On 2010-06-26, Searcher7 wrote:
On Jun 25, 12:10*am, "DoN. Nichols" wrote:
On 2010-06-25, Searcher7 wrote:
[ ... ]
There, one of the threaded holes would get a short bar screwed
into it with a large ball handle on the end for tightening and
loosening. *(Not when using it in a rotating chuck of course, because
the handle would unbalance things -- unless you had three identical
handles screwed in at 120 degree intervals.
Actually, that would be four at 90 degrees.
* * * * Oh -- eight holes total, not the six I thought there were? *I
never had a view which made it truly clear.
Yes, eight. Every other hole is threaded.
O.K. I knew that every other hole was threaded, but I somehow
thought that there were a total of six holes, not eight.
* * * * The small bar I still think might be used to turn the small ring
onto the end of the collet and back off.
There is no place for the small bar. The ring that threads onto the
rear of the collet is solid, and actually threads about halfway on
before it bottoms out.(But I assume that is enough).
* * * * The small ring has a series of depressions around the OD. *If
the spacing between that and the wall surrounding it is just right, the
pin on one end could be slid into a depression and used to chase it
around with the outer wall keeping it engaged.
The small ring is knurled, but that is all.
But is it knurled deep enough to allow the pin on the end of the
small rod to act to spin it on or off?
Nevertheless, I can thread
it onto the rear of the collet with my fingers. But like I said it
will bottom out when it is approximately halfway on.
Sure -- you could probably thread it on a little more if you
were pressing in the collet nose while installing the ring, but that
would limit the size range of the collet.
[ ... ]
* * * * No! *You would create an adaptor which mounts on the spindle
nose which has a cylindrical bore which is a slip fit for the OD of the
device, is deep enough to hold the body, but to leave the large black
ring accessible, and with a thin slot along the length of the bore and
some means of compressing it to hold the body.
Like a large collet or split bushing I assume. (Since the body of the
collet chuck is 2.75" long that would be a deep seat).
* * * * Yes -- except that the bushing would mount directly on the
spindle nose instead of through an adaptor.
Thinking about the material, thickness, and shape of this bushing, if
would appear that it would have to be made up of two main parts.
I see it as only two parts -- a cylinder perhaps an inch larger
in diameter than the holder body, and a screw threaded in to close the
slot. (Oh yes -- also the studs to mount it on the spindle nose and the
corresponding nuts. :-)
But it will need a tricky bit of work to cut the slit along one
size to allow the screw to clamp it onto the body. You'll need the mill
and some way to mount the rather large piece of metal to do that.
[ ... ]
So here is the problem. What is to keep the front of the collet chuck
from rotating clockwise relative to the body under cutting forces,
which would result in opening the collet.(And making things really
exciting). :-)
* * * * Well ... normally the anti-rotation pin is not expected to
handle much torque -- but here it might have to.
* * * * Can you verify which direction of rotation closes the collet
(moves the large black ring away from the body)? *Is it left-hand thread
or right-hand thread? *If it is a left-hand thread, the cutting forces
would *tighten* it, thus preventing your problem.
Turning it clockwise will screw it onto the body.
So turning forces would normally loosen it.
But I can understand
what you're saying. (I'm probably just worried too much).
I think that within the normal size range of the collets, it
would work. If you went to one of the pot chucks that would be a
different matter.
* * * * If not -- then it is likely intended to hold a workpiece on a
surface grinder or other low force operation.
* * * * [ ... ]
* * * * Again -- forget it. *You're thinking of the large black ring the
wrong way. *It *has* to be free to turn so you can loosen and tighten
the collets.
But how does one keep it from turning under cutting forces?
* * * * Pray that the anti-rotation pin works? *Look for a place where
the small pin slides into to prevent it from turning? *Add provisions
for clamping the ring to the sleeve which holds the body? *Run your
lathe spindle in reverse? *(I think that is not an option on your lathe
anyway.)
Yes, reverse is an option. But I think that this would probably be
secure enough either way. Especially since it was no doubt made for a
more powerful machine than I have.
Certainly for the size range of 0.750" on down I see no problem.
Light cuts up to the 1.125" maximum should work as well.
So it comes down to this. Should I proceed with this collet chuck or
concentrate on the idea at this link: http://www.sc-c.com/metallathe/MLA21.html
(The MLA-21 would seem to be the best way to go).
I agree that the MLA-21 would be the better choice. What
remains to be seen is how difficult the machining is to make it from the
castings.
Why not buy the drawing first to see what you will have to do.
The "lathe only" construction suggests that the side clearance holes for
the tommy bar access to the ring would be part of the casting -- though
a mill and a dividing head might be used to dress up the edges a bit.
Checking -- yes you still get partial credit for the drawings
which you purchased if you order them first, and the casting kit without
the drawings later.
One of the things which I consider best about this is that you
can mark the spindle and the casting where they join prior to turning
the closing taper and bore for the collet, so you will get the best
repeatability.
And instead of using the ring at the rear of the chuck, I'd use a
drawtube, if I can modify the machine to use a modified 5C spindle.
(Just throwing out ideas). :-)
* * * * You can't make your current machine have a large enough through
diameter to work that way. *For a 5C collet closer, you need at least a
1-3/8" through bore, not your near 3/4".
Yes. That is why I am investigating installing a 5C spindle. I just
may have to shorten a drawtube shortening one. And the worse case
scenario would be a need for a different set of gears, if I can't
enlarge the center hole of the existing ones that directly drive the
spindle the spindle.
Of course I'll have to open up the headstock so I can see and measure
what is possible.
* * * * I expect that you will find that the entire OD of the spindle is
smaller than the needed bore through the spindle for a 5C collet closer.
