THE TEMPLET COLLAR GUIDE
Collar guides are one or 2 piece rings that surround the router bit near the subbase of the router. They act very much like a shank mounted bearing on a pattern bit. The ring (collar), usually fastened to the router subbase, is pulled against the templet as the router is slid-along the pattern (templet). All the while, the cutter is extended below the collar and cutting sideways into the stock beneath the pattern. The pattern is duplicated on the work but since the collar is always larger in diameter than the cutter the work is always larger than the pattern, usually by no more than 1/2".
The collar guide, like way too many woodworking tools, is not a precision instrument. Do not expect ball bearing tolerances and performance from collar guides; the cutter is rarely in the center of the collar. One way to manage this misfortune, in my view, is to view the collar guide system as an approximation. You can get close on a reasonably predictable basis. However, if accuracy and precision are paramount, do the rough cutting with a collar guide system and the finish work with bearing guided tools.
Surprisingly, the dovetail templet industry is based "around" the collar guide, how can that be?
The most demanding joint in routerdom is dependent on one of the least accurate guide systems! Well suffice it to say that if the collar is used with the same few radians (points of contact) on the ring and the router not rotated during its excursion, its error will be constant. What this means is that the cuttings will be the same from stick to stick but they may shift slightly from center.
There are stops on these jigs and they can be adjusted to compensate for the translation. The work can be repositioned so the error is under your control and the pins ultimately enjoy intimacy with sockets or tails. There is more to the story and in my "Router Book" there is a section on their use, sizes, advantages, disadvantages, and control.
I mention all this so you won't be disappointed with my subbases or those from the competition.
My plates are made to match the casting whole patterns of the routers they're designed for. They are drilled from precision drill templets and consistent from plate to plate to within a few thousandths of an inch. The hole patterns in my subbases are on the same circle, centered on the diameter of the plate, and concentric to the circumference of the base (round or offset design). That is all predictable and inspected before shipping. What I don't have control of is your router.
There are machine tolerances in my subbases and in the production of routers that can add up substantially or perhaps cancel one another. These discrepancies are what account for cutter/collar eccentricity; .010" eccentricity is common and .050" to .060" is not crazy either. For example the spindle (armature), collet, and bearing seats of the router have their tolerances. The motor barrel has its slop with respect to these variables. The bore of the base casting has to be centered to the base casting's hole pattern; there is tolerance for this. The screw hole drill pattern has its allowances. The are more components in a plunger than the fixed base and this order of error should be expected with the plunge router too.
Now enter the collar and its slop, the tolerance in the subbase and the slop in the screw holes to fasten it to the casting. Reground and some new cutters are not necessarily smack concentric to their shanks. Bosch, Makita, and now Milwaukee have all converted to the default Porter Cable 690 3 hole subbase pattern on their small routers. Not having PC's spec at hand, they took their best guess but they're all different.
Furthermore, routers change their axes slightly with changes in depth. A centered cutter at 1/4" cutter extension may be eccentric at a depth of 3/4". So a custom made subbase may only be centered at the depth it was measured or created from. A monster out of control, so don't get crazy if your cutter is not smack center in the middle of your collar. Machine precision and accuracy in woodworking tools are still in the dark ages. Your black Bakelite subbase was not machined at all!
Problems with subbases, collars and cutters? Email a brief scenario of your problem, the solution may be simple.
Collar guides in sets or individual pieces available from Rockler or any Porter Cable dealer.
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Copyright © 2009 Pat Warner
Last modified: Tue Oct 17 06:42:54 PDT 2006