Moulder Tearout Problems with Hickory
Hickory is notoriously difficult to machine. Here's a discussion on how to deal with tearout while making hickory crown moulding. February 19, 2006
Question
I am making hickory crown. Is there anyway to prevent tearout? I cut 4 passes of 1/16" and still get some. Any suggestions are appreciated.
Forum Responses
(Solid Wood Machining Forum)
From contributor S:
First make sure you hone the blades. I have found sometimes just changing the grain direction helps as well. Also make sure the last 1/2 passes take an even lesser slice. You just want to kiss it.
From contributor F:
I have three suggestions.
This will seem contrary to logic, but by running a molding at full depth of cut there is thick wood "backing up the cut" and it acts almost like a saws throat plate in preventing tearout by supporting the wood fibers behind the "cut zone".
Prepare your molding blanks with the jointer to flatten them and at the same time let the jointer help you determine the feed direction that is less prone to tear out and make note it on each blank's end grain.
Buy a set of Arkansas Files and hone the cutting edges. Polish the knives backs from 120 grit wet or dry carborundum to 600 grit on a piece of 3/8" thick glass.( The flattening and polishing of the knives back needs only to be done once for the life of the cutter)
Of these three suggestions, finding grain direction will do the most good followed by cutting at full depth. Honing and polishing will yield a better finish.
I find that as Contributor S said, you can take a very light "kiss" final pass where the shavings float in the air like feathers and improve the visibility of millmarks. Taking a second pass at 1/8" deep will be asking for tearout because there is too little wood backing up the cut.
From the original questioner:
Taking it all off in one pass didn't work. The grain is too wavy and some is nice and the rest is all torn out. If I slowed down my infeed, would that help? Or would it start to burn?
From contributor B:
Putting on a Schmidt variable feed rate drive gear drive will help. However, at $500 you may find the cost isn't justified unless you run the moulder regularly.
That is the only practical way I know of to slow down a W/H moulder. Dealing with alternate chain sprockets etc. is looking for trouble. However, slowing down the feed rate shouldn't result in excessive burning unless you bring it to nearly a stop.
When we run into this issue (hickory, fir etc.) we occasionally run the wood through the W/H backwards. That is, we climb cut feeding through the outfeed side of the machine. You'll have to remove the gear box, and make sure no one is standing in the path on the in-feed side as the wood can grab and take off on you.
This is dangerous work and not taken on lightly. It can be done though and will solve your problem. Doing it on a few pieces is one thing. If you have hundreds of feet of this to run though I don't think I'd recommend doing a climb cut.
From the original questioner:
To contributor B: When you climb cut how much do you remove each pass?
From contributor R:
To the original questioner: What hook angles were the knives ground at? What hook angle is the cutterhead? I am not real familiar with W & H but have you called the manufacturer and asked them about your problem? I would suggest using a 12 degree hook angle (more scraping action) and it would help to eliminate tearout. As for climb cutting, it is very dangerous and not recommended as the above post listed.
From contributor B:
Again, be very careful if you decide to try to climb cut with the W/H. If you have a feed roller on a shaper or other tool you could bring the two machines together and swing that feeder over one end or the other of the W/H to gain some control. Remember, without the gear box you will be hand feeding the machine. A secondary guard on the outfeed side (the side you’d be feeding into) that would prevent your hand from being pulled into the cutterhead is also a good idea.
I hope I'm making it clear that this is dangerous work. As to the amount of cut it's a delicate balance between as little wood as possible and the maximum roller pressure you can manage. I hope I’ve made my point that this is dangerous and that a great deal of thought needs to be given to making it as safe as possible.
From contributor F:
It is possible that you have some hickory that is just going to tear out because of its grain structure (no matter which end is fed first). If you don’t, I recommend against climb cutting free hand for safety reasons.
Use a power feed and climb cut if you found the best grain direction with a jointer or planer and the blank still tears out in the molder. Just as a gauge for you, my molder runs at 12 feet per minute.
For the most part, I run my moldings with the grain. Sometimes, because of a defect or flaw that I need to locate on a certain face of the molding, I am forced to run the molding against the grain. At 12 feet per minute, with my knife preparation and running at full depth of cut in a great variety of hardwoods, I yield moldings that are at least 99 percent free of tearout even when some pieces are fed against the grain. From what I read, you have a better machine than mine. I run mine on a 12" RBI in a corrugated single knife head.
From contributor M:
It sounds to me like the hook angles are too aggressive. I'm with Contributor R. Try a more blunt angle and it should alleviate a good bit of your problem. I have a nice dent in one of our roll up doors from someone trying to climb cut. The dent is at least 12" deep into the door, and this was after the piece knocked over 2 fully loaded carts of 8/4 poplar on its way to the door.
From contributor B:
Here's another trick you can try if there are only a few sticks to run. Put the knives on the W/H upside down. This will create a total scraping action rather then cutting action. Again, not something we do often, but occasionally it is just the ticket - and with 1/32" to 1/16" passes it will work.
From contributor F:
If I had to turn my knives around backward and run a profile at 1/32" per pass, I would just buy some different hickory. Those who are questioning your molding knife/knives must be on the right track. Does anyone out there run hickory molding and have it machine like most any hardwood?
From contributor G:
After thinking a little more about this, I think if you could speed up the Hussey feed rate or reduce the cutter head speed, by the use of a different pulley, you can hog it off in one pass without any tearout. The magic combo for hickory seems to be about 8 feet per minute with a cutterhead speed of about 4000 rpm. You can take it from there. I have done a lot of hickory and get nice smooth results all in one pass. Two passes won’t look so good. This works for me. The Hussey cutterhead speed is too fast for Hickory.
From contributor M:
I have run plenty of hickory with minimal problems. I think the whole problem is in the knives and not in the feed rate. If possible have a millwork supplier with a full size moulder run it for you. Have them grind the knives with a grinding bevel of around 12 degrees and run in a cutter-head with a hook angle of 12 degrees. The only times I have tear out is when it is an extremely deep profile.
From contributor G:
You need minimal knife cuts per inch to make moulding from hickory. Every unnecessary knife cut will invite tearout. Hickory is a very nasty wood to make moulding from. Adjusting the head speed or feed rate will both give the same results.
