Introduction and Summary
The following proposal is to design and build a heavy duty cutter spindle and
housing capable of removing bond and resin from extremely hard grinding wheels. The
resulting design will replace an old, outdated design currently in use at Saint-Gobain
Abrasives organic grinding wheel plant in Worcester, MA. For a relatively low cost, this
new design will save lost production from downtime and expenses to repair the outdated
heavy duty cutters.
Problem Definition
At the organic abrasives plant in Worcester, MA BZZ and foundry wheels must
be faced before they are balanced, speed tested, and shipped. For BZZ wheels, facing is
the process of removing bond and resin from the grinding face of the wheel to expose the
abrasive grains. For foundry wheels, the grains are already exposed after molding but are
sharpened through the facing process. In Worcester facing is done with conical cutters.
The heavy duty three inch cutter spindle and housing design date back to 1943,
before BZZ wheels were in production. BZZ wheels are the hardest of the organic
abrasives and are used to condition hard metals such as titanium at foundries. Three
wheels at a time are mounted on the facing machine and a horizontal slide moves two top
slides, each with a 3” cutter, across the face of the wheel. The cutter spindle frequently
breaks costing downtime and lost production while the cutter is changed. The problem
has also begun costing a significant amount of money.
Background Information
While there is no doubt these spindles have broken in the past, the problem
became increasingly evident in 2004. The slides are controlled by hand and facing was
considered one of the worst jobs from an operator’s standpoint in the entire plant. In
2004 an operator went out of work on a back and shoulder injury incurred while running
the facer and never returned to work. As part of the 2004 Ergonomic Improvement
Projects, a hydraulic assist was added to the slides eliminating the operator’s feel of the
cut as they are facing.
Beginning in 2004, Richard Leslie, a 25 year employee of Norton/Saint-Gobain,
volunteered to rebuild the 3” heavy duty cutters in the Plant 8 tool room as fill in work.
Immediately following the addition of hydraulics, Rich noticed more and more spindles
were breaking. The spindles break in the exact same location, immediately before the
bearing on the work end, every time. He went to his supervisors, who went to
engineering for help, but got no where. Finally, he submitted a CIP (continuous
improvement program) form to the plant manager highlighting the problem and a need
for a solution. Along with the CIP, he tallied up the cost to rebuild the cutters from 20042007 and found about $60,000 had been spent in parts alone! This information can be
found in detail in Appendix I.
The CIP was approved and sent to engineering for review. Immediately, a
problem was evident with the current cutter design. During facing, the spindle is
subjected to tremendous radial and axial loading. When the conical cutter is brand new,
the spindle runs at around 3600 RPM, but as the cutter is worn down speeds of 4500
RPM are reached. Lubrication was standard white lithium grease not suited for these
speeds and loading. The work end bearing is preloaded through a lock nut that draws a
labyrinth seal into the outer race of the bearing. All this is old technology.
Several quick fixes were attempted to increase the service life of the cutter. On
the assembly print of the cutter, part B-162833 (the flinger), called for a 0.25 inch radius
in the ID to slip onto a 0.25 inch radius on the shaft. The thickness of the flinger does not
allow for this radius to be machined exactly, so the radius never fully seated on the shaft.
Where the flinger makes contact with the bearing is where the break always occurs. An
analysis of several shafts removed from service shortly before breaking showed a score
mark on the shaft from the flinger consistent with the breakage point of the spindle. The
flinger was redesigned, specifying the radius be opened more to better fit the spindle.
This effectively eliminated scoring of the shaft, but did not solve the problem
An analysis of the fracture determined there are two distinct types of breaks that
always occur in the same location. One fracture is from shear. In this case, the operator
tried to make too deep of a cut and the spindle broke immediately. The second fracture
shows there was significant strain and heat before the yield of the material was reached
and the spindle finally broke. This was an important discovery for the project, as the
operators always stated, once the spindle starts to resist turning it is doomed for
destruction.
This led to an investigation of how a preloaded spindle assembly could loosen or
tighten up during facing. Figure I shows the mounting of the cutters on the top slide:
Figure I
The grinding wheel on the arbor spins counter clockwise, so as the red cutter makes
contact with the wheel it spins clockwise. As the yellow cutter makes contact with the
wheel on return passes, it spins counter clockwise. In effect, this causes the red cutter to
tighten up, to the point where they often will not turn, and the yellow cutter to loosen up.
This was clearly evident when the cap was pulled off the end of a yellow cutter and the
lock nut had come off the spindle and was driving into the end cap.
After these problems were discovered, a meeting was set with Pentii Elolampi, a
retired mechanical engineer from Norton Company’s Central Engineering. After
reviewing the problem, Penttti, Ronald Leger (Sr. Electrical Engineer), and Eric Laliberte
agreed the only way to completely solve this problem was the complete redesign of the
3” heavy duty cutter.
