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Repeated router kickback, Why?

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Forum topic by RichardDePetris posted 01-27-2017 04:12 AM 1317 views 1 time favorited 26 replies Add to Favorites Watch
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RichardDePetris

61 posts in 1522 days


01-27-2017 04:12 AM

Topic tags/keywords: question

I just finished creating a pattern and roughing out the shape on my bandsaw and all hell broke loose at the router table. The pattern was made from a 1/4” piece of plywood which was taped to a piece of red oak stock. The routing paths were all along the end grain.

The router bit was a bottom and top bearing flesh trim bit with a 1/4” shank on a Porter Cable 690 on a Bosch RA1181 router table (I also have Bosch 1617, but the 690 was already mounted on the table with a 1/4” collet.) I attached a router pin and left the fence in place, since it wouldn’t obstruct the operation. I set the height of the bit so the top bearing rides along template.

I used a handscrew clamp to hold the stock as I entered the cut in the middle of the inside curve going right to left while levering against the pin. The cut was a bit rough since there was about 1/4” of material to trim and it was end grain. As I entered the cut again to finish the other half, the bit grabbed the piece and flung it out away landing on the floor. I was shaken but not deterred

I turned the piece upside down and approached it in a different direction riding on the bottom bearing. Again it grabbed the piece and flung it away. I noticed that as soon as the bit went down hill, it would grab. When I looked at the top bearing, I noticed the small top bearing had its metal seal missing. I wanted to get the piece done so I continued on, As soon as the router turned on, the bit completely disintegrated. The balls flew out and then the outer race leaving only the inner race attached by the screw.

I have done this before a few years ago and it went successfully using a cheap Ryobi round over bit on my Bosch. I’ve had a similar incident routing a piece of white pine as I was exiting the inside of a curve, shattering it into pieces. I was using a top mounted bearing expensive Freud top bearing flush trim bit on my Bosch. The idea of preforming the same operation handheld is terrifying as it might throw the router out of my hand. Had I used my Bosch, the extra power would be even scarier. What am I doing wrong?



26 replies so far

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TungOil

746 posts in 331 days


#1 posted 01-27-2017 05:01 AM

I think the 1/4” deep cut in end grain on such a small part probably added up to your kick back. roughing your oak blank much closer to the finished size before you clean it up with the pattern bit will help. If you use your pattern to draw the outline on the oak you can cut pretty much right up to the pencil line on the bandsaw and still have material to clean up with the router. I try to leave 1/32” to 1/16” max to cleanup with the router.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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Loren

9627 posts in 3484 days


#2 posted 01-27-2017 05:23 AM

That oak has real tough endgrain. Try it on something
like poplar and you’ll probably have a much easier
time.

This issue comes up here often. The best way to
go about theses sorts of cuts is with a template
guide ring because it allows incremental depth of
cut. The pattern bits make you take a whole cut
all at once, which works okay on friendly grain
and plywood, but as you discovered, end grain
is unforgiving.

There’s a way to cut to a pattern on the band saw.

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RichardDePetris

61 posts in 1522 days


#3 posted 01-27-2017 03:44 PM

Thanks. Initially I left too much material, but I went back on the bandsaw and tried again. Same thing. I did no

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a1Jim

116574 posts in 3414 days


#4 posted 01-27-2017 03:57 PM

Can this piece be made on a longer piece of wood routered and then be cut free? you will get better results if you take very small cuts raising the bit a little at a time. This the kind of operation an oscillating spindle sander work really well on if you have one.

-- http://artisticwoodstudio.com Custom furniture

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pintodeluxe

5466 posts in 2650 days


#5 posted 01-27-2017 04:57 PM

While I generally agree with all the good advise that has been given here, I think routing that small of a curved part is an uphill battle. I would spend a few minutes sanding it back to the line and skip the router on this one.

I use an oscillating spindle sander for such things, but I realize not everyone has access to one. Do you have a drill press that you could mount a spindle sanding attachment to?

In your original post you called it a “flesh trim” bit (typo). That gave me chills!

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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HorizontalMike

7658 posts in 2750 days


#6 posted 01-27-2017 05:18 PM

I agree with all of the above. Having made several totes myself, I would recommend the following after you have drawn the pattern on your chosen lumber:

  • In the tight corner/curve, I would use your DP to drill a 3/4in. to 1-1/4” (or other choice) hole using a forstner bit. That will give you a very clean inside corner.
  • With your bandsaw, cut out the remaining pattern. THAT will finish the pattern completely.
  • Choose and appropriate size “round over” bit. NO straight bit here. Work the round-over slowly against the grain. BTW, good choice of clamp for holding the tote.
  • After that, a half round rasp comes in handy to fine tune the round over curves and corners. Sand paper comes last. A spindle sander would have come in handy here.

-- HorizontalMike -- "Woodpeckers understand..."

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ClammyBallz

424 posts in 973 days


#7 posted 01-27-2017 06:33 PM

I’m surprised no one suggested buying a better quality router bit.

