Spiral router bit kickback

[FS7]

The things I make seem to require a lot of flush trimming and my primary bit is a Freud two-flute top bearing bit. It works well overall, though I do have tearout occasionally (mostly around curves and end grain).

I recently bought a very expensive Whiteside spiral compression bit (both up and down cut) which was supposed to be the best thing since sliced bread. If (very big if) it cuts well, it's extremely clean. The problem is it usually grabs the wood and wants to throw it regardless of feed direction. For the cost I'm extremely disappointed, but I assume I'm doing something wrong. This can't be intended.

What am I doing wrong? I use a Bosch router in a Bosch router table, same set up with any other bit. I'm trying to trim no more than 1/8". Before I angrily return this I'd like to see if I can figure out what the problem is.

[Stwood_]

Maybe try less removal, say a 1/16th, in 2 passes.
Is your workpiece attached to a pattern, or is it mostly straight cuts using a fence?

I've never had a bit as you describe. Maybe it's a machining bit, as for an automated, cnc, instead of a regular handheld or table mounted router?

[fredhargis]

I've never used the compression type bit, but I use their upcut spiral flush trim frequently, and it's solved a lot of tear out problems for me. I hope someone has a clue as to why that happens. What kind of wood are you routing?

[KyleD]

The things I make seem to require a lot of flush trimming and my primary bit is a Freud two-flute top bearing bit. It works well overall, though I do have tearout occasionally (mostly around curves and end grain).

I recently bought a very expensive Whiteside spiral compression bit (both up and down cut) which was supposed to be the best thing since sliced bread. If (very big if) it cuts well, it's extremely clean. The problem is it usually grabs the wood and wants to throw it regardless of feed direction. For the cost I'm extremely disappointed, but I assume I'm doing something wrong. This can't be intended.

What am I doing wrong? I use a Bosch router in a Bosch router table, same set up with any other bit. I'm trying to trim no more than 1/8". Before I angrily return this I'd like to see if I can figure out what the problem is.

More information on what you are doing with the bit could be helpful. Are you doing some type of trapped cut like the work piece between the bit and a fence or a slot cut? Are you using a pin to help start and end the feed?

[R Clark]

For me, an 1/8th of an inch is a lot of material to remove in one pass.

I use spiral upcut/downcut bits for edge-jointing work sometimes, but as you already know, reversing grain is always problematic.

[FS7]

I was using the bit to prep cutting boards for curved inlays, which in my case are just 1/8" strips. I route a shallow (1/4") channel with a straight bit, either jig or bandsaw the middle of the channel, and then flush trim each side so I have good surfaces for gluing. So the total width of the channel was 1/4", so if I was dead center with the jig it would've been 1/8" minus half the kerf width of the jigsaw blade.

I have never had a problem with my regular flush trim bit (here) other than the occasional tearout, usually only on one side. I tried this bit (here) hoping it would be the last flush trim bit I ever needed. The theory is that it produces clean surfaces on both sides because of the way the flutes are oriented. I was trying to route hard maple, no figure to speak of, and only in the long direction. I was freehanding on the router table, so it wasn't trapped. I was doing the exact same thing that I have done countless times with the regular bit, but each time it wanted to grab and throw the wood.

It wasn't even something that could be called chatter. It was butchering the wood. It doesn't appear to have anything wrong with it but to be honest the package appears to have been opened and returned several times, so I don't think I'm the first person to have this problem.

[EricU]

I'm with the people who are wondering if it's not meant for cnc.  But they probably would say that

[Cooler]

I've never used these, but some research shows that you are not alone with this issue.

https://www.woodcraft.com/blog_entries/s...outer-bits

Spiral Bits Can Be Risky to Use

Spiral bits work incredibly well in the production environment and especially in CNC (computer numerically controlled) router industrial applications. But in a hand router, their use sometimes imposes unusual risks not associated with the equivalent or bigger straight bits.The down-cut spiral bit's screw-driven forces are sufficient enough to pick the router up and twist it out of your hands—with no warning. I know, because it has happened to me. On end grain the spiral bit is getting even more traction, so the risk is even greater—a pity, too, because a sweet end-grain finish is attractive.
The up-cut spiral bit can have the opposite effect. It wants to pick up the work. So you must secure the work in some kind of fixture or hold it by a clamp. (I never rout anything that is not secured or clamped, but some people do.) The up-cut bit’s tendency to pick up the work also happens quickly and without warning.
My teaching and woodworking are centered on routing, so I have a cabinet filled with more than the weekend woodworker’s supply of router bits. I do keep a few solid-carbide spiral bits because, when I want a beautiful face cut or I am cutting narrow mortises, and I have the money, there is just nothing better. But my cabinet is mostly full of a wide variety of straight bits. For general-purpose work, for template and pattern routing, and for those times when need a large-diameter bit, I still reach for one of my straight bits.

[OldGuyDrummer]

You would never use a pattern or bearing bit on a cnc. The bearing is there to following a pre-made pattern attached to your wood. A cnc does not need the bearing to following a pattern. The patterned is programmed into the cut already.

I have several of the up, down bits and would never use them handheld, only in a table and would limit the depth of cut with the grain to less than 1/16" and even less if end grain. YMMV.

[EricU]

That's a good point about pattern bits in a cnc. Maybe they expect you to rough the part out with a straight bit and come back for a finish pass with this one.