Earlier today I watched a Mere Mortals clip that passed on another’s suggestion to use O-rings as router bit insert stop or spacer. The idea was that the fillet between a router bit shank and cutting head affects collet clamping, leading to walk-out or excessive vibrations, and that an O-ring prevents this from being an issue.
The reasoning behind this is right, but the O-ring trick is only effective when working with shorter router bits whose heads would otherwise connect with a collet upon full insertion. Relying on this tip by itself can lead to complacency and frustration. What happens if you have a long bit that bottoms-out and with its fillet well out of the collet, and you still encounter bit walking, vibration, or uneven cuts?
Inserting a Router Bit
- Ensure that there is no grime or debris on the router bit shank and check the collet as well. Make sure that the collet is open and the nut loosened.
- Insert the router bit all the way into the collet as far as it will go.
- Retract the router bit by 1/8″ or so (some manufacturers recommend 1/16″), and then hand-tighten the collet nut to hold the bit’s slightly elevated position.
- Fully tighten the collet nut with the appropriate wrench.
Note: for solid carbide router bits, step 2 is modified – try to minimize the length of the cutting edges that are covered by the collet. I try to insert such bits into the collet by at least 1″, or more than half-way if possible. Always double check with your router’s manual or the bit manufacturer’s guidelines.
If you were to stop at step 2 and then tighten the collet, there is the strong possibility that you will achieve less than optimal collet clamping. Bottoming out a router bit – or any collet-fixed bit, impedes the tightening mechanism of the collet. Then when you try to tighten the collet nut, you may get the false feeling that the nut and collet are fully tightened.
If you have a shorter router bit and insert it until the bottom of the cutting head is close to the collet, and leave it as-is, the fillet at the interface between the bit’s shank and cutting head may affect the grip of the collet. Even if there is no fillet, there will likely be a small segment that is coated. If the collet grips onto this coated area, its grip on the rest of the bare-metal shank may be looser and potentially less than ideal.
With a loose collet, even if it is almost imperceptibly loose, a router bit can “walk” and rise up out of the collet. At the very least, this can cause excessive vibration or inconsistent cutting performance. At worst, this can pose a safety hazard with the potential to cause grievous bodily harm.
This bit-insertion technique can also be applied to other tools that hold bits and burs with collets, such as rotary tools and mills.
Even with these tips in mind, it is always recommended to refer to the tool’s user manual before use and then again periodically as a refresher.
If any of this is unclear, please let me know and I’ll try my best to show this with close-up photographs.
I never really gave much thought to how properly insert a bit, ans must say that I probably have been doing it at least partially wrong for years. What you describe makes a lot of sense, and I plan to go out to the shop, and just try out several different shank length bits to imprint these steps into my mind so that I do it right next time. Thanks Stuart for a very good tip!
Everyone is missing the real reason not to bottom out a bit in your router. The collet has a slight taper. As you tighten the bit, the bit and collet are pushed into the matching taper in the router. If no clearance is available the bit will not tighten.
Very pertinent advice. Just had a trim bit come loose and depart the router at almost full speed. Luckily no one injured. But, I cannot find the bit. It was moving VERY fast the last time I saw it. I thought it was tight, but I guess it was too far in the collet.
I have a Katsu trimmer router and when ever I use it the bit comes out at high
speed. I have never been able to rout the correct depth. Please tell me why.
Either your tool’s collet is defective, the router bit won’t properly fit the collet, you’re not properly tightening the collet enough, or some other user error.
I have been reading that the bottom of the bit should be between 1/8″ and 1/16″ above the collet. The dovetail bit that I have bottoms out in the collet but rises about 1/2″ above the collet. I don’t know if I should try to use it or not. If it’s in the collet as far as it can go yet still that much shank is visible is that a good thing??
I’m sorry, but it’s tough to know what to say. 1/2″ doesn’t actually seem like a lot. Have you tried contacting the manufacturer of the router bit to see what they advise?
Generally, there is a gap between the bottom of a cutting bit and the top of a collet, so as to allow for clearance when using guides, allowing different cutting depths, to accommodate different base thicknesses, and so forth.
If the router bit is a lot longer than your other bits, perhaps it was intended for use in a special guide or in a special jig, in which case it might be too long to use in the manner of a regular bit, it’s hard to say without seeing it or knowing the exact model or measurements.
If safety is a concern, you should contact the router and router bit manufacturers, if possible, to see what advice they might give you. It could be that the bit is perfectly safe to use, or they might recommend something else.
