Rebushing an out of round barrel bushing

[GuyMontag]

I'm stripping down this Bulova 10BRC and inspection showed this out of round barrel bushing. I *wont* be rebushing it as I don't have the skill yet but hopefully someday.  However, I was wondering if I were going to rebush it, how would I locate where the exact center of the bushing should be when placing the new bushing?

[rjenkinsgb]

My (not particularly expert) thoughts would be:

The outer bore for the ratchet wheel should be concentric with the original hole position.

And possibly simpler but a bit crude - The arbour only turns while the watch is being wound, so look which way the arbour is pushed by the action of the crown wheel while winding it? It looks like to the right by torque and down by the angle of the wheel teeth?

From that I'd guess that the lower right in the photo is the badly worn area and the upper left is the nearest untouched area, that could be used as a reference for a close fitting stake or drill to locate the plate before opening the hole for the bush. That's what I'd try - though on a junk movement first to be sure it worked!

 

[tomh207]

It’s a bushing, the hole will/should be concentric with the outer diameter, you don’t need to figure out where it should be.

Tom

[HectorLooi]

Idealy for this job, the barrel bridge should be mounted on a faceplate, roughly centred with the faceplate's centering pin. Then confirmed with an optical centering microscope.

[tomh207]

28 minutes ago, HectorLooi said:

Idealy for this job, the barrel bridge should be mounted on a faceplate, roughly centred with the faceplate's centering pin. Then confirmed with an optical centering microscope.

Only if drilling a new hole in the plate, this is bushed only the bushing needs replacing 

 

Tom

[GuyMontag]

39 minutes ago, tomh207 said:

It’s a bushing, the hole will/should be concentric with the outer diameter, you don’t need to figure out where it should be.

Tom

I'm not clear on what that means. My very limited understanding is that a larger hole would first need to be reamed and then a bushing placed in that hole. But given that the current hole is not completely concentric (it's somewhat oval), how is the exact center point determined?

 

28 minutes ago, HectorLooi said:

Idealy for this job, the barrel bridge should be mounted on a faceplate, roughly centred with the faceplate's centering pin. Then confirmed with an optical centering microscope.

Is a 'faceplate' part of a lathe? I don't know what a center pin is either, so I guess I'm probably way over my head on this.

2 minutes ago, tomh207 said:

Only if drilling a new hole in the plate, this is bushed only the bushing needs replacing 

 

Tom

Oh, I get what you mean now. Yeah, that makes sense. It didn't occur to me that the center part of the circle in the plate could be pushed out.

[HectorLooi]

2 hours ago, tomh207 said:

Only if drilling a new hole in the plate, this is bushed only the bushing needs replacing 

 

Tom

I don't think there was a bush originally. If there was an old bushing, just ream it out.

[Neverenoughwatches]

It's not bushed, just an ovalised hole in the plate. A bush would wear in its hole and not need re-centering in the plate...so just the bush pushed out and a new bush pushed back in.

[nevenbekriev]

I guess there is no bushing, I guess OP just used this word instead of 'bearing hole'. To press a bushing there the hole first needs to be enlarged or bored and yes, face plate on lathe is the normal choice for the way to do this. But, on the flat face of a brass piece may be turned small step in the center, with the diam of the arbor pivot, it can be used to center the bridge when gluing it on the face with shellac.

[caseback]

I'm no expert on faceplates (still making the clamps for mine) but could either one of these diameters be used to help center the piece? Or would the hole originally be machined in another setup?

Edited March 20 by caseback

[Neverenoughwatches]

31 minutes ago, nevenbekriev said:

I guess there is no bushing, I guess OP just used this word instead of 'bearing hole'. To press a bushing there the hole first needs to be enlarged or bored and yes, face plate on lathe is the normal choice for the way to do this. But, on the flat face of a brass piece may be turned small step in the center, with the diam of the arbor pivot, it can be used to center the bridge when gluing it on the face with shellac.

I guess the brass step would then be drilled out along with the new hole for the bush Nev.

16 minutes ago, caseback said:

I'm no expert on faceplates (still making the clamps for mine) but could either one of these diameters be used to help center the piece? Or would the hole originally be machined in another setup?

