Troubleshooting Moulders

Throughout this page, we’ll cover various issues that arise when setting up and operating moulders in high volume millwork shops. These setup and troubleshooting procedures reflect how we run industrial moulders daily in production environments. This information is intended for trained operators and production teams. For a basic moulder overview, click here.

While each issue alone is generally easily solved, with moulders, the problem is a single part of a multi part process such as 5 cutter heads with multiple feed wheels and pressure elements. As such, it can be difficult to know where to start to figure out the solution. We’re going to break down issues by type. We’ll also discuss the basic causes and then the remedy and then do a little deeper dive into why it’s happening.

Troubleshooting topics
1) End snipe
2) Reducing 1st bottom cut
3) Width variance
4) Tearout
5) Feed issues
6) Chatter
7) Burning
8) Feed roller marks
9) Dimpling

Snipe can happen on any head and is generally indicative of some type of misalignment.  In real world production, this means the end of the board becomes unusable.  That’s no good.  Let’s take a look at the heads, causes, and remedies.  

1st Bottom head
Head is too high compared to outfeed table. Remedy by lowering the head to be in line with the outfeed table.

Inside Head
Head is projecting too far beyond the outfeed fence. Remedy by moving the head inward until it is flush with the outfeed fence.

Outside Head
“T” is not set in line with the cutterhead. This will also usually result in varying widths down the length of the piece. To remedy, stop a piece and then adjust the T to be snug against the material.

Top Head
Depends on the location of the snipe. Last 3” is generally because the pressure foot isn’t adjusted down enough. Snipe at 8” from the end is usually a combination of too low of feed rolls combined with too little chip breaker down pressure. If the feed rolls are too low, as the piece passes the last feed roll prior to the chipbreaker without a piece immediately following it, it tends to lift it up slightly as it comes off the feed wheel (especially with metal feed wheels), and if there isn’t sufficient chip breaker pressure to counteract that, it will allow the piece to lift up into the cutter head and snipe. To remedy, raise the feed frame and increase the chipbreaker pressure.

2nd Bottom Head
Head is too high relative to the outfeed table. Remedy by lowering the head to be flush to the outfeed table. This will change your thickness, so any changes will need to also be mirrored in the top head. For example, if your dimension is correct and you lowered this head by .020”, your piece will now be .020” thicker than spec. You’ll need to lower the top head by .020” to maintain correct thickness.

For the first bottom head, inside head, and 5th bottom head, these are all jointing heads. What this means is that as the piece is moving down the infeed fence, there is a cutterhead in line with the outfeed fence, and the material is trued up (any bow or wiggle removed) so that it is aligned with the outfeed fence. These cuts generally do not set the thickness of the piece (with the exception of the 5th head), and they’re only used to true up a face or edge.

For the first bottom head and the inside head, the amount of cut is adjusted from behind the infeed rail. For the 5th bottom head, it is controlled by a combination of the head height above the table and with shims below the outfeed table. Currently on our moulders, the outfeed bed is set .020” higher than the infeed bed for the 5th head. Ideally this head is set flush to the raised outfeed bed height.

For all of these heads, the infeed reference plane is parallel to the outfeed plane, just offset by a certain amount. In a perfect setup, the cutting circle of the head is in line with the outfeed plane. So as the piece feeds through the machine, the cutterhead removes exactly the amount of material necessary to flush the material to the outfeed table/fence. When the head is misaligned, it will tend to cause either snipe or a reduced cut over the length of the piece. We’re discussing snipe here.

What to watch for:
For simplicity of the explanation, let’s discuss the inside head here. As the piece moves through the machine, it’s moving parallel to the infeed fence. It will move into and past the inside cutterhead. Now we watch as it meets the outfeed fence. 1 of 3 things will happen.
1) it’s perfectly in line with the outfeed fence.
2) it hits the outfeed fence and pushes towards the outside head.
3) there is a gap between the material and the inside fence.

Snipe is caused by number 3. If we continue to watch this piece, we will see it contact the side pressure element prior to the outside head. This will usually push the piece tight against the fence. If you were to stop the piece and look down from above, the piece would be tight against the fence near the side pressure element, but have a slight gap (maybe just a few thousandths) at the fence near the cutterhead. It will continue to cut parallel until the end of the piece, meaning in this scenario, the width of the piece will be consistent.

