We recently purchased a 2" x 4" diameter insert style rabbeting cutter. The knifes are mounted in it at an angle to the face to give a shear cut. While using it to edge some material I found it is leaving a convex face on the lumber. I spoke with the company I purchased it from and was told it is not possible to build a insert style shear faced cutter that will give a straight edge?? This makes no sense to me at all. So are the people who use this cutter happy with the open joint on the face?

Does anyone have a insert style shear cutter that produces a straight edge?

TIA

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Gerry,

When a straight knife is slanted in a round cutter body, to create the shear cut, the ends of the knife project ever so slightly outside of the cutting circle. The issues are compounded with a longer straight knife and a smaller diameter cutter head.

To say an insert shearing cutter head can't be made to produce a flat surface is not accurate. It absolutely can be done, the problem is the blade would have to have a slight curve to match the line it follows on the cutter head. I suspect the cost would be too great to manufacture which is why we see so many of the shelix style insert cutterheads where the "curve" is achieved by using multiple smaller inserts.

Hi Pete,

Why could the body of the cutter not be milled to have the blade move in the amount they now project? A cutter that leaves a curved surface is really of no use unless you are ok with gaps in your woodwork.

Thanks

In theory I think you're correct, the cutter body could also be milled to accommodate the curve, however that would rely on some combination of thin and flexible knife steel. Carbide is too brittle without a backing plate and wouldn't flex much without snapping. Can't speak to HSS knives, maybe someone with more insight can answer that. My guess is it's more complicated to engineer a solution that involves a flexing knife than cutting a curve with modern CAD programs. Anything can be done if there's a demand, but I doubt there's any real need for a more expensive shear cutter when either a traditional rebate insert straight knife or the smaller insert shelix/helical style cutters work for most if not all applications and materials.

I agree that the surface left from these cutters is unacceptable. I have a 125mm x 50mm with the same shear setup and it's been sitting on the shelf for years. I do have a shorter version at 30mm tall that I still use on thinner stock as the imperfection in the surface cut isn't as noticeable as the taller cutter. I don't work with tear out prone woods and have great results using a standard (non-shear) insert straight knife rebate head. If tear out is an issue you might consider one of the shelix/helical style heads.

Hi Pete,

I had no idea when I bought this cutter I was making a compromise to get a shear cut. These cutters should be sold with a disclaimer.

Fortunately I am able to return it. I will track one down with no shear.

Thanks for your input.

Gerry - You are right. In fact, I just bought a larger insert rabbet head to replace our 30 yr old Amana aluminum head. I saw the shear angle and thought the blade could be spiral, like in some planers from the 80's and 90's, or curved in some way to machine a straight line. It is not.

I am considering returning it since we count on straight surfaces for our joinery. For many things it may not matter, but for some, it simply will not work as hoped.

I reasoned (but still bought...) that if one were to take the straight knife and lean its slot over further for a much stronger shear, then the effect would obvious and intolerable. Unless the knife had a concave edge, which it does not.

David,

Sounds like we went down the same road. I was replacing an old brazed carbide head we have been using forever.

I sent the cutter back and found an Amana insert rabbeting cutter with no shear. I have not found we get a lot of chipping without the shear cut on the head.

Thanks,
Gerry

I had no clue this happened.

We've got a Dimension in Tooling opposite shear four wing cutter. We use it for sizing face frame material, and sizing door sticking after the profile cut. There's been miles and miles of material passed across this thing.

I ran a piece of 8/4 through it this morning because I hadn't noticed it making a not flat cut in the past. It's definitely convex, but it doesn't look as extreme as your picture. It's a 4" diameter head, with a 1-1/4" bore running on a 1-1/4" spindle.

I wonder if the angle of the knife plays a roll in this?

I wonder if the opposite shear cancel's some of it out?

I don't think it would matter, but mine is just a straight cutter, no rabet knickers.

I wonder if spindle run out affects this as well?

What kind of shaper are you running? This was done on a medium duty SCM T130N. The machine is fairly tight, and I put a set of bearings in it a couple of years ago.

Karl - If you turn the shaper plug over, the cut is reversed and goes concave. Matches up with the convex very well.....

But seriously. Yes, if you think of leaning the knife over further, increasing the shear, you can eventually get to where it is almost 90 degrees to the shaft, and the ends of the knife are way out, making a mythical cut far from straight.

While the mis-cut is very small, I am concerned that it may affect our ability to produce the tight joints we love and need. The folks at Amana are kind enough to trade it it in for the straight knife version.

I checked with 2 other makers, neither of which was aware of the less than perfect cut their cutters make.

Machine, spindle, or political beleifs have nothing to do with it - it is the straight knife that needs to have a slight curve instead of straight, or you live with it.

Karl,

In the picture I cut the piece I ran through the shaper and turned it so the error you see is twice what the cutter is producing. This piece of cherry is 1.75" thick also.

I lost a days production because of this cutter. I used it to edge a stack of cherry for edge lamming and because of the glue squeeze out did not see the joints were not closed until I started cleaning up the panels the next day. I had to cut all the joints out and redo the previous days work!

