"Chip Dent" in Planed Lumber
Here's a long, detailed examination of the problem of denting in planed wood, caused by knives pressing chips into the wood surface. Unfortunately, no solutions. October 15, 2009
Question
I have a 20" planer (CT-508) that is an import from Sunhill but is the same as Grizzly and many other 20" planers. Overall, it works great. In the past it produced wonderful results, but lately it started denting the boards and I have no idea what is happening or the physics that would lead to this. The dents are happening just behind the knives (I know because I stopped the planer mid-cut to see if it was from the outfeed rollers or not and the dents lead up to the back edge of the knives). I then went the dust collection route, but I can't find any difference in my dust collection. I even put my dust collector, which was performing fine before, right up to the machine without the bag and still I have dents. It even dents oak, which normally planes fine. I ran it with the hood off to see if there were any obvious airflow issues and nothing. I have spent two days trying everything and I am about to send this one swimming with the fishes. Anyone have an idea?
Forum Responses
(Solid Wood Machining Forum)
From contributor A:
Inadequate dust collection is usually the problem, as you suspected. Another possibilty is the bevel on the knife grind is not steep enough or is too wide in the case of the primary grind. If the angle is too low or the primary grind too wide, it can pound chips into the board and produce the dents you are seeing. It may be a comination of all the above. Are the knives dull?
From the original questioner:
The knives are sharp. I replace them often as I run a lot of wood through. I have read some about the grinding of the knives and thought about that as the culprit and here are my thoughts. A double grind has been mentioned, but as far as I can tell no knife I have ever gotten new or newly sharpened has had a double bevel. That could go a short distance towards explaining my problem if I had always had the problem, but I haven't. It just mysteriously appeared one day. Unfortunately, I wasn't paying enough attention at the time to really nail down the thing that changed. I just thought it was the dust collector or something obvious that could easily be remedied. Going back to the grinding, I even used to grind the knives myself with a cheap grinder from Grizzly and had no problems with the dents. I had problems with knives that did not stay sharp because of the high speed dry grinding, but no dents. Here is the kicker to the grinding angle. I know that plenty of times my jig would get out of alignment and change my grinding angle. I never worried about it too much as long as it was close and never had the denting problem. So are we in agreement that it is possible for the dents to be caused by chips that are basically sticking to the knives? It that what is happening? It seems almost impossible, but if we agree that is what is happening, then it has to be something with the airflow around the knives, and in that case it could be one big thing or an accumulation of little things that have finally added up. I was hoping it was one big thing that I just didn't know what to look for, like a flux capacitor or a banana in the tailpipe.
From contributor B:
Static electricity has caused problems like this for me. The static bond doesn't cause planer shavings to stick to the cutterhead, but it causes shavings to linger under the hood, get tossed around into the wrong places, and recirculate between the cutterhead and the wood. I ran a ground wire from the blower pipe to the hose, to the hood, and then to the machine. I also made sure the machine was grounded. Even with metal blower pipe, the 6" diameter plastic hose connecting the machine to the pipe had produced static electricity in my dry (25% humidity) shop. There are probably other things that can cause your problem, too.
From contributor C:
Similar to what contributor B is saying, I don't know if it is a fact, but it has always been my impression that static problems get worse in conditions of lower humidity. We're in the teeth of winter here, is the humidity in your shop lower than usual? Perhaps an interesting experiment would be to try a dampened piece of wood. If rough wood, just a very light misting. If you run an already planed piece, just a light wipe with a dampened cloth.
From contributor D:
I would say contributor A is right on. Typically sawdust collection is the problem and you are driving the shavings back into the board. You may want to verify the chip breaker is functioning properly and also you don't have a lot of resin built up on your outfeed wheel.
From contributor E:
Air too dry. Lumber too dry.