What is actually happening
As the end of the piece passes the end of the infeed fence, the side element pushes the tail of the piece tight against the infeed fence. Remember, there was a gap there before. As the piece is forced tight to the outfeed fence, it moves into the cutterhead slightly allowing the head to remove more material than previously allowed. The infeed fence is what is holding the piece away from the outfeed fence. As it comes off the infeed fence, the piece is free to move over, so because of the side pressure from the pressure element and the slight gap at the outfeed fence, the pressure element forces it tight and it aligns itself parallel to the outfeed fence, which lets the head cut more. This is snipe.

In my experience, the initial reaction to this would be to take a larger inside cut to remedy it, but since it’s a head misalignment issue, not a thickness of material removal issue, any infeed adjustments still result in the same sniping. The remedy is to adjust the head back to parallel with the outfeed fence.  

If you’re taking a 1st bottom head cut, and as the piece is being fed, the amount of the cut is getting smaller and smaller, perhaps even not taking a cut over the entire length of the piece, there is an alignment issue. This happens when the bottom head is too low relative to the outfeed table. The more the misalignment, the faster the reduction in cut. For example, if you’re taking a big cut, say ¼” over a 10’ piece, a badly aligned head may stop cutting at 6’ or 7’. A mildly misaligned head may make the full cut, but instead of taking off ¼” all the way, it may be reduced to 1/8” or 1/16” at the tail end of the piece. In this case it’s much harder to notice than if the cut isn’t made along the entire length. You have to be physically monitoring the bottom cut and watching the amount of material being removed to see a mildly misaligned head. It’s generally not something that needs to be monitored the entire run, rather, it’s something that needs to be confirmed within the first few pieces.

Typical default reaction
The default reaction to this situation is to take a bigger bottom cut. Maybe there’s enough material to be removed and this could potentially work, however, it’s not the correct solution. The correct solution is to adjust the head to be in line with the outfeed bed.

Watching the cut
If you watch the piece being fed come across the cutter head and then contact the outfeed bed, in this scenario it will generally hit the edge of the table and walk up. That would be your first indication of an alignment issue. This can also result in snipe at the beginning of the piece depending on the amount of misalignment.

Once a head is properly aligned and confirmed, it’s unlikely to change and generally doesn’t need to be watched unless an issue arises. Unless the head is replaced or adjusted, generally this setting remains stable over multiple runs.

Also applies to 1st inside head
Note: This is also applicable to the first inside head. The potential for issues is high after swapping heads on the inside cutter (say to a TnG or shiplap profile), so watch the inside cut on the first few pieces to verify alignment.

If you notice width variance down the length of the piece, it is likely the outside T that is the issue.  If check a piece every 10″-12″ down the length of the piece, and you get a variance greater than .002″, this is width variance.

T to cutterhead misalignment
The variance comes from the piece floating between the inside fence and the outside T. For example, if the T is set .010” too wide, and your outside head is set at 1”, you may see variances in your board down to .990”, as the piece can walk .010” off of the inside fence before being guided by the outside T.  You may initially think that you would see measurements up to 1.010″, but that’s not correct.  Remember, the outside head sets the width, and since the outside head is set to exactly 1″, the maximum width the piece can be is 1″.  The T being offset by .010″ will allow the piece to drift into the cutterhead, thus reducing its width by up to .010″.

Setting the T
The T should be directly in line with the cutterhead. This can be set with a straight edge before the run, however, I find a better way is to get it close, send a piece, and then pause the piece a few inches beyond the outside head. At this point, move the T in snug, but not too tight, against the piece. The T is now properly aligned. Check the piece as it comes off the moulder to see any shine or hard line on the outside edge that was contacted with the T. A heavy shine or line indicates that there’s too much T pressure. This will be more prevalent in softer woods like poplar.

Tearout is the ripping and breaking of the wood grain during a cut, rather than a smooth slice of the knives. This becomes an issue when the grain is torn below the finished surface, leaving visible damage on the face of the profile. Tearout can happen on any head, however, for this discussion, we’re going to describe the top cutter head.

Causes of Tearout:
-Dull knives
-Grain orientation
-Excessive feed speed
-Improper chip breaker settings
-Wrong hook angle on the cutterhead

When the knives are sharp, they slice through the wood cleanly. When they’re dull, they tend to rip and lift the grain rather than cut. The duller they are, the more pronounced the tearout. The remedy is to regrind the knives. While we hone our knives after sharpening them on the knife grinder, trying to re-hone dull knives takes as long as grinding and produces an inadequate finish. It is better to regrind. Also, many times you can tell a set of knives is dull by the noise of the cutterhead. If you walk by a machine and notice that one head is excessively loud, it’s likely because the cutters are dull.  

