# Why does a plunge router leave a mark when it plunges into the wood?



## Duane Bledsoe (Jan 6, 2013)

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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## RainMan 2.0 (May 6, 2014)

This is a good question as it's happened to me to and it's never made sense


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## MT Stringer (Aug 15, 2012)

Ha ha, do you think anyone will notice? > J/K


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## DaninVan (Jan 1, 2012)

*The Dado Inspector*; 3 weeks on the NYT Best Seller list!


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## vindaloo (May 30, 2009)

Edit> Me numb nut, wrong answer.


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## Cherryville Chuck (Sep 28, 2010)

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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## harrysin (Jan 15, 2007)

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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## rpludwig (Nov 22, 2011)

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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## Duane Bledsoe (Jan 6, 2013)

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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## Stick486 (Jan 4, 2013)

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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## denis lock (Oct 26, 2007)

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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## neville9999 (Jul 22, 2010)

Duane there are some questions in this life that we are not meant to know the answer to, and there should be some. N


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## Quillman (Aug 16, 2010)

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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## mbar57 (Apr 20, 2015)

He did say he is making trim pieces and that yes people will notice. I've noticed this to but never worried because no one would notice.


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## Ghidrah (Oct 21, 2008)

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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## Stick486 (Jan 4, 2013)

rolling plunge it is...


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## Duane Bledsoe (Jan 6, 2013)

Quillman said:


> 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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## Herb Stoops (Aug 28, 2012)

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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## PaulH (May 30, 2012)

*Brilliant advice-(nota bene)*



denis lock said:


> 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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## RainMan 2.0 (May 6, 2014)

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


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## Herb Stoops (Aug 28, 2012)

RainMan1 said:


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


For what you paid for it it better not!

Herb


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## jw2170 (Jan 24, 2008)

Good question, Duane.

This happens to me when I try and rout the bottom of a dish...

Luckily, I can sand out the 'divot'...


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## RainMan 2.0 (May 6, 2014)

Herb Stoops said:


> For what you paid for it it better not!
> 
> Herb


LMAO ya no kidding eh


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## Barry747 (Jun 16, 2011)

I noticed the same problem with a bowl and tray router bit. I had set 3 turret stops to get to the total depth that i wanted. I noticed each time that the initial plunge left an impression at the point that I plunged down. Being a slow learner, I finally figured out on my second tray that if i gradually plunged down while moving the router and went over the area a couple of times gradually increasing the pressure until I hit the turret stop there ware no marks. I actually prefer this technique since it makes for a smoother cut. I'm not hogging out quite as much material at one time as I would if i plunged down to the stop them moved the router. This method does take a bit more coordination since you don't lock the depth until you hit the turret stop. Coordination also being a challenge for me, it wasn't until the end of my second tray that I finally mastered it. It was worth it since it saved a lot of sanding to get rid of the mark because the mark would have been plainly visible in the bowl cut.


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## Frankj3 (Oct 6, 2014)

Duane,

I'm not professing to be an expert. In fact I'm quite the opposite as I have zero experience with a plunge router. But I have a suggestion that may help.

I assume you are taking multiple passes, increasing the depth of cut with each pass. If it were me, before starting my final cut, I would put a piece of tape on the board or put a paper between the router base and the material. Then make the final depth of cut adjustment on the router and make the cut. When finished with this cut, DON'T CHANGE ANYTHING ON THE DEPTH OF CUT SETTING. Remove the tape or paper and then make another final cut. You would be making a very light finish cut with the router already locked in.

Again, this is just a suggestion. I don't have a plunge router but I have used this technique with my fixed based router when I want to make sure I get a really fine clean up pass to a set depth of cut.

Good luck.


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## Stick486 (Jan 4, 2013)

excellent tip Frank... psssst... duct tape works very well for that...


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## Frankj3 (Oct 6, 2014)

Stick486 said:


> excellent tip Frank... psssst... duct tape works very well for that...


Stick, you are right. I have also taped the base of my router with blue painter's tape, making sure not to overlap any pieces. A little gap between tape is ok.....just not too wide. Keep them as close as possible without overlapping. Just have to make sure it's adhered well. I make sure I go all the way across the base with each piece of the tape. I haven't had a problem with the blue tape but the duct tape is probably a better idea for its adhesion.

