Why does a plunge router leave a mark when it plunges into the wood? - Router Forums
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post #1 of 38 (permalink) Old 06-25-2015, 10:31 PM Thread Starter
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Question Why does a plunge router leave a mark when it plunges into the wood?

Using a straight bit or a spiral bit, either one, I was routing out some long and wide, but shallow mortises earlier, and I had to hollow it out a row at a time. I would plunge the router in until the depth stop hit the turret and then lock it down. From there I would slide it along using an edge guide to keep the cut straight.

I tried each bit type to see what it would do, and I noticed that no matter which type I used when I plunge the bit into the wood it would leave a circular mark at the bottom of the mortise where it went in at. As I move the router along, it leaves a smooth bottomed path, but the point of entry always seemed to be slightly deeper than the rest of the groove was. It done this on each row, and even passing the bit over top of it did not clean it up. These mortises are part of the appearance in some wood trim I am making, so I will have to sand the circular marks out. I just wondered how the router can make a deeper cut at the point of entry than it does on the rest of the cut. I thought the depth stop would prevent this. At first I thought the router had plunged to the full depth and then backed off a little before being locked. But after seeing this several times I paid closer attention to that. The depth stop was in full contact with the turret but I still kept seeing the little circular marks at the point of entry. Do you suppose it is possible that the lever lock is retracting the plunge upwards very slightly as it locks? That's the only thing I can think of. It is a DeWalt DW618 plunge router.
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post #2 of 38 (permalink) Old 06-25-2015, 11:07 PM
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This is a good question as it's happened to me to and it's never made sense
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post #3 of 38 (permalink) Old 06-25-2015, 11:18 PM
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Ha ha, do you think anyone will notice? J/K

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post #4 of 38 (permalink) Old 06-26-2015, 01:11 AM
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post #5 of 38 (permalink) Old 06-26-2015, 01:51 AM
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Edit> Me numb nut, wrong answer.

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post #6 of 38 (permalink) Old 06-26-2015, 01:56 AM
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You are expecting accuracy to 1000s of an inch in a medium that you will only get several 100s of an inch accuracy at the absolute very best. Your mortices should be about 1/16" deeper than your tenons are long to allow for a proper fit and a little room for excess glue. As Mike suggested, do you think anyone is going to notice?

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #7 of 38 (permalink) Old 06-26-2015, 02:45 AM
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Ideally for plunge routing you should be using a plunge bit, that is one which has an extra blade at it's bottom so that it cuts it's way into the wood instead of burning it's way.
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post #8 of 38 (permalink) Old 06-26-2015, 05:14 AM
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harry's got the solution, I have the same result occasionally as you do with a carbide spiral upcut bit. Try a slow, less aggressive plunge when using that bit and work it down to your stop depth with some forward motion, then back to clean up...
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post #9 of 38 (permalink) Old 06-26-2015, 05:48 AM Thread Starter
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Both of these bits have cutters across the tips. The straight bit doesn't go all the way across so I can see it leaving a worse mark but the cutters on the spiral bit actually meet in the middle so I just didn't undestand how it could leave a mark at all. Being a spiral upcut, I thought it would literally work like a twist drill bit going in and leave a clean bottomed hole. I will try rpludwig's entry approach on the next piece. I still have more work to do tonight so maybe I can get better results and learn something in the process.

These mortises will show when finished. They are not for joinery. Each one is a 6' long, 2" wide, 1/4" deep, shallow recess on the face of some door casing I am making for my entry door on the new house we bought. I will post some pics when it it finished.
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post #10 of 38 (permalink) Old 06-26-2015, 05:52 AM
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because it bumps a half of a fuzz deeper on the down stroke and then relaxes when you let off the pressure...

likw Mike said...
will anyone notice...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

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