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Clogged Dust Collector Lines on a 5-Head Moulder

When dust collection lines plug up, the problem could be vacuum, wood moisture content, or other factors. April 10, 2007

I have a standard five-head through-feed moulder, a new machine. Today the third head (left) clogged up every 15 minutes or so. This head cuts the tongue in the production of hardwood flooring. There is a six inch diameter heavy duty corrugated hose that runs in a U-shape from the head down and then up towards the metal piping for the dust collector. For some reason, dust would collect in the bottom of this hose, eventually clogging the hose completely, entailing a ten minute break to fix the darn thing. The feed rate was slowed, didn't help, perhaps even hurt. The lumber being run was KD reclaimed red and white oak. The lumber had been pre-planed to .9". The dust collector suction was good. We have run this lumber previously, uneventfully.

One thing I noticed was that the lumber had been ripped about 1/8-3/16" wider than usual. Could this have overpowered the collection system? I wouldn't think so. I did split the extra width between the two side heads.

Forum Responses
(Solid Wood Machining Forum)
From contributor S:
Sounds like a dust collector problem. You need to check the amount of CFM's and static pressure in both the line and the main. Even though it seems to have enough suction in that hose, it probably doesn't. You may also have a problem with dust falling out in the main, reducing the amount of air flow, which in turn drops the suction in the branches. I would suggest that you get a manometer and measure the actual amount of flow. If you know a good HAVC man, they should have a manometer and a scale for calculating the static pressure and velocity.

From contributor C:
Check the moisture content yourself. Don't take anyone's word for it. Moisture content makes a huge difference in dust removal.

From contributor A:
There could be quite a few things, but the extra width of the moulding as you suspect may be the culprit. Sometimes when taking a lot off the sides of the wood, it will splinter instead of shave. These splinters can then get stuck sideways in the 6" pipes. All it takes is one or two and the shavings getting hung up on them. Some woods like oak are more prone to doing this than say woods like poplar. I would always rip our wood 1/4" over size and mill 1/8" of the inside and 1/8" off the outside. Also check the MC content of your wood. Wet wood clogs pipes easier than dry.

From contributor H:
I agree with contributor A. I have had happen exactly what he described.

From contributor R:
All really good responses - may be the answers you need to fix the problem. I would also, as mentioned, have the cfm checked. About 1000 cfm per head would be good. You might also check the bag house if you have one. The cotton bags get clogged if not shaken regularly; the nylon bags seem to work better. Reclaimed lumber can really clog a bag system. Check also to see if you have proper rotation on the suction motor. That sometimes is not checked and it will suck even if running the wrong way, just not like it should. I believe it should be running clockwise rotation.

From the original questioner:
I might add that this lumber is much more brittle than the standard hardwoods that we run. When we empty the connecting hose (after it's filled up), the end nearest the head has finer dust in it than the end near the metal piping.

Also, the hose could be shortened a little. Would it make any sense to do this? And would it help to put in metal piping from the head toward the back of the moulder, only having a vertical piece of hose? Or make the entire hose to this head out of metal?

From contributor C:
Have you personally checked the moisture content? What is it?

From contributor Y:
I also believe it's a dust collector issue. My guess was stated above about the dust bags. What a huge difference shaken bags make! You might want to take apart the metal hose from the main manifold and check that it is clear from stuck debris all the way down to your flex hose. That might be restricting your suction. Although not the answer, check to see that your chip breaker is as close to the cutter head as safely possible to reduce chip size.

From contributor W:
We run flooring all the time with our SCMI moulder. We run the tongue on the first inside head. We also get a plug sometimes. Just like stated above, the wood sometimes splinters instead of making a chip. Then the splinters bridge in the flex hose and cause the plug. We had a blast gate on that head that we ended up removing to take care of the problem.

From the original questioner:
We ran a small amount (about 1000lf) of the offending lumber today. The only difference was that the lumber was ripped closely to the target of 5". The previous run was oversized in the 1/4" range. This small run went fine. Perhaps the added width is the offender.

The other culprit is probably the design of the head assembly. The dust exits at the bottom, resulting in a J-shaped run of flexible tubing about 14 feet long. As opposed to other designs, which have the dust exiting at the top, with a hose of only six feet or so, with little turn. This eliminates basically two 90 degree turns, which really slows the air velocity down.

From contributor N:
I agree with contributor S. His industry knowledge is worth listening to. Check your moisture content, then make sure your dust collector has enough CFM to pull the chips away from the cutter heads.