Mechanical Power Press Inspections - Maintenance Inspection Training
Procedure for measuring
clearances in a two point straight side eccentric crank
mechanical power press.
Figure 1 below shows a
typical set up for measuring clearances in the main
bearings, connection bearings, adjustment mechanism and
lower connection pocket/wrist pin area.
Before beginning the
Safely remove the die from the
press. Position the slide to bottom dead center ( 180
degrees of press rotation ). Lockout/tag out power per your
companies policies. Reduce the counter balance
pressure to zero and bleed off any air from the counter
Determine the size of jack
required to perform the press inspection. As a general
rule of thumb, the counterbalance pressure chart used to
balance die weight can
be used to calculate the size of jack required. For
instance, if for each 10 psi change in air pressure, the die
weight can be increased by 5,000 pounds and the balance
pressure is 40 psi, then the weight of the components and
slide is approximately (40psi/10psi) x 5,000 pounds or
20,000 pounds. In this case a jack with a rating >10
ton will raise the slide and components. If the press
is a two point press, as shown in Figure 1, the clearances
for the right hand and left hand side of the press will be
checked separately. In this case a jack >5 ton will
The jack is placed between
the slide face and the bolster. The location of the
jack should be close to the center line of the connection.
Place an indicator is close proximity of the jack extending
from the bolster to the slide face. The sum of the
clearances that will be measured should approximately match
the indicator reading at the jack.
If the jack has a serrated
top, protect the bottom of the slide by placing a brass shim
between the piston and the slide face.
The contact pressure between
the piston of the jack and the slide face should be
considered. Limit the contact pressure to 15,000 psi.
If necessary use steel spacers of suitable thickness and
size between the piston and slide face to limit the pressure
and distribute the forces.
Do not use a force that will
generate more than 150% of the total weight of the slide and
components. If deflection testing was required, larger
forces would be necessary and special considerations would
be given to assure that no damage to the equipment resulted.
Main bearing clearances
The general condition of the
main bearings may be checked by placing indicators at points
shown in Figure 1. The intent is to attach the base of
the indicator to the structural portion of the crown and
measure the vertical movement of the crankshaft when
force is applied by the jack. In the case where access
to the main bearing and crankshaft is limited by the press
design, an indicator may be placed outside of the interior
frame work of the press as shown at point "A". The
readings taken at this location will not be exact, but will
provide a good approximation that is helpful when comparing
the readings taken at point "D".
To begin taking the measurements,
lets assume that the clearance on the LH side of the press
will be taken first and that the jack and lower indicator
are positioned as shown in figure 1. Remove all
pressure from the jack to the slide face. Set the
lower indicator dial to zero. Place indicators at
position "A" and "D" on the LH side of the press. Set
dials to zero. Increase the jack pressure until the
lower indicator needle stops moving. Record the lower
indicator measurement. Record the measurements at
points "A" and "D". Release the jack pressure and repeat the
test in order to confirm the measurements. They should
repeat within 5%. Remove the jack pressure.
Move the upper indicators to
points "B" and "E". Set dials to zero. Increase
the jack pressure until the lower indicator needle stops
moving. Record the lower indicator measurement.
Record the measurements at points "B" and "E". Release
the jack pressure and repeat the test. Remove the jack
Remove the indicator at point
"E". Move the indicator from point "B" and place the
indicator at point "C" on the LH side of the press.
The indicator base is attached to the side of the connection
and the plunger of the dial indicator is set to the top of
the connection screw. The clearance from the wrist pin
to the pocket of the connection will be measured.
Increase the jack pressure
until the lower indicator needle stops moving. Record
the lower indicator measurement. Record the
measurements at point "C". Repeat the test to verify.
Remove the jack pressure.
Repeat this series of tests
on the RH side of the press.
Evaluate the results of the
As a rule of thumb, the
clearance from journals to bushings is equal to .001" per
each inch of journal diameter. If the journal is 5"
diameter, then the clearance measured should be .005".
The rule of thumb does not hold for journal diameters above
18", high speed presses, or high tonnage presses. In
most instances, the allowable clearance can be up to two
times the recommended clearance, but is dependant on the
part processing requirements, press speed, and counter
balance system operation. The press should be operated
slightly over counter balanced. The counterbalance
system will tend to hold the slide and components "tight
together", thus reducing the clearances in the system.
Blanking or stripping operations require clearances that are
more in the recommended range.
Most important is that the
clearances in the RH and LH side of the press are
approximately the same! If the clearances are
unequal, most likely there is an underlying problem that
needs to be addressed in the near future. A bearing could be
damaged or the crankshaft cracked. Also, the slide
will be subjected to "out of parallel" operation as it
operates through its stroke. This can cause undue gib
wear and possibly affect forming and blanking operations.
Upper connection bearing clearances
The notes above apply.
Lower connection screw clearances
The measurements taken at
point "B" record the clearances between the lower connection
housing and the adjustment assembly. If the adjustment
assembly is as shown in figure 1, the total clearance would
be a combination of thread clearance and nut to housing
clearance. The allowable clearances for threads range
from .007" to .020". The allowable clearances for the
nuts to housings are from .005" to 015". As stated
above, it is most important that the RH and LH clearances
are approximately equal.
Lower connection pocket/wrist pin area
The measurements taken at
point "C" are the clearances between the wrist pin and
connection head to pocket. In general these clearances
should be minimal ( in the range of .005" - .010" ).
Blanking and stripping operations will have a detrimental
effect if these clearances are too large. As before,
the RH and LH clearances should be approximately equivalent.
Periodic mechanical power
press inspection is an essential part of any maintenance
program. The above procedure should be
repeated at six months intervals. The measurements taken in
the previous inspection should be
compared with the new, and if necessary, corrective action