Troubleshooting Feed Problems with a Four-Head Moulder

Woodworkers offer suggestions about what could be causing the feed system to stick on a four-head moulder. January 17, 2011

We have a Lleadermac 4 head machine and are currently fighting feed problems. We set up the machine with the top head and side pressure bar backed off and the material feeds fine. Once we lower the head and adjust the side pressure bar (with a little slop) the material refuses to feed smoothly. We have literally backed off the top pressure shoe and the side pressure bar during operation and it makes no difference.

The last feed wheel (new) has a powered bottom roller and we maintain about 60 psi on this wheel. The rest are steel wheels (new) and we run about 25 psi on these. The chip breaker doesn't seem too tight although we haven't tried backing it off yet to see what happens. The book with the machine is useless and I am running out of idea's. Any help is appreciated.

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
I played with a moulder like that and had the same issues. I made a few calls after trying everything you have tried. They told me that the pressure shoe after the top head should be just rubbing the wood as it passes through and have the end of the outfeed table slightly raised to reduce snipe.

The other thing was pretty much the same with the chip breaker. He said "it's heavy and doesn’t really need to be under spring tension." Maybe the spring tension was too heavy, I don't know. Anyway, we did what he said and it helped. It didn't eliminate the problem but helped some.

The problem with using a lot of table lube is you don't have a fifth head at the end to clean it off from the wood so your hesitant to use it. I think that might be the main contributor. One other thing to keep in mind is sharp knives have less resistance. I’m not sure if that would really make a difference but might contribute to an existing problem. You could try backing off the tension on the chip breaker vs. raising it up so you don't have to re adjust it every time you move the infeed table.

From the original questioner:
Thanks for the quick response. We actually tried backing off the top pressure shoe during operation and it made no difference, as far as snipe I really don't care. I would be more than happy to lose some material at the ends in order to keep the material moving. I would think the chipbreaker would need to be fairly stiff as would the top pressure shoe in order to reduce chatter throughout the entire length of the board. It would seem ridiculous to sacrifice quality in order to obtain consistent feeding by reducing shoe/breaker pressure.

This machine has a chrome bed and we have tried using lube which is messy without a last bottom head as you noted, so we have also tried 3m silicone also with no better results. As far as the knives’ go, they are sharp as we actually grind them here as we also have a rondamat. We get a great finish from the moulder between the point's that are messed up from the material continuously and randomly sticking. As it is now we have one guy feeding the boards and pushing as hard as he can, while we have another guy on the outfeed side pulling as hard as he can while the whole time they are praying the board doesn't suddenly stick for apparently no reason.

From contributor J:
I don't know. You could you stop the piece, (obviously not a problem) and back everything out of the way, pull it out and look for shiny marks. You might find a heavy pressure point somewhere. It's a pretty simple machine but we never really figured it out before it left our shop. I’m interested in what other people have to suggest about this too.

"I would think the chipbreaker would need to be fairly stiff as would the top pressure shoe in order to reduce chatter throughout the entire length of the board." This might be something to look at. Those machines are weird, especially if you’re used to running something else. Backing all that off to a light point did help.

From the original questioner:
We haven't tried stopping the machine and pulling out the board to look for the problem, although I can say the problem seems to appear in random locations throughout the machining process, not when it hits a benchmark location on the machine as I have stood there with the hood up trying to figure it out while the guys are feeding the boards including adjusting the pressure shoe which is also spring loaded.

We used a good straight edge and the right fence seems straight (within a few thousandths) and we also checked the drive wheel spindles and they seem consistent horizontally. We also tried changing the idle point of the air cylinders which drive the feed rollers to be sure they weren't fully extended. We were thinking maybe they were somehow binding at full stroke and pinching the boards too tightly, and of course we also tried every possible air pressure of the feed wheels and still have found no real solution.
There must be something I am missing (this shouldn't be such of an issue).

From contributor J:
Let's go back to your fist post. Once you lower the top head and side pressure (sloppy) is when the problem starts. So it has be one or the other. Look at light pressure with your chip breaker and pressure shoe and maybe because it is what it is. When you tighten up your side pressure bar (although thinking it might be sloppy) one side might kick in enough to pinch the wood when you tighten it up.