From contributor F:
I have had this same problem for a few years now. I have a 15" Jet planer. For years it worked great. One day I put a set of resharpened knives on it and I started to get these chip dents in it. I didn't think too much about it at the time, but it continued. I told my sharpener what happened and he reground the knives. I still had the problem. I dealt with it for a good time and as time went on my small 1-1/2 HP DC started to fail. My problem got worse. The people who had told me that my DC was inadequate might have been right all along. I finally had saved up for a 2-1/2 HP Oneida cyclone and put it into action. Great suction, way more than I ever had. I had the same problem. I called up Jet Machine and talked to one of the techs, explaining my problem. The way I described it, he doubted it was the lack of vacuum. He told me to check the chip breaker. I had played with the chip breaker over and over with no success. Then I asked him about the knives. He insisted that they needed to have the double bevel, main bevel at 40 and micro bevel at 42. I tried this, but no difference. So I am still dealing with this. You mentioned static, but my problem is year round, and winter is just as bad as summer. I am stumped. I am very interested in this problem being solved.
From contributor G:
I believe that planer has a cheesy little plastic chip deflector mounted just above/behind the cutterhead. You might check the condition of this item. Is it also possible perhaps you may have moved it after a knife change? It is adjustable, so make sure it is moved as close as possible to the blade.
From contributor F:
It is plastic, bright orange. And I can't get it any closer to the knives without it getting hit. Because of this, when I turn on the vacuum it roars. It doesn't seem to make any difference whether it is close or removed. I have a good deal of vacuum, and chips that make it down to the table are sucked back in. I never believed this was a vacuum problem. I just can't for the life of me figure out what changed. I have always used the OEM knife install gauge, so I know the height of the blade is the same as original specs. The chip breaker has a flat edge and a beveled edge and I tried it up and down. I have put it as close as I can get it and everywhere in between. I have even taken the hood off and let the chips fly naturally, but it still leaves these hammered chip marks in my wood. The only time it doesn't is if I take a very shallow cut, around .007-.010. I used to be able to hog off 3/16" with my little 1-1/2HP vacuum and get a glass smooth cut. It still perplexes me to this day. I am thinking of replacing it because of this problem, otherwise it is a great little machine.
From contributor C:
To contributor F: Did you ever try a new set of knives from Jet? It sounds like you've been very thorough in your troubleshooting, but I note that you said it worked fine for several years, and the problem only started when you put on a resharpened set. I don't know if or how it could make a difference, but my thinking is that's the only thing different from when it worked ok.
I have the same problem on my Delta 15", but in my case that was from day one. It normally only shows up with softwood, and the little bit that happens with hardwood comes out easy in the widebelt. So I haven't spent any great effort trying to trouble shoot. My dust collection just ok - 2 HP generic Taiwanese single bagger (well two actually, upper and lower), but I replaced the bags years ago with way oversized needle felt bags from Oneida, so this collector is probably performing the best that is possible. It does keep up to my 24" widebelt, so it's not that bad.
From contributor F:
I never purchased a new set from Jet. I asked them about the sharpening specs and they sent me a small drawing. I gave this to my sharpener and he sharpened them to those specs. Same problem. I did think about getting another set. But I haven't as of yet. I don't see how it could make a difference.
From the original questioner:
To contributor F: We might as well be joined at the hip. Everything you mentioned is exactly what is going on at my shop. I have moved everything I can think of and the only guaranteed way to not get the dents is to make a shallow cut at the end to clean it up. That is fine if I have nothing but time and is completely frustrating otherwise. I went the static route yesterday and thought I might be on to something. I added a piece of umhw plastic to my planer bed to make everything glide through without using bed rollers (it works excellent by the way). I thought back and was hoping my problems started when I added that plastic, since it seems to create some static. I took it out yesterday and the problem still persists. And yes, for me it happens in the summer too. It has been going on for the last year and I work on it off and on, to no avail. Lastly, I made a new little deflector on the back of the blade out of Lexan so it wouldn't break. I have ruined two of them from the manufacturer by getting them too close to the cutterhead. This piece seems to make no difference. Today, I am going to try grounding the machine better and wetting the wood to see if there is any difference. I was expecting a large group of guys to jump in that have had this problem, but it doesn't seem to be too common. The guys at Sunhill said they had heard of this problem before, but have no remedies either.
