Moulder chatter

      Moulder operators help troubleshoot the problem. January 16, 2002

Question
I run moulding in a small shop. I am currently running a Profimat 22n 4 spindle machine. My problem is an inferior finish on the top and bottom spindles. The top seems to be the worst. I have done everything I know to do: level machine, align fences and infeed table, new air cylinders, new cutterheads, both spindles are within 2 microns runout, tightened and reset dovetails, new belts, retentioned belts, set all drive wheels to same height (according to scale), checked balance of gibs and knives, made sure tooling is all sharp.

Still, I get chatter on any flat surface (s4s, t&g, base, etc.). My profiles seem to do better since I use formed pressure shoes I pour myself. The machine is set up very similar to the new Profimat 23e, except for the pressure shoe being 1.5" wide and mounted onto a piece of spring steel (unlike the large steel one used on the 5 spindle machine). The biggest disadvantage is the chain drive system (even though it is a 1986 model?). The feed seems to run smooth without any jerky movements. The one thing I have found is some slight wear in the bedplates. They are flat across (no dips), but are about .002 difference from side to side. Is this enough to cause my problem?

Forum Responses
From contributor M:
You have not mentioned one of the more important adjustments. Is your pressure plate parallel to the bed from front to back? Even though you have custom fit to profile, which would be a definite advantage if your plate is not parallel, it really won't help a whole lot.

Inconsistency in knife marks is a sign of vibration. Are you getting this, or is there some sort of consistent pattern to your problem?

Another problem I have experienced on our Profimat is that the operators fail to tighten the spindle after making an axial adjustment.

You could also look into the spring assembly attached to the pressure plate. Is this working properly and free of obstruction?

Only .002 difference from side to side should not cause a significant problem. I have seen them as much as .020 and still running.



From the original questioner:
The chatter is not in any pattern; it is consistent throughout the whole board. Whether the board is 2" wide or 7" wide, the chatter is the same (being worse on the outer edge of every piece of s4s, narrow or wide). I am running 30'/min, and if I slow the speed down, no change. The only change I see is when I really slow it down, and a pattern of chatter develops. I guess this is the variable speed belt slipping. The belt looks in good shape. Is there anything else there to look at?

The pressure plate is Mickey Mouse. It is not on a dovetailed way like you're used to. The main bracket that adjusts the height bolts to the hood. Once your height is set, you lock it down. The spring action is provided by a piece of spring steel mounted to the main bracket, cantilevered out 3-4" under hood to meet top head, with small 1.5" x 7" pressure plate bolted to it. The spring action does not move perpendicular to the bed. It moves up at an angle (bends back), therefore the pressure plate is milled at an angle to compensate for this. The nose of the plate is lower than the rear when it touches the board (nose touches first), and as you keep on putting more pressure, it flattens out. If a board passes through not back to back, the pressure element nosedives, and the second board can sometimes jam. To eliminate this problem you must raise the pressure bracket. When you do this, the rear of the shoe is off the work piece. You cannot get equal pressure on the front and back of the 1.5" wide pressure rail.

Have you encountered anything like this?



From contributor M:
How severe is this chatter? You can expect knife marks in all moulders and these seem to be more obvious in wide, flat profiles. Dark stains on the wood will accent these knife marks even more. I have found that indicating bare spindles is not a true gauge of what happens when heads and a cutting load are placed on them. When were the bearings changed last?


From the original questioner:
The spindles were gone over by Weinig just a short time ago. Everything checked out fine. This chatter is not severe--you can take a random orbital sander with 100 grit and make a few light passes and it's gone! I have noticed that pine has the least, then poplar, and oak has the most. I wonder if improper dust extraction may be the culprit. Pine and poplar produce more shavings versus oak producing more fine dust. Maybe the cutters are trapping this dust, causing this "chatter" or "shadow".


I suspect the problem is deeper than the setup. Recently I have taken two similar moulders apart and found that, in both cases, the feed beam dovetail had severe wear on it and on the main frame of the machine. This was probably caused by the wood being fed into the machine and the feed beam dovetail being forced toward the outfeed. On both machines we were able to repair the damage and continue with the program. Another possibility is that the top and/or bottom spindle assemblies are out of square. This is caused when the self-locking nuts are worn from vibration in the motors or from the tools.