From contributor C:
A 4- head machine should be relatively short so there should be a minimal amount of points where the material binds. The top and side head pressures may just be the last straw that breaks the camel's back for feeding.

Check that the bottom head is level with the outfeed side bed plate. There may be some binding issues there, same with the fence side head and the outfeed fence. Are the chip breaker pressures spring loaded only or spring and air pressure? Either way, set those at a minimum to keep the material to the fence and bed.

It may be that the feed beam is misaligned so that the feed rollers are dragging the material into the side pressures or into the fence where the force is going sideways instead of through the machine. What is the condition of the stock you are running? Is there a big variation in thickness or width between pieces? Does it have an overly high MC? Try pre-machining some stock to fixed dimensions and see how that feeds, that would be my next step.

From Dave Rankin, forum technical advisor:
A few things to consider:

1. Type of bed lubrication, this makes a major difference in the way the material feeds.

2. Type of feed roller, good sharp metal rollers will feed much better than ones that are starting to dull.

3. Air pressure on the feed rollers, for the rollers to the top head 50psi (no more than 60psi) and for the rollers after 30psi. Adding additional pressure reduces the ability of the machine to feed.

4. Fence alignment, make sure that all of the fences are properly aligned.

5. Cutter head settings. It is very common for tools, especially the first bottom, to be run dull or out of align to their control point.

6. Reference engraver. Make sure you have new inserts and proper alignment.

From contributor T:
It sounds like you've looked at most possibilities, however one area not mentioned yet is the feed belt. Is it slipping, fine, or are you lucky enough to have a frequency drive where you don't have to worry about that. If all that is good and you’re sure about the rest of the setup, my initial thoughts turn to the feed rollers. I just spent a half hour surfing for what I consider the best feed roller but could not find it online. If I dig hard enough I could probably point you to a person who would know. To briefly describe them they are like a 5 1/2" saw that is 1/2" wide that you stagger and stack on the feed spindles, usually just the first one or two. The teeth are a carbide insert so you could change them if they get dull. I was involved in the testing and have been running mine for nearly ten years through millions of feet of hardwoods and have not even turned them once! They are very aggressive and you would need to leave yourself a 1/16" to clean them up on the top head.

From contributor M:
These smaller machines are a real nightmare when it comes to feeding issues. I would check the pressure shoe first. They bind up quite frequently even when lubricated. On older equipment the uprights on the feed beams will naturally become sloppy with wear and begin a pendulum effect. Also, the more feed pressure applied will force the feed beam to tilt back slightly and force the material to ride harder against the assemblies trying to keep it tight to the fence. From my experience wider parts will normally run better than extremely narrow parts. Issues with the feed beam will also result in extreme width fluctuation or kerf on the fence side from not cleaning up on the right spindle. Most smaller machines only have one upright on the feed beam. The last thing I would look at would be the pressure plate being true to the bed plates. If this is not perfect it could be binding front or back. When this happens it will act as a wedge. The harder you try to feed it the tighter it will get.

From contributor G:

Short coupled molders can be kind of cantankerous. There are no gremlins in woodworking machinery, but there are basic rules of physics that dominate the mechanical advantage that the machine may have. The mechanical advantage or the force exerted by the freed roles has to be greater than the resistance caused by the power of the stock removal and the bad plates. If everything is not parallel with the cut surfaces no amount of pressure at the feed rolls can overcome the mechanical advantage of the pinched would in the machine. I'm sure you've run a jointer and a shaper and a planner with the hand feed. The mechanical force required to feed each one of these individually is not a tremendous amount provided you're removing a reasonable amount of stock as long as it is not pinched or binding. The amount of reasonable stock is also determined the sharpness of the cutters, the chip load being removed, and the horsepower applied to the spindle. If all of these are reasonable you have a binding problem in the machine.

