a router bit: close call

[Susumu Mori]

I read a story that a router bit jumped out of a router table and hit the face. I thought it was a short article in FWW, but not sure.
And similar thing happened to me yesterday.

I was making a 1/4 wide, 3/8 deep groove for a 8x12 inch cabinet door frame to accept a panel.
It was a usual spiral bit and a PC fixed based router attached to a table.

After a while, I started to experience chatter and stopped the router.
What I found after I lifted up the wood was the bit almost falling off from the router and dug deeply into the wood.

I suspect the upcut spirals tend to be pulled into the material?

Similar to what the writer of the FWW story said, I believe I tightened the collet as usual. Not extremely tight but with a good squeeze of two wrenches. I guess better than what we can easily do with the usual one-wrench operation for many modern routers.

It is a bit of worrisome to experience like this without a clear idea about the cause.

I wonder if you had ever experienced something similar and share your idea about the causes and prevention.

p.s.: I always lift bits in the collet for a small amount, as suggested.

[Andrew Pitonyak]

My first thought was "oh boy, that could happen to me" (I did not think the word "boy", I thought something else).

My next thought was sawdust in the collet..

Glad you are safe.

[Susumu Mori]

Actually, now I remember that I just changed the collet from 1/2 to 1/4. Maybe something was not engaged properly or saw dust sneaked in...

[Mel Fulks]

Bit should be seated in bottom of collet and then PULLED BACK about an 1/8 inch before tightening. Holds better.

[pat warner]

1/4 x 3/8 in one pass?
The cutter was screwing itself into the work like a drill.
Change cutters, waste/pass, and maybe your attitude.
Routers are trimmers not hoggers.
Moreover, don't use spirals, they're full of surprises.

[Mel Fulks]

Excuse me...did not see the PS

[John TenEyck]

I've had bits come loose two or three times. A couple others have broken under load. In all cases, they have never done anything but stop spinning. They didn't go flying off somewhere or hit me, nothing like that. They just stopped dead in the piece of wood they were in, or fell on the floor if it was an edge cut. I can understand how a really large bit would have a lot of inertia if it broke, and might do some real damage, but small diameter bits have very little. But I still double check that the collet is clean each time I change bits and make sure to tighten the new one very well.

John

[Phil Thien]

1/4 x 3/8 in one pass?
The cutter was screwing itself into the work like a drill.
Change cutters, waste/pass, and maybe your attitude.
Routers are trimmers not hoggers.
Moreover, don't use spirals, they're full of surprises.

This.

That is just way too much depth of cut for a 1/4" spiral bit. I'd have taken at least three and maybe four or five passes.

And I'm pretty sure where Pat says to change your attitude, he means to change your approach.

[Rick Potter]

Sure glad you turned that router off.

Years ago, I had half a dozen people from a local WW club at my house, and I was 'show and telling' them my method of making cabinet doors on a bench top router table with a PC 690. While I was talking, one guy 'helped' me by putting in a cope bit in the router, and re-inserting it in the table. Unfortunately, he did not tighten the router in its base. As I started it up to show how this step was done, the router vibrated right out of the base, dropped on the table, bounced down on the concrete of my driveway, took a couple divots out of the concrete, and wrapped itself up in the cord, ruining it. All this, right at my feet. If you think a fat guy can't move fast, you should have seen the jig I danced, trying to stay out of the way.

I don't care if the ghost of Maloof comes over and helps. I check everything now.

BTW, if anyone happens to have a bench top setup, I solved the problem the next day. A simple wooden donut screwed to the bench with a 1 1/2" wooden dowel right under the router, so it cannot possibly vibrate out. Just pop out the dowel to change bits, etc.

[Susumu Mori]

Pat and Phil, I guess that was it.

It was actually 5/16, not 3/8 but you'd do it in 2-3 passes. I see. Yes, it seemed screwing itself in the work. I thought it was not much material to remove and I became lazy but I certainly need to change my,,,, approach. I learned my lesson. Thanks, your advise is so valuable.

Also, I'll use regular cutters as much as possible in the future. As a hobbyist, I want to minimize any risk, if I have a choice.

[Jim Dwight]

A dado blade on the table saw is easily capable of doing this in one pass but not a router bit, especially with a 1/4 inch shaft. A cut or two with the table saw to remove some of the material could also make it a one pass situation.

Overloading a router has several potential outcomes and none that are very good. I like my PC690s and have raised panels with them but I make 3 or 4 passes. Two is probably enough for what you describe. I listen to how the router sounds and if it is laboring, I reduce the depth.

[ian maybury]

Cutters screwing themselves into the work are a widely recognised potential problem when milling metal - it's one reason why it's not regarded as good practice to use a drill chuck to mill with a spiral slot drill or end mill on a mill drill. Or a taper mounted tool holder not secured by a tie bar or whatever either.

Against that the ER type chuck/tool holder commonly used for light milling is at least superficially similar/ similar in principle to a router collet chuck. Much larger in diameter and heavier though - permitting much heavier tightening.

Hard to make a meaningful comparison, but it would seem definitely to suggest that significant forces can be generated by spiral cutters on routers - especially during heavier cuts on tough woods...

[Lee Schierer]

I have an older Craftsman Router with a single split cone type collet. I've gotten in the habit of tightening the bit in the collet, setting the depth, then making a short cut on a piece of scrap and rechecking the tightness of the collet. This short "test run" insures that I don't ruin a good piece of stock.

