This is posted in the hope of triggering a wider discussion on hand held router capabilities/quality/inaccuracies. (and work arounds if they exist)
Also on the relative capabilities of differing brands and models.
We ran up against the limits of a lightly used (i.e. not worn) blue Bosch GMF 1400 (UK spec) plunge router when cutting a 45 x 39 deep x 400mm long parallel sided and flat bottomed slot in beech via multiple passes of about 5mm depth. This using a 50mm cutting length x 19mm dia straight sided bit.
The router was set up with two fences on extra long mounting rails - one at each side of the work with the router in between. The fences were pushed in tight and definitely did not permit movement.
It turned out despite this that when plunging to a set stop the cutter was going perhaps 0.2mm deeper at that point so that its end left a circular impression in the otherwise flat base of the slot. i.e. once the plunge was locked the cutter was lifting by this amount..
It turned out too that during the plunge the cutter was tipping out of vertical enough to very obviously mar the sides of the slot.
It was also being pulled about 0.2mm past the set line of cut by the cutting force - enough to move it from one side of a pencil line to the other.
Examination showed that these inaccuracies were down to sloppy tolerances in the guide posts - that the cutter was free to move around during the plunge and the tool free to tip upon hitting the offset depth stop.
It's pretty well held once the plunge lock is done up tight but that's not much help.
A fixed base router clearly won't suffer from this problem, but it would be difficult and risky to cut this slot without plunge capability.
We having used the router primarily for bearing guided profiling had not previously seen the problem.
It's not at all acceptable for this sort of work (or for plunging to cut accurate mortises), and is disappointing in what once was a quality brand.
We're going to have to replace the router, but the question is with what.
Does anybody have any feeling for how the other brands stack up in this sort of situation?
People are paying double to buy Festool routers, are they in fact well enough engineered to avoid these and other problems caused by sloppy fits and tolerances?
Better still is there a brand that's a bit more cost effective that does so?
Thanks..

For over 30 years I have been consistent in using Porter Cable routers. Mostly stationary fixed base, but we have used several of their plunge routers without any unusual problems due to the routers themselves. We have used the plunge routers in a variety of jigs in making louver slots for exterior shutters, plus mortise and tenon joints, where the tenons may be 1 1/2" in length. I do find that plunge routers tend to be tall in height, due to the housing that is allowing the plunge travel. This sometimes makes the router feel top heavy, and easy to tilt some, even in a jig. But many of my guides are shallow to allow ease of travel with less friction, so I'm not trying to control tilt. We try to do that with a steady hand, but sometimes the torque of a deep cut with a 1/2" bit gets the best of us. But this is no fault of the router. I do currently use two different Porter Cable plunge routers. One has the basic 1.75 hp motor, and it is a lighter router and easy to handle. But accurate in my opinion. The 1.75 is the basic motor found in most PC routers. I also use 3.25 hp router which is a 5 speed. It is a large router and very heavy. I believe it is best used in a fixed position on a router table, which I do at times. But in certain jigs where I have better control, I use it as a hand held router, mostly where I do not have to lift it constantly. As for as being reasonable in price or expensive, I believe that is relative to every woodworker in a different way. I'd suggest simply looking on line and making that decision if you are interested in Porter Cable. I will add I sometimes rework my routers and I find the parts easy to get and not too expensive.

Hi Mitch. Sorry, but I've been away.
One difficulty from this end is that we're in Ireland and Porter Cable is not sold here.
A while spent tonight to disassemble and measure up the Bosch GMF 1400 router described above shows clearly why in plunge mode it's definitely not a precision tool.
I've attached a couple of pics which show the problems experienced while routing a 39mm deep slot in beech - the white marks in the side of the slot in the first pic are filler in divots caused by the cutter tilting and perhaps moving sideways while plunging.
The circles in the bottom of the slot are the pretty deep marks produced at the locations where the tool went over depth when it was plunged to the final stop.
It performed OK once the plunge lock was done up tight - but doing this seems to lift the cutter a bit. (or else the cutter was permitted to drop below the nominal setting when plunging to a stop with the lock undone)
The big question is whether other mainstream routers are any better. If not then is say the the Festool 1400?
It turns out that only one of the two guide posts runs in a bronze bushing, it's a relatively small 5/8in dia. The fit is by precision engineering standards very loose. Multiples in fact of the clearance specified by the tables for even a basic class 3 sliding fit.
The looseness of this bush alone likely permits an angular misalignment which allows the cutter to move up and down within a 0.008in plus range and which would also take it out of vertical.
The other less than 1/2in dia post just slides in a rubber o ring mounted in the plunge housing which while fairly stiff must deflect when pressured. Since it realistically only prevents rotation around the other post this would translate into a sideways deflection of the cutter.
The result of this arrangement is that the router motor and cutter are cantilevered from a single rather skinny post which is well offset to one side.
This single post, the overhang and the fairly light base in combination likely result in significant flexing too too.
The bottom bearing is tight, but there's an audible clunk from the top bearing when the cutter is pushed sideways - which must mean a sizeable clearance there.
More movement...

View higher quality, full size image (3072 X 4096)

View higher quality, full size image (3072 X 4096)

If this is an ongoing product, would it be possible to fixture it on an inverted router, such as C.R. Onsrud or similar?
An inverted router can probably be pick up fairly cheap since the proliferation of CNCs

I managed to accidentally delete the opening line on my message above Jim which thanked you for the input.
I edited the message but the system somehow didn't put up the edited version...