In most cases, the problem can be repaired with a simple machine tear-down and clean-up.

Dave Rankin, forum technical advisor



From the original questioner:
After reading your message, I headed out to the shop. I started a piece into the moulder, paying close attention to the feed beam. When the first roller climbed onto the wood, the feed beam raised up and towards the outfeed. When the end of the work piece passed by the first roller, the feed beam fell back into position. How does this movement affect the finish? What is there to do other than replacing the gib? How do I check for this same wear on both top and bottom spindles?

Are you talking about the self-locking nut that threads into the spindle barrel and has the shoulder for the cutterhead? If so, these have been set to reduce the spindle runout to near zero. Would this put them square?

Even if I were to fix these problems, do you think a quality finish can be obtained?



The self-locking nuts are located on the back of the machine and hold the gib or wedge for the dovetail. If the feed beam is moving when feeding the wood, the dovetail is moving during the running of the machine. This can cause finish problems because the wood is no longer being controlled. To check on the top and bottom spindles, I would check them for square. To do this, remove the table under the top spindle and using a spindle spacer as a gauge, check the spindle for square. Lower the spindle down just until it touches the spacer. Slide the spacer from the fence side of the spindle to the front side. If it is not the same, the spindle is out of square and this will cause chatter.

If the machine is gone through and all the internal adjustments are cleaned, it should work fine.

Dave Rankin, forum technical advisor



Your questions about dust are good, but you would find that if there was a dust extraction problem, it would show up more with poplar. Poplar tends to circulate around a cutter head more than pine or oak if dust extraction is poor. This can be proven with a simple strobe light.

The description you have given of the very slight chatter problem makes me think you have a spindle problem that the great Weinig did not catch. A lot of Weinig spindles that I have dealt with do not have tight enough tolerance on the spindle housing where the outer race of the bearing fits. This will cause the problem you have described, even if the setup is perfect.

I noticed you are using new heads. What brand of head and what style are you using? If you are using a straight bore head and the spacers have any dents or dings, this will allow a spindle to distort when you lock the head on the shaft. In testing, we have found that we could distort a 1-13/16 spindle as much as .024 runout with slightly dinged spacers. Install a five-inch wide straight knife head on the top and bottom spindle.

Use a good straight edge a half inch away from the inside fence and set the bottom head. Now come to the outside of the bottom head and check the setting. If these are not exactly the same, this will cause the problem you are having. Repeat the same procedure for the top head. The bed wear is to the point that if you have not compensated for it you can also have the chatter problem.

In the last place I was, we rebuilt five of these. The tables we had surfaced and a special coating installed on the bed plates. The coating outlasts chrome by four times, and had half the coefficient of friction. This made the machine feed easy and eliminated chatter.



The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Check your sprockets teeth and chains. If your sprockets are worn, the chains will ratchet as the links go over and hook in the links, causing a jerking motion in your feeding of wood into the machine.



Comment from contributor T:
I run a 9 head Weinig moulder and had very bad chatter problems when it first arrived. We went through the spindles, the heads, the frame, and the outboard bearings, which I highly recommend if you use any heads over 3 inches wide. None of this helped.

We were all staring at this moulder one day and thought maybe how it was sitting on the floor was causing the chatter. It had the original pads it sat on, which are pretty small, so we thought we would try some nice new rubber pads like we use on all our Diels. It was 100 times worse!

So we took those off and cut some nice thick steel pads and it was 110 times better. So we were on to something. 4 months ago we poured a new concrete pad for the moulder. 14 inches thick and 2 feet wider and longer than the moulder on both sides. Wow, what a difference. The little bit of chatter we had before was now gone. Now we get a glass-like finish on all the parts we run.



Comment from contributor D:
I was at Weinig today installing a new balancer. We had some discussions about spindle preloads, unbalance and vibration at various times. An unbalanced head can pull a spindle several thou. A new head is usually balanced bare but can have errors in the serrations that can generate unbalance when you load knives and gibs. Getting a machine rigidly bolted to the floor without distorting the base should make a big improvement.

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