TROUBLESHOOTING FINISH PROBLEMS ON THE
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CONDITION |
DESCRIPTION |
PROBABLE CAUSE |
HOW TO CORRECT |
Glazing | A glazed surface is simply one where there are too many knife marks per inch. |
The desired number of knife marks per-inch is determined by the cutterhead knife speed, the feed rate of the material, and the number of knives involved in the finish cut. |
Raise the feed rate of the material. |
Use less knives in the finish cut. | |||
Reduce spindle RPM’s. | |||
Burning | Burn marks on the finished surface of the material. |
Will usually occur when feeding is stopped with material in the machine. |
Keep material flowing through the machine. |
When cutterhead knives are dull, some species like hard maple, will tend to burn. |
Keep knives sharp. | ||
The edge of the knife will burn on a vertical plunge in the pattern. |
Grind a relief angle on plunge of knife. | ||
Skipping | Areas on the finished part that did not get cut. |
Sometimes a cutterhead prior to the finish spindle removes too much material. |
Check the depth of cut on the cutterheads prior to the finishing spindle. |
Not enough material will be left for the pattern head to make a finish cut. |
Stock preparation. Enough material should be present in the rough material to allow at least 1/32″ depth of cut per cutterhead. |
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Parallel lines | (Ridges) – Can be seen along the length of the material. |
Parallel lines can be caused by irregularities in the cutting edge of the knife due to grit and lumber defects. |
Keep knives sharp. |
Use a pre surfacing cutterhead to remove grit before the finishing cutterhead. |
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Heavy Joints on knives cutting soft wood can crush the grain instead of cutting it. |
Keep joint on the knife to a minimum. | ||
Chatter | (Washboard effect) – Will show as a ripple in the finish. |
Can be caused by improper setting of chipbreakers or holddowns. |
Keep chipbreakers and holddowns tight enough to prevent the material from moving. |
Unbalanced cutterheads. | Balance knives, gibs and cutterheads. | ||
Worn spindle bearings. | Replace or repair spindle assembly. | ||
A one-knife finish at high feed rate. | Joint the cutterheads or slow the feed rate. | ||
Taper | The finished material is tapered down the width. | Is caused by improper adjustment of guiding surfaces. | Realign the side guides. |
The finished material is tapered down the thickness. | Is caused by improper alignment of the bed plates and outfeed table. |
Realign the bed plates and outfeed table. | |
The finished part is tapered side to side (or top to bottom). |
Can be caused by improper alignment of the bed plates or outfeed table. |
Realign the bed plates and outfeed table. | |
Can be caused by cutterhead knives not being ground parallel to the cutterhead. |
Check the alignment of the grinder. | ||
Can be caused by the jointer not being parallel to the spindle. |
Realign the jointer bar. | ||
Can be caused by the spindle not being parallel to the bed plates. |
Realign the spindle. | ||
Fuzzy grain | The fibers of the wood project from the finished surface of the material. |
Usually caused excessive moisture content. It is most prevalent in basswood, elm, and aspen. |
Proper drying of wood will help eliminate this problem. |
Decrease the feed rate. | |||
Increase the cutting angle of the knife. | |||
Can be caused by the wrong cutting angle of the knife for the material being cut. |
Increase the cutting angle of the knife. | ||
Face grind the knives. | |||
Can be caused by dull knives. | Keep knives sharp. | ||
Corrugated grain | Occurs mostly in yellow pine or red wood when the summer wood fibers project above softer spring wood fibers. |
The feed system or holddown crushes the wood and it springs back after being cut. May be amplified by wet material. |
Reduce feed pressure. |
Keep knives sharp. | |||
Reduce the feed rate. | |||
Layered grain | The growth rings curl up, giving the surface a raised grain appearance. |
A defect found most often in yellow poplar when annual rings curl up. |
Keep knives sharp. |
Feed material with bark side to the pattern as much as possible. |
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Chip Marks | Abrasion marks in wood surface caused by chips being scraped across the finished surface. |
Wood chips dragged across the surface by the cutterhead knives. |
Decreasing the feed rate. |
Keep knives sharp. | |||
Increase the dust removal system. | |||
Wood chips clinging to feedrolls on through-feed moulders. |
Increase the dust removal system. | ||
Tear-out | Can occur as moderate to severe; where sections of the material have split along the grain. |
Can be caused by knives cutting against the grain (such as near knots, etc.). |
Align grain directions in glued stock. |
Decrease the cutting angle of the knife. | |||
Lumber is too dry. | Set the knives in to the cutterhead. | ||
Machining glued stock with grain variations. | Set the chipbreakers and inserts as close as possible to the cutterhead. |
Questions?
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