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I just finished making another set of Radius Dishes. I used a 1/2" straight carbide bit at first and my 1st. mistake with a 1/4" shaft which was probably my 2nd. mistake. I glue my dishes back to back and did the 25' radius first which is usually no problem ( I've had this happen before but didn't learn my lesson) and flipped the dish over and went to work on the 15' radius. When I was about 2/3rds. finished the bit is cutting about 1/4" or more on edge and it slipped in the collet. And it started to act like a drill bit and went down 1/8 or so into the dish. After getting angery at myself, " You should have known better you dummy." Well I looked through my bits and pulled out the Whiteside carbide 1/2"/ 1/2" shank spiral downcut bit and made two more dishes again. With a SDC bit the bit will push down on the work piece and push the work down and if it slips in the collet it will be pushed up and not down. And a 1/2" shank will hold better then an 1/4" too. So it's better to use downcut bits when routing out material like on a dish or when doing grooves or milling opperations . Just a tip to consider that might save you time and material.

A corollary that I learned the hard way: if you use upcut bits, make sure they're cranked down good and tight in the collet.

It isn't the bit , it is the collet. As a machinist I avoid the downwards unless I have a clear cut. Be sure the collet is clean and free of oil and dust. Always check the bit is seated . What router do you have? I never had an issue with Porter Cable , Makita , or Milwaukee. Harbor freight are noted for throwing bits.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

It's a PC 690 and I've had it happen when I made the dishes before. You're also assuming the shaft on the router bits are made better then the collet. My point is if you use a SDC and if the bit gets loose for whatever reason, it happens and is more likely to happen with long continues routing like on a dish, that the bit will be forced up into the collar and not ruin the piece as you can always tighten it and remove material. I have no doubt that it's either the router collet or the shaft or both. The collet was as tight as I could get it, trust me on that John. I can see when milling metal that you want to clear it but you're also usually running at slower rpm with different feed rates too. And the 1/4" shaft wasn't the best choice for that opperation too. Next time I'm at Woodcraft it probably wouldn't be a bad idea to pick up a new collet for it. Might be it gets hot when the bit slips and wears the collet too. What do you think?

John, I was told once to NOT seat bits in a router, but to leave an 1/8". Something about tightening the collet draws the bit in and...? Was that bad advice?

Thanks,

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Mike Lindstrom

I was taught this with the rationale that a bit heats in use, and if seated will tend to push itself loose.

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Gabriel Regalbuto
Carlsbad, California
Freedom 35!

I used to work as a finish carpenter and did a lot of trim work on window sills and such with a router. The reason I learned not to fully seat the bit is that sometimes it can make it almost impossible to remove.

I've also had 1/4" bits come loose in full-size routers and always try to use a bit with a 1/2" shank for that reason.

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Steve Smith
"Music is what feelings sound like"

John's correct on the likely cause. A VERY sloppy shaft will hold in a proper collet, even a piece of threaded rod! The shaft on any cutter is essentially guaranteed to be concentric by merit of being turned.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Most people , once fixed to an idea don't want to change. They need a paradigm shift to change their opinions . The bit needs to be seated. The collet needs to be checked. If you look close at the collet ,it isn't solid but has slots. All you need is a bit of something in one of the slots and you loose true fit. As you rout and the obstruction gets dislodged by vibration or as the collet heats up , this allows things to loosen.
Now as for DSC , I have seem the do catastrophic damage. Unlike the up cuts that will start to work loose , downward bits will stay up in the collet until they can be thrown. Trust me , it isn't a pretty sight. Downward bits are designed to be used in a milling machine , and to be used only on cleared holes.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Here's a good article explaining the difference between upcut and downcut bits.
http://www.newwoodworker.com/updowncutbits.html

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John--I've been under the impression that a shank inside a collet should be left out 1/8" or so from bottoming (as mentioned above) because the collet is pushed back into the spindle taper while tightening. I guess the theory is that the collet won't be completely tight if the shank is bottomed out first?
What are your thoughts on this?
Thanks
Nelson

I have been bottoming my tools for ever. That is how my Father taught me and that is what I learned in trade school. If a bit gets stuck a light tap usually clears them. I am 56 yrs old and never had a bit stick that couldn't come out. You need to look at the design of the collet. It is designed to hold the bit. If you have a gap you allow the bit to vibrate and run a risk of it loosening.
Vibration and heat are the enemy

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

http://newwoodworker.com/stuckbits.html
John, I did a little reading and find that I'm all wet.
The idea is to not let the router bit bottom out on the collet but doesn't mention not seating it in bottom of the hole in the spindle.
P.S. Got you beat--I'm 63!
Nelson

It sure does if you read it. It says exactly that.

The Big No-No
Probably the most common mistake made by woodworkers is seating the bit fully in the collet when installing it. With the end of the bit shaft against the bottom of the collet, the fingers that grip it can be put into a tension that makes it very difficult for them to release. To allow the self-releasing collet mechanism to work as designed we need a small amount of clearance between the end of the bits shaft and the bottom of the collet.

But I've read disinformation before.