My Freud router has a 6 finger collet that has never slipped or loosened when making a cut.

[Jim Neeley]

I once read about inserting a rubber "O" ring into the empty collet prior to inserting the bit. That way when you tighten the bit and the collet draws the bit down, the ring just compresses. I added one to each of my routers about 5 years ago and voila.. no more bits coming loose.

Jim

[Phil Thien]

I once read about inserting a rubber "O" ring into the empty collet prior to inserting the bit. That way when you tighten the bit and the collet draws the bit down, the ring just compresses. I added one to each of my routers about 5 years ago and voila.. no more bits coming loose.

Jim

Having an o-ring isn't a bad idea but it wouldn't have saved him here, that is just too large a cut with that bit.

[Bob Potter]

I have and had this happen with a hand held router and one mounted in a table. Both times the bit's were in correctly. I don't have one but wondering if a guard above the bit would keep the bit from flying out and doing damage to people and wood. So glad your ok.
Bob

[lowell holmes]

1/4 x 3/8 in one pass?

----Moreover, don't use spirals, they're full of surprises.

Pat,
I would be interested to know more about the surprises. I kind of like the spirals, but I respect your knowledge.

[Phil Thien]

Pat,
I would be interested to know more about the surprises. I kind of like the spirals, but I respect your knowledge.

Well I had a spiral climb right up through my stock once. Hit the edge of a knot in my board and climbed right through the board. Good thing my hand wasn't there.

[Mark Patoka]

I use a 1/4" spiral bit in my handheld PC690 quite regularly to route arcs and circles, trying never to cut more than 1/4" deep at a time. I have had a few instances where the bit did start coming loose and started working itself deeper in the groove as I was routing. As far as I can tell it was because the collet just started working itself loose so I make sure I have it as tight as I can and then usually don't have a problem.

[Phil Thien]

I hesitate to mention this because some people will think it allows them to take a larger bite.

But I color the shaft of spiral bits with a permanent marker.

This is an old machinist trick I found, it gives the shaft a super-fine grit that allows the collet to grab better. The solvent in the pen also likely helps rid the shaft of any remaining oil (although I clean the shaft with 409 and let if dry first).

Still small bits, though.

[pat warner]

"Pat,
I would be interested to know more about the surprises. I kind of like the spirals, but I respect your knowledge. " Lowell Holmes.
*********************************************
12) What about solid (spiral ground) carbide bits, the silver bullet?

Not in my view.

The spiral cutter (solid carbide) has its place and since it does slice continuously (not an unbroken cut like 2 straight flutes) it can produce an impeccable finish; it may still tearout, however. They do bore well too and plunge better than any flute design. They are harder than brazed-on carbide tools, last a lot longer, cost more, and are difficult to re-sharpen. They have associated vectors (force with direction) that make them unsafe except in production situations where the work is well fixtured and feed rates constant.

The down spiral will produce a top clean corner (in a mortice e.g.) and fire the chip into your socks on outside cuts. Its force vector wants to pick up the router and has scared this furniture/maker silly, but only once.

The up spiral will fray x-grain , perform well down grain, and pull its chip from the excavation. The force vector in the up spiral wants to pick up the stock but at the same time pulls the cutter from the collet, the most likely of the 2 cutters to change depth of cut. Expect analogous and perhaps unexpected performance in the router table. Keep east/west cutting depths to a minimum for safety.

Few diameters are available in solid carbide. All tools (for 1/2 shank routers) have been ground into their shanks and none have cutting diameters >.500". Skinny and long cutters whip and deflect whether solid carbide or steel. Expect some chatter as the cutting depths increase. 2+hp routers flywheel the cutter better than small routers and will help smooth out the ride and reduce chatter. Larger straight (>5/8 CD) brazed on carbide cutters are preferred by this furniture maker, especially for safety and outside cuts. There is a lot more to the story, but in my view, their risk and expense is not worth their performance benefits, except in a production environment. More on this in

[glenn bradley]

Similar to what the writer of the FWW story said, I believe I tightened the collet as usual. Not extremely tight but with a good squeeze of two wrenches. I guess better than what we can easily do with the usual one-wrench operation for many modern routers.

It is a bit of worrisome to experience like this without a clear idea about the cause.

I wonder if you had ever experienced something similar and share your idea about the causes and prevention.

p.s.: I always lift bits in the collet for a small amount, as suggested.

First off, glad you weren't hurt. My experience was also with a captured cut . . . thank goodness. The only time I experienced this was when, like you, "I believe I tightened the collet as usual"; I obviously had not :o. I inspected the area for some other cause but, I couldn't find anything that looked suspect.

The reason I believe I was the culprit is that I have not had a repeat event in all these years and I use the same one-handed, two-wrench method as I always have. This method assures a snug bit without the danger of over-tightening. I have to assume that I just got distracted at the wrong moment or something since tightening a bit in a router isn't exactly an involved process :D.

[Mike Wilkins]

As soon as I read the 2nd paragraph, it hit me. I never attempt to take a 3/8" deep cut in any material, even with a larger bit than 1/4". And with a spiral upcut bit, it would have a tendency to pull up on the bit. It has always been advisable to make incremental passes with deeper cuts than attempt it all at once. Less strain on the router/better and smoother cuts/and ultimately safer.
Stay safe and watch those fingers.

[lowell holmes]

Pat,

I really appreciate you taking the time to answer me.

[Jerry Olexa]

Be careful and tighten securely.