Compound Angle Plate Jig
Archived page. See Bracket page.
A jig is described that can hold different precision ground angle plates against the lathe's compound for accurate taper-cutting setups.
A base clamps to
the cross-slide table to hold & position the upper bracket.
The centrally relieved area allows the
compound's mounting plate to clear the base.
The upper bracket holds any one of the different
precision angle setup plates against the compound's front edge.
Three, counter-bored holes were made for the 6-32 SS attachment bolts.
I used a
dial test
indicator mounted in the spindle to make the
final alignment.
The lathe spindle is engaged at its lowest speed to hold it steady.
CAUTION: DO NOT TURN THE LATHE ON.
First, snug only a left (or right) bolt before making the fine
adjustment/alignment then tighten the other two bolts & recheck tram.
The 6-32 bolt holes were sized for a free fit (#25) to allow
for this adjustment.
Jig alignment animation.
Detail of corner relief & toe clamp.
A 1° angle is held by the jig & toe clamp.
The jig was designed to hold this smallest angle plate thus all others work,
too.
Another view showing the
relief required to clear the compound bracket.
This extra clearance was needed for only the very small angle plates (1° to 5°).
The left side is longer than the right side which had to clear the cross slide's
gib adjustment screws.
The cross slide's top edges are heavily
chamfered so no relief cuts were needed on the bracket.
Detail of the ¼"
thick toe clamp.
The thumb screw is a plastic cap pressed onto a 6-32 cap-head bolt.
A brass washer is under the clamp knob.
The channel is exactly ¼" deep, same as all of the plates.
A ¼-20 set screw clamps the
base to the cross-slide table.
The end
plates were bolted on using 10-32 flat-head screws & then the surfaces were fly cut.
Note how the square plate corner fits into the relieved
corner.
A 3° angle setup plate
placed into the jig bracket.
Compound is rotated as the jig is (iteratively) brought into
tight contact.
The compound is then locked down. The toe clamp clears the (rotating) tool post.
The compound was set at 3° to make
a 6° included angle taper cut on a ½" steel rod.
The taper shown is after smoothing & polishing with progressively finer grit
sandpapers
each alternately applied at right angles to effectively remove the machining
marks.
Here a 45° angle plate is held against the compound's top, back edge.
The compound gib adjustment screws are on the front side for this cut.
The angle plate bottom edge must clear the gib adjustment screw nuts, too.
The corner has since been relieved to assure that the
angle
plate seats completely against the vertical edge.
CAUTION: DO NOT TURN THE MILL ON.
To verify the accuracy of a
cut after using the angle plate jig
to set the compound, I measured the taper's nominal 3° angle.
The part is resting on a precision, ¼"-thick
parallel & is clamped by the
vise.
A dial test indicator is mounted in the mill quill using a 3/16" R-8 collet.
The quill was moved down so the indicator touched the part.
I moved the Y axis back & forth until a peak on the round part was indicated.
I then zeroed the indicator & the DRO's
X & Z axes.
The quill was retracted & the X axis moved (1.5000") on the DRO.
The quill was then lowered until the dial indicator zeroed &
the DRO's Z-axis
value (0.0790") was noted.
ANGLE° = ATAN (HEIGHT" / LENGTH") or
ANGLE° = ATAN (Z" / X")
The calculated
angle was 3° 1'. A good value considering the tolerance of the
angle plate is ±10' & the effects of the other tolerances (parallel, vise, mill tram, part
shank), too.
This calculation is analogous to that for
sine bars. Note
the calculator must be set to degrees.
Archived page. See Bracket page.