You're right, Chris.
I need to go back to the first grade and learn how to read or at least interpret correctly what I do read.
Edit Oh wait, they probably don't allow 63 year olds in first grade.

They'd allow sixty six-year-olds, though.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Very funny, Bob! That would be a very stressed-out teacher faced with handling 60 of the little monsters.

In 54 years... I've had one upcut bit "auger" it's way out of the collet and into a neck... Sad for me and terminal for the neck... Now I just tighten them really tight and hope for the best. I don't know why... but I always leave a bit of a gap between the bit and the bottom.
long

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"No man ever steps in the same river twice, for it's not the same river and he's not the same man.” -Heraclitus of Ephesus

A collet is not so much pushed back as it is pinched. A mill collet different is that it is wedged . The collet designed for the router is not tapered. For lack of a better term , the head of the collet is angled , as is the collet nut. The collet itself is straight in. As you tighten the nut , the angles are to grab and bind. They don't actually drive the collet in. You want the shaft in as this is what helps to control vibration. There is a space designed between the actual collet and the nut. In most cases , this is often fowled and full of dirt. This is a critical part of the design. Keep them clean and free of dust.
http://www.oldham-usa.com/Router%20Bit%20Safety.pdf
check this link out , I think you will find it useful. It backs up what I have been saying.It also will have some very useful information in router safety/

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John,
This is from the link you provided. This implies that there is no need to bottom out as long as you have at least 5/8" of the shaft burried in the collet.
I don't see how this backs up what you are saying. Unless I am misinterpreting what you are saying I think you are saying to bottom out the bit in a router. I can't agree with that and the link you provided doesn't say to bottom out bits either.
Link

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Cut to size.....Beat to fit.....Paint to match.

Higher up in the article it's also ambiguous but does state: "Be sure the router bit or tool is positioned completely into the collet to the full depth of the shank and clamped only on the smooth, straight surface of the shank (see Figure 2). Never clamp only a portion of the shank to "extend" the cutting depth, or clamp on the body below the shank."

This could be a recommendation to bury the shank as far as possible, even if that means bottoming out.

http://www.highlandwoodworking.com/index.asp?PageAction=Custom&ID=28
This is an interesting discussion where the topic sounds simple on the surface but goes much deeper.
(Pardon the metaphor, purely unintentional)
All input is appreciated.
Nelson

Edited spelling.

The link John posted absolutely backs up what he said. That it's completely unsafe to run a cutter with less than 5/8" of shank in the collet doesn't imply in any way that it isn't safer to have the maximum amount of shank possible in there. The 5/8" was a minimum

With regard to the highland woodworking article: the 'sliding down' of the collet onto the shank of the cutter is at amazing leverage advantage and won't be stopped by the grip of the collet on the cutter. The nut pushing down is stronger than the collets grip on the shaft, even though that grip is also very strong.

John's giving good advice. All I've got to back that up is being 2nd place in routing mileage behind John W, with no collet issues ever, while heeding John's advice

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

http://woodworking.about.com/od/bladesbits/qt/BitInstallation.htm
http://www.woodworking.com/dcforum/dcboard.pl?az=read_count&om=5756&forum=DCForumID9
http://books.google.com/books?id=CYy5hoY-tZwC&pg=PA110&lpg=PA110&dq=tightening+router+bits&source=bl&ots=GKVFijkPmU&sig=3ocFV0SeDBR-QGkrGFXloXRrI30&hl=en&ei=ua5JSpeQMobiMOKnoawB&sa=X&oi=book_result&ct=result&resnum=2
http://www.answerbag.com/articles/How-to-Change-a-Router-Bit/dffc5cf2-697e-1196-7cd6-879dfa85f04a

Some more bedtime readying for those of us having trouble sleeping tonight.

What I learned from rereading it , is that the most important thing is if you have a shaft that has a hollow , he sure your shaft is full thickness at the collet pinch point. I copied the section and pasted it. It states to have the bit in completely. This may be bottomed or not. It is dependant on the bits shaft.

4. With all machine power off and locked out, remove the test bar and mount the router bit or router tool in the machine after inspecting the tool. Do not mount any tool that is dull or damaged and check shank of bit to be sure it fits securely into collet. Be sure the router bit or tool is positioned completely into the collet to the full depth of the shank and clamped only on the smooth, straight surface of the shank (see Figure 2). Never clamp only a portion of the shank to "extend" the cutting depth, or clamp on the body below the shank. If there is a radius between the tool shank and body, be sure to clamp above the radius. Check the tool with the dial indicator (as in Figure 3). Tools that have excessive runout (more than + .002) or that wobble, are unsafe at the high spindle rotating speeds of router machines, and must be corrected or replaced.

The router bit goes in full depth , This means to the end of the shaft ,and if it hits the bottom , it hits and if it doesn't it doesn't. The bit has to be loaded to the router per the shaft. I use very few 1/4 inch bits . All my 1/2 inch shafts hit bottom. I am finding this topic interesting. It is good to go back and refresh ones education.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I put an "O" ring in the bottom of my collets. Auto spaces the shank but with room to move from the tightening process and/or heating up. And, wherever possible I use 1/2" shanks-90% Whiteside bits.Mike T.