Good idea Stick.


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## harrysin (Jan 15, 2007)

It isn't a sin to rout a mortise with the plunge router unlocked, it just takes a little practice to hold the depth steady during each cut. On completion the router must be instantly retracted to avoid a friction burn circle, thus negating the method.


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## Duane Bledsoe (Jan 6, 2013)

I tried the plunge and slide technique last night with great results. That's a new kinda smooth right there. Worked like a charm. Now if only I hadn't tipped the router while making a rabbet along the edge, I wouldn't have made any marks at all. Fortunately, the rabbet is a recession being made for storm door hardware to fit, and will be covered. This is a big rabbet, an inch wide and half inch deep, and I don't have a dado blade for the table saw, so the router was my next choice.


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## Herb Stoops (Aug 28, 2012)

Duane Bledsoe said:


> I tried the plunge and slide technique last night with great results. That's a new kinda smooth right there. Worked like a charm. Now if only I hadn't tipped the router while making a rabbet along the edge, I wouldn't have made any marks at all. Fortunately, the rabbet is a recession being made for storm door hardware to fit, and will be covered. This is a big rabbet, an inch wide and half inch deep, and I don't have a dado blade for the table saw, so the router was my next choice.


Your learning ,Duane, only gets better with time.

Herb


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## Stick486 (Jan 4, 2013)

Duane Bledsoe said:


> sion being made for storm door hardware to fit, and will be covered. This is a big rabbet, an inch wide and half inch deep, and I don't have a dado blade for the table saw, so the router was my next choice.


table saw...
standard blade w/ intersecting 90° cuts...
cut close to where you need to be and finis w. the router...
or cut exactly what you need on the TS...

bonuses...
a usable parting bead left over...
less noise...
faster...
less mess...
less wear and tear on the cutters/bits...


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## Ghidrah (Oct 21, 2008)

I feel your pain Duane,

Yest. I set up to route the opening for a disk in the back of the current proj, it was the last cut required and I could begin assembling the pieces for glue up. I forgot to install the offset collar on the guide, as soon as I plunged the bit my good eye locked onto the collar on the bench about 5" from the project. The damage and tantrum done I went up stairs to sulk. Later I came up with an idea, (another set of cuts for me to possibly screw up) I routed some purpleheart for 3/8 and 1/4" dowel and then marked off 8 points.

The arrow shows the point of Biork, I think I need something in disk Ø, it looks barren .


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## Herb Stoops (Aug 28, 2012)

Good fix, Ronald, not sure what you are making, but it looks good to me, and you are doing a good job.
Herb


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## Marco (Feb 21, 2009)

RainMan1 said:


> This is a good question as it's happened to me to and it's never made sense



2nd that!


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## Marco (Feb 21, 2009)

Finally read the entire thread........ some very good information and techniques......... one of the reasons I love the router Forum!


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## Ghidrah (Oct 21, 2008)

Thanks Herb,

It's the back side of a 3 unit weather station, (clock, thermometer and barometer) I'll post component and completed pics when it's done. It's one of a couple 3 things for wifey and her Highfield Hall Restoration benefit thingy, she gave/donated (whatever) the bentwood clock I made last yr. Now they want more.

Here's the thing, I had to put the disks in to cover the layout Ø holes that I blindly bored through both sections, I didn't need a through hole in the backside.


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## Barry747 (Jun 16, 2011)

Ghidrah said:


> Thanks Herb,
> 
> It's the back side of a 3 unit weather station, (clock, thermometer and barometer) I'll post component and completed pics when it's done. It's one of a couple 3 things for wifey and her Highfield Hall Restoration benefit thingy, she gave/donated (whatever) the bentwood clock I made last yr. Now they want more.
> 
> Here's the thing, I had to put the disks in to cover the layout Ø holes that I blindly bored through both sections, I didn't need a through hole in the backside.


That's not a mistake. It's a design element. :laugh2:


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## Herb Stoops (Aug 28, 2012)

Barry747 said:


> That's not a mistake. It's a design element. :laugh2:


Turned out to be one ,didn't it. 

Herb


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