ACME Precision Bushings - Acme Industrial

INSTALLATION TIPS
Bushing/Liner
In stal la tion Tips
(cast iron or unhardened steel jig plates)
Production accuracy requires extra
care when preparing mounting holes and in -
stall ing bushings/liners. The following fac tors
should be considered: diametral interference
fits, alignment, chip clearance, and how close
the bushing is to the workpiece.
Because of the many variables, no
definite rules can substitute for the skill and
judgment of the experienced toolmaker. The following
suggestions should be helpful to oth ers.
Interference Fits
Interference holds press fit bushings
in place on the jig plate. Too much interference
may cause a number of problems: (1) jig
plate distortion; (2) bellmouthing (bushing/
liner walls bow inward); (3) tool seizure, or (4)
trouble with slip-fixed renewable fitting into
the liner.
Too little interference may allow slippage,
thus causing inaccurately drilled holes.
In most cases, interference of 0.0005 to 0.0008
inch is sufficient to properly install press fit
bushings and liners.
mounting Hole Roundness
It is recommended that all mounting
holes be jig bored or ground to assure roundness.
Ordinary twist drills seldom produce an
ac cu rate ly sized or truly round hole!
Bushing/Liner Installation
First, lubricate the inside diameter of
the mounting hole and the outside diameter of
the bushing/liner – before pressing into place!
Lubrication prevents scoring of the hole wall.
White lead is a typical lubricant.
Second, use an arbor press to press
the bushing/liner into place. If an arbor press
is not available, draw the bushing/liner into
place by tightening two steel plates connected
by a nut and bolt. A bushing/liner should never
be ham mered into place! Why defeat the main
purpose of the bushing? – Accuracy!
4
Chip Clearance
One school of thought suggests a
space between the workpiece and the drill
bushing. The other suggests direct contact.
In order to decide, you should consider the
abrasiveness of the material being drilled, the
drill size, and the type of bushing/liner being
applied.
Chips produced from drilling will be
ejected either through a space or through the
bushing. If your drill clogs or heats up, try
increasing the space between the end of the
bushing and the workpiece. Normal spaces
vary from one-half the drill diameter for small
chips (as from cast iron) to one and one-half
times the drill diameter for long stringy chips
(as from cold-rolled steel).
Vary the length of Slip-Fixed Re newable
bushings to achieve proper spacing for
your operation (see number 4 below for a more
detailed explanation). A rule of thumb is, the
greater the space between the bushing and the
workpiece, the greater the chance for error.
Where possible, test your conditions and contin
ue to check for accuracy throughout your
pro duc tion run.
Hints for more Accurate
Pro duc tion and
Longer Bushing Life
1) Align Bushings Properly.
Carefully align the drill with the bushing
axis to avoid poor alignment and excessive
wear. The radius on the bushing will help
center the drill point. ACME No-Counterbore
bush ings help the operator accomplish this
with ease.
2) keep Tools Sharp.
Dull drill bits defeat the preciseness
of bushings. Sharpen by first grinding each
drill with the point in the exact center. This
helps avoid “walking” by the drill when it first
enters the workpiece.
3) Use Proper Coolants.
Check the coolant label to be sure you
are using the right coolant for your machining
process.
4) Use Slip-Fixed Renewable Bushings
for multiple Operations.
Slip-Fixed Renewable Bushings of
different lengths provide for both accuracy
and chip removal during multiple operations.
For example, a short bushing during drilling
will provide the proper clearance for chips to
escape. A longer bushing during reaming will
provide maximum guidance.
5) Adapt Bushings To Irregular work
Surfaces.
The exit end of the bushing should
conform to contours of the workpiece. For
maximum guidance, hold to a minimum any
space for chip clearance. A drill point that
does not enter exactly perpendicular to the
work sur face will skip or wander. In such a
case, side load exerted by the drill is concentrated
near the exit end of the bushing. The
bushing can wear prematurely. Slip-Fixed
Renewable bushings could simplify replacement
of worn bushings, and also aid alignment
with the contoured work surface. For short
production runs using press fit bushings, form
the bushing end to the workpiece contour.
6) For Long Production Runs, Use
Tung sten Carbide or Titanium Nitride
Coated Bushings.
ACME Carbide bushings last up to
50 times longer than hardened steel. ACME
Ti ta ni um Nitride (TiN) coated bushings can
last up to 40 times longer than conventional
bush ings. Both types of bushings could save
valuable replacement downtime. The additional
cost is small when you consider the extra
long life possible. Call us for more details.
Acme Industrial Company • 441 Maple Ave. • Car pen tersville, IL 60110