Troubleshooting Finish Problems on the Through Feed Moulder

      Checklist table of problems and solutions for moulder operators. December 1, 2006

Reprinted with permission from Diehl Machines, www.diehlmachines.com.

Troubleshooting Finish Problems
on the Through Feed Moulder
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.

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.

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.

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.

Reprinted with permission from Diehl Machines, www.diehlmachines.com.


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