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Chipping/splitting on edge of casing, American beech

5/14/14       
James Member

We are having a problem with chipping/splitting on the left edge (thin side) of casing when running American beech for paint grade. The problem also shows up when running white hard maple, but not quite so bad. The knives are sharp, and we are using a Helicarb head. I have tried using straight knives too, and it does not make a difference. The hook angle on the Helicarb is 5°, and on the straight knives I have tried both 20°, and 15°. The machine we are running is a Weinig Powermat 1000 with 12,000 RPM spindles.

We also run window jambs out of beech as well, and they do not chip at all. We are using 4/4 and re-sawing it at an angle for the casing. I have taken apart the chip breaker assembly and had the edge machined so it's straight again, and I also move it in as close as absolutely possible. Could it be that the spring tension is no longer strong enough?

Any suggestions would be greatly appreciated!!

Thanks!


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View higher quality, full size image (4128 X 2322)

5/14/14       #2: Chipping/splitting on edge of casin ...
Gene Wengert-WoodDoc

The first thing to do is to check the MC with either an oven test or a pinless moisture meter. A pin meter will not register accurately under 6.5% MC. It does look like one cause or a partial cause is over-dried wood--under 6.5% MC, especially in the outside layers of wood where the knife is working. Even when over-dried, bringing the MC up does not restore machinability.

This sort of failure is most likely when the grain is 45 degrees to the knife. So, with a curve, it is much more likely that the 45 degree angle exists instead of flat planing. Not much we can do about grain angle however.

What is happening is that the knife comes around and then has to decide which is the easiest way to cause the wood to fail--that is, make a cut and remove the wood material or split it off. A dull, slender knife (large rake) will find that it is easier to split the wood rather than cut it--wood is quite weak in splitting failures. We can reduce this splitting and make the knife more apt to cut in various ways, including a sharp knife, small rake angle, 7% MC or higher, large clearance angle, slower feed, strong wood, and so on. So, ...

This type of failure can occur because the wood is weaker than normal (usually bacterially infected is the main cause and then it would show up not very often). It can also show up if the back clearance of the knife is small so that the heel of the knife hits the wood and pounds it. This defect is also more likely with a knife that is trying to remove a lot of material compared to small removal per knife. In this case, high feed rates (meaning more removal per knife) should be avoided. This defect is also more common with dull knives--carbide would see it more than HHS or diamond.

This failure does not respond real well to pressure bar adjustments. Look for brittle factors 9low MC) or pounding.

Questions?

5/14/14       #3: Chipping/splitting on edge of casin ...
James Member

Thank you for the response!

Dry, brittle wood is something that we have considered. We have checked the moisture with a pinned meter, and it says 6%. I had also considered that due to the fact that we are angle re-sawing the material that it may be that the grain is hitting the knife at a poor angle. The primary knife that we use for straight sides is the Helicarb, which has a 5° hook angle, and ground at 15°. The 15° head I tried is a carbide insert head from Great Lakes, and the 20° is just a standard Weinig 2 wing with a 15° finish angle, and a 20° back angle.

Would I benefit by not removing any material on that side at all, and letting the top cut all the way down to the bed to finish out the width?

Thanks!

5/14/14       #4: Chipping/splitting on edge of casin ...
Gene Wengert-Wood Doc

The 6% MC value does indeed indicate over dried wood. If 4% MC it will read 6%.

5/16/14       #5: Chipping/splitting on edge of casin ...
rt

My first question would be, why that species for paint grade? I personally have never had much affection for american beech, mainly for the same issues you are having. I would suspect that the carbide side head is shredding that edge before it hits the top head and\or you are removing way to much thin tapered stock with the side head. Beyond that I would work on different hook angles and back bevel because the tear out is obviously not normal. Remember HSS can be ground a lot sharper than carbide, you may try that also.

5/17/14       #6: Chipping/splitting on edge of casin ...
russ

Website: http://www.mirror-reflections.com

Great information on this post,I would agree with the doctor on over dried wood.

Maybe you can let us know what the feed rate is when your manufacturing on your high RPM machine? I would imagine its 60 feet per minute if your looking for 16 knife marks per inch. Can you slow the feed rate down to maybe 50 fpm.

I would suggest trying a Weinig 12 degree hook with 20 - 25 degree back grind and a 15-20 degree finish grind see if that helps. (see article below).

Also try graining the lumber if you can before feeding, what I mean is, feed with the cathedrals of the grain pointing toward in feed side of the machine ( I know is tough on beech) or heart side down on bedplates, bark side up by looking at the end grain and see if that helps increase yield.

I agree that the real problem is the M/C can you sit the lumber under a humidifier for a day or so as to give it a chance to get some moisture back into the lumber, don't know if that will really help but your loosing profit in your current situation.

Good luck!

http://https://www.mirror-reflections.com/information/cutter_head_hook_angles.php

5/17/14       #7: Chipping/splitting on edge of casin ...
Russ

Also I have one more question, are you using a custom pressure shoe on this profile?

I believe you must have direct pressure on the flat area where the chipping is taking place, is this profile oriented in the machine so the thin side is to the out side of the machine using the angle to force the profile against the fence? If not the pressure shoe might be pulling the profile away from the fence causing gaps and no support while milling which leads to tear out issues, just a shot in the dark but thought I should ask :)

5/20/14       #8: Chipping/splitting on edge of casin ...
James Member

Hey RT!

Trust me, Beech is not our first choice for paint grade! If it was up to us, we would be using Poplar, but the customer doesn't want it because it's too soft. We have tried brown maple as well, but the tiger stripe is unacceptable, and soft maple get too much fuzzy grain.

I have not tried HSS, but will do that just to see. The Great Lakes insert heads are pretty darn sharp, and I didn't figure HSS would be that much different. It's surprising because we run Helicarb twisted carbide heads on the sides, and they are supposed to eliminate the tear/chipping, but it's no different when we run them or the straights.

Hey Russ!

Yes, we are running 60 fpm. I have tried slowing it down, but it does not make enough of a difference to justify the slower speed. I will try a 12° head, but the Helicarb is in fact 5°. Tried your link, but I get a 404.

The grain is pretty much a "is what it is" situation due to the fact that we are re-sawing the stock at an angle, and yes, thin side is out (1st left).

I am using a reverse shoe on the top, but the chipping is taking place at the 1st left. Next time I run this, I am going to not take anything off at the left side, and allow the 2nd top to finish out the width when it cuts the profile.

Thanks again for all the input!!
James


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