Router bit slipping

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Forum topic by Bernie posted 05-22-2011 04:59 AM 5319 views 0 times favorited 13 replies Add to Favorites Watch
View Bernie's profile


422 posts in 3892 days

05-22-2011 04:59 AM

Hi folks – I started a new project today using 12 X 1 maple. I was trying to assemble the top of the carcase with half blind dovetails and put a bit too much pressure on my PortaCable plunge router. First time this has happened to me so I could use some advice. It seems the bit slipped out of the collet and it wasn’t cutting, just burning on the shank. The collet seems fine.

My question is – can I clean the shank with 300+ paper, and redo my cut? Can I or do I clean the collet and mar it a tad to give it some grabbing power? Last but not least… what caused this to happen? Looking at a dovetail bit, I can see how it would tend to slip out of the collet… so was I feeding to fast? The router is set at top speed 15000?

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

13 replies so far

View Minorhero's profile


373 posts in 3660 days

#1 posted 05-22-2011 05:37 AM

I had this happen to me the other day when I was routing at a channel for some t-track in my home-made router table top.

This may be a silly question, but are you moving the router in the right direction? If you move it the wrong one it will be significantly harder to cut and the bit has a better chance of slipping. I solved the slipping part by using my supplied wrenches to really tighten up on the collet. I was in a position where I couldn’t go the right direction so I just stuck with it till the cut was done, I was only cutting MDF though so it wasn’t too bad.

View TomHintz's profile


207 posts in 4453 days

#2 posted 05-22-2011 08:24 AM

You have to be very careful with any abrasive on a router bit shank because reducing its diameter even a little can be very bad news. You should check its diameter before cleaning anyway just to be sure it was not already smaller than it was supposed to be.
Look for dust or resin buildup inside the collet or the recess in the routers shank. Either can make the collet tighten up before it really grips the shank of the bit.

-- Tom Hintz,

View DaleM's profile


958 posts in 4439 days

#3 posted 05-22-2011 08:35 AM

I might wipe the bit down with some solvents, and remove the collet and do the same, but I wouldn’t use abrasives on the bit as it would reduce the diameter as mentioned above. I had a bit slip before and a thorough cleaning fixed the problem for me. If this doesn’t fix the problem, then sure, try what you need to try and if it doesn’t work, you may need a new collet.

-- Dale Manning, Carthage, NY

View bubinga's profile


864 posts in 3722 days

#4 posted 05-22-2011 08:53 AM

Make sure your collet is clean, and the router shaft,where the collet seats is clean , and get it tight
When you put a bit in ,put it all the way in ,and then pull it back out 1/8” or so,and tighten, you want most of the bit shaft in the router collet. If most of the bit shaft is not in the router collet ,it can cause vibration

-- E J ------- Always Keep a Firm Grip on Your Tool

View Bernie's profile


422 posts in 3892 days

#5 posted 05-22-2011 04:02 PM

Thanks for the tip about cleaning my bit with solvent rather then abrasives… you are right in warning me about changing the shanks thickness. As for putting the bit all the way and backing off 1/8” I’m a bit disappointed in the engineers that design the tools. I’m using a manufactured dovetail jig and bit that came with the kit, and when using the guide, the shank can not be slipped into the collet as far as it should go. If I use another guide, the from a set, the problem is even worse because the guide is even deeper and another bit from a set has a shorter shank… figure! I’ll be cleaning the shank and collet… thank you.

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

View MrRon's profile


6006 posts in 4298 days

#6 posted 05-22-2011 08:17 PM

Bernie: Were you using a carbide tipped bit, a solid carbide bit or a high speed steel bit? If the bit was solid carbide, the shank is too hard for the collet to grip securely. Are they quality bits or something out of ACE hardware. Some el cheapo bits may have undersize shanks making them susceptable to slipping.

View Bernie's profile


422 posts in 3892 days

#7 posted 05-23-2011 04:46 AM

I was using a carbide tip good quality bit. I’ve been reluctant about naming the brand because most (maybe all) of the store bought jigs are problematic. My choice was Rockler because I’ve used their products in the past and haven’t had any problems with them. I do have a digital caliper and will measure the shank in the morning.