From contributor A:
I said "primary grind" in my previous response but actually meant secondary grind. Either way, that doesn't sound like it is your problem. Even though contributor F had no luck with replacing his dust collector, can you borrow a different one to try? Have you added more flex hose to the dust collector or anything else that could restrict airflow? Any other blastgates open to rob the dust collector of suction at the planer? Are the filterbags getting plugged and in need or replacment? As you can tell, I am thinking it is still a dust collector problem.
From contributor F:
That is what everyone thinks. But the problem turned on like a switch. It happened after a knife sharpening. I went from a 500CFM single stage single bag collector with 15 ft of 4" flex hose to a -1/2 HP 1400 CFM cyclone with 5' of 7", 15' of 6" and 5 ft of flex and a 5" to 4" reducer at the end. It is designed to have 650 cfm flow. Jet says 500 cfm is enough for this planer. I still think somehow it has something to do with the knives. I had changed the knives several times before that so it is not like I did something unusual or incorrect. I just did what I had done before. Hearing someone else having the same issue makes me feel a bit better. I hope he can solve the problem so I can have something to look forward to. I have given up. I just deal with it now.
From contributor H:
This is a great thread. I had the exact same problem with my 15" Grizzly, the new style one. The problem, as previously stated, was worse with softer wood. I use almost all poplar, soft maple, and cherry. Poplar was terrible. I never considered static. The only thing that helped me greatly was to blow air into machine while planing. This improved performance greatly but was really not a good solution due to noise, mess, etc. I ended up selling it and buying a
Dewalt735. Problem solved.
From contributor F:
I used the "blow air into the planer trick" too. I never got a system to do it while I was planing, just hand held. It was very inconvenient to handle the wood while holding the air nozzle.
From contributor I:
The last time this came up, I posted my attempts in defeating chipbeat - chips riding around in the suction hood only to be pressed into the wood.
We called it chipbeat as a result of a weekend seminar on wood machining techniques and tooling sponsored by Purdue University. Dr. Dan Cassens of Purdue, a Weinig chief engineer, a Weyerhauser engineer, and about 25 seasoned woodworking production managers all were very familiar with the problem. All had dealt with it, and all disagreed somewhat on the causes, and all had failed to eliminate it or control it predictably.
I can tell you that I spent a year going thru each change and modification to knives and angles, dust hoods, additional air, and even combinations of the above in an attempt to remove chipbeat. Nothing seemed to work.
I also monitored temperature and humidity. This is where I found more predictability than anywhere else. High humidity correlated with higher instances of chipbeat, and the opposite with lower humidity. No 100% correlation, but some alignment. Nothing was ever resolved.
So today, I keep one finger crossed, I watch for the full moon, and drink a little bourbon and branchwater to minimize chipbeat. And I thickness sand everything.
From contributor J:
How can you tell the difference between the chips leaving dents and tear out? I have seen the marks you guys are talking about but wasn't sure what was going on to make them.
From contributor I:
Chipbeat will decrease some if you get it wet and let it swell back up, just as you would remove a dent in any surfaced wood. Tearout is missing wood, and will not respond to water.
From contributor J:
I do understand that part, but looking at the wood, how can you tell by looking at the marks?
From contributor G:
The best description I can come up with is if you were to somehow randomly lay small grains of rice aligned along the grain of the wood and pressed them in, the indentations left would resemble chipdent. Not very technical but the best I can do.
From contributor K:
To contributor J: I asked about this problem a few weeks ago and Gene Wengert said that the pictures I posted were of classic chip marks. I call them freckles.