The Need
Facing is a critical part of grinding wheel production, but for BZZ wheels is
actually purely cosmetic and done specifically for the customer. Facing is done with a
red and yellow (left and right). The operator first uses the red cutter to remove the bond
and resin and start the beveled edges. The edges are cleaned up on the return pass with
the yellow cutter. BZZ wheels are the so-called bread and butter of the organic business
with a retail value of around $400 per wheel (depending on size and grade). Depending
on the customer, BZZ wheels are faced on the facer or in a Wheelabrator. In the
Wheelabrator, the wheels are stacked flat on an arbor on a rotating table that is pelted
with steel shot inside the machine. The steel shot removes the bond and resin but does
not cut the abrasive grains. The facer gives the wheel an aggressive look right out of the
box that customers have become accustomed to. The need is to design a heavy duty
cutter that will consistently face wheels and keep the customers happy.
The Objective
The objective of this project is to design a right and left heavy duty cutter spindle
and housing capable of facing BZZ and foundry wheels. Currently, if the operator makes
an error in cut the spindle is the first to break, the weakest link, and the most expensive,
in the design. When completed, the new cutter spindle should not break before the cutter
cone, or the bolt that secures the cone breaks. The final design will have to abide by two
restrictions: the effect of cut on the wheel cannot be changed and the position of the
cutters on the machine cannot be changed.
Functional Requirements
Functional Requirements for this project are as follows:
 Design a new spindle (left and right)
 Design a new housing
 Use oil lubrication
 Specify bearings that can handle measured speeds and estimated loading
In designing a new spindle, a new material may be specified to handle the abuse
of facing. A new housing will then have to be designed to secure the spindle. Bearings
should be specified to handle the speeds and loading of the final assembly. The housing
design will incorporate new preloading of the bearings to get away from the labyrinth
seal and loading the entire assembly from the lock nut. Because of the speeds the
bearings will see, oil lubrication will be preferred over grease.
Project Work Plan
While the group posses a good understanding of the problem and the solution, a
final design has not yet been determined. Field testing is currently underway in
Worcester to answer a few questions. One important question is the position of the cutter
cone in relation to the grinding wheel. Standard practice is to have the centerline of the
cone below the centerline of the main arbor to create down pressure on the cone helping
the cone to cut. Measurements show the current centerline is 0.75 inches below. We
need to make this smaller to be able to increase the shaft diameter and housing size. The
second test is a thermal analysis to determine the heat being seen by the components.
Following the results of this testing, design will begin. The group has already
begun researching bearings and shaft material. Our goal is to have a final design by the
end of June so the prints can be released for manufacture. We will use a local shop with
a quick turnaround time to get the parts machined and returned for assembly. We would
like the design tested in Worcester before the scheduled final presentation.
Qualifications
Eric Laliberte:
Two co-op semesters at Saint-Gobain Abrasives, Worcester
Originally assigned the facer CIP
Coursework in machine design, strength of materials, materials science, heat transfer, and
kinematics at Wentworth Institute of Technology
Frank Colantuoni:
Coursework in machine design, strength of materials, materials science, and heat transfer
at Wentworth Institute of Technology
Travis Fanion:
Westfield Vocational Technical High School, Machinist
Employee of Tell Tool
Coursework in machine design, strength of materials, materials science, heat transfer, and
kinematics at Wentworth Institute of Technology
Mark Zumbahlen
Coursework in machine design, strength of materials, materials science, and heat transfer
at Wentworth Institute of Technology
Project Budget
Saint-Gobain Abrasives has already approved funding for this project. Project
accounting is explained as follows:
Projects in excess of 10,000 Euros ($15,400) require a formal proposal to Saint-Gobain
known as a request for authorization (RA). Projects of $2,500 and less can be approved
by a local plant manager and overseen by the plant’s engineering group. This project will
have a contact, Ronald Leger, in Worcester. Charges for the project are paid for on a
central work order. Charges to the project are as follows:



Non exempt support help: technicians conducting the above mentioned testing
will charge time to the work order
Manufacture: the spindle and housing manufacturing charges
Parts: bearings, seals, lock nuts, lock washers, bolts, and lubrication
The estimated cost of the project is $1,200.00
Project’s Future
This is only the first phase of a large project to improve the facing operation at
Saint-Gobain Worcester. Following the completion of this phase, new larger heavy slides
will be placed on the machine to help take the abuse of facing. A tailstock will be
designed and installed to capture the wheels on the main arbor significantly reducing
vibration. Through the slides and tailstock, vibration may be reduced enough to open the
machine up to CNC controls, ultimately eliminating a variable, the operator, from the
facing operation.