Wood is weakest along the grain lines. Tearout can happen, even with sharp knives, where the grain starts high and then runs down into the board towards the bottom face. The wood will tend to separate and rip along the grain, and since the grain is running down into the board, the tearing follows the grain down into the board until it’s severed, Sometimes this will be below the finished surface. In severe cases, the grain will run from the top face of the board down to the bottom face of the board at a steep angle. We call this short grain. Short grain in smaller pieces is extremely likely to cause breakage of the blank and cause a jam inside the machine. The remedy is multi-faceted – make sure the knives are freshly sharpened, slow the feed speed way down, and make sure the chip breaker is properly adjusted. In cases of short grain, it may be better not to run the blanks than to risk jams. You’ll notice that around knots, even if the knot has been cut out on the gang rip, that the grain swirls. For moulder operation, this means some of the cut will be uphill (likely to tear out) and some will be downhill (no tearout).

Align the blanks for the predominant grain orientation
 It is good practice to review your blanks prior to feeding and align them so that the predominant grain is rising so that the top cutter is cutting downhill. This means the grain starts at the bottom face and runs angled up towards the operator and towards the top face. In this orientation, the grain is running out of the cut from the top cutterhead and is thus, unlikely to lift and tear.  

On our moulders, the heads spin at 6000 RPMs. This is a constant speed and is not adjustable. The one variable that we can control is the feed speed. The faster the feed rate, the more material is removed by each knife on each rotation. The slower the feed speed, the less material that is removed. As an example, if we feed a board at 20 feet per minute, the knives are removing a certain amount of material. However, if we bump the speed to 40 FPM, the same knives are now removing twice the amount of material per rotation as at 20 FPM. In terms of tearout, the more material removed per knife, the higher likelihood of ripping the wood along the grain and tearing the wood. The remedy is to slow the feed down to reduce the size of the cut per knife.

The chip breaker performs two functions. First, it provides downward pressure to hold the blank against the feed bed. Second, as the name implies, it breaks off the wood chips as the knives lift material during the cut. This provides a shearing action and stops the wood from tearing further than it should. There are three chipbreaker adjustments – height, spring pressure, and set back. When any of these adjustments are improper, the likelihood of tearout is greatly increased. We generally keep the spring tension screws fully seated, meaning maxed out. So normally we don’t adjust for those.

Chipbreaker height
For the height setting, we have to understand how the chipbreaker works. The chipbreaker is set lower than the height of the blank coming through, and as the piece passes below it, the chipbreaker raises up against the springs to put down pressure on the board. There is a certain amount of travel that the chipbreaker can move up and down. If it is set too low, the travel will max out before the piece has fully cleared and the piece will jam. If it is set too high, there won’t be adequate down pressure. Ideally max travel for most of what we do is about 3/16” above the height of the blank.

Chipbreaker set back
The last adjustment we can make is the set back on the chip breaker itself. The metal piece on the bottom of the chipbreaker that contacts the blank is adjustable toward the cutterhead or away from the cutterhead. Ideally, the chip breaker is adjusted as close to the knives as possible (making sure to have clearance during the cut). In this setting, as the knives lift the wood, the chipbreaker is there to shear the piece right next to the knives, which limits the amount of tearing possible. The further away the chip breaker, the more tearing is allowed and the likelihood of tearout on the finished face is greater.

In general, we use two hook angles – 12 degrees and 20 degrees. For hardwoods (including poplar), we use 12 degrees. For softwoods such as pine (and occasionally poplar), we use 20 degrees. 20 degree heads will tend to stay sharp longer, but will tend to lift the grain more on hardwoods and as such, will tend to tear out more. 12 degree heads will need to be sharpened more often, but limit the amount of tearing out.

Feed issues arise when the friction or resistance from one or multiple items is greater than the amount of force being exerted by the feed system. There are quite a few reasons for feed issues, and most of them are self-induced, meaning they’re due to improper settings on the moulder. Settings which we control. Sometimes it’s not just one thing but a combination of two or three and it can be a little tricky to track down. These include but are not limited to the following:

1. Feed frame height too high
2. Air off or not connected to the machine
3. Side pressure element too far in
4. Chipbreaker too low
5. Varying thickness blank material (coupled with chipbreaker too low)
6. Pressure foot too low
7. T adjusted too far in
8. Lack of lubrication
9. Dull knives
10. Feed speed too slow
11. Wet “green” lumber
12. Broken pieces causing jams
13. Chips packed between blank and bed/fences
14. Head alignment (on jointing heads)
15. Large cut with dull knives
16. Air regulator set too low

Is the air on?
When troubleshooting feed issues, the first question to ask is “is the air on?” The air controls the pistons that apply down pressure on the feed wheels. The wheels may be turning and their height may look correct, but if there air isn’t on, you won’t have any down pressure and the piece will jam. 

