Using bearings in dovetail jigs

[me]

Basically all my problems with dovetal jigs seem to be in getting (and keeping) the dovetail bit centered in the bushing. I got to thinking that Keller and others are right - use a bearing. I have spent countless hours on the internet looking for 7/16 OD for 1/4 bits. Seems it is a size totally skipped by everyone.

So, this brings me to several questions:

1.) Does anyone know a source for 7/16 bearings? 2.) Is there a reaon not to use a bearing on a bushing designed guide? The manual warns against it like it would cause the end of life as we know it if you do. I accept the fact that it might wear the fingers slightly more and would be willing to accept that. 3.) If I can't get a bearing and am stuck with a bushing, does anyone have suggestions on routers/bearings that would be most friendly? I see Leigh has a bearing that allows you to micro-adjust the size of the bearing. Seems there should be a router or bushing that somehow allows you to click in a perfectly centered bit. I use a a centering bit on the bushing but it doesn't take too much use before it is slightly off center. Tightening it usually only worsens the problem. I've tried it on 3 different routers with two different bushing sets. They have all been Porter Cable type bushings.

Thanks for any suggestions.

[Leon]

Most bearings have a shorter life than the bit, especially if you have the bit resharpened. If the bearing starts to wear, it no longer holds its tolerances. IOW it may allow the bit to cut deeper than when new, this would result in inconsistant spacing cuts. Also if the bit ever locks up it will begin to chew into you template guide immediately and then that particular location will forever from that point forward telegraph the damaged shape of the template to you work. As far as being willing to accept template finger wear, that is going to cause you more problems that a guide bushing that may be off center a slight bit. Again with fingers that are worn, they are not going to wear consistantly and unevenly so your tails and pins are no longer going to be cut so that they mate properly. You may not be able to get the tails and pins to fit together.

The better routers have a base that can be centered to the bit. There are aftermarket bases that will allow this to be done with routers that do come with adjustable bases. What you need is a centering point, basically a pointed bit like tool to mount in the collet and adjust inside the bushing while the base is loose. This will center the base. Then you tighten the base adjustment screws. Adjustable bases typically use pan head screws in over sized holes in the base. This allows movement of the base for centering. The pan head screws do not try to center the screw in the holes as flat head counter head screws do.

Now having said that, proper router technique can lessen the problems associated with a guide bushing that is not centered with the bit. If the bushing is off center the bit will tend to cut off center and more so to one side or the other between the template fingers. This will not be a big problem as long as you make all of the cuts with the same off center off set. Proper router technique will require you to "always" hold the router in the same orientation at all times when making cuts. Basically if the handles on the router point at 9 o'clock and 3 o'clock when you begin cutting the material, keep the router handles in this position for all cutting. DO NOT let the router rotate during any of the cutting. I and many others for years successfully cut tails and pins with off centered guide bushings. A perfectly center bushing typically only affords you the ability to hold the handles in different positions.

[smandel]

the dewalt 621 router I use has a removable base insert. (for large bits). The insert takes a bushing, and it's dead - on. I've checked the best I can, and it seems that all I have to do is put the bushing on, and go - I've never had to use the centering pin that comes with the bushing set

shelly

[Kevin]

Often the subbase has been overtightened at the factory and the screws have left a slight indent in the subbase. This results in the subbase always working its way back to where it was originally. You might try a aftermarket subbase .

Another thing that might help is to wax the underside of the subbase periodically. This lets the router glide around on the jig a lot easier, so you aren't slamming it around into the guides. I was shocked at the difference it made to the whole experience. The downside is when you let go of the router to flip the stock around it starts moving around by itself.

-Kevin

[routerman]

Caveat, I do sell a center-able subbase. Now, in my view, bearings center the cutter better than anything but for a price. They spin (decelerate) like hell and when they hit the templet the templet can transfer some material to the bearing. Now then, a bearing with aluminum stuck on it will abrade the next tine, collect more metal etc. and gall the templet over time. Not so serious on phenolics but can be on thermo-plastics. Moreover, as the roller bounces along the templet tines it transfers these undulations to the work. As such, the fit of the joinery can be sloppy or tight. Study the link.

plate will get you within a few .001"s of center. Secondary advantage: The ring won't spin and spoil your templet and your tool (cutters & collars) selection latitude is far greater than bearings and cutters to go with those bearings.

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[Chris Friesen]

A bearing supply house. Look in the yellow pages.

Chris