This article will provide some safety tips, suggestions, causes and solutions on how to
by-pass moulding knife damage and or breakage on industrial style moulders.
Industrial moulding knife damage occurs daily in our business, it is an unfortunate situation but it is
inevitable; this is something that will materialize with all moulding machine operators eventually.
Everybody’s main concern should be the safety of the moulding machine operator and others around the moulding
machinery; this reiterates that obligation, all moulding machine guards, hoods, and other safety devices should
always be in there proper place and accurately functioning throughout the service life of the moulding
Below is an image of a damaged moulding knife we received for sharpening. It is obvious these crown-moulding
knives hit multiple foreign objects in the lumber while in the milling process. We will refrain from speculating
on how these moulding knives were broken, thankfully no one was injured.
We have compiled a list below of possible causes and solutions of items that might contribute to possible
moulding knife fracture and breakage. Your safety and health are our primary concern, it is your duty and
responsibility to abide by all safety practices set forth by your employer and the manufacturer of your moulder
- Cause: Moulding knife encountered the bedplate, chip breakers and or fences while in
- Solution: Rotate moulding knives slowly by hand in reverse of normal rotation during setup.
This procedure will confirm moulding knives will clear all obstacles they may encounter during milling
operation. Perform a crash test on all chip breakers, chip deflectors, and pressure elements with a 2x4 during
set up, adjust cutting circle if necessary.
- Cause: Knots in the lumber may dislodge while milling, they became projectiles striking the
moulding knives, which causes fracturing, and or breakage.
- Solution: Possessing a small rubber or hard plastic mallet would allow the moulder operator
to lightly tap the knot or knots to assure oneself that these knots in the lumber would proceed thru moulder
milling and remain intact throughout the process.
- Cause: Moulder operator halted the moulding spindle motors prior to the moulding machine’s
feed system. Motor spindle brakes stop the moulding spindles very quickly, if moulder spindle brakes activate
while the feed system is in operation it could be the origin of moulding knife breakage, some moulders have
safety limits in place to avoid this action from occurring.
- Solution: Incorporate systematical procedures for starting and stopping of the moulder
spindles and feed systems, all moulder operators are required to obtain extensive training in these
- Cause: Moulding operator neglected to remove the lash or slop in the adjusting screws
threaded rod from moulding spindles during set up procedures. The probability exists that when running a
moulding profile where the moulding knives are close to the bedplate, while operating, slop or lash in top
spindle adjusting screw threads will allow moulding knives to encounter bedplates resulting in breakage of the
- Solution: While setting up moulder, all final movements of moulder spindles should be
toward the lumber except the top spindles, this action will assure the moulder operator that all lash in
adjusting screw threads was eliminated. On top spindle, set knives horizontally during set up the top spindle
cutter head, this procedure will eliminate the possibility of the moulding knives encountering bedplates when
removing lash from top spindle adjusting screw.
- Cause: Moulder operator started moulding machine with woodwork piece already in moulder,
overlooking manual hand spinning heads in reverse of normal rotation prior to exclude any tension that might
occur on work piece before starting.
- Solution: If moulder was shut down with lumber still in machine, while in the off position,
manually release spindle breaks if applicable, check spindle rotation by hand, in reverse of normal rotation
to assure cutter head is capable to spin freely when spindle motor is activated.
- Cause: The Moulder operator placed the moulding machine under workload before the machine
had a chance to reach full rpm’s causing stress on moulding knives even breakage.
- Solution: Most new style moulders that utilize flat belts on spindles and motor pulleys
have soft start motors. Soft start is a two-stage start up procedure to achieve full rpms and keep the belts
from burning or breaking during startup. Soft start motor stages are controlled by timers in the electrical
cabinet, give the moulder about 15-20 seconds after starting, this time allows for the second timer to engage
giving full rpm’s power to the motor, eliminating the opportunity for moulding knife breakage.
- Cause: Improper moulding machine set up techniques; fences, chip breakers, and guides
tightly adjusted, feed system not properly fine-tuned for thickness of lumber, this triggers feeding issues.
Whacking the ends of boards against one another to get the lumber to advance through moulder feed system will
increase probability of breaking moulding knives quickly.
- Solution: A firm setup is fine, the tighter the setup the more friction and increased
pressure on the feed system, the feed system should be set at the finish thickness size. Proper training will
eliminate most feeding problems for moulding machine operators.
- Cause: Improper cooling of moulding knife steel after cutting and while grinding can cause
fracturing of the tool leading to breaking upon use of moulding knife. Please refer to our article on
aligning moulder knives.
- Solution: Do not submerge moulding knives in cold water after cutting to length; let
moulding knife blanks cool at room temperature, the sudden temperature change can cause the knife to fracture
without you even realizing it. Use enough coolant from the face (smooth side) of the moulding knife while
profile knife grinding. Burn marks in the knife steel indicate burning of the knife steel, which makes the
moulding knife fragile, the more brittle the knife steel the easier it is to break.
- Cause: Dull moulding knives, the spindle motor will generally always make the knife cut,
but if the knife is dull it will build up heat, initiate finish issues, and eventually fracture leading to
moulding machine damage.
- Solution: This is an easy fix; keep your moulding knives sharp!
- Cause: Improper steel size, we always supply you with the correct steel sizes on all our
moulding profile cad drawings, if you routinely use a bigger size steel to make it last longer your only
increasing the size of your cutting circle, this can lead to knife breakage.
- Solution: Please refer to our article on
cut steel size for moulding knife blanks
this will detour the possibility of moulding knife breakage.
We have provided you with some very important information about moulding knives and some reasons for failure
during moulding manufacturing. Although we may not have covered all the reasons for moulding knife failure,
these solutions will solve many issues. A highly skilled, experienced moulder operator with proper formal
training can significantly reduce the possibility of the concerns expressed in this article. We also recommend
reading our article on
production tips for moulder operators to eliminate
concerns not discussed in this article.
If we can be of any further support, concerning moulding knives or any other topic in wood
mouldings please, contact us.