I was thinking the same a while back Cees, I cant remember when or what I was looking at, I expected the bearing hole to be concentric with the milled circles , but it wasn't, it will have been a cheap movement though. 

Theres a great video by " times radical " where he bushes the plate on a Rolex. The guys ways are...a bit controversial . But the tool he used was very nice.  A hand driven faceplate  with a rear mount holder for reamers. It looked very accurate. 

[caseback]

31 minutes ago, Neverenoughwatches said:

I cant remember when or what I was looking at

Might have been the movement you were working on when you set your lathe free 

[Neverenoughwatches]

51 minutes ago, caseback said:

Might have been the movement you were working on when you set your lathe free 

It wasn't an Actual repair attempt as such, I just noticed that the milling was not perfect.

[rjenkinsgb]

Having slept on it - and realised that I have now got a suitable lathe - my new approach would be to turn a bit of brass to fit the ratchet wheel outer bore and drill the centre to act as a guide to drill though as a guide for the bushing drill.

[caseback]

5 minutes ago, rjenkinsgb said:

Having slept on it - and realised that I have now got a suitable lathe - my new approach would be to turn a bit of brass to fit the ratchet wheel outer bore and drill the centre to act as a guide to drill though as a guide for the bushing drill.

That will work, providing the original hole was concentric with the outer bore. But as @Neverenoughwatches points out, that is not always the case.

[nickelsilver]

3 hours ago, caseback said:

I'm no expert on faceplates (still making the clamps for mine) but could either one of these diameters be used to help center the piece? Or would the hole originally be machined in another setup?

These other features can be concentric, but aren't necessarily and often simply aren't.

 

My preferred method is like Hector says, faceplate with optical centering. You can see quite easily the unworn portion of the hole and center on it.

 

But- many watchmakers simply ream out the hole with the jeweling tool, press in a bushing and off it goes. There's the false belief that the reamer somehow (magically?) follows the original hole, but what's really happening is the hole center becomes the average of the original center and worn center- and this is usually good enough that all's well. However, when opening a hole like this to take a bushing one would have to go through several sizes of reamer to get the hole large enough for a reasonable bushing, and each reaming operation risks drifting the hole a little more (even in a jeweling tool with everything just so they can drift).

 

10 hours ago, GuyMontag said:

 

Is a 'faceplate' part of a lathe? I don't know what a center pin is either, so I guess I'm probably way over my head on this.

 

This is a faceplate. In the image a "wobble stick" is being used to find the center. The pointed end goes in the hole, the body rests on the T-rest, and the extended end nutates as the faceplate is slowly turned, indicating the out of center direction. You can get very well centered with this method, but it takes more time than optical centering. It doesn't account for a worn hole though- it will average the location of the original and worn locations.

 

 

Edited March 20 by nickelsilver

[Neverenoughwatches]

2 hours ago, rjenkinsgb said:

Having slept on it - and realised that I have now got a suitable lathe - my new approach would be to turn a bit of brass to fit the ratchet wheel outer bore and drill the centre to act as a guide to drill though as a guide for the bushing drill.

My take on it is to make a wax chuck that has a tight arbor to take the plate or bridge bearing. Once the plate is cemented up, the arbor is drilled out with the new bush hole.

1 hour ago, nickelsilver said:

You can get very well centered with this method, but it takes more time than optical centering. It doesn't account for a worn hole though- it will average the location of the original and worn locations.

So the wobble stick method is a bit more accurate than multiple reamers in a jewelling frame ?  Taking just one drilling operation in a faceplate.  What are seeing through your optical centering device Nicklesilver ? 

[nickelsilver]

1 hour ago, Neverenoughwatches said:

 

So the wobble stick method is a bit more accurate than multiple reamers in a jewelling frame ?  Taking just one drilling operation in a faceplate.  What are seeing through your optical centering device Nicklesilver ? 

The wobble stick is more certain to keep the hole on center. Then the hole gets bored in the faceplate, with the slide rest. Drill is another very uncertain way to put a hole in a true location. It can work, but it often doesn't work perfectly.

 

I see the part through my optical centering device!

