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Subject: Re: wood chip denting

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Message Thread:

wood chip denting

11/8/15       
shaner

ok. I have been experiencing some wood chip denting on s4s and some profiles in all woods as I look more closely at them I can see the marks. Mostly in S4S boards. It is vary random on some boards compared to others and even not at all. Usually in top head and sometime the left side head as well.
So I checked dust collector and that was tested at 1100-1300CFM on all 5 heads. That was before and after I cleaned return air bags and changed out all the bad dust tubes to 3 of the 5 heads, slowed down the speed to 22-25FPM, and all knives are sharpened before I run any medium to large runs, and on one if the jobs of s4s I changed to 12 degree slots on the dual angle heads I use and still had some. Also moisture content on lumber has been around 9-10 from most suppliers.
Now read 1 article that static electricity is could be keeping the wood chip on the knife and then making the marks in my runs??
Also does adding a supply air line somehow to blow across as it is cutting to help push chips off and be sucked up into dust collector??
I am looking at changing also my dust collection main lines to eliminate some beds to increase air flow to the top head and left head to see if that would help.
Any other suggestions would be much appreciated.
Thanks!!!

11/9/15       #2: wood chip denting ...
David R Sochar Member

Do a search on "chip beat" on the entire Woodweb site and you will see a lot of info in the knowledge base. The good news is you aren't the only one that has faced this. The bad news is that there does not appear to a simple, definitive solution.

Chip beat appears to be the preferred term, and it dies occur as a chip is pressed between the knife and the wood. Poor dust suction would seem to be the culprit, and definitely can be, but there is more to it, as it appears you have found out.

Blowing air across the head, in the enclosure, up the pipe, etc did not help us. Making sure everything is well grounded may have helped. Dry days and dry lumber did help. 9-10% sounds a bit wet to me, but it depends upon where you are.

I even presented this to 3 top wood technologists/engineers at a tooling problem solving seminar in 1988 - samples, CFM, moisture and humidity readings, etc, and got nothing but blank stares.

I wish I had a better answer for you.

11/10/15       #3: wood chip denting ...
Chuck Rankin

Hi Shaner:

I think what you are referring to is Hammer Marks. These are the result of the wood chip not having enough time to clear the cut before the next knife in the rotation contacts it and hammers it into the work piece causing the defect your have.

Inadequte dust collection issues are a common cause. Another could be too many knives in the cutterhead at too slow a feed rate.

Hope this helps. Please feel free to contact us with any questions. here is a page from our web site with a chart on finish rates of speed that should help.

best regards,

Chuck Rankin
Wood Tech Enterprises, Inc.
P.O. Box 2226
Fairview, NC 28730, USA

1-800-TOOLING (866-5464)
Phone: 828-628-4414
Fax: 828-628-4490

Finish Rates of Speed Chart

11/11/15       #4: wood chip denting ...
Russ

Website: http://www.mr-moulding-knives.com

Shaner
In reference to the above post

"Another could be too many knives in the cutterhead at too slow a feed rate."

I would not agree with this statement based on the information you provided. You only have a single knife finish meaning only one knife is cutting because of bore tolerance in the cutterhead. I actually believe having four knives in the cutter head will help shovel the wood chip out of the way quicker than just two knives.

Chuck has been a respected leader in the industry for many years and has help thousands of clients. No disrespect intended, I just wanted to voice my opinion that's all.
Good Luck
Russ

11/11/15       #5: wood chip denting ...
Jason

We have had this problem planning pine for flooring. We increased the blower speed on our dust collection when ever we ran that and it fixed the problem.

11/11/15       #6: wood chip denting ...
shaner

What do you mean by blower fan?? The actual dust collector or something else??
Our dust is dropped into a wagon with air lock on bottom of dust collector.

11/12/15       #7: wood chip denting ...
Jason

we increased the speed on the motor of our dust collection system. We can do this by reprogramming it on the main breaker box.

11/12/15       #8: wood chip denting ...
shaner

ok. That is what I was thinking. I have to see if we can do that. For some reason when we set this up in 2008 the electrician said something about speed of fan but left it at the standard I think that it came.
I will look into this.
Thanks for the posts, I just ran a job of cherry casing and after I have made several changes this profile has not shown any of those dents. Seems to be mostly in more flat type profiles and of course MAPLE.

