Moulding Knives by Mirror Reflections

Moulding Knives
by Mirror Reflections
(801)451-5987

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Moulding Knife Breakage

This article will provide some safety tips, suggestions, causes and solutions on how to by-pass moulding knife damage or breakage on industrial moulder's while milling lumber.

Industrial molding knife damage occurs daily in our industry, it is an unfortunate situation, but is more common than one would think, this phenomenon will eventually materialize with all machine operators throughout their careers.

Everyone's concern is the safety of the machine operator and others around the milling operation; this reiterates the obligation that all cutterhead guards, hoods, and other safety devices should always be in there proper place and functioning throughout the service life of the machinery.

Below are a couple of images of damaged knives we received for sharpening. On the first pic, look where the pencil is pointing, it is obvious these blades lightly struck one of two areas on the moulder, either they came in contact with the left adjustable guide fence (most likely), or the machines bedplates. What's notable is, we had the knives designed the exact opposite before these cutters were signed off, and manufactured, but the business owner insisted we mill the thin portion of the profile closest to the left outside edge on the machinery. We explained that the blades could easily be damaged while milling, Mirror Reflections has designed and manufactured moulding knives for over thirty years, but some people have no interest in useful information, sometimes you cannot save people from themselves luckily no one got injured.

Knives with Blunt Edge from Striking Machinery

In the crown knives image, the blades struck multiple foreign objects buried in the lumber, or end grain of the wood while milling. We will refrain from speculating on how these knives were broken, in some cases we just do not know.

Damaged & Broken Crown Knives

We have compiled a list below of possible causes and solutions of items that might contribute to possible 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 machinery.

Cause:
Moulding knives encountered the bedplates, chip breakers, guide, or stationary fences while in operation.
Solution:
Rotate moulding knives slowly by hand in reverse of normal rotation during setup. This procedure will confirm cutters will clear all obstacles they may encounter during milling. Perform a crash test on all chip breakers, chip deflectors, and pressure elements with a 2x4 during set up, adjust cutting circle if necessary. Proper knife design is essential in all profiles for this to be problem free.
Cause:
Knots in the lumber may dislodge while milling, they became projectiles striking the blade, which causes fracturing, and or breakage.
Solution:
Possessing a small rubber or hard plastic mallet would allow the machine operator to lightly tap the knot or knots to assure oneself that these knots in the lumber would proceed thru moulder and remain intact throughout the process.
Cause:
Moulder operator halted the cutter head spindle motors prior to the machine’s feed system. Motor spindle brakes stop the cutterhead spindles very quickly, if motor spindle brakes activate while the feed system is in operation it could be the origin of knife breakage, some newer models of moulder’s have safety limits in place to avoid this action from occurring.
Solution:
Incorporate systematical procedures for starting and stopping of the cutterhead spindles and feed systems, all machine operators are required to obtain extensive training in these guidelines.
Cause:
Machine operator neglected to remove the lash or slop in the adjusting screw threaded rod on moulding cutterheads during set up procedures. The probability exists that when running a profile where the knives are close to the bedplates while operating, slop or lash in top spindle adjusting screw threads will allow the knives to encounter bedplates resulting in breakage of the cutters.
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 operator that all lash in adjusting screw threads was eliminated, it is commonly referred to as the loop on CNC spindles. On the top horizontal spindle, set knives horizontally during set up, this procedure will eliminate the possibility of the knives encountering the bedplates or guide fences 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 the moulder was shut down with lumber still in machine, while in the off position, manually release spindle brakes 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 operator placed the machine under full workload before the machine had a chance to reach full rpm’s causing excessive stress on 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 machine set up techniques; fences, chip breakers, and guides tightly adjusted, feed system not properly fine-tuned for thickness of lumber, this causes 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 the 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 the high speed knife steel after cutting, and while grinding can cause fracturing of the tool leading to breaking upon using the knives please refer to our article on aligning moulder knives in the cutterhead.
Solution:
Do not submerge knives in cold water after cutting to length; let the knife blanks cool at room temperature, the sudden change can cause the knife to fracture without you even realizing it. Use enough coolant from the face (smooth side) of the knife while profile grinding. Burn marks on the face side of the knife steel indicate burning of the tool, this makes the blade fragile, the brittle the knife steel, the easier it is to break.
Cause:
Dull knives, the spindle motor will generally always force the blades to cut, but if the knife is dull it will build up heat, initiate finish issues, and eventually fracture leading to 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 height sizes on all our profile cad drawings, if you routinely use a bigger size steel to make it last longer, you are only increasing the size of your cutting circle, this can lead to knife breakage from unsupported lumber while machining.
Solution:
Please refer to our article on cut steel size for moulding knife blanks this will lessen the possibility of knife breakage.
Door Casing Knives

We have provided you with some especially important information about high speed steel and carbide cutters, and some reasons for failure during manufacturing and milling of lumber. Although we may not have covered all the reasons for knife failure, these solutions will solve many issues. A highly skilled, experienced machine operator with 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 for moulder operators to eliminate concerns not discussed in this article. If we can be of any further support, please, contact us .

Superior Quality Moulding Knives, Profile Templates & Tooling Since1997
Custom made in the USAMoulding Knives Made in the USA

Moulding Knives by Mirror Reflections

1588 South 250 East | Kaysville, Utah 84037

Phone/Fax: 801-451-5987 

Moulding Catalog Updated Thursday, February 29, 2024

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