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I bought a router and am practicing. When I cut across the grain (actually, it does not matter, see "conclusion") I noticed that sometimes it tears bits of the wood out. For example, here are two ends of the same piece of 3/4" pine:

enter image description here

Both ends were cut by me but on the bottom you can see the rough cut. This is a hand held 1.5 hp router at ~20000 rpms using a straight blade with 2 flutes. The blade is 3/8" diameter and I removed about 1/8" of uneven material. I used the router base against a clamped piece of wood as a guide. The feed direction was against the blade rotation.

Why is this happening and can I avoid it? Did the router actually rip those bits out or do those pockets already exist in the wood? Is it a problem with my technique, wood quality, or just a normal unavoidable thing?

Conclusion (Probably)

Following CoAstroGeek's answer I inspected my equipment and tried more consistent cuts to repeat the problem.

I sawed away a portion of the wood near the tear and verified that it was not an internal defect, it looks like I did the damage:

enter image description here

I then cut material off in the same way as above using all four straight bits from the same set, increasing diameter each time. I kept my speed more consistent this time and tried to go a bit faster. Cuts were made right to left in images below. Looking closely, even though I did not have tearing as above, the results are very poor (I burned the first one a lot cutting off too much material, so I couldn't move quickly):

enter image description here

The second bit was OK. The third is the one I was using in the original images. The streaks are in the same positions as the tears. This is probably not coincidence. All four blades also leave light horizontal streaks the whole way down, which I initially attributed to sanding.

Also while I thought my cuts along the grains had no issues, on closer inspection there is still notching:

enter image description here

When I inspected each bit under a magnifying glass, one of the flutes was slightly chipped or dented at the location of every deep scratch. I could not determine the cause of the lighter more frequent scratches.

I tried similar experiments with my other bits, not part of this set and from a different manufacturer, and none had any of these issues.

The general conclusion is this set of bits is probably just crap. It was fairly cheap. It also taught me that I should be very careful when storing bits because even small defects can ruin a cut. I do not know if the dents are manufacturing defects or damage to the bits done by me in storage (all of the bits used were brand new before this post). Time to go shopping.

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    Pine tar can do awful things to the sharpness of router bits. It can coat the edge in full or in part. That can give you jagged, uneven cuts, complete with blackened bits of overheated pine tar marring the finish of the wood. You may have better luck with Beech or Maple. End routing on oak can be its own nightmare.
    – Wayfaring Stranger
    Oct 12, 2015 at 19:26
  • @niall Nah, not a duplicate. The tear out mentioned in that link is probably a different effect (although I don't actually know what's happening in my case). That link is about cut direction relative to bit rotation, not grain. Good find though! :) Also nice to see a woodworking site I also think this should be moved.
    – Jason C
    Oct 13, 2015 at 2:18
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    Just to mention, you can sharpen router bits (even carbide-tipped) so in theory at least you can refine the edges of these bits to remove the defects, giving a cleaner cut. I also wanted to say something about perhaps modify your expectations of using the wood straight from the router, it should be expected that at least some refinement is needed from any machine-made surface, whether shaped or sawn. With some woods this would be ubiquitous, others where the grain swings around you'll get some (nearly unavoidable) tearout on an otherwise flawless surface.
    – Graphus
    Oct 15, 2015 at 9:06

1 Answer 1

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I don't think I've ever seen that. Is the bit sharp? Have you checked it for burrs or other defects? The top picture seems to have some artifacts going across the face also, but they didn't result in tear outs.

The burn on the right side indicates that maybe you paused or slowed down at that point, which may contribute or may be a separate problem.

Was the feed direction the same for both cuts - ie. from the center of the log (right side of both pics) toward the edge, or vice-versa?

In summary, check your equipment, and try to replicate taking note of your feed direction, speed, other aspects of your technique.

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    I did some other tests (see updated answer) and inspected the bits closely. You appear to be correct, every bit from this particular set had small chips in the blade of one of the flutes at the position of the tears and scratches. Also the light close scratches were from the bits as well, not from sanding as I thought. In conclusion, the tearing was probably from damaged bits, and this set seems to be very poor quality. It's all the same set; I tested with my other bits from a different manufacturer and none of these issues were present.
    – Jason C
    Oct 13, 2015 at 7:06

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