Fabricated a compound bracket
that is now just one piece of steel.
9x20
Lathe Compound Bracket
& Angle Plate Jig
Last updated on
Tuesday, September 19, 2023 04:33:29 PM
Mountain US Time Zone
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Solid Compound Bracket,
Compound Angle-Plate Jig,
Jig Alignment Animation,
Taper Angle Measurement,
Compound Bracket Archive,
Compound Pivot,
Annular QCTP Spacer
Solid Compound Bracket
Fabricated a compound bracket
that is now just one
piece of steel.
Test fitting parts.
Low tool post to cross slide deflection
while cutting-off a
1" mild steel rod.
The added support increased tool
post rigidity
while lowering chatter.
Compound Angle-Plate Jig
A jig holds precision ground angle plates against the
l
athe'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 of the different
precision
angle setup plates against the compound's front edge.
Three, counterbored clearance holes were
made for the 6-32 SS attachment bolts.
Hardened, 1/4" thick, precision-ground angle setup plates;
1, 2, 3, 4, 5, 10, 15,
20, 25, & 30 degrees.
Use 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 ON THE LATHE.
It is good practice to activate the
E-stop button while setting up the lathe.
First, snug only a left (or right) bolt before making
the fine
adjustment/alignment then tighten the other
two
bolts & recheck alignment.
The 6-32 bolt holes were
sized for a
free fit (#25) to allow
for this adjustment.
Jig Alignment Animation
Jig alignment animation.
Detail of corner relief & toe clamp.
A 1 deg 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 pedestal bracket.
This extra clearance was
needed for only the small angle plates (1 to 5 degrees).
If the top plate had been made wider, the relief cut would
not have been needed.
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.
Detail of the 1/4"
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 clamping
area is exactly 1/4" deep, same as all of the plates.
A 1/4-20 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 deg angle setup plate
placed into the jig bracket.
The compound is rotated as the jig is
(iteratively) brought
into tight contact &
then locked down. The toe clamp
clears the (rotating) tool post.
The compound was set at 3
deg to make
a 6 deg
included angle taper cut on a 1/2" steel rod.
The taper shown is after smoothing & polishing
with progressively finer grit
sandpapers
each alternately applied at right angles to
effectively remove any machining
marks.
Taper Angle
Measurement
CAUTION: DO NOT TURN THE MILL ON.
To verify the accuracy of a
cut after using the angle plate
jig
to set the compound, the taper's nominal 3 deg angle
was measured.
The part is resting on a precision, 1/4"-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.
Move the Y-axis back & forth until a peak on the round
part is
indicated. The indicator plus the DRO's
X & Z axes were zeroed.
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 deg = ATAN (HEIGHT" / LENGTH")
or ANGLE deg = ATAN (Z" / X")
The
calculated
angle was 3 deg 0' 53.25".
A good value considering the tolerance of the
angle
plate is +/-10' & the effects of the other tolerances
(parallels, vise, mill
alignment, part shank), too.
This calculation is analogous to that for
sine bars.
Note
the calculator must be
set to degrees.
Here a 45 deg 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.
Compound Bracket Archive
The photos below archives earlier
bracket designs & modifications.
Early website scanned photos showing the
plate's center
being drilled. Initial 1" drilled hole.
A piece of annealed, free-machining, 303
stainless steel
was selected for plate material. The surface was covered
with red
layout
dye
to make the marks & cuts easier to see.
The locations of the four, 6mm mounting
bolt holes &
the center were laid out using a
surface plate
& height gauge.
Mount piece onto the faceplate that has been
accurately faced using
carbide tool bit.
Drill out a large
hole, 1" in this
example.
Lock the carriage when facing.
There is a scrap plate under the part to avoid cutting
the faceplate.
Use the tailstock to
quickly find the
pre-drilled
center the piece before tightening the bolts.
Also made a bracket using a
6-inch,
4-jaw chuck.
Counterbore started.
A boring operation shown using a right-hand
1/4" carbide
tool bit.
Bottom of the bracket shown. Before removing
the
part from the faceplate, chamfer the inner edge so the
protractor corner fits well.
The corners are rounded
to allow the compound clearance when pivoting.
The protractor is
too inaccurate to use so I chose
to not expose it & thereby not weaken the plate.
I use a
compound angle-plate jig, instead.
Part mounted onto a rotary
table using a miniature
hold-down clamp set.
Machined the round corners &
bolt
recess using a 5/16" carbide end
mill. I have since
eliminated the bolts recess cuts in an
updated plate.
6-in, 4-jaw chuck holding a
plate to make a thicker bracket.
Compound bracket bolted into place using
M6-1,
10mm
length,
SS
hex bolts to keep all the wrenches metric.
The mounting bolts screw into
long,
steel nuts that are about 0.2"
x 0.4" x 1".
New, thicker plate with no bolt recesses;
minimal flex.
A lathe must have a
functional,
pivoting
compound for such
operations
as
threading,
chamfering & short tapers.
Compound Pivot
Have now
increased the size of the compound pivoting
mechanism of several dimensions by about
50%.
Larger bearing surfaces, less flexing & the
incorporation
of full-sized, M6-1
cap-head screws.
The center hole was
precision reamed to 15/32" &
the lapped onto the compound's
bottom indexing
post for a super-tight fit.
The inner pivot edge has
to have a chamfer to allow a good fit into the plate
counterbore.
As was the original, three roll pins
have been added. OEM is shown on the right.
The plate flexes much less now that
the pivoting foot is so much larger.
Annular QCTP Spacer
Decided to add a
Delrin collar
in-between the base
of the compound & the bracket for a test evaluation.
Delrin is very slippery & it was used
to allow easier compound rotation.
The disk, already 3.1" in diameter, was centered in
the
4-jaw chuck & then cut down to 0.305" thick.
Drilled out a 1.5" hole before boring to design size.
Bored open to 1.9" ID.
Chamfered the inner edges with a
razorblade while turning
slowly.
The close fitting collar is shown installed in-between
the parts. A
tight setup with increased rigidity.
Shown parting at the lowest spindle speed (146 RPM)
a 1" soft
steel rod using a
carbide insert tool bit.
Always lockdown the carriage when
performing a cutoff operation.
The prototype collar worked so well I decided to
make an aluminum piece. Increased
the OD to 3.2".
Fly cutting the cylinder on the
mill.
1.5" drill bit quickly removed a
lot of material prior to
boring.
Bored a 2.1" ID hole.
Very tight fitting metal collar installed under
the compound.
There is adequate clearance to
loosen & tighten the four hold-down plate bolts
using a 10mm open-end wrench.
Chamfered the
four bottom edges & corners
of the compound base
to assure smooth
rotation when unclamped.
An added benefit is that the collar
effectively keeps
all of the swarf out of the pivoting
mechanism.
I then added six, 4-40
screws (every 60 deg) to
securely fasten the top spacer ring to the base plate.
Solid Compound Bracket,
Compound Angle-Plate Jig,
Jig Alignment Animation,
Taper Angle Measurement,
Compound Bracket Archive,
Compound Pivot,
Annular QCTP Spacer
