Moulding maple versus oak

      Why such problematic tearout on one and not the other? September 23, 2003

Question
We are starting to run maple mouldings along with our oak mouldings. Everything I have read says that they should mould the same. They both need similar hook angles, and knife cuts per inch. My problem is that I am getting a great amount of tearout on the maple. I can run oak pieces right behind the maple and they turn out fine. I have also checked the moisture content of the wood, and it is very close for both species. The oak is at 8% and the maple is about 8.75%. Why am I getting so much more tearout on the maple?

Forum Responses
(Solid Wood Machining Forum)
This worked for me. Grind your knives at 23 degrees. One angle - just 23 degrees. I don't know why, but it got rid of tear out and chip out on our maple.



Sometimes you need to play around with angle. I found out in the past that not all woods are dried the same, so it might give you some problems. Not all mills dry the same, so there goes that chart everyone follows. I grind at 25 and it works for me. Look at where your tear out is - is it where you have funky grain patterns and it's not straight? That will come into play, too.


My opinion is that four knives in the cut will cut this down a bunch. I know that if you do not joint, that only one is doing the work, but the chips are smaller so the advance tearing is shorter and this means that you don't have it tearing out on the final face.


What hook angles do your cutterheads have? We have found that a 10 degree, or even a 5 degree hook, will result in a much more acceptable finish on maple. There is a larger horsepower draw from the lower hook angle; 30% more horsepower is needed to run a head with a 12 degree hook than one with 20 degrees.

Hard maple is tougher to machine than soft maple. Hard maple varies dramatically depending on where it was harvested.



There are a few things to consider about running maple compared to oak.

The moisture content is important. Dry maple will tear out more. If you are running maple at 6% or so then a 10 degree or 5 degree hook head will help. If the maple is 8% or a little higher then a normal 12 degree hook head should work. If the wood was dried too fast and not conditioned, then a hook angle change may be necessary. The direction that the wood is fed into the moulder, grain direction, can cause more problems.

The thing I have found works the very best is to use a shear cut corrugated cutter head. We have used them for years doing both straight and profile knives. It requires a different style of tool rest for the grinder is all. The shear action greatly reduces the tearing of the wood and reduces the extra horse power requirements that are seen with non-shear heads.

Dave Rankin, forum technical advisor



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