From contributor G:
The usual cure for this is simply increasing the CFM at the machine. There are a couple of other factors equally important. The design of the hood should be of sufficient size and aligned to direct the flow of air in line with the natural flow of chips as they are thrown off the cutterhead by centrifugal force. Its outlet must be of sufficient size to maintain velocity of the air flow as the hood fans out over the cutterhead. The deflector does what its name implies and directs the fraction of chips that would make it around back into the airstream. In my opinion, the outlet in the hood of these type of machines is way too small, 5" if I'm not mistaken. A 16" planer will typically have a 7" outlet. Even if your collector is of a sufficient size, it will not be able to pull a sufficient volume of air through the undersized outlet. The angle of attack seems a bit too flat as well,and, if so, would result in the chips bouncing off the top of the hood and back down into the cutterhead. You can compensate for inadequate suction somewhat by taking lighter cuts or slowing the feed speed a bit, however that won't compensate for poor geometry of the hood. I have an old 16"
Powermatic paired with a 2HP Onieda cyclone. The hood is fairly well designed with a 7" outlet and I still find this setup marginal at times (I should have bought the 3HP). I also sand to dimension, which not only takes care of chipdent if present, but also eliminates knife marks and any tearout.
From contributor B:
Ditto the note on bad hood design. I bought a
Powermatic 20" planer 2 years ago. The hood required the chips to scoot along a horizontal platform for 20", and then jam their way into a 4" port. This design feature was to allow some rollers on top of the machine for rolling wood over the top of the planer. I never needed to roll wood over a planer. That's what carts are for. I got rid of the rollers, and cut a big hole in the top of the hood, and put a regular V shaped hood made out of plywood and a cheap HVAC fitting, at an angle over the chip steam, to a 6" pipe. It works way better. I still get chipbeat sometimes, and it seems worse in dry weather. In addition to grounding everything, I also run the wood through the planer in a staggered pattern, to allow chips to clear in one area while another section of the head is being used.
From contributor L:
Try making a plexiglass and plywood hood and blowing the chips out sideways with a high powered leaf blower or centrifugal blower pushing instead of pulling air. I had this problem with cedar and you can watch the chips exit. By changing the speed and angle of the blower you can minimize chip suspension. Blastgates and plywood are cheap to experiment with.
From contributor M:
I'll go out on a limb here and suggest that your knives are the problem. Since you insist that the issue "came on like a switch after changing knives" then the knives have to be the problem. It might be that the temper is gone and they simply won't hold an edge, or that after too many sharpenings they are not wide enough (although if you are using a gauge to set them, this is unlikely) or something none of us have thought of. Before ditching the machine, you may want to simply buy a new set of blades from the factory and see if that fixes it. Cheap enough experiment if it works.
From contributor N:
I'm not going to suggest than any of the other reasons and solutions suggested here are wrong, but for me, over the 20 years or so that I have had my
Powermatic 180 with knife grinder, I have had a variety of chipdent conditions or changes based on how I sharpen at the time, trying to stop the problem. I see changes in the same species of wood where the dents are wider sometimes and narrower other times. I just sharpened the machine last week getting ready for a new job and spent more time and effort taking the burr off the edges than I normally do. This time the results were very narrow short chip dents but a lot of them. Before sharpening they were wider, longer but fewer of them. I have always been of the belief that good dust collection is a primary factor but I also believe that not just sharp knives but knives sharpened in the correct way is also a major factor in chips re-circulating through the head. The knives must be cleaned of the burr that is caused when sharpened to prevent the shaving from possibly hanging up on that burr. On a machine like mine where they are ground in place, it's hard to remove that burr. I would like to hear from anyone who has a true helical carbide head like Northfield makes for their machines with a side discharge for shavings, to see if those machines have the same problem. Before I had a central dust collector I used my
Powermatic 180 with the factory cover that would shoot the shavings out on the outfeed side and I never had chipdent then. Only after setting up a dust collector did I develop chipdent. I don't have an answer yet so I just rely on the widebelt to take them out but everything gets widebelted anyway so I have stopped trying to fix it and just moved on. But I have never stopped wondering about it. From that, I guess the solution is for everybody to get a widebelt!
