I think he's referring to the attachments for the Bergeon. It usually comes as a set with the Bergeon 6200. I have those and use them, but if a bushing is badly worn the center is not always that obvious even with the center finder. To me anyway.
If you examine the movement carefully you will see that the worn pivot holes are "egg shaped". The driving power forces the pivot to one side of the hole and over time that side of the hole wears forming the small end of the "egg". The large end of the "egg" is what is left of the original unworn part of the pivot hole. Under ideal conditions the Bergeon center finder will "find" the large end of the "egg", but if the hole is extremely worn so the hole looks more like a slot than an egg, then you may need to position the center point toward the end where the original hole was.
That's the easy part. Now you have to deal with the limitations of "bushing machines" generally. It's not a milling machine and there is usually a little "slop" or side to side movement of the reamer and the quill of the bushing machine. Simply inserting the reamer and turning the crank
will not ream the hole on true center in most cases. The oval shape of the hole will tend to cause the reamer to cut both the worn and unworn sides of the hole more or less evenly forcing the reamed hole to be off center. There have been a number of suggestions regarding how to solve this problem, but they all result in the unworn side of the hole being cut away first until the hole is round before continuing to ream the hole to side. With the Bergeon machine centered up on the original hole, I start with the smallest reamer that will go into the hole and cut, then turn the crank to position the cutting edge of the reamer to cut or "nibble" the unworn end of the oval hole until the hole is round. You will feel the resistance to turning the crank as the cuts. Use a back-and-forth motion of the crank until the hole is "rounded up", then use 360 rotations with progressively larger reamers until the hole is the right size. It is a mistake to begin with the final size reamer; start with the smallest reamer that will cut work up.
As for hand bushing methods, I never do hand bushing unless it is absolutely necessary, but you need to accomplish the same thing - "nibble" or file the unworn end of the hole until it is rounded up before reaming to size. It is largely an eyeball operation. With a mill or bushing machine, the original hole center is located, and the plates clamped "on center". With hand methods, once you start filing or nibbling your only reference point to the original hole center is lost. A lot will depend on your skill and good eyes. For hand nibbling I find that the appropriate size regular "D" shape reamer in a hand handle works better than a file because one can feel when it is cutting the high spot and when it begins cutting the entire diameter. It seems that those with the least skills often benefit the most from the best machines while some who call themselves professionals have used hand bushing methods for years. I'm afraid that's not me in either case.
RC
