Table Accessories and Tips
I own a Phase II 8" horizontal/vertical
rotary table that I purchased from Kap Pullen's Getmachinetools.com store.
He has them at a good price, BTW, and he's a darned nice fellow to deal
with as well as being a frequent HSM contributor. Anyway, its a nice little
table, but I hadn't done a whole lot with it for quite a while after purchasing
it. As is so often the case, one day, a project landed on my doorstep
and I was glad to have it.
Before I could get started,
however, I had to make some accessories for it. Basically, I needed some
T-Nuts to fit the table, as well as a little fixture that makes it easy
to hold a plate up off the table through a hole in the center so you can
machine it. The latter, what I call a "plate machining fixture",
was inspired by something similar I saw the Widgitmaster of CNCZone fame
using to make Dremel clamps for his mini-router:
The Plate Maching Fixture and 3
Homemade T-Nuts. T-Nuts are easy to make: square a block to the proper
dimensions, mill the side reliefs, drill, and tap. These are much smaller
than the mill's Bridgeport standard T-slots, so I made them myself and
I'm using 1/4-20 bolts with them. They're made of mild steel.
I turned the round spigot using the 4-jaw
on the lathe. I'm making the fixture out of MIC-6 aluminum plate, which
is pre-ground very flat on the sides. This is a 5 inch by 3 inch piece.
I've clamped it to the rotab using my T-nuts and the regular mill clamps
and step blocks. It is sitting on parallels to make sure I don't cut into
the table. You can also see how I've clamped the rotary table to the mill
table using a big cast iron V-block I have. You can never have to many
blocks with precision faces hanging around!
Here I have just finished milling the slots
that will be used when clamping the Plate Milling Fixture to the table...
Here is the plate milling fixture in use...
a Chuck to the Rotary Table
Having a 4-jaw
chuck on your rotary table is mighty handy! Because it's a 4-jaw, you
can dial in the workpiece by adjusting the jaws until it is perfectly
concentric with the table's axis of rotation. The best way is to make
an adapter plate that attaches to the back of the chuck in the same way
that your lathe does so you can exchange lathe tooling with the rotab.
Here is an example:
A proper adaptor
For the example,
the chuck is threaded onto the adaptor plate, and then the holes in the
adapter plate's flange are used to bolt down to T-nuts on the table.
In my case, I
bought a 4-jaw from Shars brand new, and simply drilled some through-holes
in the chuck to mount to the table directly without an adapter plate:
Tips for Rotary Table Use
a Rotary Table
The procedure I follow is taken from the
Machine Shop Trade Secrets book, which I recommend. There are two steps.
First, you want to make sure your part is
properly centered on the table. To do that, I clamp the table down on
the mill table (no special place is needed), put my Indicol indicator
holder on the mill spindle, and find some round feature on the part to
indicate on. For example, on the plate milling fixture above, indicate
on the round boss, or on the center hole. Spin the table and bump the
part in until spinning the table doesn't move the indicator.
Second, locate the center of rotation directly
under the mill spindle. You can simply use the X and Y table handwheels
to do this. Use that Indicol to indicate off of a circular feature you
want centered under the spindle. Turn the indicol around on the spindle
and adjust the handwheels until the indicator stays put relative to the
spindle position. A Blake Coaxial indicator will make this last even simpler.
Rotary Table Rounding Fixture
The rotary table with a chuck mounted is
a good place as any to set up a rounding fixture. This idea from HMEM
Avoid Rotab Overrun When Rounding With
When you're rounding partially by cranking
a part around on the rotary table, it's really easy to go a little too
far and screw things up. The answer is to drill the end points to make
the exact stopping point on the rotab a lot less sensitive:
This idea from HMEM
Use a Collet Fixture on the Rotab to Center
Under the Spindle
Centering with a Blake indicator is really
fast, but what if you don't have a Blake, or worse, what if your mill
is too small to accomodate one? Here is a nice solution I found on
a German site. This fellow has made an ER collect fixture for his
rotary table, and has taken care that when installed on the table, the
axis of the collet is aligned with the table's axis. He can then place
a dowel or other straight pin in the collet and line up until it will
go into a similarly sized collet on the spindle. Nice trick! It's similar
to how Widgitmaster showed me to align a drill chuck on a QCTP to the
lathe centerline with a dowel pin held in the lathe chuck.
Here is the collet chuck in use. You don't
just use them for round stock!
Here is the little clamping arbor used
to hold the plate in the collet chuck...