From contributor C:
To contributor N: If I understand your post correctly, your problem showed up immediately after adding dust collection. An interesting thought - I wonder if the DC is creating turbulence that is causing some chips to hang. And to expand on your question - are there any guys out there with Shelix heads that are having the same problem? Or even better, anybody have the problem and then have it go away after switching to a Shelix head?
From contributor F:
I tried to use the machine without the hood and I still had the problem. Vacuum made it better but didn't eliminate it. I don't see why I need more vacuum, I am already 150 CFM over recommended. I still believe it is in the knives. By contributor N's account, it does sound like the problem lies within the knife sharpening.
From contributor N:
Sorry guys for adding to the confusion. I had a point about the dust collection I wanted to make. That point is that over 22 years I have had 3 dust collectors. The first a Dustvent 3000 cfm cyclone. That's when I first noticed chipdent. After about 10 years I went to a Murphy Rodgers 5000 cfm Collector which made a great improvement on the general shop collection but no improvement on the chipdent. Now I have a 6000 cfm Murphy Rodgers and still no improvement on chipdent.
Contributor C makes a good point about turbulance but as my Collector supplier pointed out to me when I purchased the first Murphy Rodgers, all collectors and their pipe work create turbulance. Air moving through the pipe work actually tumbles, not just drifts through as we might think. I have wondered if the design of planers in general can add to the difficulty of chips not being picked up due to a lack of air volume being able to move into the running and loaded machine? In the case when I had just a cover shroud on the planer, there was no resistance to keep the shaving in and around the cutter head. If there is not enough air flow to grab onto the shavings, they don't benifit from the vacuum pressure of the collector and as a result just tumple around inside the dust hood. This would explain why each time I upgraded, I got no better results. It's not the lack of vacuum pressure coming to the machine, it's the lack of air flow into the machine. There is another point I would add to this. When I purchased the planer, the knives were factory set to protrude out of the head what I thought was an unreasonable amount (don't recall any more how much that was) so I adjusted them down into the head so they now only protrude about 1/8" above the diameter of the head. Is it possible that a greater protrusion of the knives actually help the shavings evacuate the space by acting like propellers and creating more centrifical force?
From contributor F:
I would think the opposite about the knives being higher up in the cutterhead. I think it would tend to capture the chip more. It wouldn't be the first time I was wrong though.
My knives are really close to the outside diameter of the cutterhead, and they really don't protrude much at all. If I could figure out a way to get them to stick out more (a different setting gauge) I would give it a try. But when I was talking to the Jet tech, that is one of the questions he asked, if I had used the gauge to set the knives. He wanted to make sure they were tucked into the cutterhead as OEM calls for.
From contributor D:
I guess I would take a more analytical approach. "Chipdent" seems to be the term used for what you are seeing which tells me something is "pressing" the sawdust shavings into the wood as opposed to more of a tearing. In the planers I have used the only thing past the cutter head pressing on the material would be the pressure shoe and the outfeed wheels. So why are the chips not being pulled away, or are they being lifted and then re-deposited on the other side of the pressure shoe? I mentioned in an earlier post to check the outfeed wheels for debris stuck to them, but perhaps while running some material you could monitor that more closely to see if any chips are settling under the outfeed wheels and then being pressed into the material. I owned an SCMI 24" straight knife planer that, unless we had a DC plug which leaves a much different look that can't be categorized as "chipdent", we never had an issue. Perhaps there is a way to create a barrier on top of the frame directly behind the cutter head to not allow chips to get behind it, even if it was out of cardboard for experimentation purposes. I would also be interested to know if simply putting a piece of material at an exaggerated angle produces the same result, or if by changing the shape of the chip it behaves differently with the dust collection. Ultimately, there could be a design flaw in the aerodynamics of the chip hood that will never resolve itself, that is inherent to that model or design. Lastly, for what it's worth, we have a top and bottom planer that has a chevron design insert head which literally directs the shavings and shoots them out the hood.
