Bit Slipping Out of Collet in Router Table

[TomInNC]

I was making some grooves for a panel yesterday on the router table. After a few passes, I realized that the router bit was starting to come out of the collet and that the depth of cut had increased significantly. The collet was tight on the bit and I was careful not to bottom the bit out when it was being installed. I was using a 1/4 upcut spiral bit with a 1/4 inch shank, and the depth of cut when I ran into these issues was approximately 1/4 of an inch. I'm trying to figure out why the bit slipped. At least to my eye, both the collet and the bit are fine. Is 1/4 of an inch too much to take in one pass in this case (it's in Sapele, for what it's worth). After reinstalling the bit, I took much lighter passes (an 1/8 or so), and I did not have any issues. 

[Tom King]

Collets do wear out so they won't hold any more.  I never bothered to figure out how or why, but it does happen.

[TomInNC]

Ok. Is there a way to figure out what collets are compatible with the router? This is the router (https://www.amazon.com/Bora-3-25HP-Variable-Router-PM-6200/dp/B09GL4MTD3?th=1). It says that the collet is an ER20. I have no idea what the means, but I see that there are ER20 collets for sale online. Should those be compatible?

 

Thanks

[wtnhighlander]

Tom is correct, but your collet may not be worn out just yet. Taking a cut depth equal to the cutter width, especially in harder material, places a good deal of strain on the system. If any tiny amout of sawdust or dirt gets trapped between the shank and collet, a pivot point is formed, and the bit will exhibit some runout. Under high loads, the runout causes the bit to 'see-saw' against that pivot, and walk the bit out of the collet. Reducing the cut depth cann often lower the force below the point where this action can occur.

Almost every case where I have experienced cutter walk-out has been caused by a bit of smutz getting into the collet. Very prevalent in a table router, where the collet faces up.

[Gary Beasley]

Its also a good idea to wipe the threads and the collet with a little light oil to discourage rust and let the parts move against each other as you tighten them. It will not make it liable to loosen, actually lets you get it tighter without seizing.

[TomInNC]

On 3/12/2023 at 12:59 PM, wtnhighlander said:

Tom is correct, but your collet may not be worn out just yet. Taking a cut depth equal to the cutter width, especially in harder material, places a good deal of strain on the system. If any tiny amout of sawdust or dirt gets trapped between the shank and collet, a pivot point is formed, and the bit will exhibit some runout. Under high loads, the runout causes the bit to 'see-saw' against that pivot, and walk the bit out of the collet. Reducing the cut depth cann often lower the force below the point where this action can occur.

Almost every case where I have experienced cutter walk-out has been caused by a bit of smutz getting into the collet. Very prevalent in a table router, where the collet faces up.

Thanks. This is very helpful and makes a lot of sense. Guess I should be more proactive with the compressed air. 

Is there a rule of thumb that you recommend for maximum depth of cut? Internet recommendations seem to be all over the place, and oddly enough I cannot find this issue even mentioned in all of the books that I have.

 

[Tpt life]

Depth of cut recommendations are not likely to be helpful unless they tell you about watching bit heat and motor bogging. Cutting a plunge that buries the entire end of a bit is going to vary from a side cut that only contacts tangentially. This means recommendations need to be based on the specific process, and experience levels in that process. 

[TomInNC]

On 3/13/2023 at 12:17 PM, Tpt life said:

Depth of cut recommendations are not likely to be helpful unless they tell you about watching bit heat and motor bogging. Cutting a plunge that buries the entire end of a bit is going to vary from a side cut that only contacts tagent-illy. This means recommendations need to be based on the specific process, and experience levels in that process. 

Ok. I'm still a relative novice with a router, but my approach so far has been to back off when it seems like the motor is struggling. 

[gee-dub]

On 3/13/2023 at 8:01 AM, TomInNC said:

Is there a rule of thumb that you recommend for maximum depth of cut? Internet recommendations seem to be all over the place, and oddly enough I cannot find this issue even mentioned in all of the books that I have.

 

We were all taught what we were taught.  I was taught that an area of greater than a square 1/4" would start to strain bit and tool.  This means that I take 1/8" passes on a 3/8" bit for example.  Probably good as a rule of thumb but others will have been taught other methods of guesstimating max loads for routers and bits.  I have read that collets wear out.  I have to assume that this is in the areas of pro work and long hours of long term routing.  I am still using the original collets that came with my Milwaukee back in

[curlyoak]

All good advice. If you were to use a bigger router with 1/2" bits. I had problems early on in woodworking with bit slippage. I went to 1/2" with more power and not an issue. I have a 1/4" makita router. That gets light work only.

[wtnhighlander]

@Tpt life is spot on, and the others provided good rules of thumb. A late member here, who was a very experienced professional cabinet maker, could probably have given you exact details for rpm, cut depth, and feed rate. He used to say it was all about the "chip load", or how much each flute of the cutter removed as it passed through the wood. Too much chip (too deep or too fast feed) overloaded the motor and strained the cutter, but too little chip (slow feed at high rpm) could overheat the cutter. Wish he was here to answer.

RIP, Particleboard 

[Sophia0110]

I can suggest:

Collet was not tightened properly

Worn Collet

Bit was not inserted fully

Excessive depth of cut

Dull bit