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Discussion Starter #1 (Edited)
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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This is a good question as it's happened to me to and it's never made sense
 

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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?
 

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Discussion Starter #9
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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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...
 

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Hi Duane

What you are referring to is called a 'divot'. It happens because most plunge routers have a bit of play between the columns and the router body. The depth stop only stops the one side. The other side can move fractionally deeper if you apply too much downward pressure on that handle. I keep telling my students that they are trying too hard - "let the weight of the machine do the work!" Place your router on a flat surface, set the depth stop so that the bit is clear of the surface, plunge to and lock at the depth stop. Put some downward pressure on the handle opposite the depth stop and see how much 'play' there is in your router. Ron's advice is good advice - a less aggressive plunge.

Denis Lock - "Routing with Denis"
 

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Not usual. Turrets rock & roll x design. When you press on a stud your tilting the turret.
Not much but enough to over plunger & burn the work at entry.
I scrap all turrets and plunge x feel (what ever the cutter can handle/pass).
The end point is all I care about and the stop is on the anvil not some clumsy turret.
An aside: Plungers are supposed to be safer than fixed tools.
But are they? If you have to remove your hand from the head-handle to rotate the turret, you've lost some control, no safety there.
If you sweep and plunge simultaneously you can minimize all the adversity of a cutter trapped in a pathway in its own waste,
 

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I believe Stick has it right.

The effect never bothered me relating to the quality of my work because the dimple, (my name for the result) is always covered by another piece of wood. When I 1st noticed it in my router inlay work, (shallow plunges) my curiosity, (and nothing better to do) got the better of me and I half ass*d went through a couple random tests and tripped over the answer immediately. I moved the bit to a different spot of the completed excavation and plunged down with as close to the same energy as the 1st plunge. I got nearly the same depth results in multiple attempts.

My quick theories are, in general when the plunge is made most of the time the router is stationary.

1. The routers plunge springs counter reaction to the plunge provides a natural rebound effect.
2. We may unknowingly relax downward pressure just enough when the lock is engaged.
3. Engaging the lock forces the bit up a micro fraction of an inch.
4. One or more of the above.

When I made a rolling plunge I did not see the dimple
 

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rolling plunge it is...
 
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Discussion Starter #17
An aside: Plungers are supposed to be safer than fixed tools.
But are they? If you have to remove your hand from the head-handle to rotate the turret, you've lost some control, no safety there.
The way I do it, I set my depth with the turret before I start, then turn the router on and plunge. If I need to remove more material, I turn the router off, rotate the turret and make a test plunge to make sure all alignment is still good, and then turn it on again and plunge for the second pass.
 

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If these mortises are open on one side like a butt hinge mortise , make a template that is larger on the open side so that you can plunge in the open, away from the work and feed into the work like we used to do before plunge routing. Another way is to do a skim cut after you have made the depth cut and clean it up, since it doesn't have to be a critical depth.

Herb
 

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Brilliant advice-(nota bene)

Hi Duane

What you are referring to is called a 'divot'. It happens because most plunge routers have a bit of play between the columns and the router body. The depth stop only stops the one side. The other side can move fractionally deeper if you apply too much downward pressure on that handle. I keep telling my students that they are trying too hard - "let the weight of the machine do the work!" Place your router on a flat surface, set the depth stop so that the bit is clear of the surface, plunge to and lock at the depth stop. Put some downward pressure on the handle opposite the depth stop and see how much 'play' there is in your router. Ron's advice is good advice - a less aggressive plunge.

Denis Lock - "Routing with Denis"
With any hand routing you have to practice the cut on the same material multiple times and get the feel(speed, ,depth of successive cuts etc),. Your eyes and hands are as important as the bit you use. For repeated cuts then use a jig. The accuracy in the making of the jig is directly proportional to end product. For any mass production then you have to resort to specific bits and machines. For remcoving any burn marks I ensure that I do lots of passes at inreasing depths particularly at start and end of cut. .any burns can be taken out by hand with sandpaper on a suitable shaper, or a burr on a flexi-arm.
Cheers
Paul
 

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I should try my Festool and see if this issue doesn't happen :D
 
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