From contributor O:
Is that 7" at the planer and 4" at the DC or vice versa? If you have 7" at the planer then you may have cfm but you're losing static pressure. And that may be your problem or at least contributing to it. The fact is that chips are sticking to the blades and not being removed by suction or they are floating around for a few seconds before leaving and getting pressed into the out going wood by pressure rollers.
From contributor N:
While running some lumber thru the planer a few minutes ago I realized that in regards to my question in my last post about enough air getting thru the machine to help shavings get pulled out, clearly the only time that would be a problem is when you are planing the full width of the machine, otherwise air can easly get thru.
To contributor D: In regard to your questions, I was running material in the machine today but no change. Also, if chips were getting past the pressure shoe to the outfeed roller, the shavings would collect on the board on the outfeed side of the machine and they don't. The outfeed rollers are clearly clean as the wood is fed through. I agree with the idea of bad hood design. I have wanted to change mine since I purchased it.
From contributor F:
Mine is definitely chips being pulled around by the cutterhead and being slammed into the wood making scrapes and dents. It is not caused by the chips being pressed into the board by the outfeed rollers.
From the original questioner:
My dents are also happening at the knives. I determined this by stopping the machine and the dents were there before anything applied pressure. When I have had dents from the outfeed rollers they were in a consistent pattern. The dents we are having problems with are not in a consistent pattern. The weird thing is that it worked great for years, even with me sharpening my own knives, and I never had the chip dents. I know that I did not have a lot of dust collector either because it would plug up in the hood with white pine and poplar all the time, but no chip dents. Now, I get the dents on everything, including oak, which just seems crazy. Last thought before I go to bed knowing that I need to widebelt everything. My machine came from the factory with three belts. As they have worn away I have removed them and replaced them, but not all of them. I am now only running one belt and everything seems fine. It doesn't stumble, slow down, or otherwise appear different. I am just wondering out loud if there is any way that my rpm's could be slow because of the belt situation and it doesn't really stand out. Obviously, this is the next thing for me to check out, but I wondered if those of you out there that are having this problem could chime in on your belt situations. Maybe we could find some commonality (or not) before another lost day in the shop screwing with this planer.
From contributor N:
My machine has 3 belts and I have never run it with any less than that. If you were losing RPMs you would know it by the last belt on there possibly squealing or even causing a burning rubber smell and probably wearing out quickly. Inspect the belt for wear. I think it's a good idea anyway to just replace the missing belts. Some will tell you that you are losing some power by not having them on there, otherwise there would be no reason for more than one belt. I also don't see a correlation between running one belt and chipdent.
From contributor D:
Reprinted from "Knife Grinding and Woodworking Manual" by Charles G. Monnet Jr.
Chip Marks. Chip marks are caused by chips that cling to the edge of the knives and are carried around and pounded into the wood on the next revolution. They are dents in the surface and not bits gouged out. (see figure 130) This is sometimes referred to as "pitting" because an indent or "pit" is made. Chip marks may be caused by newly jointed knives where jointing is heavy and a feather edge is left on the knives. This causes chips to cling to the knife edges. Dull knives can also cause the same trouble. Partly seasoned or surface wet lumber is more likely to cause chips to stick to the knife edges than completely dry or wet lumber. Some woods seem to be more likely to cause chip marks than others. These usually have the type of chips that cling to the knife edges and the wood is usually of such a structure that breaks down easily. Some woods having the greatest tendency to develop chip marks in machining are birch,' elm, blackgum, maple and tupelo. The chips of most wood planed under usual conditions are not severed cleanly from the stock at the knife exit but are broken away from the wood surface near the end of the cut. Such chips are apt to have a multitude of attached fibers which tend to hook onto the knife edges and are carried around into the cut causing bruise marks. Some types of wood produce chips which are curled, firm and not too light and in spite of the attached fibers are thrown off the cutting edges by centrifugal force. Unfortunately however, woods which are the most subject to bruising do not produce this