Broken router bit

  • Advertise with us

« back to Jigs & Fixtures forum

Forum topic by stripit posted 11-24-2019 09:52 PM 364 views 0 times favorited 13 replies Add to Favorites Watch
View stripit's profile


55 posts in 2606 days

11-24-2019 09:52 PM

Topic tags/keywords: router circle broken bit jig

Hi. I’m trying to cut a circular frame using rocker elipse circle jig. I watched the video, set everything up and started. I thought I was going the right way, clockwise, It looked like that in the video. The bit came loose twice, then it broke.
I’m using an up cut spiral bit 1/4”, cutting 1/8” at a time. Am I going the wrong way, is that why the bit came loose and broke????

I did one already out of pine and had no problem, this one is ash.

Thank you any suggestions you may have.

-- Joel, People ask what I make. I tell them I make sawdust, and now and then a nice box or frame,or clock, or lamp pops out.

13 replies so far

View BobAnderton's profile


308 posts in 3352 days

#1 posted 11-24-2019 10:04 PM

The bit came loose twice? That sounds like the problem. Once it came loose the 3rd time no telling how deep a bite it took. Is the problem that your 1/4” collet needs replacement? I take it you’re forming the groove with the bit, so clockwise vs counterclockwise shouldn’t matter.

-- Bob Anderton - Austin, TX - Nova 3000 lathe, Alaskan Mark III mill, Husqavarna Saw

View Rayne's profile


1268 posts in 2101 days

#2 posted 11-24-2019 10:14 PM

I’m thinking 1/8” in Ash is probably too much to take out at once. You’ll need ot take about 1/16” at a time for that one. My guess on coming loose is the bit is heating up too much and came loose. Bits will definitely break if taking too much out at a time.

View stripit's profile


55 posts in 2606 days

#3 posted 11-24-2019 10:16 PM

I took the collect out and cleaned. I have another collect to try, but have buy a new bit first.

-- Joel, People ask what I make. I tell them I make sawdust, and now and then a nice box or frame,or clock, or lamp pops out.

View MrUnix's profile


7531 posts in 2761 days

#4 posted 11-24-2019 10:17 PM

+1 to what Bob said – sounds like your collet needs some attention… either cleaning/roughing up or replacement. Under no circumstances should a bit come loose. As for direction, it doesn’t matter when you are doing a plunge cut (as opposed to an edge cut). But just an FYI, the video I watched from Rockler shows them going counter-clockwise, not clockwise :)


-- Brad in FL - In Dog I trust... everything else is questionable

View bondogaposis's profile (online now)


5570 posts in 2913 days

#5 posted 11-24-2019 10:19 PM

An upcut spiral bit will try pull itself down into the wood if it isn’t tight in the collet. You likely ruined your collet or maybe it was worn to begin with. Try it with a straight bit.

-- Bondo Gaposis

View BurlyBob's profile


6770 posts in 2827 days

#6 posted 11-25-2019 02:42 AM

Joel, If you’ve got access to someone with a sand blaster Get them to shoot the shaft of your router bit. It doesn’t to be heavy just enough to abrade the surface of the shaft so the collet can get a grip on the bit. I had a router bit traveling out of the collet as I was making a dovetail. No matter how hard I tried to tighten that collet the bit would travel out. That little bit of abrasion made all the difference.

View Lazyman's profile (online now)


4183 posts in 1949 days

#7 posted 11-25-2019 03:33 AM

Is it possible that your bit is actually a 6mm bit instead of a 1/4”? They make upcut bits for CNC machines in metric sizes and it may be close enough in size that perhaps your 1/4” collet can hold it, just not tight enough?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View HerringImpaired's profile


29 posts in 271 days

#8 posted 11-25-2019 03:43 AM

Was the bit bottomed out in the collet? Best practice is to bottom the bit out, and then pull upward about a 1/16” to 1/8” or so, and then tighten the collet.
(Nice shoulder decoration! I have an African Grey on my shoulder as I type this)

-- "My greatest fear is that upon my demise, my wife will sell my tools for what I said I paid for them."

View CaptainKlutz's profile


2041 posts in 2056 days

#9 posted 11-25-2019 04:40 AM

Hmm, when the bit became loose the 1st time, did you check if it was bent?
Bent bits will vibrate themselves out of a good tight collet.
1/4” bits bend really easily if you push them too fast in hardwood.

I always try a different bit before blaming the collet.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View stripit's profile


55 posts in 2606 days

#10 posted 11-26-2019 03:18 PM

Thanks to everyone who took the time to right. I tried all your suggestions, change to a sright bit with a 1/2” shank, which meant a new collect, even sand it a little. The bit still came loose. I think I have found the problem, I needed the smallest circle I could get.with this jig which is 9 1/4”. To get this you have to leave off the base plate, and just use the small dove tail piece (about 1 1/4” long) and this does not give a enough support for the jig. the jig tends to tip just a little, and I think that is putting stress on the bit. So I guess I’ll go to plan B for Christmas.

The bird is a sun Conure and rules the roost around here.
Thanks again.

-- Joel, People ask what I make. I tell them I make sawdust, and now and then a nice box or frame,or clock, or lamp pops out.

View Gerald's profile


52 posts in 2348 days

#11 posted 11-26-2019 03:44 PM

I would have put my money on the bit being “bottomed out” in the collet. If the bit shaft is bottomed out, the collet cannot grip adequately. My solution to the issue is to cut and slip on each bit’s shaft really short sections of Tygon (clear plastic) tubing to effectively make an “O-ring” that prevents the bit from sinking too deeply in the collet while you are trying the get the nut tightened.

-- Gerald, Rural North Central Arkansas

View Tony_S's profile


1046 posts in 3645 days

#12 posted 11-26-2019 04:14 PM

Don’t convince yourself that the jig is the problem. It isn’t.
It doesn’t matter what happens as far as tipping, jamming, kick back etc. or the type of bit. The router bit should NEVER come loose.
I understand that you put on a new collet and router bit….but there’s something wrong with either the collets, the chuck, the bits, or you’re not tightening the bit properly.
Once in a rare while, I’ve come across bits that have a slightly undersized shaft, but it usually isn’t anything that an extra crank on the collet won’t solve.
Does the router vibrate? Maybe the bearings are shot and the vibration is causing the collet to loosen?

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

View DrTebi's profile


360 posts in 3829 days

#13 posted 11-26-2019 04:59 PM

I am with Tony_S on this one. I have cut dozens of large circles for speakers, and never had a bit come loose.

Maybe tell us how exactly you are tightening your router bit, or show us some pictures of the setup. There just might be something else that causes the problem.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics