Router bit of-the-month (February 08)

This month, I am not highlighting an actual bit, but something that can make the difference between a bit, or a jig etc being usable, and not being able to do the job required.

The bit this month is in fact a router bit extender. I am certainly not condoning the use of router bit extenders for every operation, but in some instances, for some jobs, they are a much better solution than the alternative. (Shown here with a router bit fitted).


This version of the router bit extender is quite impressive. It is made by CMT (an Italian router bit manufacturer) who are well renowned for the quality of their router bits. Here in Australia, CMT bits are supplied by Carbatec.

The concept is pretty simple – have a shaft the diameter of a normal router bit to mount in the router, then some form of mechanism to hold the router bit itself, and in this case, CMT have opted for quite a traditional style router bit collet, which is reassuring given that it needs to tightly hold the router bit in the extended position.


This is the extender broken down into its individual components (not all extenders can come apart like this) Working from left to right, we have the collet outer ring, which screws into the collet base (part 3). Inside each of these is a cone which matches the cone on either end of part 2. Part 2 is the split-ring router bit holder. As the collet is tightened, the split-ring is squeezed together, gripping the router bit. The cones facilitate this, as well as ensuring the bit is maintained in the centre of the mechanism. The final part (4) is the 1/2″ shank which is fitted to the router’s collet.


There are a number of occasions where the extender can be a god-send, and it is useful having one in your collection for if/when it becomes needed. These include, needing some extra plunge length, when using the router with a jig where the router doesn’t have sufficient plunge capacity to expose enough of the bit, and for bits that have too-short a shaft (to name a few). Some people also use them religiously with their table-mounted router because of a combination of too thick a table and/or too short a router bit and/or insufficient plunge capacity of the router and/or because they want to be able to change router bits above the table.

My personal preference is that these extenders are only used when they are justified, and there isn’t another solution (like purchasing a longer shanked router bit if that becomes a regular problem, or getting a router that can inherently do above-table bit changing). There is a reason router bits don’t come with an extra inch or so of shaft length (just for the convenience), and it isn’t because of cost (well that’s not the major reason). They do increase the load on the router bearings – there is a lot of extra leverage caused with the extra length. If you are running a Festool (triple bearing), or a Triton, then the router should cope, but not all routers are as strong. Remember too, we are talking about a high-speed rotary tool here (up to 20000RPM).

So the bottom line is, for a particular job, a router bit extender can be invaluable. I’d rather use an extender, than not properly inserting the router bit fully into the collet for example. However, it is not for every job, and in particular, it is strongly recommended that you don’t use one when the router bit exceeds 40mm diameter. This rules out panel raising bits!

Finally, here’s something a bit exciting for Stu’s Shed (and I’m hoping we can do more of this in the future, but it will depend on how successful it proves!) The CMT Router Bit Extender featured here was generously supplied by Carbatec, and is normally $79 (inc GST). For this month (Feb 08), if you tell Carbatec that you saw it featured on Stu’s Shed, then you will be able to purchase it for $69 (inc GST). (That’s almost 15% off). This offer has been made by Carbatec only for Stu’s Shed viewers. (Cool huh!)

Mounting a Router Bit

One question that comes up quite often is how to secure a router bit in the router.  After all, it is quite a large chunk of sharp material (HSS or carbide, or combination) to have spinning at speeds up to 20000RPM, and then having it engage with, and cut into a piece of wood.  Certainly for the inexperienced, installing a router bit (and then turning the router on), can be quite daunting.

It is a bit hard to describe just how tight to tighten up the collet – you want it to really grip the shaft of the bit, but not so hard that you can’t get it undone again!  The thread direction does mean that as the router is used, it will have a tendency to tighten further (not that that helps you if the bit is already wanting to slip!).

If you are using a reducer (such as a 1/4″ reducer so you can use 1/4″ bits in a 1/2″ collet) then you need to tighten the collet more than if you are using the correct combination of bit and collet.  This is because you have to squeeze the metal of the collet onto the reducer sufficiently that it squeezes tightly enough on the bit.  Where possible, it is much better to use the right sized bit for the collet you have.

Don’t play games with not setting the bit fully inside the collet – if the bit isn’t long enough for the job that you’d have to only insert it partially in the collet, buy a different bit.  It is way too dangerous not to have the bit properly held.  Alternately, get one of the commercial router bit extenders.