Where did the piece stop?
If the air is on, the next question to ask is “where did the piece stop”? If the start of the piece hasn’t fully made it through the machine, the location of the beginning of the piece is generally your trouble point. Perhaps it stopped at the chipbreaker. This is either a T issue (since the T starts below the chip breaker) or a chipbreaker over pressure issue. Perhaps it stopped at the pressure foot.

The piece stops in the middle 
If the piece stops in the middle of the run and we’ve already confirmed the air is on, then we have to look for clues. Have you been pumping the lubrication? Did the thickness of the blank change (get thicker and jam under the chip breaker)? Is there a heavy shine from over pressure on the T? Is there a heavy shine from the pressure foot? Can we see a broken piece jammed somewhere causing bind (generally around the outside head/T/chip breaker)?

If the piece jams before exiting the machine
If the piece has nearly made it all the way through the machine, but the piece jams with the back end still inside the machine, we look at where the tail of the piece stopped. Generally, it will stop after coming off of a feed roller. For instance, maybe it stops after the last feed roller before the chip breaker. That could be one of three things, or a combination of all three. 1) Excessive T pressure. 2) Excessive chip breaker pressure. Or 3) Excessive pressure foot pressure. The friction from any or all of those items is greater than the amount of pressure able to be exerted by the remaining feed rollers. If we can see any shine from the T or the pressure foot, it’s likely that they’re too tight. If no shine is visible, then perhaps the chipbreaker is set too low.

Green lumber
We rarely run wet or green lumber. Occasionally we’ll process some S4S teak that has a high moisture content, and when we do, our only solution is to use a lot more bed lube. Green lumber is stickier against the metal beds and creates more friction. This in turn requires more feed pressure to overcome the friction. Excessive bed lube helps in this scenario.

Broken pieces causing jams
If broken pieces are causing jams, it’s generally because we’re sending pieces that either should be trimmed or not sent at all. Often we’ll see short grain on the last 6” of a board. In these cases, there’s a high risk of the last few inches breaking off. When it breaks off, it’s generally heavy enough that the dust collection won’t pick it up and so it stays on the bed until the following piece pushes it. It may push it out of the way, or it may jam. As an operator, we don’t blindly feed the moulder. We have to choose and approve of each blank that goes through. If we feel the piece may cause jams, kick it off to the side and have a manager review the piece and make the call. This is much faster than clearing a jam, or multiple jams.

Chatter looks like waves across a face or edge of a board. This comes from the board oscillating into and out of the cutterhead. The simplest remedy for this is increased pressure opposite the head that is creating the chatter. For instance, if we’re seeing chatter from the inside head, which may also telegraph into chatter on the outside head cut, it’s likely because we don’t have enough side pressure from the pressure elements before the outside head.  

Chatter is usually the worst on the top cutterhead, as this is generally the profiled face cut. Some reasons for chatter on the top head are:
1) Inadequate pressure foot pressure (most likely)
2) Inadequate chip breaker pressure
3) Dull knives on 5th bottom head
4) Dust collection backed up at 5th bottom head
5) Head out of balance
6) Worn out bearings

Pressure foot adjustments
Most times chatter is from inadequate pressure foot pressure. I prefer to adjust the pressure foot by sound as the machine is feeding. You can lower the pressure foot until the hammering sound diminishes. Most moulders have interlock switches that shut the machine off if the hood is opened during operation. Ours have been bypassed to allow us this adjustment. In theory, you can set your pressure foot using a straight edge off of the bottom of the pressure shoe aligned to the knives at the thickest part of the molding. I’ve done it that way but find it incredibly finicky to get just right.  

If you adjust the pressure foot too low you will either leave a shiny flat spot on the contact point or you’ll have feed issues, so it’s a fine line between eliminating chatter and causing other issues.

