dangerous router bit practice????

[Greg Muller]

All,
I just heard something that sounds a little dangerous, but maybe I'm overreacting...
A fellow woodworker told me that since you shouldn't insert a router bit all the way into the collet, he sometimes places a rubber O-ring around the bit shank for a consistent depth and to reduce vibration.

Have any of you ever heard of this practise?

Greg

[Glen Blanchard]

I have read of this, yes. Have never done it though.

[Bruce Page]

I have heard of it several times. What do you see as dangerous?
I don't think it would do much for vibration but it would give a repeatable depth.

[Mike Goetzke]

I've heard on a router table of placing an o-ring in the bottom of the collet but not on the bit itself.

[Norman Pyles]

I've heard on a router table of placing an o-ring in the bottom of the collet but not on the bit itself.
That's the way I heard it also.

[Jason Beam]

Yep, heard of it and it's perfectly fine. It's actually a good idea. The idea of a collet is that you tighten a nut, shoving a tapered piece into a tapered hole. The tapered piece has slots cut in it so that as the tapers meet, the piece can contract around a hole. Well obviously as the collet tightens down on the bit shank, it needs to be able to move inward a little to cinch up the grip on the shank. If you bottom out the bit, the collet can't grip it nearly as well. Some collets are actually tough to loosen if you bottom out the bit and you can have trouble getting the thing out.

I'm not 100% sold on the reduction in vibration theory, though it does make some sense. If a collet has a good grip on your router bit's shank, the collet is firmly seated into the collet shank, the nut is tightly secured on the outside of the shank, just about all the vibration the bit sees will still be transfered to the motor and vise versa. But, since it's bit to collet to shaft and nut instead of just bit to shaft (since the bit isn't actually touching the shaft), it may make a difference.

Suffice it to say, if not bottoming out the bit lets the collet grab it better, any other benefits are just gravy. :)

[Chris Padilla]

That's the way I heard it also.

+2

The o-ring is placed within the collet to prevent bottoming-out so your bloody router bits can be removed without a hydraulic press. :o

[Dave Falkenstein]

I doubt an o-ring would still be in one piece if you put it on a router bit shaft and tightened the collet. The collet would crush it and cut it. As mentioned, placing an o-ring in the bottom of the collet is fine.

[glenn bradley]

I do this. It works great. The other method is to put the o-ring into the collet so your bit will land on it. A couple of my routers have really deep collets so I went for the o-ring on the bit. I have them on all of my 1/2" bits and did not do this for any vibration issues.

[Greg Mann]

I think the bottoming out of routerbits is, for the most part, a harmless practice. There are occasions which would be specific to some routers where the bit may hit the bottom unevenly and cause problems. Collet holders in the metalworking industry routinely come with threaded stops in the bottom to help in setting cutters to a specific and repeatable height. Of course this means you are purposely bottoming out the bit and subjecting it to far more stress when using it than a router could generate. If it isn't a problem cutting space age alloys I don't know why it would be cutting wood.

[Don Morris]

Marc Sommerfeld mentions it in his video as a way to get consistency in bit height when changing bits e.g. changing between rail and stile. That way since his bits are calibrated you don't have to adjust the height of the router inbetween bit changes. I've been doing it and it doesn't seem to be a problem.

[Greg Muller]

He was specific about the O-ring being on the shaft of the bit between the cutterhead and the collet, not in the bottom of the collet. I do see how an O-ring in the bottom of the collet could help, though.

I don't know why I thought it may be dangerous on the shaft- all I could think of is that splinters could wedge themselves into the rubber or between the O-ring and the collet or bit cutterhead. I suppose the bit is spinning so fast that nothing substantial has much chance to maintain a grip.

Hmmm- I may have to try these out myself if so many of you like the practise...

Thanks,
Greg

[Jon Bonham]

I can't imagine how any reasonable person could consider this dangerous. What are you worried about, the rubber o-ring flying off and bouncing off your chest?

[Lee Koepke]

I can't imagine how any reasonable person could consider this dangerous. What are you worried about, the rubber o-ring flying off and bouncing off your chest?
as a reach, maybe the collett not gripping the bit properly???

