As you can guess, mine aren't. I think it's causing alignment problems with the dovetails made with my Leigh D4. So, with a Porter Cable 690 router, what is the way I get my bushings centered? The bushings screw in to the center hole, so they can't be adjusted. I hesitate to enlarge the holes in the base - that would allow me to adjust the centering, but it would probably also allow the base to slip, game over.
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As I understand it, the key isn't to center the bushing (as you said they screw in and are fixed) but to center the whole sub-base before you tighten the screws that hold the sub-base to the base. My DW618 came with a "centering tool" (cone + pin). You can loosen the sub- base screws, chuck the pin in your collet, slide the cone over the pin, and then lower the pin+cone until it hits the sub-base. The cone centers the sub-base, and then you tighten the screws while the sub- base is held at the center by the cone. Did that make sense? I found a similar item available after a quick google search; it looks like it's all one piece with a smaller diameter than my "cone", so it might only work with the bushing already installed. Only $5.99 at Amazon, with free shipping if you can come up with another $19.01 of something you need.
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'm sure there are several other similar items available if you do some more detailed searching. Good luck, Andy
Most of the wooddorking outlets well a centering pin that chucks up into the router, allowing you to center the base on your router. I got mine at Rockler. Can't have cost more than $10, prolly less.
The problem in my experience is that usually when they tighten the screws at the factory they overdo it and they actually depress into the plastic. So as soon as you retighten the screws it goes right back where it was. Or even worse, it stays there long enough to make you think it's going to stay there, but the second time you do anything with it it goes back where it was. So my advice is either freshen up the counterbore surface, make new holes altogether, or get a new subbase altogether.
You can get close; maybe within a few mils. You stand the best chance with a plunger. They pretty much stay on the same axis through the plunge stroke. Not the case with your 690. See link for pin centering:
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******************************************************** As you can guess, mine aren't. I think it's causing alignment problems
That's why I purchased a DW 610 and later a DW 620. My 690 will not center and when you raise and lower the router in the base, it moves off center because of the design. I use my 690 in a table where it doesn't matter.
On the other hand, if you are careful not to rotate the router while using it in the Leigh jig, it should compensate for any eccentricy .
If you don't know how to change a countersink into a counterbore, perhaps you are in the wrong newsgroup, and maybe in the wrong hobby. Used to be, folks took great pride in being able to make their own jigs & fixtures. Nowadays, everyone wants to know where to buy a solution.
Aargh. That is disturbing because (1) I didn't think of it, but you're right, that inclined ramp and pin are going to move all over the place, and (2) making those fidgety little depth adjustments is unavoidable when setting up for the dovetails. Question - did you ever try the plunge base for the 690? I got the kit with two bases.
I thought of that when I was having trouble, and took pains to keep the router positioned exactly the same for every cut. Still had problems. It could be that when you flip the guides going from tails to pins that the eccentricity must be reversed or you get *twice* the error. I don't know. And I don't know if it's even possible to compensate for an error in-and-out as opposed to side-to-side, or an error that occurs at some angle other than a right angle or parallel to the work. I was never good at geometry.
To those who suggested an alignment pin, I've got one. The problem is securing the sub-base after changing its long-term positioning. I think new holes in the sub-base is the answer.
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Drill new larger flat bottoms holes in a different location on the base plate. Use pan head screws and use a centering point un the collet to center the plate.
the problem with the 690 is that as you adjust the depth of cut, the slop in the mechanism will let the base move off center.
for use in dovetail jigs (I have the Leigh), the best solution is to maintain the sma position in all of the routing. I use the cord position anh handles to make sure that I am always in the same orientation. It is important to keep the same positioning when you flip the guides to go from tails to pins. If you are carefull and consistant, you can get good results, but you do have to pay attention.....
I've been fighting with this issue for along time, and only recently decided to start looking for another solution (new router). I haven't made any decisions yet, but hopefully inthe next couple weeks I'll get a chance to really dig in and see what the options are....
It isn't absolutely necessary to center your guide bushing when using a D4, but if you don't, then it will be absolutely necessary to not rotate the router while you are cutting both the pins and the tails. Put a mark on the base of the router and then hold the router with this mark in the same orientation while you are using it. The more that the guide bushing is off center, the more important it will be to hold the router oriented the same way.
Even though I center my bushings before use I always hold my router in the same orientation while I'm using my D4R, or any other router application where a centered bushing or bit to router base dimension is important (which means almost any time the router is used without a guide bearing to reference the bit to the work).
I'm inclined the same way - put the 690 in the table and get another router for fine work. The Bosch D-handle EVS (forgot the number, but it goes for $200) claims to have an adjustable sub-base specifically for centering the bushings. It gets good reviews. Maybe this will be the 'treat' I get myself for saving $10,000 by building my own chest-on-chest. First I'll try new holes in the 690 plunging unit sub-base ......
===== Those are my principles. If you don't like them I have others. ===== {remove curly brackets for email}
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