# Cutters in or 1/8" out



## harrysin (Jan 15, 2007)

Regarding the question "does the cutter really move when the collet is tightened", this evening I attempted to find the answer, I don't claim this is a scientific or definitive test but the best that I could come up with. The set-up is self explanatory. The difference in the reading between loose and hard tightened was only 0.0015", this was not consistent, sometimes in one direction, sometimes in the other. What it does appear to indicate is that any difference is negligible in woodworking terms and for the life of me I can't see that inserting a cutter fully in can in any way be dangerous. There may be some cutters with short shanks with a reduced diameter at the top, in such a case an O ring slipped all the way up would prevent the collet from gripping the reduced diameter.


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## dovetail_65 (Jan 22, 2008)

This has been discussed in another thread pretty extensively. At a certain point the discussion becomes non productive so I say do whatever floats your boat, *the important this is make some saw dust!*


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## allthunbs (Jun 22, 2008)

harrysin said:


> Regarding the question "does the cutter really move when the collet is tightened", this evening I attempted to find the answer, I don't claim this is a scientific or definitive test but the best that I could come up with. The set-up is self explanatory. The difference in the reading between loose and hard tightened was only 0.0015", this was not consistent, sometimes in one direction, sometimes in the other. What it does appear to indicate is that any difference is negligible in woodworking terms and for the life of me I can't see that inserting a cutter fully in can in any way be dangerous. There may be some cutters with short shanks with a reduced diameter at the top, in such a case an O ring slipped all the way up would prevent the collet from gripping the reduced diameter.


Hi Harry:

Thanks for taking the time and trouble to measure it. My router manual says "Insert the bit deeply in the collet chuck hole." Talking about ambiguous! I still can't get the 1/8" from bottom thing accomplished. I pull the router out, hang onto the bit with one hand, hold onto the arbour lock with the other, and with the other I'm tightening with the wrench and with the other I'm holding the router solidly so I can put some weight behind the wrench. Oops, that's 2 too many hands. Ah well, you get the picture. I'm still going for the grommet inserted into the bottom of the chuck, though. I'm looking at using plumbing washers from my inherited inventory.

Thanks again.

Allthunbs


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## Mike (Nov 22, 2004)

There are two reasons given for not bottoming a bit in your router. One is to allow for proper tightening and the other is to prevent heat transfer to the motor shaft. The tip as first published was to insert an O ring that had a cord thickness of 1/8" into the bottom of the shaft hole. This would prevent contact of the bit with the shaft and allow for compression when the collet was tightened. With all the grief caused by this simple tip I wish it had never been published.


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## Bogydave (Nov 14, 2008)

If all this is true & has been the norm for years, Why has the router manufacturers not installed a synthetic stop in the inside of the shaft where the collet goes to prevent bits from touching the shaft? Their engineering department could surely figure all this out & even promote after market inserts. 
Also, as the bit shafts get hot, they expand in width & length. Gonna move in some direction. (seems to me the nut is tighter when I remove the bit before its cool)
Different metals expand at different ratios.
It is a PIA sometimes to lift the bit a little before tightening, but I do it because it makes sense to me.
Something to query the manufacturers?
Don't grieve Mike, it's making folks think & respond. All good stuff.


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## bobj3 (Jan 17, 2006)

HI Guys

I think we got off the point just a little bit, the rubber grommet is not needed for all the router bits, it's just for the matched set of router bits the norm..

It's just a stopping point for them, but it works well for all router bits.
It just takes the guess work out of it..

It's not for every one , it's just for the ones that want it to come out right every time. 

Just a note about the heat *** if your router bit or router motor is that hot you need to power it down and take a break.. 

=======





Bogydave said:


> If all this is true & has been the norm for years, Why has the router manufacturers not installed a synthetic stop in the inside of the shaft where the collet goes to prevent bits from touching the shaft? Their engineering department could surely figure all this out & even promote after market inserts.
> Also, as the bit shafts get hot, they expand in width & length. Gonna move in some direction. (seems to me the nut is tighter when I remove the bit before its cool)
> Different metals expand at different ratios.
> It is a PIA sometimes to lift the bit a little before tightening, but I do it because it makes sense to me.
> ...