[Greg Heppeard]

I used to bottom out bits, but started having the problem of the bit coming loose and climbing in the collet. I started to raise the bit slightly and no more problem. I seem to remember reading somewhere that an "O" ring will keep the bit from bottoming out, thus preventing the climbing bit. My Triton router actually has a small upward dimple in the collet, preventing the bottoming out of the bit. It seems that an "O" ring on the bit shank will do the same thing, but it would take a lot of "O" rings to put on all my bits.

[Greg Mann]

Back when Marc S. was promoting the Hitachi MV12 as THE router to use he encouraged using a rubber faucet washer under the bit as a way of controlling the insertion height without bottoming the bit metal to metal. I am positive this was his recommendation because he even packaged the washers with the bits he sold (then CMT). I have seen the o-ring on the shank recommendation elsewhere and that is for a different purpose, primarily as a convenient way to keep the bit from going in deep enough that you are tightening on flutes instead of solid shank. Burying the flutes in the collet is a definate no-no. I remain unconvinced that bottoming the bit on a uniformly shaped, i.e., a flat surface, against the end of a bit is a bad thing. Unless, of course, it is now deep enough that it is encompassing the flutes, or, hitting the fillet on bits bigger than the shank diameter.

[Aaron Beaver]

I always heard that the router bit shank may taper a bit when it gets close to the head, so to ensure good grip on the shank you should raise it that little bit so that the taper doesn't interfere with the collet tightening.

[Michael O'Sullivan]

I doubt an o-ring would still be in one piece if you put it on a router bit shaft and tightened the collet. The collet would crush it and cut it. As mentioned, placing an o-ring in the bottom of the collet is fine.

I think the O-ring is supposed to sit on top of the collet -- between the end of the collet and the base of the cutter.

I actually have a related router bit danger question. How much of the shank (assume 1/2 inch shanks) needs to be in the collet for safe operation? The reason I ask, is that I am building a coping sled for my router table using 3/4" melamine as the base. However, the collet on my router (a Milwaukee 5625) barely protrudes from the router table at max elevation. So if I wanted to, for example, use a tongue cutter, I would not be able to insert the bit all the way down.

What do you guys do in this situation?

[Chris Padilla]

I remain unconvinced that bottoming the bit on a uniformly shaped, i.e., a flat surface, against the end of a bit is a bad thing. Unless, of course, it is now deep enough that it is encompassing the flutes, or, hitting the fillet on bits bigger than the shank diameter.

I've gotten a few router bits stuck in my collet and the only thing I can think of was that they bottomed-out on me and got stuck for some reason. Perhaps my router has other issues but when I stumbled across the o-ring idea to prevent this, I haven't had a stuck bit since. This was on a good old PC690, FWIW.

[Don C Peterson]

The o-ring on the shank seems perfectly harmless, I would quesiton the o-ring inside the collet though. For that to work as advertized, all router bits would have to have the same length of shanks which is not the case.

Personally, either approach seems like overkill to me. This strikes me as a cleaver solution to a non-exitent problem. Anyone who would go to the trouble of finding little o-rings to put on all their router bits, knows better than to jam them into the collet.

[Rick Christopherson]

This notion of bottoming out the router bits is so grossly overstated that most woodworkers aren’t even aware of when and why the problem may exist. For 90% of routers on the market, it is a non-issue yet people repeat the story as though it is common to all routers.

This issue came about because of the likes of the Hitachi M12V, which has the shallowest arbor bore of all routers. With this router, it is possible for the end of the routerbit shank to contact the bottom of the arbor bore. When the collet is tightened, the bit bottoms out and this prevents the collet from being properly drawn tight. This will cause the bit to loosen with usage.

On the majority of routers on the market, the arbor bore is sufficiently deep enough that it is virtually impossible to bottom out a standard bit. A few years ago I did a tool test of 3 hp routers for The Woodworker’s Journal and I specifically measured each of the arbor bores. I can't find the data anymore, but if memory serves me, the M12V arbor is only 15/16-inch deep, but most other routers are between 1-1/2 inches and 2-1/2 inches deep.

So unless you have the M12V, there is no need to worry about o-rings and bottoming out.

P.S. The purpose of the o-ring in the bottom of the arbor bore is that it provides a cushion when tightening the collet. Instead of a metal-to-metal bottoming out, the o-ring will be compressed as the collet is tightened.

