Author Topic: Can runout or deflection cause a router to kickback?  (Read 988 times)

Offline RichardDepetris

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Can runout or deflection cause a router to kickback?
« on: February 04, 2017, 02:05:43 PM »
I am asking my question here instead of the woodworking forum because my question is really a general machining question. I haven't had a satisfactory answer from my woodworking forums, nor any searches.

I am pattern routing a plane tote on my router table and I have been experiencing a kickback the moment the cutting edge of the bit touches the work piece.  It happens on both a 2 flute, top and bottom bearing flush trim bit and a top bearing flush trim spiral bit. I am trimming away less than 1/8" of red oak end grain.  I am also routing from right to left.  Oddly, I was able to round over the piece with a 1/2" roundover bit with no kickback. I did get lots of burning and tear out. 

After trying several suggestions, I decided to inspect the router.  It's Porter Cable 690 and it is very old and it is the first time I am using this particular router.  I checked it with my indicator without the bit and I got .005" runout at the shaft and nearly 0 inside the collet.  With my thumb, I pressed with firm pressure against the shaft and got over .010"  runout depending on how hard I pressed it.  During use, there is a lot of vibration, very loud and makes rattling clanking sound as it spins down. I assumed it was because routers are supposed to be noisy.

Can such a deflection on the shaft cause a kickback?  If so, why?  Moreover, why did the roundover bit not kickback, albeit the finish wasn't very good? 


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Offline John Rudd

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Re: Can runout or deflection cause a router to kickback?
« Reply #1 on: February 04, 2017, 02:11:58 PM »
I'd say your cutter is blunt....and needs sharpening, if its not a new one..or judging by the description further on your router has worn bearings
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Offline RichardDepetris

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Re: Can runout or deflection cause a router to kickback?
« Reply #2 on: February 04, 2017, 02:31:53 PM »
I'd say your cutter is blunt....and needs sharpening, if its not a new one..or judging by the description further on your router has worn bearings

Thanks! Would the observed deflection worsen or effect the TIR even with light pressure as the bit spins at 25,000?  My guess is that the centrifugal force and heat may play a part. 


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Offline Biggles

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Re: Can runout or deflection cause a router to kickback?
« Reply #3 on: February 04, 2017, 02:37:37 PM »
I agree with John its more than likely the bearings and made worse by using a blunt bit. :coffee:

Offline chipenter

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Re: Can runout or deflection cause a router to kickback?
« Reply #4 on: February 04, 2017, 02:57:34 PM »
How firm is the mounting to the table a little bit of rock will grab and kick , my table is a dual saw and router and the plate has to be set level and tightend down well .
Jeff

Offline Jasonb

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Re: Can runout or deflection cause a router to kickback?
« Reply #5 on: February 04, 2017, 03:27:27 PM »
If it is kicking the moment you touch the work it sounds to me that you are not using a "lead on pin" This is a small pin that you run the work against as it is fed into the cutter to stop the work being kicked the other way. Most router table inserts will have a threaded hole or two for the pin to screw into.

What happens is as the corner of the work touches the cutter it will want to climb cut across the end until you have the bearing in contact with the side being cut, the pin gives you a fulcrum to steady the work against.

Jason
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Offline mexican jon

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Re: Can runout or deflection cause a router to kickback?
« Reply #6 on: February 04, 2017, 04:08:14 PM »
very loud and makes rattling clanking sound as it spins down. I assumed it was because routers are supposed to be noisy.


I would also say 100% that your bearing are shot  :bang:
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Offline RichardDepetris

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Re: Can runout or deflection cause a router to kickback?
« Reply #7 on: February 04, 2017, 04:10:48 PM »
If it is kicking the moment you touch the work it sounds to me that you are not using a "lead on pin"

Jason
Who makes his living turning wood into sawdust.

Yup, tried it with this too. No difference. 


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Offline sparky961

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Re: Can runout or deflection cause a router to kickback?
« Reply #8 on: February 04, 2017, 05:17:07 PM »
Add another vote for the bearings, but that may not be your only issue.

I stopped on "routing left to right" and was trying to figure out if you were (in machining terms) climb or conventional cutting.  I have had much less success with climb cutting and if there's a safe way to do it I haven't yet learned it.  Your description, however, could be interpreted either way so it's hard to say if this is part of the problem.

A quick video of your process and a seasoned woodworker (not myself) could probably point out the issue very quickly.