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## harrysin (Jan 15, 2007)

I thought that all was said on this point in this and one of the other threads, however, at the risk of being likened to a dog with a bone, I must tell you that I have read in articles that raising the cutter is to prevent heat transfer FROM the MOTOR to the cutter, and in other articles to prevent heat transfer FROM the CUTTER to the MOTOR. Now consider this, most of the cutter's shank is in contact with the collet which in turn is in contact with the motor shaft, now, only the END of the cutter would be added to the contact area, a relatively small percentage of the cutter. By the way Mike, my intention was and is to make people think for themselves and to lighten what is at times a dull forum.


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## allthunbs (Jun 22, 2008)

Mike said:


> With all the grief caused by this simple tip I wish it had never been published.


If this is grief, you'd better rewrite your dictionary. You suggested a solution to a problem. That you suggested it means that you wish to participate and that is appreciated. That others may agree or disagree is what makes a forum. "Forum - A place for discussion (Wictionary.org)" Discussion does not imply agreement or disagreement, only the presentation of a point of view and the examination of the strengths or weaknesses of it. We are trying, by testing the strengths and weaknesses of each argument, to find the safest way to operate a router. You suggested a compromise that everyone acknowledges is valid. But the strengths and weaknesses of the other arguments have not yet been settled. As Harry notes, this is a "quiet time" for the forum. We need a little spice thrown into the fire to stir things up a bit

The only time grief is encountered is when a thread is arbitrarily closed.

Allthunbs


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## Ghidrah (Oct 21, 2008)

Good one Thumbs!
You don't have to like an opinion/claim, and one has the option to rebut, even an absolute can be argued. Personal choice is arbitrary and there are often many right and wrong , (read safe and unsafe) ways to solve a single puzzle. 
As Harrysin pointed out the obvious fallacy for heat transfer, the chaff can be winnowed to reveal the truth.

The whole point of forum is to find the truth and build on it.


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## TWheels (May 26, 2006)

I am forced to do things a little differently. I take the collet and collet nut, and insert the bit so that the bottom of the shaft is even with the bottom of the collet and nut. I then mark the bit shaft at the top of the collet, all way around and then insert the collet, collet nut and bit into the router, adjusting the bit shaft so the mark is just above the top of the collet. 

I have always intuitively agreed with Harry's point about area of heat transfer. I also want to thank Harry for the tests he carried out. Harry, did you carry out the test on your Makita 3612C or on your Triton?


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## harrysin (Jan 15, 2007)

"Harry, did you carry out the test on your Makita 3612C or on your Triton?"

It was done on the 3612C, the Triton is a fixture in the table.
My grandson is taking a years break from university, doing a mechanical engineering course,hopefully I'll still be around to ask him to do some scientific tests.
Another thought on the subject, the hole in the shaft appears to be drilled, so leaving a tapered hole and so only the edges of the cutter actually contact the shaft, not much extra heat transfer here !


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## Skyglider (Nov 2, 2008)

mftha said:


> I am forced to do things a little differently. I take the collet and collet nut, and insert the bit so that the bottom of the shaft is even with the bottom of the collet and nut. I then mark the bit shaft at the top of the collet, all way around and then insert the collet, collet nut and bit into the router, adjusting the bit shaft so the mark is just above the top of the collet.


 +1 on this method.

A router book I'm reading, "Wood working with the router" by Bill Hylton advises against bottoming the bit before tightening since: (Paragraphs 1-3 below are paraphrased by me and not direct quotes from Mr. Hylton’s book.)

1. The act of tightening the collet pulls the shank down into the socket as the nut tightens. If the bottom of the shank is already against the motor shaft, it cannot be pulled down and must slide against the collet, hampering tightening. 

2. If the shank is short and does not reach the motor shaft when the bit is pressed all the way in, and if the diameter of the shank is smaller than the diameter of the bit, there is a rounded transition from small to big. If the collet catches on this rounded transition fillet, it won't seat on the shank tightly.