Oh, P.S.S. Some people have mistaken this issue for inserting a bit into the collet to the point of touching the carbide to the collet. That is Not the reason behind the O-rings, but it Is the reason why it gets repeated so often. Bottoming out the bit means that the bottom end of the shank touches the bottom of the arbor.

[Don C Peterson]

P.S. The purpose of the o-ring in the bottom of the arbor bore is that it provides a cushion when tightening the collet. Instead of a metal-to-metal bottoming out, the o-ring will be compressed as the collet is tightened.

Which is kind of my point (although you expressed it better) that in most router/bit combinations the router bit shank is nowhere near the bottom of the collet, which makes putting an o-ring in there, pretty useless unless you have either a router with a very shallow collet or very long router bit shanks...

[Tom Veatch]

...So if I wanted to, for example, use a tongue cutter, I would not be able to insert the bit all the way down.

What do you guys do in this situation?

Never thought much about it, but my initial reaction is to advise that you take the collet off the router, insert a bit into the loose collet until the end of the bit is flush with the normally hidden end of the collet. Then observe how much of the bit's shank is exposed. Then I'd use that as a "never exceed" extension of the bit.

Reasoning behind that advice is any of the shank that extends into the router beyond the collet isn't adding anything to the collet's ability to retain the bit. On the other side of the coin is that the longer exposed portion of the bit would contribute to greater side forces in the router bearings and might contribute to increased vibration/runout. The latter effect may or may not be significant.

[Gary Keedwell]

It seems to me, if my memory seves me right, that bottoming out the bit then raise it 1/16" so the space will not transfer the heat from the router to the cutting part of the bit. Acts as a buffer.

Gary

[Eddie Darby]

I got some router bits that had listed that they should be at least 3/4" in the collect. They were 1/2" diameter shafts.

I've read that not allowing the router bits to bottom out prevented heat from transferring to the main body of the router.

I would check to make sure that there is no wear on the shafts form slippage, and that the metal is smooth and round for a good grip.
That is also important as far as safety goes.

[Rick Christopherson]

Please, let's not get another myth rolling, and nip this one in the bud before it gets repeated too much. I have never heard of heat transfer as being a reason for how the bit is inserted, but there is absolutely no foundation for it. You already have metal-to-metal contact on the shank of the bit with the collet, so any heat transfer will take place here, not at the bottom of the arbor bore. If there was any major heat to transfer, it would happen regardless how the bit was inserted.

Gary, if the motor is heating up enough to transfer significant heat to the router bit, then the motor bearings are long-ago shot. The motor will not get hot enough to damage the bit.

Eddie, the same is true for the router bit passing appreciable heat into the router. If, given the small mass of the router bit, it can pass enough heat into the motor to cause an appreciable temperature rise, then the router bit would need to be virtually glowing red.

[Gordon Harner]

On the subject of the milwaukee router and the sled. I've seen collet extensions advertised and I think tested. I think they add about 1.5 inches in depth. I never have used one but, an option.

[Dave Falkenstein]

I doubt an o-ring would still be in one piece if you put it on a router bit shaft and tightened the collet. The collet would crush it and cut it. As mentioned, placing an o-ring in the bottom of the collet is fine.


I think the O-ring is supposed to sit on top of the collet -- between the end of the collet and the base of the cutter...

Aha! Of course. Thanks.

[Eddie Darby]

Please, let's not get another myth rolling, and nip this one in the bud before it gets repeated too much. I have never heard of heat transfer as being a reason for how the bit is inserted, but there is absolutely no foundation for it.

http://www.routertips.com/index.htm

"Another way to keep router bits from dropping too far into the collet.
When a router bit falls too far into the collet and makes contact with the end of the router's motor shaft, the heat developed by the bit during routing is transferred directly to the shaft. This can shorten the life of your motor bearings and perhaps the motor, as well.Try clipping a spring-loaded clothespin over your bit prior to inserting it into the collet. Surely, we don't have to remind you ... but ... don't forget to remove the clothespin before starting work."


