1. Glazing (too many knife marks per inch).
Probable cause: Three factors determine the desired number of knife marks per inch: the cutterhead knife speed, the feed rate of the material and the number of knives involved in the finish cut. Solutions: (1) Raise the feed rate of the material; (2) use fewer knives in the finish cut; or (3) reduce the spindle RPMs.
2. Burning/burn marks on the surface.
Probable causes: (1) This can occur when feeding is stopped; (2) when the cutterhead knives are dull; or (3) the edge of the knife burns on a vertical plunge in the pattern. Solutions: (1) Maintain an even flow of material through the machine; (2) keep knives sharp; and (3) grind a relief angle the plunge of the knife.
3. Skipping (areas that didn’t get cut).
Probable causes: (1) The cutterhead prior to the finish spindle removes too much material; or (2) not enough material is left for the pattern head to make the finish cut. Solutions: (1) Check the depth of cut on the cutterheads prior to the finishing spindle; or (2) ensure enough material is present in the rough cut material to allow at least 1/32 inch depth of cut per cutterhead.
4. Parallel lines/ridges visible along the length of the material.
Probable causes: (1) This can be caused by irregularities in the cutting edge of the knife due to grit and lumber defects; or (2) the heavy joints on the knives are crushing the grain instead of cutting it. Solutions: (1) Keep the knives sharp and use a pre-surfacing cutterhead to remove grit before it reaches the finishing cutterhead; or (2) keep the joint on the knife to a minimum.
5. Chatter (shows as a ripple in the finish).
Probable causes: (1) Can be caused by the improper setting of the chipbreakers or holddowns; (2) an unbalanced cutterhead; (3) worn spindle bearings; or (4) a one-knife finish at a high feed rate. Solutions: (1) Keep chipbreakers and holddowns tight enough to prevent the material from moving; (2) balance the knives, gibs and cutterheads; (3) replace or repair the spindle assembly; or (4) joint the cutterheads or slow the feed rate.
Probable causes: (1) Tapering down the width may be caused by an improper adjustment of the guiding surfaces; (2) tapering down the thickness can be cause by an improper alignment of the bed plates and outfeed table; or (3) a side-to-side taper, which can be caused by the reasons listed above, knives not being ground parallel to the cutterhead, the jointer not being parallel to the spindle or the spindle not parallel to the bed plates. Solutions: Check alignments. (1) Realign the side guides; (2) realign the bedplates and outfeed table; plus (3) check the alignment of the grinder and realign the jointer bar or the spindle.
7. Fuzzy grain.
Probable causes: (1) Excessive moisture content; (2) having the wrong cutting angle of the knife for the material being cut; or (3) dull knives. Solutions: (1) Ensure the wood is dried properly, decrease the feed rate and increase the cutting angle of the knife; (2) along with increasing the cutting angle, face grind the knives; and (3) keep the knives sharp.
8. Corrugated grain.
This occurs mostly in yellow pine or red wood, when the summer wood fibers project above the spring wood fibers. Probable cause: The feed system or holddown crushes the wood and it springs back after being cut. Solutions: Reduce the feed pressure, keep the knives sharp and/or reduce the feed rate.
9. Layered grain (the growth rings curl up).
Probable cause: The feed system or holddown crushes the wood and it springs back after being cut. Solutions: Reduce the feed pressure, keep the knives sharp and/or reduce the feed rate.
10. Chip marks/abrasion marks.
Probable causes: (1) The wood chips are dragged across the surface by the cutterhead knives or (2) the wood chips cling to the feed rolls. Solutions: (1) Decrease the feed rate, keep knives sharp and increase the dust collection; and (2) check or increase the dust collection.
Probable causes: (1) Knives are cutting against the grain; (2) the lumber is too dry; or (3) you’re machining glued stock with grain variations. Solutions: (1) Align the grain directions in the glued stock and/or decrease the cutting angle of the knife; (2) set the knives in to the cutterhead; or (3) set the chipbreakers and inserts as close as possible to the cutterhead.
Source: Diehl Machines. For more information call (260) 563-2102 or visit DiehlMachines.com.
Have something to say? Share your thoughts with us in the comments below.