3. If the shank is not inserted to the bottom of the collet, in other words only partly into the collet, there will be leverage on the unsupported portion of the collet where there is no shank in it.

So it seems to me that the goal of bit insertion is to have the bottom of the shank just past the bottom of the collet without hitting the motor shaft. 

I just bought a router and it is in transit now. When I receive it, my plan is to measure the depth of the ½” collet and nut. Then paint a thin circular mark around the shank of all of my 1/2" bits slightly above that measurement using model paint. Then do the same for any 1/4" shank bits using the 1/4" collet depth. This will give the optimum gripping power on the shanks while having the bit extended to its maximum cutting depth.

BTW, the router book I referenced, American Woodworker, "Wood working with the router" by Bill Hylton, a Reader’s Digest book, is the absolute best power tool book I have ever read which includes all other power tool books. It only covers the router and associated stuff but every explanation goes into much further depth than I have ever seen in any other book. Plus the author’s writing style is very enjoyable to read without giving a lot of useless info. Very highly recommended if you are looking for a router book. I have no affiliation with Mr. Hylton in any way. I just love this book.

$.02,
Skyglider


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## TWheels (May 26, 2006)

harrysin said:


> I thought that all was said on this point in this and one of the other threads, however, at the risk of being likened to a dog with a bone, I must tell you that I have read in articles that raising the cutter is to prevent heat transfer FROM the MOTOR to the cutter, and in other articles to prevent heat transfer FROM the CUTTER to the MOTOR. Now consider this, most of the cutter's shank is in contact with the collet which in turn is in contact with the motor shaft, now, only the END of the cutter would be added to the contact area, a relatively small percentage of the cutter. By the way Mike, my intention was and is to make people think for themselves and to lighten what is at times a dull forum.


Harry, you have identified one of the great sources of confusion. In my professional field I am appalled by the amount of popular literature and "news" reporting done in an authoritative (as in unquestionably correct) manner that is in reality so wrong that it can do great harm to those who do not know better. 

I seem to be a natural crusader, and one of my present crusades is to get higher education to be factually correct (too many textbooks are oversimplified to the point of being wrong) and to teach students to think for themselves and investigate contradtictions and oversimplification for themselves.

Thanks for bringing up this point.


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## boldford (Jan 21, 2009)

Sorry for the very late post. I'm a newbie from the UK here. I was always under the impression that the reason for not "bottoming" a cutter shank was nothing to do with heat transfer. My understanding it is to do with the collet gripping concentricly. The theory being; if the cutter pulls in as the collet is tightened there is the possibility of the shank being pushed slightly to one side thus upsetting concentricity by a few thou.


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## AxlMyk (Jun 13, 2006)

boldford said:


> Sorry for the very late post. I'm a newbie from the UK here. I was always under the impression that the reason for not "bottoming" a cutter shank was nothing to do with heat transfer. My understanding it is to do with the collet gripping concentricly. The theory being; if the cutter pulls in as the collet is tightened there is the possibility of the shank being pushed slightly to one side thus upsetting concentricity by a few thou.


It's more a case that if the bit was bottomed out, when you tighten it the bit would be forced further into the shaft. Thus, the collet may not tighten around the bit.
The bit shank should NEVER be pushed to the bottom.


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## allthunbs (Jun 22, 2008)

*Comments Please*

..


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## John Bartley (Dec 13, 2008)

AxlMyk is correct. As the collet tightens, it pushes the bit very slightly into the hollow in the end of the motor shaft. If the bit is already bottomed out then it can't move into the hollow and so the collet can't tighten properly. The bit may look and feel tight, and may work under a light load, but under the correct working condition it might come loose.

cheers

John


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## bobj3 (Jan 17, 2006)

Hi allthunbs

I'm sorry you just don't get it but in time you will I'm sure 
The rubber grommet way works  you don't need to be _Einstein to run a router you just need to have your head on right _

========


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## allthunbs (Jun 22, 2008)

bobj3 said:


> Hi allthunbs
> 
> I'm sorry you just don't get it but in time you will I'm sure
> The rubber grommet way works  you don't need to be _Einstein to run a router you just need to have your head on right _
> ...


..


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