One thing that is worth mentioning is bottoming out of the router bit.  It is quite a common mistake to allow the router bit to drop to the bottom of the collet then tighten the collet up.  There are a number of different theories why this isn’t a good idea, but at least all theories agree on one thing – let the bit bottom out, then raise it up a small amount (1mm or so) then tighten the collet.

Some of the reasons I have heard in the past are: it allows heat to transfer from the router bit to the shaft of the router, it transfers vibration from the routing operation to the shaft of the router, it can cause the router bit to vibrate loose of the collet….and others.

Some, or all of these may be good reasons for not doing so, but I don’t accept them to be the major, or main reason.  Mine is this: as the collet tightens, (given it operates on a thread), it will carry the router bit in the direction that it is tightening, ie towards the bottom of the hole.  If it hits the bottom before it is fully tight (or starts in that location), then there is a possibility that it will feel that the router bit is held tightly because you feel the resistance through your spanner, but it isn’t actually that the collet is fully tight – it is the bit pressing into the base of the hole.  Then during operation, the bit can slip, or even start working its way out of the collet.

Instead, if there is a little bit of clearance between the router bit and the bottom of the hole, then the collet can grip fully around the shaft of the bit, holding it securely and as it is designed.

I have also heard some people drop a small o-ring into the bottom of the collet so the router bit starts off resting against it before the collet is tightened.  I don’t see any problem with this solution – the o-ring can easily compress as the collet is tightened, and if it helps you ensure that you consistently insert the router bit properly, then go for it.

Router Lift and the Triton Router

(Updated Oct 08)

It has come up a number of times in discussions whether there are benefits of a router lift.

The router lift has a single purpose: to accurately control the height of the router bit, and provide a stable platform for that bit in operation. The reason for having one, is if your router’s features are not fulfilling this requirement already. Many (most) routers are not designed for table use. They may be plunge routers (with or without a microadjuster, or one that you have to engage then wind through the whole plunge range to set bit height), fixed base routers etc. Setting the bit height when the router is inverted is an absolute pain. They also may be cheaper construction, so are not particularly stable until fully plunged.

Then we have the whole issue of bit changing. Trying to get 2 spanners (or 1 and engaging the shaft lock) while under the table can be an absolute nightmare. Or, you have to design the table in a way that it lifts out of the way providing better access to the router.

For all these reasons, the router lift is a god-send. You plunge the router to full depth (stability), and lock the plunge mechanism. You mount the router in the lift, and never see it again! All height adjustment is done above-table, and you rely on the quality of the router lift mechanism to maintain the bit height when subjected to the vibrations of a router running at speeds up to 20,000RPM. A good lift has no problem with this. To change bits, you buy a bit extender ($A120 – $A180)- which is simply a collet on a 1/2″ shaft, so at full height, it is accessed above the table. Some secure the router bit with a simple cam others have a more traditional collet mechanism. So now we have: above table height adjustment, above table bit changing, and any weaknesses in the plunge mechanism of the router (reasonably) taken care of.

The Triton router does overcome a fair bit of this (although I now use a Triton router with a router lift!) What does the Triton router give me? Easy height adjustment, with geared macro, and micro adjusters that work through the entire range of the router, and you can start using the micro adjuster at any point. Through table bit changing built into the router. (And not to mention, 3 1/4 horsepower, 1/2″ collet, and a whole heap of other features built in). So you don’t have above table height adjustment, but that isn’t critical. Why? Because I am already kneeling down when setting my bit height as I am sighting across the bit to the ruler, or the bit of stock that is about to be machined etc, so it makes no difference whether the handle is above or below the table – either way it is right there in easy reach. While there, I then lock the plunge mechanism, and turn the router on. (A good router table has a second on-off switch that is easy access, especially for stopping, so you only turn the router off at the router itself for bit-changing).

My solution is both a router lift, and Triton router.  I don’t need to use an extender, so long as I am prepared to use the Triton quick plunge (reaching under the table).

Did I say that I really don’t like router bit extenders? They have a purpose, for the occasional job, but I don’t like seeing them in every day use. There is a lot of load on a router bit – why multiply that load with an extender? (Like putting 2 kids on a seesaw- one much further from the centre than the other – it multiplies the load) All that extra load has to be borne by the router’s bearings, and collet. And I really concerned about extenders that use a cam to hold the router bit – one small contact area on the cam itself, and by it’s nature, you are pushing the router bit off-centre against the opposite wall of the collet to secure it. Did I mention 20,000 RPM?

Food for thought?


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