router bit problem

[paul wiser]

am trying to dado some cheese boards to inlay wood strips. was going fine, then if i had the router bit set to go 1/4 inch deep, then by the time i finished it was 1/2 or more deep! help please. not sure what i am doing wrong. any info appreciated. thanks :confused::o:confused::confused:

[Bill Huber]

The bit is walking I would say.

Are you sure you are NOT setting the bit all the way to the bottom of the collet, that will do it every time.
So make sure the bit is not bottoming out in the collet and and make sure it is tight and that should take care of it.

[Dave Gaul]

Are you using a plunge router? Check to make sure your plunge lock is tight enough.

[Jay Allen]

It sound to me like your bit is "walking" out of the collet. This is very bad, not only is it dangerous to your person and distructive to the project, it damages the collet and the bit shank too.

How wide is this cut? How long is the cut? What type of wood?
Personally, I am not a fan of 1/4" shanked router bits on anything but the smallest bits. no more than 1/4" diameter for straight cutting bits. I will go for larger diameter on smaller things like dado clean-out bits or laminate trimmer type bits.....but other than that, if it is available in 1/2" shank, go for that.
The added mass of the bigger shank adds to the stability of the bit and provides for a better hold in the collet itself.

Inspect your bit and collect carefully. If either of them has "shiney" wear places they need to be replaced. Once it has been "sprung" the collet can never be used safely again.

[Paul Girouard]

Jamb nut wasn't tight or the collect is worn. A 1/4" depth of cut should NOT be considered to deep, so check how tight you normally tighten the lock nut, check the collect for a crack or if possible buy a new one , throw the old one out.

And last it could be just cheap equipment , what brand and model router are you using? I'd guess if it's a "Harbor Freight / Ace brand " router that could be the start of your issue.

[glenn bradley]

Can you confirm if the bit is slipping in the collet or is it the motor slipping in the base? The collet shouldn't have to be extremely tight to hold the bit. If the collet is worn it should be replaced. If the motor is slippig in the body, a good cleaning will usually put an end to that.

[paul wiser]

i am not setting the bit all the way into the collet. have checked to see that it was tightened. thanks

[paul wiser]

no crack in the collet. it is a 693 series porter cable. i am using the fixed base. did tighten the jamb nut, but as i used it to make a dado it seemed to ride up in the collett by the time i finished the cut

[paul wiser]

using a fixed base porter cable 693 series

[Carl Beckett]

You definitely want to evaluate this and DONT use it if the bit is walking. I had a router table for years that I just couldnt keep the collet tight enough to prevent bits from walking out (it seems I must have been doing something wrong, but I worked as a machinist for a few years so know a little, and had several other people take a look and nobody could really figure it out - it just shouldnt have been walking but it did). (ya, I tried changing depths, different bits, NEVER used 1/4" shanks, etc)

I finally chalked it up to insufficient margin in the design (it was a small Delta "shaper/router" table). It scared the bejebes out of me when I used it.

Finally just got rid of it and have never had a problem with any other router I have owned (up to about..... 6 now)

Just saying - it might not be anything you are doing (or not) - but dont take chances!! Either solve it completely, or get a different tool.

[Bill Huber]

From what you are saying I would get a new collet, it is only $16 and it would be well worth it to not have a problem like this.
http://www.ereplacementparts.com/collet-and-nut-assembly-p-72681.html

I would also look at getting a new bit, I don't use 1/4 that much and would look at getting the same bit in 1/2" shank.

[Chris Fournier]

I think that the first question we should ask you is what type of bit are you using? Is it a straight flute or is it a spiral upcut? The spiral upcut makes sense for this type of work because it ejects chips so nicely but due to the nature of the cutting flutes the cutting forces can draw the bit out of the collet. If you can't clean and tighten the collet any better than now I would go to a straight flute bit which has far less tendedncy to extract itself out of the collet.

I personally have no issue with a 1/4" shank on a bit that is cutting 1/4" wide. Metal machinists use these bits all the time and their cutting forces are huge compared to most of ours.

[Bill Huber]

If you can't clean and tighten the collet any better than now I would go to a straight flute bit which has far less tendedncy to extract itself out of the collet.


I disagree 100%, if the collet will not hole a spiral bit then you should NOT use any bit in it and get a new collet.

[Ray Newman]

Bill Huber's most recent post triggered a memory.

Is the diameter of the bit shank undersized??

Once tried to use an L. Cheapo Brand "Quality Import" bit that had an undersized shank. It would not hold even though tight in the collet....

Also is the shank is perfectly clean of any oil, grease, etc., that would keep it from holding.

[Chris Fournier]

I disagree 100%, if the collet will not hole a spiral bit then you should NOT use any bit in it and get a new collet.

Bill, I mentioned that the collet should be cleaned and tightened, I expect that this will indeed hold the bit securely. Two weeks ago I had a spiral upcut bit extract itself a good .125" from my industrial pin router collet. There was no need to get a new collet. I removed the bit, cleaned the collet and re-tightened it. The set up is still in the machine and working perfectly.

Unless you can see serious wear on your collet, replacement is totally unnecessary. Serious wear would entail bits spinning around in the collet and galling it. My pin router collet is over 15 years old with many miles on it. The collet was not my problem, I took a heavy cut and the collet was not tight enough - I tend not to be a grunt and groan tightener as this destroys things all too often.


Perhaps the OP's router bit shank is under spec! A new collet will be a total waste of time and resources then! I have recommended a walk before you run solution.

Also having had more than a couple of bits this size break while in the cut I can tell you that the broken end falls like a drunken sailor with no drama. Pretty safe stuff.

[paul wiser]

the cut is 1/4" wide. the cut length was 5 3/4" long. thanks for the input on the collet. i will check for shiny spots.

[paul wiser]

porter cable 693 series

[paul wiser]

eagle america bits

[Jim Neeley]

I'm with the others in suspecting the collet but... if somehow you got some metric 6mm shank bits, they are only 0.236" dia... close enough to appear good. You may want to check it.

A router forum I'm a mod on has had several people experience this... seeming all with with foreign import bits.. but it doesn't take long to run it through your calipers!

[paul wiser]

i purchased a new collet today. have to get a new collet nut tomorrow. think this might solve the problem. also ordered some 1/2 shank bits from eagle america. thanks to everyone for their assistance!!