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splintergroup

1699 posts in 1059 days


#8 posted 01-27-2017 06:35 PM

I do this often.

You have the correct bit. Place (DS tape) the template on the workpiece then head to the bandsaw and remove the excess to within 1/16” inch or so of the template.
Make sure your router speed is high enough for the bit diameter!. I then run the workpiece/template against the bearing such that all cuts are “downhill” with respect to the grain. I then raise the bit and flip the workpiece/template over to finish the remaining cuts (should also all be downhill now).

The only times I have had things launched from the table are when either the RPMs were too low or there was a defect in the wood.

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TheFridge

8301 posts in 1323 days


#9 posted 01-27-2017 06:36 PM

Stick the template to ithe piece and bandsaw it close.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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dbray45

3295 posts in 2613 days


#10 posted 01-27-2017 07:24 PM

I would check that bit to see if it is bent. When you kick out a piece of wood like that, I have found that I bent the bit.

If possible, I would use a 1/2” bit. Create a 1/4” MDF template and glue it to the piece (with a piece of paper between them). Run the bit at its rated speed and the MDF against the bearing. Go slow and steady.

-- David in Damascus, MD

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RichardDePetris

61 posts in 1522 days


#11 posted 01-27-2017 07:33 PM

Thanks for the suggestions. I greatly appreciate them.

I just put in an order for 1/4” a top bearing spiral cutting bit from Yonico. At the possibility of unleashing wrath from the “I uh tole yuh so manys”, the flush trim was a $4 cheapo from China off eBay. Yeah I know, like a .99 cent burger, it was hard to say no until the reflux sets in.

In the meantime, I am determined to find a reason. I would at least like to use a round over bit at some point. So I pulled out my dial indicator and measured the runout. At the base of the bit, I read very close to 0. At the top of the bearing screw, I read .005. which is more than the suggested 3 thousands. As I was unchucking the bit to chuck in the trash, I noticed the nut bareky finger tight! Somehow the collet loosened itself. I retightened the collet and the top of the bearing read near zero. Perhaps, the heavy hogging made the nut loose.

I might try the operation again with the cheapo bit after building up my courage. Can such a run out or loose bit cause such a kickback?

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OSU55

1424 posts in 1826 days


#12 posted 01-27-2017 08:04 PM

Ive made many totes with the same type bit. I made a combination pattern/clamp to hold them because a wood screw clamp didnt seem reliable enough, but I do use one with round over bits on the totes. I suspect you had the bit bearing riding the pattern and put it into a heavy cut. As mentioned, cut as close as possible with the bandsaw, and drill out the tight corners to remove excess material, but I still have areas that extend too far out of the pattern for one pass. I can feed the part into the bit and guide it through a light cut w/o being on the bearing. I just keep working the excess material down until the bearing rests on the pattern. I do several passes with the roundover bit, raising it some each pass. Gluing sandpaper to one or both faces of the screw clamp with hold the work more securely. Here is a blog entry, with modified drawings, you might make use of.

If you cut an end grain surface all the way through against bit rotation, i.e. in your pic the lower front of the tote toe, the wood will blow out. I leave that as clean up, and feed with bit rotation so the wood is removed ahead of the next cut. Its only an 1/8” or so in length, not enough for the bit to grab the piece and throw it. One of the reasons I made the pattern/clamp jig – to control the operation well.

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RichardDePetris

61 posts in 1522 days


#13 posted 01-27-2017 11:50 PM

You have all been very helpful. I’ve determine that the cheap router bit is at fault. With the runout issue solved by tightening the collet nut, I did a cleanup pass and it went smoothly. When I started from the apex of the curve for a last pass, it kicked back even though there was hardly any material to trim. I checked the runout afterwards and noticed that it worsened with a slight bend to the bit. I believe the small diameter makes the cutting edge attack the fibers on the flat under edge part of the blade. The kickback has a perceptible blunt hammer feel to it.

This bit will be chucked and not in any router. It will be chucked in the trash! No more bargain basement bits for me, Again thanks for all the help!

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waho6o9

8027 posts in 2413 days


#14 posted 01-28-2017 01:17 AM

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RichardDePetris

61 posts in 1522 days


#15 posted 02-02-2017 01:23 AM

Thanks for the help. Unfortunately, I cannot blame the router bit.

Yesterday, I successfully rounded over part of the profile using a round over bit with a 1/2 shank, The cut was burnt and there was lots of tear out, but suspected it wasn’t sharp or my feed was too slow. Today, I just tried out my new spiral top bearing router bit and had the piece kickback at me as soon as I entered the cut. There was only a tiny bit of material to trim. I don’t think this kind of kickback from a router bit is normal.

I noticed since the first time I tried this operation that there was quite a bit of vibration on the router table, Enough to cause a piece of wood to walk off the router table top. Also, when the router powers down it makes some squealing noises. The shaft turns, but not smooth and easy. Could a bad bearing or collet cause the issues I’ve ben experiencing? I could try the operation on my newer 1617, but at 2 1/4 HP it could turn into more than a kickback. Any suggestions.

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