Offline RichardDepetris

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Re: Can runout or deflection cause a router to kickback?
« Reply #9 on: February 05, 2017, 12:51:04 PM »
I stopped on "routing left to right" and was trying to figure out if you were (in machining terms) climb or conventional cutting.  I have had much less success with climb cutting and if there's a safe way to do it I haven't yet learned it.  Your description, however, could be interpreted either way so it's hard to say if this is part of the problem.

I said "right to left" which is the conventional direction on a routing table, since the bit is facing up.  I also tried climb cutting as well. They were both tried using a spiral and two flute bit.  The amount of material to trim was about 1/16", which is hardly a lot to bite and even less when it is limited by bearings at the top and bottom.  Regardless, the bit throws the work piece the moment the bit touches it. 

I am siding with the bearings as the culprit.  Perhaps my eyes fooled me, but at one point a saw a significant wobble of the bit shortly after the work piece was kicked away.  Strange rattling noises can be heard as the router spinned down to a stop. 

Offline awemawson

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Re: Can runout or deflection cause a router to kickback?
« Reply #10 on: February 05, 2017, 01:30:44 PM »
Surely you would be able to feel significant play in the shaft if the bearings are bad enough to be causing your problem  :scratch:
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Offline seadog

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Re: Can runout or deflection cause a router to kickback?
« Reply #11 on: February 05, 2017, 03:41:33 PM »
I'd go for bearings too. The initial bite kicks the cutter away from the workpiece which, because of the speed involved, then throws the cutter deeper into the wood.

Offline sparky961

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Re: Can runout or deflection cause a router to kickback?
« Reply #12 on: February 05, 2017, 04:04:12 PM »
Still seems odd the part would get launched so quickly/easily.  Maybe too light a grip on the work piece due (understandably) to fear of the screaming router with spinning sharp tool right next to one's fingers?  This is one reason I suggested a video showing what's going on.

Offline RichardDepetris

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Re: Can runout or deflection cause a router to kickback?
« Reply #13 on: February 05, 2017, 04:05:56 PM »
Still seems odd the part would get launched so quickly/easily.  Maybe too light a grip on the work piece due (understandably) to fear of the screaming router with spinning sharp tool right next to one's fingers?  This is one reason I suggested a video showing what's going on.

Hmm. Thought about that as well, but I was able to use a round over on the same piece without issues aside from burning and tear out.


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Online PekkaNF

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Re: Can runout or deflection cause a router to kickback?
« Reply #14 on: February 06, 2017, 03:14:38 AM »
I bought a router and learning curve was steep and riddled with flying pieces and splinters.

If the router makes screaming or "brakes skidding" sound when it is winding down bearings are shot and needs to be replaced. On old router the grease has been expired long ago. often the bearing is a bit marginal for the rpm to start with. Note to myself: buy bearing for Festo. These are not normal RS sealed bearings, but they are noncontact seal types, or they would heat up in no time. Spare parts here the way to go and not "new old stock" but new-new. Bearings are shot way before you feel anythings, so probably it is not the bearings for kick back.

I'm just saying that that it takes a little time to get used to routing. Unlike metal, wood has a structure and it might dictate to climb mill, but you really have to be slow, controlled and delibrate or you will be performing some awkward new dance moves...

My first advice would be clamp the workpiece down like there is no tomorrow. Don't rout slender pieces. If you need a small piece, first rout it while it is nice big piece to clamp, then saw it of. Even a little bit vibration and it will bite and piece or router will ricochet.

Don't get greedy and hog out. Take small cuts.

Control the speed of the cut and soft initial touch. Or actually slow and delibrate initial touch. Also 800 w router with 5 mm bit will need completely different approach (easy to snap the small cutter) than 2 kw monster with big "disc".

And keep your all digitt up where you can see them.

But when it works. It makes a lot of stuff so easy and fast.

Pekka

Offline awemawson

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Re: Can runout or deflection cause a router to kickback?
« Reply #15 on: February 06, 2017, 03:30:44 AM »


But when it works. It makes a lot of stuff so easy and fast.

Pekka

And when you are using it, all the neighbours within a couple of miles will hear what you're up to  :lol:
Andrew Mawson
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Online PekkaNF

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Re: Can runout or deflection cause a router to kickback?
« Reply #16 on: February 06, 2017, 05:41:12 AM »


But when it works. It makes a lot of stuff so easy and fast.

Pekka

And when you are using it, all the neighbours within a couple of miles will hear what you're up to  :lol:

And if pieces ricochet, they will hear me bellowing on top of the screaming router while it is winding down. And then quiet.  :bang: :bang: :bang: :bang:

Pekka