This is why the idea is to replace the existing MT3 spindle with a 5C
spindle
What I am trying to say is that there is not enough metal in the
headstock to hold a large enough spindle (and the bearings) to accept 5C
collets.
Typically, everything else has to be scaled up when you scale up
the ID of the spindle. Multiply the size of *everything* by 1.83,
including the spacing of front bed way from the rear.
You have bearings at each end of the spindle, you have a gear
setup to switch speeds. You *may* have a belt pulley in the headstock
as well. (I did not see photos of the interior.) All of these things
have to be increased in size by the same ratio.
If you tried to increase the diameter of the spindle without
increasing the size of the headstock casting, you would have to use
thinner bearings -- which would not be strong enough to handle the
cutting loads.
For comparison -- the spindle for my 12x24" lathe (made to
accept 5C collets with an adaptor) has an OD of 2.000" at the chuck end
bearing mount, and an OD of 1.875". Look for tapered roller bearings
which accept those sizes on their ID, and see how small an OD for the
outer bearing race can be found. The compare that to the size of your
headstock casting.
Without actually going down and measuring, I think that the OD of the
bearings on my Clausing 12x24" with a 1-3/8" spindle bore is on the
order of 5" -- which I think is larger than the dimensions of your
headstock in the area where the bearings live.
I'm sure *everything* is bigger on your Clausing than on my mini-
lathe. :-) (Including the bearings).
That is why it can accept 5C collets in a spindle adaptor -- it
is big enough. Yours is *not* If you want to handle 5C collets, plan on
at least a 10" lathe -- which you will probably have to strip down to
components and carry them up one at a time.
I believe that even the South Bend "Heavy 10" woll not handle
the 5C collets in the spindle -- just the 12" swing or larger.
[ ... ]
* * * * Yes -- but it does not matter -- the wedge is trapped between
the angled surface on the post body's dovetail and the inside of the
holder's dovetail. *A little play there won't hurt when you have holders
which will not fit onto the post. *And it will not be as critical a
surface as the dovetail itself.
And the wedges are more replaceable than the toolpost body. :-)
* * * * They would cost less -- if you could find a place to buy them
separate from the toolpost.
Making new ones would probably be easier. (After all, I have the
templates). :-)
If you are up to cutting a three-start internal thread on an interrupted
cut. And look at the complexity of the other parts of the wedge. You
have to make some of those to use for fixturing while you cut the
threads.
* * * * But I think that they would be easier to file or sand down in the
critical area.
How about emery paper on the edge of a glass plate? (Or perhaps I can
use this item I won on eBay: 330442158063)
Hmm ... depends on the quality of the surface plate. He says
that he checked it flat with a square. :-) To *really* check it, you
need a setup with a micro-inch reading sensor traveling on arms
supported above the surface. The lowest grade should be flat within
0.000050" (50 micro-inches), and as the grade goes up, the number of
allowed micro-inches of deviation go down. There is no way you are
going to check that with a square. :-)
But if it is not sufficiently accurate, it should work fine for
your task. (Be sure to keep the abrasive grit from getting on the
surface anyway.)
A piece of glass perhaps 1/4" or 3/8" thick should suffice for
the purpose of adjusting the wedge. Remember to keep trying it
frequently for fit, or you could get too small.
[ ... ]
I'm assuming that a jig wouldn't be needed to accurately remove
material equally along the length of the wedges.
* * * * If you have a flat surface on the wedge which meets the
dovetail's angles surface, you can probably simply slide that face flat
on some fine emery paper on a hard flat surface.
Yes, that's the plan.
I would still go for tuning the gap in the wedge myself. Or --
sell it on eBay and get a better one.
BTW There has been a discussion of Shars tools on the local
metalworking mailing list, and the general opinion is that
they are very good -- with specific good reports on the
clone of the Kurt vises.
[ ... ]
* * * * Until something happens which needs the force working overtime,
leaving a lot of places without guards. :-)
That's happened already... But it obviously won't be a big concern of
the businesses who hire them. Especially since such an event would
close businesses anyway.
Which means that people could consider warehouses easier to
burglarize.
[ ... Blake Coax indicator ... ]
[ ... ]
* * * * Yes -- as long as there is room between the spindle and the
workpiece. *Sometimes things are just too crowded for a Blake.
Thanks. Tramming is the priority. I can use other ways to measure the
workpiece on the table.
* * * * O.K. *One thing to keep your eyes open for is a fairly large
diameter outer race for a tapered roller bearing -- one about as large
in diameter as the width of the table. *You roughly center that under
the spindle, and run the feeler of the Blake around on that. *That way,
you don't have the problem of the feeler dropping into the T-slots every
so many degrees.
Ok. I'm sure that would make more sense to me once I learn how to
tram. :-)
Essentially, you are rotating a feeler around the center point
of the spindle and measuring how much it goes up or down. Since the
table is interrupted by the T-slots, something of precise thickness and
ground smooth (e.g. a bearing outer race) can give a surface for the
feeler to travel over without problems.
* * * * Oh yes -- a Blake can be turned under power -- but only up to a
certainly rather slow limit. *My lathe, with a 55 RPM minimum speed is
well within that. *No bets on yours, so you would have to turn the
spindle by hand. *Same is likely for the mill.
My lathe is variable between 100 and 3,000 rpm.
O.K. Their page says:
"It is recommended that operating speed not exceed 800 RPM
approx."
so you should be fine as long as you keep it at the low end.
These are all of the *largest* eBay vises I could use:
380087874872
300373085985
280518320722
230486712282
* * * * O.K. *Nominally 3" chucks. *I kind of like the first two more,
for various reasons. *But is the second one a shars? *And they are the
makers/importers of the troublesome toolpost?
And the report from the local club says that their vise is very
good.
Good Luck,
DoN.
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