Thank you for your quick response! I do believe I will certainly call the bit manufacturer! Most of the bits that came with the router have shorter shanks, but the others are longer. I’m new at routing and didn’t want to kill myself the first time I use it. ; )
That 1/8″ to 1/16″ advice is not bad but far too simplistic and not to be taken literally.
There are many cutters that engage fully in the collet (I don’t mean bottomed out) that leave a significant lenth of shaft exposed before the cutting edges begin. Long straight 1/2″ shank cutters a case in point.
Have some sympathy for the machine. The longer the shank and cutting edges extend from the collet, the more leverage they exercise. This places more stress on the mechanics, so take shallower cuts and don’t push the tool so hard through the material.
A tip : you need to know how to take the collet apart for cleaning. Do this. Look at the inner part (the collet) that actually grips the cutter. They are usually about 3/4″ to 1″ long. As long as you have this much shank inserted into the collet, you should get a perfectly secure grip tightening the collet fully but by hand only using the supplied spanner(s). Then just remember the advice about being kind to the machine while you use it.
Thank you! I tried it Saturday and it worked just fine. It was secure in the collet and cut without any kind of play.
Seems like everyone repeats the same obsolete advice without actually trying it. In most current routers if you bottom out the bit it will be way too deep. Somewhere in the middle of cutters.
While not applicable to most situations these days, it can still happen.
I purchased a Sears Craftsman dual function router set and it comes wit the 1/2″ collet .I purchased a 35 piece router set and when I went to insert it, it will not go in the opening ? is this router need a certain router bit ? Manufacture ?
Loosen and remove the collet nut. Test-fit the router bit in the collet. Does it fit? If so, remove the bit, attach the collet nut loosely, and then tighten it as per the tool’s user manual instructions. If not, then something’s wrong.
James W Guy
I’ve got an old Craftsman router and table. I followed the instructions in the manual I found on-line. If I install the bit (shank 1″ long) into the collet (1 1/8″ deep) per the above I can’t get any part of the cutter on the wood. The depth adjustment ring can backup another two inches as though some bit shanks are two inches longer. Does that sound correct? Anyway the only thing I can figure to do if I want to use this bit with the router and table is to only put the bit in about 1/2″. In addition that means that all the bits I have won’t work unless I don’t insert the bits per instructions which doesn’t sound reasonable. Any comments?
You should follow the user manual for proper safety guidance. Since you already referred to the manual:
In my opinion (which should still be considered at your own risk), 1/2″ is not enough engagement for safe operation. If the shank is 1″, and your router collet can accommodate the full width, you should follow the user manual and fully seat the router bit as it says to. Router tables can sometimes be tricky because the additional base or mount heights can take away from cutting height.
If in your shoes, I would either 1) seek out longer router bits, or 2) consider the use of an extension collet, something like these from MLCS or CMT:
I can’t comment on the safety of using extensions, and it seems that matching collet wrenches are an additional expense. But in my opinion, I would think extensions to be safer to use than shallowly inserting a bit for the extended reach needed for router table use.
I have never needed to use router bit extensions, and so I can’t recommend any particular brand (although I generally recommend the brands mentioned above), but hopefully this gives you a good springboard for your future research.
Help! I just bought dewalt 618 router and some separate 1/4 bits. With no bit in the collet tightens all the way down with no problems, however with a bit in it will not tighten all the way down so bit is not flush with router. What am I doing wrong is it the bits?
Is the router bit secure?
Are you concerned that the collet nut does not tighten as far down with a bit as when there is no router bit inserted?
When you tighten a collet nut, it surrounds the collet and tightens around the diameter of a router bit. With no router bit inserted, the collet can come together a little closer, up to its minimal tolerances. Because of this, the collet nut won’t be tightened as far along the threads when a bit is inserted.
I don’t know what you mean about the router bit being flush with the router, can you please be more specific?
T C THOMAS
What is the maximum you can pull out a cutter from the collet? Is 1/4″ away from the bottom of the collet too far? With a router guide, I need another 1/8″ to do the cabinet door joinery. The guide base is 1/2″ thick.
As long as you have enough engagement on the cutter it *should* be okay. The circumstances are different depending on the tool and cutter pairing. 1/4″ should be okay with my router and the router bits I use, but I can’t speak the same for yours. When in doubt, contact the router manufacturer for guidance if it’s not something they address in the manual. I can’t tell you it’ll be safe or perfectly okay, but I can say that I’d likely feel confident using the tool only 1/4″ backed off from bottoming-out, and that you use this opinion at your own risk.