Edited March 20 by nickelsilver

[caseback]

As a alternative optical centering microscope, I've ordered something that is called an "usb otoscope". Apparantly it is a tiny camera meant for looking in one's ears.. but it looks slim enough to fit in the tailstock. Worth a shot imo. I'll let you know if it works or not..

[Neverenoughwatches]

10 minutes ago, nickelsilver said:

see the part through my optical centering device!

Sorry Nicklesilver I meant - are you lining up the center of the hole with a cross hair ?

[nickelsilver]

1 hour ago, Neverenoughwatches said:

Sorry Nicklesilver I meant - are you lining up the center of the hole with a cross hair ?

Yes, my scopes have cross hairs and concentric circles. There are some dedicated centering scopes with one hair, which is all that's needed. You move around until it's near the border of the hole and it just serves as a reference.

 

 

I do lots and lots of faceplate work, so I have a dedicated setup that's a bit extravagant but for all the use it sees worth it. The faceplate is on a 35mm quill, which can switch out between a measuring microscope (a Hauser M1 jig borer, but it only gets used as a scope) and a short Schaublin 102 lathe bed. Parts get glued to a little base, then that goes in the faceplate and gets centered on the scope (the base gets tapped with a brass bar, having the part glued like this avoids any damage), then over to the lathe. Centering to a couple microns takes about 30 seconds.

 

This was a LeCoultre 409 that needed a new jewel. I bored out the rub-in setting, and put the new jewel in a bushing that mimics the look of the setting.

 

 

 

 

 

 

Edited March 20 by nickelsilver

[Neverenoughwatches]

4 minutes ago, nickelsilver said:

Yes, my scopes have cross hairs and concentric circles. There are some dedicated centering scopes with one hair, which is all that's needed. You move around until it's near the border of the hole and it just serves as a reference.

 

 

Thats cool, are the hairs integrated into the eyepiece ?  

[GuyMontag]

 

6 hours ago, nickelsilver said:

But- many watchmakers simply ream out the hole with the jeweling tool, press in a bushing and off it goes. There's the false belief that the reamer somehow (magically?) follows the original hole, but what's really happening is the hole center becomes the average of the original center and worn center- and this is usually good enough that all's well. However, when opening a hole like this to take a bushing one would have to go through several sizes of reamer to get the hole large enough for a reasonable bushing, and each reaming operation risks drifting the hole a little more (even in a jeweling tool with everything just so they can drift).

I can see how even a new bushing that isn't completely centered could be 'good enough' for some as I was surprised just how well this 65 year old watch that hadn't been serviced in many decades was running, especially the amplitude given how worn that barrel arbor bearing is.
 

 

 

6 hours ago, nickelsilver said:

These other features can be concentric, but aren't necessarily and often simply aren't.

 

My preferred method is like Hector says, faceplate with optical centering. You can see quite easily the unworn portion of the hole and center on it.

 

But- many watchmakers simply ream out the hole with the jeweling tool, press in a bushing and off it goes. There's the false belief that the reamer somehow (magically?) follows the original hole, but what's really happening is the hole center becomes the average of the original center and worn center- and this is usually good enough that all's well. However, when opening a hole like this to take a bushing one would have to go through several sizes of reamer to get the hole large enough for a reasonable bushing, and each reaming operation risks drifting the hole a little more (even in a jeweling tool with everything just so they can drift).

 

This is a faceplate. In the image a "wobble stick" is being used to find the center. The pointed end goes in the hole, the body rests on the T-rest, and the extended end nutates as the faceplate is slowly turned, indicating the out of center direction. You can get very well centered with this method, but it takes more time than optical centering. It doesn't account for a worn hole though- it will average the location of the original and worn locations.

 

 

Thanks, seeing that photo really helps in understanding what was being said.

Edited March 20 by GuyMontag

[nevenbekriev]

7 hours ago, Neverenoughwatches said:

My take on it is to make a wax chuck that has a tight arbor to take the plate or bridge bearing. Once the plate is cemented up, the arbor is drilled out with the new bush hole.

This is what I tried to say in my post

[Neverenoughwatches]

2 minutes ago, nevenbekriev said:

This is what I tried to say in my post

And i think you said it very well Nev....otherwise I would have not known what you meant