Using a KWM Style Centering Point

[Rob M]

When bushing a clock plate can I use a KWM Style Centering Pointer instead of filing away the same amount of material opposite of the worn area of the plate? Seems to me that if I use a Centering Pointer ($7 at Timesavers) I wont have to file the hole any larger than it already is....

 

[bruce linde]

no. the centering point will follow the path of least resistance to whatever the 'center' is of what you've got.

filing is the way to make sure a centering point... or drill... or reamer... finds its way to as accurate a center as possible.

 

[wow]

Rob, are you using a bushing machine or a hand bushing tool?

 

[Rob M]

Rob, are you using a bushing machine or a hand bushing tool?

I assume it would not matter if I am using a bushing machine or not, correct? I am hand bushing but a centering bit would work the same either way correct?

 

[wow]

I assume it would not matter if I am using a bushing machine or not, correct? I am hand bushing but a centering bit would work the same either way correct?

The centering bit is used in a bushing machine to center the hole you are cutting while locking down the plate in the machine. It locks into the shaft and sets up the hole so the reamer will cut the new hole in the center of the original pivot hole. Perhaps I am wrong, but I can’t see how it would help find the original center using a hand bushing tool. That’s the reason I asked the question. Maybe others will
know more than I.

 

[bruce linde]

guess you don't like my answer? 8-(

i suppose if you had a centering bit mounting in something that could not possibly shift under pressure, and a front or back plate mounted in such a way that it could also not shift under pressure, it might be possible to maintain hole center when reaming.... but i've not been able to make that happen.

try drilling reentering a hole slightly in a piece of brass using a drill press. even with the piece of brass clamped so it can't move, the drill bit is going to flex and follow the open road of least resistance ... so to speak.

what's the big deal about filing opposite of the wear in a pivot hole? i find it's one of the more rewarding parts of the process as i 1) start observing really closely under magnification and get a better sense of what i'm dealing with, and 2) maintain the legacy hole center. yes, that might have been shifted by someone else previously, but the tiniest bit of filing means i won't be compounding any errors.

 

[Rob M]

Agree on all fronts. I did not accurately explained my process - sorry. I use my drill press (power off) to bush. I have a mount on my drill press that holds my clock plate and I planned to use a centering bit to align the plate so I can ream out the center of the hole in the plate. I believe since the same process is used on a bushing machine that I would get the same results. When using a KWM or Bergeon Bushing machine must the users file the plate to ensure they get the center or can they just use the centering bit?

 

[R. Croswell]

As already explained, the centering point is intended to position the plate on center in a machine where the plate is securely clamped in place. Depending on the precision of the machine, the reamer will ream true center. The only use I can think of for a centering point in a hand bushing situation is that the point will settle into the original (larger part) of the worn pivot hole and when a light is placed under the plate, the worn section of the hole is visible so one knows which direction to file or nibble the hole to hopefully end up with a bushing on center.

RC

 

[bruce linde]

i (obviously) think you need to file... but you could experiment and get one of those tools that lets you true up stuff in a lathe... clamps on, and has an arm that comes out and touches the stock in (for example) a three-jaw chuck to make sure it's centered. you could put one of those on your centering bit and see if shifts at all if you DON'T file. i think it would, though.

 

[R. Croswell]

Agree on all fronts. I did not accurately explained my process - sorry. I use my drill press (power off) to bush. I have a mount on my drill press that holds my clock plate and I planned to use a centering bit to align the plate so I can ream out the center of the hole in the plate. I believe since the same process is used on a bushing machine that the same process could be followed. When using a KWM or Bergeon Bushing machine must the users file the plate to ensure they get the center or can they just use the centering bit?

In all my years of bushing clocks I have never filed a pivot hole and almost always use the Bergeon bushing machine. I prefer the "nibbling" method which is first use the centering point, clamp the plate, using the smallest reamer that will enter the hole, use partial rotations to cut away in the direction of where the original hole was until the hole is round. With this bushing machine one can feel when the cutter has rounded the hole, then go to the next size reamer. One needs to know the limitations of the machine being used. I know that my Bergeon cannot hold the reamer on center if I just plunge in as the instructions say to do. You will likely experience the same issue with the drill press. I good quality milling machine with the proper clamping system can mill a round hole directly centered over an oval hole. I suggest that you check your drill press for runout and looseness with a dial indicator before trusting it to hold center without any help. Very likely you will need to file, nibble, or otherwise center up the worn hole if you expect it to ream true. Take an evening or perhaps several evenings and read all the threads on how and how not to install bushings and all the arguments pro and con for each.

RC

 

[wow]

Like RC, I have never used a file. I can see where using a centering bit in a drill press may work. Especially if you have a way to secure the plate. You may also be able to use KWM reamers in the same way RC mentioned to nibble away the hole and move it to center. I have never tried it in a drill press.

 

[shutterbug]

I don't file either. Center with the point, lock down the plate, nibble until the hole is round and then ream it.
A good drill press, operated by hand, should work fine.

 

[disciple_dan]

a centering point will settle into the original (larger part) of the worn pivot hole

edited from post #8
Well, I'm back to questioning my bushing machine technique. I'm working on a 340-020 that I think is a lot less forgiving of error than the 341 is. Pendulum clocks seem to be more tolerant of friction.
You may have seen some of my posts that state I have been using reamers for centering the bushing. While I have had pretty good success with that method, I'm having to rethink it.
As per an observation by RC in his quote above, I think that a centering point will always find its way to the larger part of the hole and that is always the original part of the hole. The pivot is smaller and t a smaller hole in the side of the larger one.
If that is true(and I think it is) then with a true centering tool in a precision bushing machine, if there is such a thing, you should be able to get very close to the same as the original center. You really don't even have to know the direction of wear.
I'm going to look into that more. What do you guys think?
Danny

 

[Willie X]

Yep, you must file or nibble. A drill press (or a bushing tool) has WAY to much flex to hold the cutter at the position found by the centering tool.

If you want to do it your way, you will have to buy a mill and use tiny end mill cutters, followed by sizing the hole, using factory reamer/s.

Willie X

 

[Uhralt]

And don't forget that the centering point may actually be off center, especially the economy version of it. I had one that was clearly off center. When I tried to straighten it, the arbor broke off.... Test it in a lathe before you rely on it.

Uhralt.

 

[wingardclocks]

I never file with machine either

 

[bruce linde]

uhm... it's not what you've got, it's how you use it.

it doesn't matter if you file or nibble... you're going to have to do one or the other to maximize your ability to maintain the original center of the hole.... unless you can guarantee no runout on your setup (even with a milling machine.... and by 'guarantee', i mean post a video showing a dial indicator confirming your setup is true )

i would also posit that a very large amount of bushings were done by hand before commercial bushing and milling machines came along. i suppose if you have the right equipment and are willing to take the time to do exact setups and can guarantee no runout and that your drill bit or centering tool will not drift as it goes into a not-perfectly-round hole then there is some ideal out there worth chasing.

in the meantime, if it takes maybe a minute to nibble or file accurately. why over-complicate things?

is what i think.

 

[shutterbug]

Just a hint on testing your centering point. Clamp a plate into the tool, insert the point and lower it to the plate. Turn the point one rotation and look at the imprint. If it's not a single point, the point is off 1/2 the circle diameter.