On Dec 21, 2:28*am, "Michael Koblic" wrote:
DoN. Nichols wrote:
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.
Yay!
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.
Tell me about it! I routinely chuck my gnomons (even those without a
shoulder) in my drill press, hold the die in the drill press vise and thread
that way. So far so good...
It's easier if you leave extra stock on the far end to clamp onto, and
a short turned-down stub to guide the die straight. If the die cuts a
shallow thread on the stub it will self-align and bite well into the
full-diameter section.
If the die needs more torque than the work will stand I thread it most
of the way on the lathe first. Then the die turns easily and stays
sharp longer. For me at least dies seem to cut smoother when they only
have a little metal to shave off. You can run the die on backwards to
extend the thread start and smooth it with the less-used edges.
But if you have a lathe can you not turn the diameter to something usual? I
did this in the drill press with a file. Fortunately it only needed a small
amount to take off.
Since you have a mill now, you can cut one surface down to a polygon
centered on another cylindrical part quite easily. To cut smaller,
extend the shaft out the end of the vise and turn it slightly after
each cut. For a large disk with a good round center hole you put an
axle through the hole and rest the axle on the vise jaw tops or
parallels, clamp the disk upright and mill off flats. The axle can be
much smaller than the hole. When you have enough small closely spaced
flats, round them with a file and belt sander. For your thin brake-
rotor-shaped disks the mill should cut lengthwise to reduce vibration.
You could make custom taller vise jaw pads and C-clamp them near the
top. An undersized R/T will work better if there isn't much metal to
remove around the edge of the disk.
This is also an easy way to round the ends of linkage bars etc:
http://picasaweb.google.com/KB1DAL/H...33136395165634
Gripping strongly has not been a problem. Chewing up the piece by doing so
was.
A trick that's claimed to work is to drill a slightly undersized hole
between two hardwood clamp blocks and sprinkle in powdered rosin, like
baseball players use for grip. Or scrape some off a tree.
I saw that in a gunsmithing book as a method to unscrew tight barrels
without scratching them. I don't do gunsmithing but it's one of
several well-documented crafts with good tricks that can be used
elsewhere. Others are watchmaking, aircraft sheetmetal and model steam
engines. I haven't found much written about my real interest,
industrial prototyping and R&D.
The most useful watchmaking idea was the button / disk technique for
accurate hole layout on their manufacturing jigs. The disks are
circular drill bushings whose radii add up to the desired hole
spacing. When pushed together they locate the centers very precisely.
The OD can be turned to the accuracy of your best micrometer, so
potentially you could space holes to within 0.0002".
Rough out the disks, drill and ream the center holes, then turn a snug-
fitting shouldered plug to fit the holes and finish the disks, and
leave it in place in the chuck until done. I ream them all 0.125" and
use a 1/8" spotting drill to drill the work. Then I put dowel pins in
the holes and recheck the measurement. If it's good I center the dowel
pin under the mill spindle, drill and bore.
You can make a custom index circle for an R/T by turning the disks to
the chord distance between the holes and clamping them around a
central disk, which you shave down until the circle of disks closes
into contact. The index hole disks must all be the same diameter but
the actual measured size isn't critical, so you can turn them to match
the smallest, or finish them all without moving the bit.
This relies on measurment and hand fitting, not so much on the
accuracy of the lathe. If it's badly worn you make a separate simple
headstock with ball bearings and drive the back end of it with a dog
from the lathe spindle. Offset the new spindle higher and to the rear,
driven by a belt, for larger work. Then you only need to raise the
toolpost which should be more rigid than a cantilevered adapter. The
belt drive is your speed reducer.
Here is a simple way to adjust the spindle bearings parallel to the
bed without precision machining. The end flanges could be bent up if
you can't weld. Level the shaft by shimming under the lower block:
http://picasaweb.google.com/KB1DAL/H...48334136663058
Four-bolt pillow blocks on spaced parallel plates should also work.
You could have a roughly rounded disk welded onto a mild steel shaft
for the faceplate and turn a center point on the protruding end of the
shaft. I would make the welded steel disk small and bolt on a full-
sized aluminum faceplate.
Right now it is 3.5 degrees C in my "workshop" and I do not really want to
be there :-).
Mine is twice as warm, 7C. It serves as my winter refrigerator.
...I have also developed a line of clamp
knobs from bottle tops, 1/4"-20 bolts and epoxy. They are ugly but cheap and
can be made in the warmth of the heated house.
Cheap, simple, effective. I've used plastic and copper water pipe caps
tapped for the bolt and backed up with a nut. Iron pipe caps make very
solid knobs but they cost almost as much as commercial thumb screws,
which I can get in a surplus store.
Some hardware stores carry plastic knobs that press onto socket head
cap screws.
I make large knobs for the release fitting on hydraulic jacks out of a
knurled disk of aluminum scrap, bored to a press fit and with a milled
slot for the cross pin. If you don't have a knurl, roll a coarse file
or rasp over the disk. They give much better control than the slotted
end of the jack handle for carefully lowering the load.
I wonder what there is in the gagage that is going to freeze...
Michael Koblic,
Most household chemicals seem to freeze without bursting the
container, becoming a slushy mix of small ice crystals rather than a
solid rigid block. They do have to survive warehouse storage.
Jim Wilkins