# tear out - what went wrong ?



## jkristia (Jan 18, 2009)

I ran into a problem today when I was routing a 1/4" rabbet for the back panel on the router cabinet I'm building.

I was running the router at 16000 rpm, using a freud rabbet bit and cutting it 1/4" deep on the edge of a 3/4 ply. While cutting I suddenly got a huge tear-out, almost 2 of the layers were torn out in an area of probably 1x1". I did not force the bit when it happened, but I did cut full depth (had it running on the guide bearing). After that I tried to cut in a couple of passes where I would only on the last pass have it running on the guide bearing, and it did help some, but I still had some tear out

So my question what did I do wrong, was the bit running too fast?, slow?, bad quality of plywood (from Lowes, and I actually think it is a really cheap quality as it onyl have 5 layers and a super super thin face veneer).

The place where it happened is not going to be visible, so in this case it doesn't matter, but I would like to prevent doing the same mistake next time.

Any suggestions

Jesper


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## Sawatzky (Jan 1, 2009)

Perhaps the problem was that you were routing plywood? I have never routed plywood before, but I would think it would not rout well. I may be worng here though so someone else will have to chime in.


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## nzgeordie (Oct 22, 2006)

I'm not an expert on routing ply but I guess that at one moment your routing with grain then the layer under that is cross grain and so on. Maybe you could try a different bit such as a spiral downcut.


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## Birchwood (May 13, 2005)

From my modest experience I know routing plywood can be annoying. I would look at two things: dull bit, speed too slow. That's what I would look at, but I expect the more experienced guys will be commenting soon.


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## Ghidrah (Oct 21, 2008)

Jkirstia,
At the start of the cut you have the rest of the stock resisting the cutter, at the end of the cut there is no material resisting the cutter.

Tear out occurs with solid stock as well as plywood/lams especially when making a cross grain cut, you should have a backer to prevent tear out for all.

Bear in mind the cross lams in ply are about 3/32 thick and the inner layers aren't as solidly grained as the exterior layers

To point out the obvious but often ignored, whether you're using a table saw or router you are pulling material away from the stock. Regardless of the sharpness of the bit/blade and or the speed at which you move the stock though the cutter.


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## jkristia (Jan 18, 2009)

>>At the start of the cut you have the rest of the stock resisting the cutter, at the end of the cut there is no material resisting the cutter.

So are you saying I should be going right to left instead of left to right ?


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## Hamlin (Dec 25, 2005)

Yes, right to left. Ply is tricky. You're dealing with cross grain. Remember what it's made of. I'd recommend increase bit speed. There are ply bits on the market. You said you got the ply from Lowes, is this cabinet grade or the reg stuff? The type of ply also makes a difference.

I don't like cutting dado's or rabbets in ply with the router for this very reason. With the TS you'll get a cleaner cut. I'm not saying it isn't doable with a router. Just the experience with tear out with ply.


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## CharleyL (Feb 28, 2009)

I think you are trying to remove too much wood in one pass. Either significantly reduce the depth of cut and make several passes, or change the bearing on your bit reducing the width of your cut. Then make repeat cuts with different bearings to reach the 1/4" width that you want. Plywood edges are more fragile than solid wood, especially if the laminations haven't been glued together properly when it was manufactured. Voids and knots in the internal laminations can also cause trouble. Use a backer block scrap at the end of your cut to reduce tearout there too.

CharleyL


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## Ghidrah (Oct 21, 2008)

Jkrista,
You could back cut the ply before proceeding with the standard cutting direction, but you still risk tear out with the cross lam of the ply. You're safer with a backer on the tail end of the plywood and (IMO) a simpler method providing a better cut


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## jkristia (Jan 18, 2009)

I'm not sure how I would use a backer board when using a rabbet bit with bearing guide.
Would I use a 1/8 hardboard for the first pass and let the rabbet cut 1/8 of the ply and the hardboard and then remove the hard board for the second pass ?


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## bobj3 (Jan 17, 2006)

Hi Jesper

Here's just one more way to get it done without the rip out...
Run it backwards on the router table,,,this is a advance way of doing it..

You must keep your hands/push block on the stock at all times, when you run it backwards you don't have the bit pulling the stock out..it will push the chips back in the stock/plywood but don't take more than a 1/4" at one time....you will come out with a nice clean edge..
The safe way is to use your hand router,,,,but do it backwards, that's to say pull it to you and not push it away from you..

If you clamp it on the bench and you are looking a it from the front side of it..you would start on the right end and go to your left..the norm with a hand router..this is called a climb cut/pass...

I should Note*** the rabbet bit you use on plywood will make a big diff.

See the snapshot below, you want to use the one with a skew angle on it, they sale all types of rabbet bits but for plywood you want the one that will cut clean and not chop the rabbet out..  so to speak ,this very true for vern.plywood..

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jkristia said:


> I ran into a problem today when I was routing a 1/4" rabbet for the back panel on the router cabinet I'm building.
> 
> I was running the router at 16000 rpm, using a freud rabbet bit and cutting it 1/4" deep on the edge of a 3/4 ply. While cutting I suddenly got a huge tear-out, almost 2 of the layers were torn out in an area of probably 1x1". I did not force the bit when it happened, but I did cut full depth (had it running on the guide bearing). After that I tried to cut in a couple of passes where I would only on the last pass have it running on the guide bearing, and it did help some, but I still had some tear out
> 
> ...


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## AxlMyk (Jun 13, 2006)

I would run it on the table saw to cut the back of the rabbet first. If the panel isn't too big, I would use the TS to finish it.


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## larry t (Sep 8, 2007)

I also believe you're taking too deep a cut . I would suggest shallower cuts and multiple passes. And it helps to make a LIGHT climb cut also.


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