"Keeping Router Bits from dropping too far into the collet.
When a Router Bit falls all the way into the collet and makes contact with its bottom, the head generated during the cutting process is transferred directly to the shaft of your router motor, potentially shortening the life of the motor. One way to prevent this is by wrapping a rubber band (or tiny orthodontic rubber band or "O-Ring") around the shaft of the bit prior to insertion. Be sure to remove the band prior to routing, as any heat build-up could melt it to the bit's shaft."

"Keeping router bits from falling too far into the collet.
When working with routers mounted upside-down in a router table, it's important to keep the bit from falling too deep into the collet, lest it transfer damaging heat directly to the shaft of your router motor. You can prevent this by laying a strong magnet on the router table surface, in contact with the side of your bit, during installation."

"Two Reasons NOT To Allow Router Bits To Bottom-Out In The Collet
First, bottomed-out bits will almost always make direct contact with the shaft of your router's motor...transferring the heat created by cutting directly to your motor's shaft. This will tend to shorten the lift of your router motor. Second, if a bottomed-out bit seizes in the collet (which frequently happens), you'll have to PULL it out with pliers, which can be difficult. If your bit isn't bottomed-out, you can tap it with a piece of wood, freeing it from the collet much more easily."


Whatever? lol :rolleyes:

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I also found this at the Lee Valley site which is a nice tip on router bits:


http://www.leevalley.com/shopping/TechInfo.aspx?c=&type=a&p=44399

[Bill Huber]

This notion of bottoming out the router bits is so grossly overstated that most woodworkers aren’t even aware of when and why the problem may exist. For 90% of routers on the market, it is a non-issue yet people repeat the story as though it is common to all routers.



I have a Bosch 1617 and I bits that will hit bottom and that router is still being sold today, so it is still an issue.

I have had the problem once when I let the bit hit the bottom and then it walked up on me so there are still some routers being sold that do have the problem.

Why could you not just drop a Space Ball in the end of the shaft, it would do the same thing as an o-ring, right?

[Allan Froehlich]

I put a space ball at the bottom of my router collet.

What is nice is that when you loosen the collet, the router bit will pop up slightly when it is loose.

[Rick Christopherson]

Yeah, I read it on the internet, so it must be true, right? So do you suppose the collet is made from thermally insulating ceramic or something? Is the high-compression contact of the collet, shank, and arbor going to be less thermally conductive than the light contact the shank can make with the bottom of the arbor?

Whoever wrote that information doesn't have the first clue about thermodynamics, but it sounds good, so you bought into it without even questioning it. So just how hot do you run your router bits?

[Tom Veatch]

In the opinion of a retired Professional Engineer (me), the "heat transfer" problem seems to have the makings of an urban myth. I'm going to have to side with Rick on this. The amount of surface area available for heat conduction into the motor shaft from the collet contact (which is wedged tightly against the inside of the motor shaft) is approximately 0.9 square inches for a 1/2" router bit. The area added by the shank of the bit touching the bottom of the bore is less than .2 square inches.

Now consider two additional factors. First, the heat transfer through the contact area at the end of the shank is through a high resistance path having a relatively low contact pressure and a greater distance from the heat source. Second, as the heat energy progresses up the bit shank, the majority of the heat will be removed from the bit at the collet. That results in a lower Delta-T to move the heat through the remainder of the shank and across the interface at the end of the bit.

Taking those things into consideration, I'll venture to say that the ratio of heat transferred through the collet compared to that transferred through the end of the bit is considerably more than the 4.5 factor indicated by the area ratio alone.

I'm afraid I'm going to have to see the results of engineering tests before I can attach much plausibility to the quoted passages. Remember, simply because something is published does not guarantee that it's factually accurate.

[Rick Christopherson]

Tom, We posted simultaneously and you were thinking the exact same things that I was. Unfortunately, I just didn't have the energy tonight to write it up as eloquently as you did. Nice posting.

[Eddie Darby]

I was merely pointing out that Rick had said he had never heard of this, and yet it seems to be prevalent, as I just took the first thing that Google came up with.

I guess he can now say that he has heard of it.:eek:

The article does not say that this is a way to 'totally' eliminate heat transfer, but it is a way to reduce it, or slow it down.

I also was not interested in getting into a "peeing" contest, but was actually trying to help answer the original posters question. :D Something that this thread seems to be drifting away from.