This cutter is 1.25" bore 2 knife opposite shear 125mm diameter.

I don't know if my supplier was aware this straight knife cutter does not leave a straight face but I was not made aware of that fact or I never would have purchased it.

We are using a good heavy Rulong shaper with a 1.25" spindle and 7.5HP. There is no run out in the spindle, the concave face is all about the cutter.

As David says the more shear you have the more the face is convex. This is not something I considered before purchasing this cutter and I was not looking for a cutter with a shear cut. This was the only rabbeting cutter the supplier stocks.

I tried to attach a picture before, didn't stick for some reason

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I was not aware of this either. My most used shaper cutter is a 18 year old Z4 Garniga rebate head with shear. I tried it yesterday on some 8/4 and my results were identical to what Carl shows. We don’t edge stock with this but used mostly for rebating where this would not be an issue. We do some shiplap type joints on doors where this may cause some gaping but have never noticed gaps before.
I dusted off my old Stark Z2 straight knife rebate head to use for joinery where this might be an issue.
The Z4 shear head cuts slightly better but not by much.

As a side note we use the shaper to prep glue joints on exterior door panels using T&G or spline. Just to get more glue surface and reinforce the joints to the weather. Lately we have been running a glue joint cut on this and works very well.
I normally like a outboard fence for this but because of various widths use the split fence instead. Makes a nice tight joint with lots of glue area.

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Interesting seeing the different results. The only explanation I can think of is the shear angle is different and/or the cutterbody diameters are different. If the various cutterheads used have the same specs then my head just exploded.

I had the same issue as Gerry with a visible gap after edging for glue up and was pretty disappointed so I stopped using that cutter although I can see how the convex cut wouldn't affect other operations.

The shear angle on the cutter I had looks to be more than the one Joe has shown us. The curve on the face of the produced cut is also more extreme than the one Karl posted. This is the sort of thing that can cause a lot of head scratching trying to sort out why your joints are not closing up tightly.

It is worth noting that when doing rabbets with this cutter up to the mid point in height the gap will be hidden in the bottom corner of the joint.

I think with the cutter Karl and Joe have this problem would be a lot harder to diagnose than with the one I had.

Joe I like the look of that glue joint cutter. How do you apply the glue to that edge?

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Gerry,
I think more angle of shear makes the convex worse. Mine is pretty slight compared to yours.
Good to know about this, I have used this cutter for many years and had no idea.

We glue with a pressurized pot. I just put a small bead in every dip then rubbed the joint. Interesting, because it was more glue than a normal square joint gets and not much squeeze out.
I am sure Pizzi makes a nozzle for this but it worked well doing it this way.

Joe,

The glue joint looks invisible on the end. How does it look after panel raising? I find the glue can show more when cut on angle.

I like the alignment that would eliminate a lot of fooling around when gluing up.

Thanks,
Gerry

is this also a problem with insert style jointer cutters? I have an eight inch shelix cutter head in my jointer and jointed a piece of wood today and put a straight edge across it and could not tell if it was convex or not. Is any one using an insert cutter in there jointer for edge gluing?

Thanks.........nicko

Niko,

The Shelix head will not cause this problem.

If you look at the carbide they are curved on the face. I have a Shelix head in my thickness planer and glue up off of the planed face with no problem.

Gerry,
We hardly ever do raised panels anymore.
Not sure how this cutter would work for that.
Most of our panels have a step around the edge. The joint disappears on those.
We have another type glue joint cutter for the four slider that would be better for raised panels.

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Joe,
That is consistent with my experiments with that style of cutter.

Thanks

I was thinking about this again for whatever reason. The shear angle looks much more significant on Gerry's head than mine. Which probably contributes to the convex cut being more pronounced.

I never knew this until this thread. Good stuff to know.

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We will run a few things to see how it actually performs. Amana agrees to take it back for a full refund.

My problem is that I like absolutes where I can get them. Usually, getting a solid 90 degree corner is not difficult. Having to remember that what we get on that one surface may not be trustworthy is a problem to remember.

We sent the cutter back and have received a new Amana head with no shear. I don't notice a lot of difference in finish quality and this one cuts a 90 degree square cut with flat faces in both planes. I think this is a much better option.

My rabbeting cutter has 4 knives. Two tilt forward at the top, two tilt forward at the bottom. Each knife sticks out a little bit further at either the top or bottom depending on the direction of tilt. Not easy to see in the photo. It does cut square as best as I can determine.

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David,

If the knives are straight and tilted it will cut a convex face. It is very hard to see on the head. The best way to see it is to edge a piece of 8/4 stock then cut it and fold it back against itself.

The way David described it makes it easy to visualize. The knife is pivoting on it's center point if you imagine it turned 90 degrees the tips are a long way out. The more sheer the more the cutter will over-cut on the top and bottom unless the knife is custom ground to compensate.

Doesn't help with the rabbet part, but if you want a head that shears and doesn't leave a convex surface, you could use a cone shaped head in a tilting shaper.

Not an original idea, I was just thinking about how the Lamello lipping planer works.