To all… thanks for your time. Folks like you make Lumber Jocks a great site. We woodworkers have the love of working with wood, but we all have our own way of working. I learned something by asking. Thanks!

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

View auggy53's profile


159 posts in 3735 days

#8 posted 05-23-2011 06:02 AM

i clean my bit shanks with 400 grit and w.d. 40 , just enough to get the gunk off . i have had bits move and it allways seems to be the straight flute bits .

-- rick

View philip marcou's profile

philip marcou

265 posts in 3652 days

#9 posted 05-23-2011 07:44 AM

Here’s my take on this one:-
You can clean up the shank with abrasive paper or scotchbrite by hand without fear of significantly reducing the diameter , trust me. If you have a brass wire brush mountable in your bench grinder or bench press you can do it with power too. These collets are designed to accept a fairly generous tolerance.
Check the diameter of that shank-if it is supposed to be a 1/4 inch then be sure it is that and not a 6mm diameter shank, which requires a 6mm collet, not a 1/4inch collet. I have found that 1/4 inch shanks can vary from around 6.20 to 6.4mm in daimeter. (1/4 inch = 6.35mm). If the shank diameter is less than 6.2mm then it is tending to be undersize and the collet gripping power may be reduced enough to cause slipping.
Clean the collet, the collet nut and the spindle threads with a suitable solvent.
And here is what most folks fail to do: apply A LITTLE oil to the threads and lip of the collet which bears against the nut when it is tightened. Just a little oil, enough to enable full tightening without too much force-this way you can get it much tighter than if it were dry, and it stays tight.
I don’t agree that carbide shanks cannot be securely held by the usual spring type router collet- a quality E R type spring collet is designed to hold any milling cutter regardless of it being tungsten carbide or hardened high speed steel. It just needs to be clean, correctly tightened and the shank diameter needs to be within its tolerance range.

View Bernie's profile


422 posts in 3892 days

#10 posted 05-23-2011 06:47 PM

I used oven cleaner (it’s what I use when my saw blades collect gunk) and it cleaned nicely. The shank is 6.33mm in diameter so sounds like I’m good. After all of that, I discovered the real problem. Learning the hard way, I started my router (Porter Cable 8529 plunge) and made my test cut to adjust the depth. When I picked up the router, it slipped up and chewed up the 7/16” guide and stopped the bit with the machine still running.
I took out the manual and read on how I can adjust the tension on the plunge lock. Never thought about them stretching and wearing. Thanks for the help. I hope my post will help someone else avoid the slippage. I keep my shop clean and tools sharp, but I better recheck all of them for problems I might avoid.

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

View miles125's profile


2180 posts in 5060 days

#11 posted 05-23-2011 07:30 PM

I think this is most commonly caused by too big a bite heating things up and therefore slightly changing the crucial size of metal in the bit and collet. Or a dull bit with even a small bite can produce the same effect.

-- "The way to make a small fortune in woodworking- start with a large one"

View 404 - Not Found's profile

404 - Not Found

2544 posts in 4024 days

#12 posted 11-09-2011 01:39 PM

Maple is just about as tough as it comes, it might help in future to run a 1/4” straight bit in first – just slightly shallower than the dovetail bit, so when you rout the dovetail you’re not taking out as much waste.

View ajosephg's profile


1897 posts in 4616 days

#13 posted 11-09-2011 03:03 PM

@Bernie: ”I’m using a manufactured dovetail jig and bit that came with the kit, and when using the guide, the shank can not be slipped into the collet as far as it should go.”

If you can’t put it in to the proper depth you are asking for bigger problems than slippage. The bit could come out and fly around the shop, leading to all of kinds of bad stuff including serious injury to yourself.

I use a Porter Cable router, Porter Cable bits with a Porter Cable dovetail jig and have no problems getting the shank into the collet to its full depth less 1/8 inch.

I think the problem is that you are using a plunge base instead of a fixed base. I’m not near my shop at the moment, but I think the fixed base depth is less than the plunge base, allowing you to use shorter bits. If that is the problem than your solution is to buy a fixed base if you don’t have one, AND a new collet because you may have damaged the old one by overheating it.

-- Joe

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