Rabbeting Knives for a Moulder

Tooling suggestions to enable clean rabbet cuts, without burn marks on the shoulders. March 3, 2006

I need to make some rabbeted solid cherry door jambs on our Wienig moulder and I am wondering how you keep your knife from burning on the side. Can you grind a cutting edge on the side? We have a Rondamat 950 grinder.

Forum Responses
(Solid Wood Machining Forum)
From contributor C:
I'd suggest using an insert rabbetting head with spur insert knives on the sides to take care of the edge burning and cut a cleaner rebate. These will hold an edge better and longer, and can also be used for jointing. The disposable replacement knives are solid carbide and very inexpensive. No grinding is needed! A number of manufacturers offers these type heads. Stark's TH03 head is made for linear operations on a moulder and has spur cutters on both ends.

From contributor S:
When I grind the knives for jamb stock, I always put a 1 degree bevel on the side of the stop. That way, it is cutting instead of rubbing.

From contributor R:
Yes, I recommend putting at least 5 degree side clearance on the side of the rabbet. Just move the stops on the R-950 to 5 degree or 10 degree. A draft angle is also recommended on the template at about 2 degrees. This will make the cut out of square. The amount out of square will be determined by the depth of cut.

From Dave Rankin, forum technical advisor:
I agree with the other posts. A couple of things that may need to be verified. Carbide insert tooling, if you will be doing some large runs or repeat production runs. Otherwise, I agree with contributor R on the angles. 1-2 degree on the template. 5 degree side clearance, but make sure that the clearance comes to the cutting edge of the tool. If you will be running 5,000 lineal feet or more, you may want to consider using DGK knife steel. Shorter runs, I would use M2 or T1.

From contributor J:
This is all true. I tilt my wheel 10 degrees and clean the inside of the rabbet knives. One thing to remember - axial constant will go out the window. It's not supposed to with a template that has that two degree draft angle, but usually the side clearance will cut deeper than you wished when you bring it to the edge. Of course, I use an antique R934, but that's pretty much the same machine. It won't change a lot, but a thou or two each time. Just something to keep in mind.

From contributor S:
I have done a lot of rabbetting with my Quattromat and would suggest getting the custom head with side carbide cutters. Every time I try with a standard knife, no matter what the back bevel on the side, I get tearout on the face. It never burns. The only way that we have gotten away from that is to run a kerf cut on the face before sending into the molder. This adds an extra step and isn't nearly as precise as you'd like. It's easily done on a table saw with a powerfeeder, but if going to that much trouble, you might as well use a good dado head and forget about using the molder. If you have very much of this, it'll be well worth the investment in the head. Most companies can get these to you in as little as two days.