5th head – 2nd bottom head
Occasionally the 5th bottom head can cause issues. If it’s taking a big bite and/or the knives are dull, it will tend to hammer more pushing the piece upward. If the pressure foot isn’t correctly adjusted, it can allow the piece to bounce up into the top head with each knife strike. This is remedied with additional pressure foot pressure and/or a sharpening of the dull knives.

Sometimes there will be a dust collection issue at the 5th head, especially if it’s taking a large cut, and the chips can build up which can cause a multitude of problems from feed issues to fires to chatter, so it’s something to be aware of.

Head out of balance
If the knives were improperly ground and are uneven in weight, the head may become out of balance.  When spun at 6000 RPMs, this creates a terrible vibration.  If ran in this manner, the cut quality will be poor (chatter) and you’ll be damaging the bearings on the spindle.  To remedy, properly balance the knives.

Worn out bearings
Similar to the head out of balance, worn out bearings allow the head to move up and down while it’s rotating, which results in chatter.  However, this chatter usually is unable to be cleaned up by adjusting pressure elements.  To check, remove the head from the spindle.  Try and wiggle the spindle up and down or side to side.  Any movement here means the bearings are bad and that the spindle will need rebuilt.  

Burning is a result in friction of the cutter on the wood and is more common with harder species of wood like oak, ash, and maple. The most common type of burning results from 90 degree cuts into the wood – think shiplap or tongue and groove cuts into the edges. However, burning can also result in regular cuts from dull knives, knives that are covered in resin, or too slow of a feed speed.  If you’re starting to see burning, it’s time to regrind the knives.  If the knives are freshly ground, and you’re burning at a 90 degree angle, then there is a problem with the grind.  

Think of the set of knives that cut the groove on a tongue and groove.  The tip of the cutter is doing all of the work.  The sides of the cutter that make the top and bottom of the groove aren’t doing any work at all.  They’re just along for the ride.  If those sides start to build up pitch, that pitch rubs on the top and bottom of the cut creating friction.  When it gets hot enough, it leaves burn marks.  We remedy this by relief cutting the sides of the cutter to the point the side edges are slightly sharpened.  Any flat along this edge will build up pitch and burn.

Also, when possible, I like to not use 90 degree angles.  I’ll try and cheat the angle by half a degree or so, so that the side is doing a little bit of cutting also.  Not enough that it’s noticeable, but enough to reduce burning tendencies.  This also helps for regrinding.  Even with using this method, you still must grind a relief into these edges.

If you’re finished moldings are coming out with feed roller marks, that’s a problem. The feed rolls press against the top face of the blank. Usually, this is the finished face. As the feed rollers pass over the blanks, it leaves dents and marks from the wheel grabbing onto the material. If the top head isn’t taking a big enough bite to clean off these marks, they’ll be visible in the finished product. There are two ways to remedy this – take a larger top cut or change to a different style feed roller.

Larger top head cut
To take a larger top cut, we either must lower the top head, which changes the thickness (generally not allowable) or we must have a thicker piece going into the top head. To get a thicker piece into the top head, either we need a thicker blank to start with or we need to reduce the amount of the cut on the first bottom head. If we’ve reduced the amount of bottom cut and are still having the issues, it’s time to swap feed wheels.

Types of feed wheel
There are 3 types of feed wheels. Two are metal – serrated and knurled. The last type is rubber. Rubber wheels are normally used after the top head. Serrated wheels are the most aggressive, which helps remedy feed issues, but leaves the deepest damage across the face. We figure we need around .090″ to remove serrated wheel markings in softer material like poplar. The next style is a knurled wheel. These wheels are covered in fine dimples. They don’t damage as deep but they also don’t grip quite as aggressively as the serrated. They may need .050″ to clean up. Last are the rubber rollers. These don’t damage the finished surface but they also don’t grip as well as the metal wheels. However, if you’re in a situation where you’re removing less than .030″ of material from the top head, they may be a necessary evil.

A third option
One last option that can occasionally work if you’re cutting a profile with the top cutterhead, is to align the serrated wheels with low areas of the profile (where more material is being removed by the top head) instead of hitting on the high points.  This may not work in every scenario, but can be a simple solution when it works.

If your finished molding is coming out with dimples on the surface, you likely have a chip removal issue.  If chips aren’t removed as they’re being made due to lack of air movement from the dust collector, they can be pushed down into the surface by the cutterhead creating small dents or dimples.  

We generally only see this if we’re running too many machines at once and have too many blast gates open, which reduces the suction at each machine.  For us, if we notice this, we’ll pause the operation until we can finish running another machine and close its blast gate.