeed so.
snip
(I think the originator thought he would attach 4 toolholders
at the same time - in its present form the toolpost does not allow
this.) OTOH come to think of it each toolholder has 3 set-screws so
maybe I can draft the middle one for this duty (or replace it by a
suitable post).
Perhaps -- though try to also retain its function as a setscrew
(just use a longer one) so you grip the tool in the middle as well as
at the ends to minimize bowing in the middle which could lead to
chatter when cutting.
OK, I did not realize that could be a problem. The Taig toolpost that came
with the machine has only two set screws. I note that the LMS toolholders
have four.
The more setscrews you have, the more rigid the clamping for a
longer tool. If you only can use two, use one near the cutting end and
the next one in, so the spacing is minimized.
Perhaps this sort of arrangement might work:
http://littlemachineshop.com/product...y=100520820 4
Hmm ... if you've got a place to mount it. As shown, it would
remove the middle screw from play as a clamping screw.
Or I can splash $100 on the commercially available QCTP. I
understand that the toolholders that come with it include one for
parting tools although the details are sketchy. Parting has been a
major problem - the only parting tool I have has been ground at a
slight angle from a 1/4 toolbit so it binds and chatters terribly. I
have not got around to grinding another one.
Not sure about the ones which fit the Taig size of lathe,
I found it:
http://littlemachineshop.com/product...ory=-419988835
O.K. Those are piston style, which certainly could not handle
two tool holders at once. The lever turns a cam inside the body, and
the clamping position for the lever is 90 degrees different for the two
stations. (The wedge style moves two wedges down at the same rate, so
two holders of *precisely* the same size in the dovetail would clamp at
the same point of lever travel -- but the odds of such precision in
dovetail width are pretty slim. :-)
http://littlemachineshop.com/product...y=100520820 4
The holder for the parting tools has no rake -- this one simply
clamps through the bar along the top being held down by the four cap
screws. This means that you will have to grind a little rake at the end
of the parting tool's top. And after a certain number of
re-sharpenings, you will have to grind off the end and make a new rake.
http://littlemachineshop.com/product...dID=-316770619
All of these parting blades seem to be of the 'T' shape which I
described.
the ones for the AXA and BXA sizes hold a pre-made blade parting tool,
and hold it at an angle so you don't have to grind a rake angle into
the top of the tool. I tend to use "T-profile" parting tools in
mine. The profile looks sort of like this (view with a fixed pitch
font like Courier, as proportional pitch fonts are likely to produce
distortion).
The one I have has a V-profile with the top of the V whole 0.002 wider than
the bottom and the whole V is tilted about 7-10 degrees off vertical.
That is the kind which was made for the old Armstrong style tool
holders to go into lantern style toolposts. Those used the angles at
the top and the bottom to clamp the parting tool into the holder, but
you would have to grind the top flat from side to side, and with a rake
for proper parting.
A trick to make the 'T' style work even better is to grind a
shallow 'V' parallel to the length along the top. This causes the chip
formed to be pinched in narrower, and thus to clear out of a deep
parting slot more readily.
As a matter of fact I wondered about the rake angles for parting tools. They
also sell (as do others) parting tools ground from a 1/4" bit. I could find
no info about their geometry.
The tool itself probably has no rake, but some toolholders can
provide an adjustable rake. One style, which I originally found on
jeweler's style lathes, has a segment of a circle at the bottom of the
slot, and a rocking steel wedge which fits the curve. You adjust the
angle (and the height of the tip) by loosening one clamp screw and
tightening the other, to change the tilt of the rocking steel wedge. Of
course, the bottom of a lantern style toolpost has a similar rocking
piece, but only one clamping screw.
The top of the tool fits against the top of the slot in the
holder, and near the front of the slot is a cutaway where a tapered
piece fits in and is drawn by a long screw to wedge the blade in
place. If you adjust the degree of extension (either by sharpening
the tool bit by grinding off some of the end, or by loosening the
clamp and sliding the tool out to cut closer to the center of a large
workpiece, or pulling it in to make it more rigid for cutting a
harder material) you will need to re-adjust the height. If you have
an extension which you use most of the time, you might want to make a
gauge which could allow you to restore the normal extension quickly
after sharpening, so you don't have to adjust the tool height.
I shall have to look at one to appreciate it. But it answers one of my
questions (I think): The parting tools also need a rake (at least for
aluminium and steel).
Yes. You *can* make a rake by grinding the top, but your tool
lasts through more resharpenings if you have the rake built into the
holder.
In the case of the holders which you pointed out, this would
require the parting tool holder to be taller. Perhaps aim for about 8
to ten degrees rake.
I like the choice of thicknesses offered in the actual parting
tools.
[ ... ]
O.K. As long as you realize that it is an awkward tool to use
in metals with such a small lathe. It might be nice for getting a
nice finish on plastics.
I think the guy had to have worked with plastics a lot. Some of the other
tools have big contact areas. There are other what I take to be parting
tools with the top of the V 1/8" or more and no rake. I tried them on
aluminium just to see what happens and stopped pretty sharpish.
:-)
This is turning into a full time job :-)
Of course. :-)
Today I bought $15 digital calipers and after an hour of experimenting I
think I found a way to convert them to measure the carriage travel.
The main thing is to preserve the part covered with the fabric
in the beam. The jaws can be milled off without problems (ideally with
the head removed at the time. :-)
Some flower baskets are next...
:-)
Enjoy,
DoN.
P.S. That 3" milling vise looks cute. A clone of the Kurt Anglock
style, but smaller and more affordable. Now if I could just
find a 2" of the same design for the Emco C5 mill (adaptation of
the mill column for the Compact-5 lathe, but with a heftier X-Y
table below it.
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