Endmill slipping

I’ve had this happen a couple of times now. I’m using a 1/4" endmill, cutting aluminum and have the precision collet for carbide router installed. I have the endmill installed all the way up and pull back just a tiny bit and then tighten the collet.

After a while, it seems the endmill slips down and the next thing I know, it is plunging way deep in the material and comes to a stop and I have to panic power down.

The only way I seem to prevent it is to use the standard non-precision collet and to gorilla tighten it.

Did I overtighten and damage the collet, or maybe I don’t have a good enough chip load it’s causing some sort of heat cycle that causes it to loosen up?

Edit: Looks like I should have searched a bit more.

Please contact us about this at support@carbide3d.com and send us photos of your collets, of the stock collet, and of the interior shaft of your trim router.

Are you using a pair of wrenches to tighten?

I wasn’t using a pair of wrenches because the thin 13mm wrench was bent. I ordered another based on a post I think you made in one of the other threads.

I’m pretty sure this is just another end user issue. A combination of not using 2 wrenches and the endmill too far up in the router. I didn’t think I had it bottomed out, but I might have. If I continue to have issues after getting a better set of wrenches I’ll let you know.


Keep in mind that when you tighten it, the nut pulls the collet and bit up into the housing a “bit”.


When you get your collet issues settled try this for you router bits. Take the collet and insert out of the router. Measure the length of the collet. In the future maximum clamp is achieved with the router bit inserted fully into your collet. I do not know the length of a C3d precision collet but just for example lets say it is 1 inch. You can mark your router bit with a mark with a permanent marker 1 inch from the top of the bit on the shank of the router bit. You only need to insert the bit to the black mark. This will give you the maximum bite on your router bit and maximum possible stickout of the router bit. So if you have 2.5 inch overall length router bit with one inch inserted you would have a maximum stickout of the router bit of 1.5 inches.

I have a Dewalt 611 router with the stock collet and some precision collets from Elaire. I only have a single wrench with a button on the router base to lock the router shaft. I have to really tighten up my collets but I have never had a bit slip.

The collets make a sort of W pattern and the inside of your router shaft is an inclined plane. When you insert the router bit and tighten up the nut you are forcing the collet up inside the inclined plane squeezing the router bit inside the W shape of the collet. Upon loosening the bit most colllets you can feel them release at a point but because the nut and collet are attached and the nut is pulling the collet down out of the inclined plane. On my Dewalt you can feel the bit release but it is still too tight to remove the bit and you continue loosening and eventually the router bit comes loose or falls out.

With a two wrench router it would be very hard to over tighten a collet. If you are a body builder or have incredible hand strength you could over tighten but better tight then loose.


I have two Makita Routers, one in my Shapeoko and the other handheld both of the same model as many on this forum use. In my handheld unit I use one 1/4" countersinking cutter and rarely remove it.

The occasion did arise where I needed to insert a different cutter - but I had a lot of difficulty in loosening the collet nut to the point where I had to use two spanners (wrenches). I had to lay the router on its side oriented so one spanner was resting on the bench top and I had to hit quite literally the other with a hammer to loosen the nut.

I surmise the collett nut locked because the nut self tightens with the rotary motion. Rarely removing the cutter means that the nut continually tightens itself. I should also say that initially I tried to loosen the nut using only one spanner - the result, I cracked the casting around the finger locking mechanism fortunately this did not affect the operation of the Makita. Now I always use two spanners my machines.


One point to make about tightening collets with two wrenches instead of one wrench while using the built in rotation lock button, is that when using the button you are putting forces on the router mounting system. If that system is loose somewhere, you will move it (perhaps a little at a time). By using two wrenches, the forces are much less on the mounting system.

You may not see the change until you begin cutting or perhaps while cutting your last pass. :smiley:


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