11/12/15       #9: wood chip denting ...
Jason

Sanding maple sux lol. Like stated above there are many reasons for this.
I wonder if because your crown profile knives stick out of the head more than your flat straight knives it just creates more wind so to speak and blows the chips out of the way easier than a straight knife?

11/15/15       #10: wood chip denting ...
Rob

Missing or damaged baffles or chip deflectors can cause this problem. On some machines some of these may be adjustable , in which case they should be moved as close as possible to the cutting circle.

11/16/15       #11: wood chip denting ...
shaner

ok. I mad some adjustments and changed out many hoses and cleaned out my return air bags several weeks ago.
So this weekend I had to run some radiate Pine jambs for a job. I ran the 5-3/4" wide jambs 1st with 2 euro carbide knives just sharpened in the 20 deg slots of my dual angle heads. When I ran this I had a ton of chip dents all over the 6 boards I ran.
Then I tried what Russ said even though I had dual angle heads I still wanted to try it. So I put in steel knives in the 12 deg slots and got them close to same depth as the carbide. The steel when I got done ended up being out a few thousandths more than the carbide. So to me it seemed like the carbide would clean up most of bad wood before the steel knife would make the finished cut.
So I then ran 450lft of 3-3/4" wide jambs and was amazed how much better this ran and seemed like the chip dent had gone away. Saw very little marks on all the boards I ran. Then of course on the 5th to last board must have hit a rock to put a chip in it.
then for last run of 150lft of a 2" wide jambs I switched out to a 2 knife 100 mm carbide. As I was running it the chip dent came right back just as bad as the 1 st run. So I think I am on to something here. I still need to move my plenum about 2-1/2' back and over 2' to get the hoses to line up closer to the top of the moulder and hopefully help get better suction as well than having so much slack due to how far apart it currently is even though I still have well over 1100CFM per head.
Thanks for the post responses and will keep at it.
Shane

12/19/15       #12: wood chip denting ...
Kelly Craig

Though, obviously, different, the situation provides food for thought on the matter.

I'm a newbie to turning. I've noticed even sharp blades occasionally get a tiny chip trapped between the blade and the wood being turned.

Since there is not real pressure between the stationary blade and the rotating in wood, dents and drag marks are imperceptible.

The more moisture, the more this happens. For example, when I turn a branch from the wife's recently fallen pine tree, I can feel the water spitting from the cuts. If I'm not getting nice, long shavings, I notice the frequent momentary stops when a chip lodges between the blade and the wood.

Just turning slightly solves the problem. Though not always practical, it would be interesting to see what affect it would have to move the board left and right as it moved through the planer.

At any rate, my experiences with the lathe do suggest chip clearing is the number one priority, right beside the number one priority of watching moisture content during events.

These things aside, what about rollers? Do they become soft over time, such that they might be more inclined to pick up and hold chips?

Do the rollers have resin residue on them that would cause them to hold chips?

12/19/15       #13: wood chip denting ...
David R Sochar

We see chips stuck on rollers when we run Sugar Pine. Resin gets on the rollers and odd chips get stuck.

This is easily seen as the chip dents are a repeated pattern along the board. They are also quite a bit deeper than the chip beat.

12/19/15       #14: wood chip denting ...
Kelly Craig

It appears something to remove chips from the rollers, such as the brush used to remove build up on band saw wheels, would be worth manufacturers considering.

12/19/15       #15: wood chip denting ...
Russ

Many moulders already have these built in to the bed plate roller assemblies, it a piece of thin metal that barely touches the roller and scapes any debris to eliminate any chips from damaging the wood.
Merry Christmas to all.

12/19/15       #16: wood chip denting ...
David R Sochar Member

The problem as described by the OP is not dents made by chips on rollers. This is easily detected and eliminated.

The problem as experienced by the OP and many others is a bit more surreptitious: involving dust collection velocity, knife angles, head angles, even humidity and wood moisture content. The Knowledge Base has more. I will say that there are times when it is just hard to eliminate.

 

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