On 2008-12-20, Michael Koblic wrote:
DoN. Nichols wrote:
I am pretty much looking at it as two distinctly separate jobs:
In which case you probably will eventually want two different
machines -- one set up for each job.
I have two pillow blocks and a large pulley and 1" shaft ready for one of
them :-)
:-)
[ ... ]
That -- or the Taig with perhaps even *two* riser blocks? Not
very rigid, but probably sufficient for edging the face. I would have
to check whether two blocks stacked up would give you sufficient
center height to turn a 9" face.
You see no other issues except rigidity?
Hmm ... thinking about it -- you would need to make an L-shaped
mount for the toolpost to get it far enough out to pass in front of the
workpiece at center height. But *that* is something which you should be
able to make using your mini-mill.
According to Lee Valley a pair of
risers (head and tail) will increase the swing by 2", so I make it total
81/2" with two pairs (but only headstock needed for my prurpose). How about
speed?
Speed would depend on the workpiece material used. Steel would
need rather slow speeds at 8 1/2" diameter. Let's see -- that works out
to 1168 SFM at the maximum of 8 1/2". O.K. For aluminum, you can
handle it even with HSS, and for brass you would probably want a very
sharp carbide, or PCD (Poly Crystalline Diamond), which is not as
expensive as you might initially expect. :-)
The taig in the basic configuration only goes down to 525 rpm with an
AC motor (1725 rpm). I have thought that a DC motor would be the thing but
that raises the price even further and the mini becomes even more
attractive.
Hmm ... I thought that it ran slower than that with the
multi-step pulley which came with mine. I do know that the top speed is
quite scary. :-)
But a different AC motor -- at half the speed -- should do fine.
O.K. I presume that you would like to make the gnomons tapered?
For that, you do what work is needed on a cylindrical basis (probably
between centers) and then shift to between centers with an offset on
the tailstock so you can produce a nice smooth taper.
Tapered or different patterns.
O.K. The patterns will probably be freehand with a half-round
file.
At this point I see no need to cut threads. However, as these things
often work out, I will want to cut one the moment I buy the Taig :-)
Hmm ... part of that cylindrical work on the gnomon might be to
turn a shoulder, and then thread up to the shoulder so the gnomon
could screw directly into whatever it mounts to -- as long as the
gnomon should be perpendicular to the mounting point. That saves you
from having to stock screws and work at hiding them in the assembled
sundial.
Absolutely. I have done one like that so far using a die to cut the thread.
Is that not quicker to do than on a lathe?
You produced a shoulder as well as a thread with hand tools?
The problem with a die is that it is easy to start one out of
line and then very difficult to get the thread back in line.
And -- if the diameter is an unusual one, dies to cut that
thread can be quite expensive.
Yes -- a die can be quicker -- if you can grip the workpiece
firmly enough. But lathe cut threads can be a nicer appearance than
most die cut threads.
[ ... ]
You'll also find it very useful for drilling the initial central
hole before boring it to larger diameters. IIRC, the tailstock
chuck will hold 1/2" drill bits -- but the motor may have a bit of
struggle doing it all in a single pass in steel.
I thought the Taig only did 1/4".
I just went down and verified. *My* (rather old) Taig has a
Jacobs 1/2" capacity chuck which screws onto an external thread on the
tailstock ram. IIRC, it also screws onto an arbor to allow you to use
it powered in the headstock as well.
One of the reasons I am hesitant about the Taig. The descriptions from
various sources are rather confusing. Lee Valley sell 1/4" chuck to go on
the 3/8"-24 tailstock.
The 3/8-24 tailstock thread is the same -- but various size
chucks are available with that thread -- and the one which came with
mine was 1/2".
That can be a problem, too. The Mini-lathe or the Taig are low
enough power so you can afford to make mistakes without producing
serious catastrophes. A 12" or 13" lathe is a different matter, let
alone larger ones. For *those* the class first would be a *very* good
idea. And you *will* learn things from the class even with the
smaller machines. (Granted, I never took such a class -- but I
learned (as an Electronics Technician) from some good machinists at
work, and as a result was one of the few technicians allowed to use
the machine tools in the building.
No argument! Such course would be an excellent idea, which is why I have my
name on the list. But it becomes a matter of allocation of resources. Then
there is a matter of my predisposition to learn things by myself. Many
skills which were supposedly taught to me over the years were learned by the
time honoured method of "see one, do one, teach one". I still have
nightmares about some of the stuff one did in one's youth through arogance,
ignorance, stupidity and total lack of guidance and supervision. But that is
no excuse now, one should have gained the wisdom of age. Fat chance...
:-)
Enjoy,
DoN.
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