Since you have removed side and top pressure in various combinations, it seems only logical that there is something out of alignment with the beds or the fences. Something is not parallel. If you are trying to run the wood uphill into the machine you're going to bind. Back your bottom head all the way out and get a good machinist straight edge, make sure all the plates on the bottom are parallel and level. Use the same principles that you would use in setting up a jointer as far as stock removal in the adjustment of the bed plate in front or in back of the bottom head. You're outfeed bed plate must be no higher or lower than the stock removed. The infeed whether it includes feed mechanism or not must all be parallel and equal to the amount of the desired stock removal. The planer head and the feed rolls need to have a parallel relationship with the beds and 90° to the side heads at least until you get the machine running S4S stock smoothly. I would highly suggest troubleshooting your feed issues with S4S. If you can't run flat stock delivered being overrun pattern cuts.

The next step in troubleshooting would be to make sure that the feed rolls are not only parallel at the fence across the face of the bed plates from left to right. It is also absolutely necessary for this troubleshooting exercise to make sure your bottom bed plates are parallel left and right to the spindle on the bottom. The goal would be to make sure that at the end of this troubleshooting exercise that you're cutting a true rectangle S4S. Once you have the bottom parallel end to end and right to left you have the foundation or a reference to work from.

The next objective would be to make sure that the top spindle is parallel bottom and 90° from the vertical head dovetails machine guide's on which the top spindle assembly is mounted. Then the top spindle must be parallel right to left with the bottom bed, chip breaker and the pressure bar also must be parallel right to left, if you hadn't cannot achieve this you will be pinching the wood against the bed plates after it exits the top planer head and the pressure bar. Your pressure bar must also be parallel end to end of the machine or with a very minute amount of incline on the infeed side of the pressure bar. If your pressure bar has a slight bevel this should not be necessary. Opinions vary on this.

Your chip breakers also should be adjusted as reasonably close to parallel as mechanically practical. If you have a solid chip breaker this is more critical. If you have a sectional chip breaker it's not quite so important. Find out what the recommended detent should be on your chip breaker and adjust accordingly. Too much pressure will pinch as you already know. The pressure bar if it is a solid pressure bar with no detent must not be lower than the highest point of the stock coming from the top head or the amount of compression that you're willing to stand on the material run through. Different product will tolerate more pressure but never less. By experience you eventually will know how much measurable pressure you can/will want to put on.

In the troubleshooting stages is a magnetic dial indicator to tell the amount of detent or pressure that you are applying. Start out for your controlled troubleshooting experiments using S-4 S. stock so that you can control the variables as much as possible. Starting with smooth parallel product gives you the ability to measure with calipers how much stock removal you are taking with each cut. Have a number of pieces so that you can use to control run to measure your success. Without doing this you're going to twist dials and screws and springs and you may by trial and error accidentally get there, but you will not know how you got there, just like taking a rifle down to the rifle range you need to control the process reduce variables and find a way to measure your results.

At first run pieces that are long enough to stop them part way through the machine. Only work with one head at a time and measure the stock part way into the head and what's on the other side. Start with the bottom head, then the planer head, then the right head, then the left head fences - again straight knives only. On the right-hand machine the input fence will determine the amount of the cut will determine the amount of cut and the exit fence needs to be to the limit of the cutting circle. Uses straight edge and turn the head backwards so that the knife just touches the line of the exit fence. Make sure the head is vertical 90° to the bottom bed plate. After you have the top and bottom and right beds heads and fences lined up then you're ready to truly determine the amount of pressure required by the left fence and the cut to be successfully accomplished on the left head. If everything is parallel and everything has the minimal amount of pressure on removed no more than 1/32 and 1/16 stock from each face.

By the way, using paraffin on the beds can help for high-speed production but shouldn't be necessary. If the wood is dry it should slick the beds down and if you keep your dust evacuated production in a product free of dints and scratches. Extreme dust problems will cause sticking as well. From there you can increase the amount of stock removal that you are chip load and horsepower will allow. Once you can successfully run S4S stock mold patterns should be on123. It's all science, not black magic.

From contributor R:
It seems to me you have overlooked one thing. The alignment of the bed rollers has given me problems in the past. They may look level with the surface but may actually be a tad low.