type of chip. Chip marks may be eliminated by grinding a back bevel or increasing the cutting bevel of the knives. This reduces the vertical force acting on the Wood so that it does not exceed the tensile strength of the wood perpendicular to the grain. Setting the chip¬breaker closer to the cutting circle will also help eliminate this. When straight knives are used, a sheet metal plate can be inserted in the hood opposite the chipbreakers for the top and side heads. This, if set very close to the knives, will help knock the chips off of the knives. Chip marks may be caused by insufficient throat room between the head and the cutting circle. This may be particularly true when taking deep cuts. This can be remedied by giving greater projection to the knives. Another cause of chip marks is lack of sufficient blower suction or improper piping. The exhaust pipe for the machine may join the main blower pipe at too large an angle, or may be too small, or there may be a loose connection in the blower system. When an inadequate exhaust system causes shaving choke the knives recut the shavings. This decreases their life between grindings. Always use a blower sufficiently large to take the chips away even when making heavier than usual cuts. As the cutting speed feed speed is increased there will be a decrease in the number of chip marks. There is no economy in having a blower that is too small. Dependable manufactures a complete line of heavy duty, blower fans. Even though these fans should outlast two standard blower fans of other makes, they are considerably cheaper than other blowers on the market. Proper blower hood design also plays a very important part in preventing chip marks. Dust hoods should be designed in such a manner that the shavings are thrown directly toward the opening in the hood where the suction pipe is attached. Hoods designed in such a way that the shavings hit the side of the hood will cause serious trouble as the heavier shavings will rebound. The force of these shavings should normally have carried them into the high velocity air stream but now instead they are likely to rebound and be carried around by the cutter head. When machining. pine and some other similar woods pitch will continually build up on the inside of the hood. This can build up to such an extent that it causes inefficiency in the removal of shavings. The operator should check for this regularly and clean off the pitch when an appreciable amount has collected. Chip marks are sometimes eliminated by increasing the feed speed, increasing the depth of cut, or reducing the moisture content of the stock. Most tests have shown that if the cutting speed-feed speed is increased there will be at least a decrease in the number of chip marks and in some cases they may be eliminated altogether. Chip marks are usually produced by the top head of the moulder. This is particularly true and is likely to cause the greatest amount of trouble in running wide, flat material in using jointed knives. Shavings used under such conditions are often as long as the full width of the stock. Shavings of this type, therefore, must be "folded up" by the suction of the blower to be able to get through the pipe.
From contributor N:
To contributor D: That was very informative and will be helpful. I read several things there that I intend to change on my machine.
From contributor P:
I just want to put some information out there that might help some folks. When I first bought my Grizzly planer, I had a major chip dent problem, even after putting the spiral head on. I did some research, and had a guy tell me to rip off that little strip of foam that is glued to the inside of the hood. Problem fixed - it was interfering with the draft, obviously. Simple, yet so frustrating.
From contributor Q:
I don't know if anyone else is still checking on this problem. I have a Woodmaster 18" planer. We recently had a Byrd spiral cutterhead made for it. I plane a lot of exotics and have never had a chip-dent problem. I usualy run the feed at the highest possible rate. With the spiral head, the main motor is able to handle the load and I get a sandable finish. On the rare occasion that I do slow the feed rate, I get a lot of carry over of chips. Is it possible the problem could be caused by too much vacumn, which in turn creates the turbulence?
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor R:
Very interesting insights on chip dent. I also have the same issue on my five head Weinig molder. The only foolproof way I've found to combat this is to finish with my bottom head. The added help of gravity seems to make the difference but it's hard to turn your planer upside down. You mentioned the re-sharpened blades starting the problem. Most grinding shops grind across the sharp edge, and some use too coarse a stone. Highly magnified, this edge looks to be made up of tiny needle points that are able to hang onto the feather-weight chips. Grinding length-wise or hand honing length-wise with a diamond file may make a noticeable difference.
