Can't get clean plunge router cuts

[djwong]

Been a while since I posted...

I have a 1010 router, and cannot seem to plunge cut without causing the hole to be off-sized - see photo...  Happens when I initially plunge, and when I "un-plunge" the bit.  I have used both a 8mm shank 2-flute straight bit, and a 1/4" shank spiral uncut bit.  The results are the same.  In both cases, I am using the edge guide.  I am making shallow plunges of 1/16" - 1/8".  I tried as best I could to measure runout with a dial indicator, and there seems to be little or none at the motor shaft, and at the router bit shank.

I am new to routers, so I am assuming that this is a technique issue, but I don't know what I should change.  I am holding the edge guide tightly against the wood, and let the bit spinup before plunging.

Any suggestions would be appreciated.

David

 

[PaulMarcel]

I'm going to guess by the picture that your edge guide was on the top edge and you ended the cut here.

When plunging a bit, one side of the bit is "climb cutting" and will pull the router into that direction.  You want that pull tendency to work for you so you want it to pull the edge guide tighter to the stock.  If you are pushing the router to make the groove, you want the edge guide on the right of the router.  The 'climb cut' happening up near the front of the cutter is on the left side and will try veering the router towards the left as you push it.  That will pull the edge guide tight to the stock.

That tendency to move the router is more pronounced when you first plunge.  Usually you shouldn't get it much when you 'unplunge', but that assumes you don't have any lateral motion.

 

[ccarrolladams]

David and Everyone,

Effective use of routers requires practice and experience. In some ways plunge routing is more complicated.

Paul explained about climb cuts. From the photo it seems this project is a dado blind on both ends, since "unplunging" is mentioned.

The downside to making dadoes with a router using a bit the width of the finished dado is that one side of the cut will be "climb"

A popular work-around is to use a bit smaller than the finished dado. Then slide the guide over and finish the dado to correct width pushing the router in the opposite direction, so it is "non-climb" on the finished side. Again as Paul stated, try to make the "climb" work for you by the way you arrange the router guide.

 

[djwong]

Thanks to both of you for your helpful comments.  I am aware of the effects of climb cutting, but was surprised that it was so pronounced at the start and end of the plunge.  During the straight portion of the cut, the sides are clean.  These were practice cuts.  In my actual project, I need to make some stopped dados, so using a router would be much faster and cleaner than using a plow plane like I would normally do for through dados.  I do intend to use a smaller bit and "creep up" on the final widths.

Not having experience with a router, is it fair to say that all initial plunge cuts will suffer from climb cutting effects, for the first pass?

 

[PaulMarcel]

Like Carroll said, it takes some practice.  You shouldn't expect to get a wiggle on the start and end of a stopped dado.  If you plunge and route so the edge guide is to the right, you should be fine.  Also, at the end of the cut, I usually pull back a hair before unplunging; you shouldn't be cutting anything as you already plowed the groove, but it gets you away from any stock (i.e., the end of your cut) that a wiggle while unplunging will grab and move the router.

If you opt to do two-pass dados, remember to do them in the correct order to avoid a climb cut on the second pass.  For the first pass, the bit is buried so there's just a veering tendency, but not a "grab and run" like you'd get climb cutting with the cutter only halfway in the stock.  That said, for a multi-pass dado, you want to make your first pass closest the outside edge so your second and subsequent passes have the stock to cut on the left side of the bit.

I use a KM-1 from Bridge City to adjust the position of the router to exactly size the groove in two passes.  If you haven't seen that measuring tool in action, give it a look here where I show how to use it on a number of tools; crazy useful for the tablesaw and bandsaw, too. 

 

[djwong]

Thanks again Paul for clarifying things.  I'll go back to garage for more practice.  Routers have always scared me for their ability to quickly ruin a workpiece - especially in unpracticed hands like mine.  I got a 1010 for its small size and ease of handling.  I really like the dust collection and the potential for amazingly clean cuts.  Just have to get a competent operator.

 

[PaulMarcel]

Ah, I was editing my post to add the KM-1 information while you replied.  Might want to give that a look.  Sure beats the "nudge nudge cuss nudge" for sizing a groove.

 

[harry_]

I very rarely do stopped dados with a router. Will the climb cutting be an issue with less stock removal like from going from a 3/8 for a first pass then to 1/2 for a cleanup pass? This wai a correctly positioned rail could just be left in place?

 

[ccarrolladams]

Way back in history, when "3/4 inch" plywood was actually 0.750" thick and a router with a 700 watt motor was considered extra powerful, I often had to make dadoes using such a router. I would have preferred to use a dado head on a large cabinet saw in the shop, but sometimes I needed to make dadoes on site with just a router. Frankly I was not overly concerned that when I used a 3/4" bit the climb-cut side of the dado would be slightly ragged. From a strength standpoint it did not make much difference. To keep the job neat, I would do my best to keep the climb-cut side in a position where it was hidden. That is, to the bottom of low shelves and on top for shelves about eye line.

What I have always found to be the case when making dadoes in plywood is that it is best to slow down if the router is not powerful so that all the cuts are full depth, typically 3/8". Doing so really helps control the tendency for the bit to climb.

When I use the two-step dado approach, for an approximate 3/4" dado, I use a 1/2" bit, so that the final pass on the far side is removing a substantial amount of wood. For me this results in a cleaner dado. Of course today most cabinet plywood is 18mm thick, so the dadoes are typically 9mm deep. I mostly use a 12mm bit.

On the CNC machines I program the movement such that the climb side on the first pass will be cleaned by the second pass going the other way. Both passes being full depth.

I also have a bench router, which is sort of like a radial arm saw with a router instead. I arrange the job so I push the initial cut, slide the job to the final stop, and pull the finish cut toward me. That machine is also very efficient making rabbets. I just use a bigger bit. To collect dust that router surrounds the bit with a brush, similar to the arrangement on my CNC machines. This means I cannot see the rabbet or dado being cut. Long ago I became confident with the calibration of that machine.