Bushing for clock arbor

When a clock needs bushing, the hole is usually extended to one side. When drilling the hole for the new bush how would you keep the hole in the correct place without allowing the drill to centre itself mid way in the stretched hole?

Thanks, David

Use a small end mill

Hello again, David ... Good question !

When doing this by hand: The trick is to file the unworn side od the hole to match ... thus making it oval rather than egg-shaped ... The broach should then self-centre.

[ There are of course tools available to do the job mechanically. ]

MichaelG.

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Edited to add emphasis to 'broach'

Edited By Michael Gilligan on 29/08/2019 08:35:45

Michael Seeing that a lot of clock pivots can be 1 mm or even less diameter how small a file can you get ?

Roy

Hello Michael, Ahh! thank you, simple when you know how : )

David

Edited By David Noble on 29/08/2019 09:01:40

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Certainly smaller than it is within my personal ability to use !!

MichaelG.

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P.S. ... My edit was not a reaction to your post: I simply wanted to empasise to David that, for hand-work, the hole is best opened out with a five-sided cutting broach [not a drill]

Michael, thank you, yes, I understood the emphasis.

Thank you Roy, an end mill would work but I was interested in how a clockmaker would do it.

David

David, you might want to get to know a Preacher.

This is a device with three sharp prongs. Regard it as being a three pronged punch. You place one prong exactly in the location of where the arbor should be sitting and then orient the device to allow the other two to sit somewhere on the clock plate and then give it a sharp tap. This will leave two reference dimples that you can refer back to in order to verify your new arbor hole is in the correct position. The three prongs are usually set to have a uneven spacing so you cannot get the orientation wrong. You can knock one of these up in no time.

If the hole you are working on is really adrift you can use the Preacher to set the two references and then drill the arbor hole out completely oversize and plug it with a piece of brass. You then replace the Preacher in position and tap it gently once again to get a new centre in the plug to re-drill the arbor hole in the correct position. If you put a slight taper on the drill out hole with a reamer/broach then the plug can be tapered to match. The taper needs to be from the inside of the plate so the plug is being 'pushed' deeper into the taper by the arbor (in practice it doesn't move). Use a graver to get the taper on the plug. Overall it is quite satisfying process to do.

You will find that finishing of the plugged hole can be done to completely remove any witness marks that this remedial work has been done. Clearly you don't want to mark the plate surface when removing the excess of the plug that with even the best skills will initially be sitting proud. It helps if you have a piece of 35mm camera negative, punch a similar size hole in it to the plug and then glue it to the plate surface to sit around the plug. This will protect the plate until you get the plug pretty much flush.

I am sure Michael will be able to find you lots of references to Preachers and the process I have outlined.

Alan

Hello Alan, that's fascinating, thank you. I wonder where the preacher got its name?

David

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... and I'm sure than anyone else should be equally capable !

I was simply describing how I was taught to do the job.

MichaelG.

No offence Michael, you just seem to be respected as being the go to reference source for all things web.

Alan

I was taught to use your thumb to press the 5 sided clockmaker's broach over toward the lesser worn side (not too much). Then broach out whilst keeping upright then bush in the usual way.

That is the French technique and very good it is. A fair number of old English clocks show an older technique. Use a round ended punch and anvil to belly the brass on the worn side. A few dents around the hole on the worn side and then use the broach and then burnish with a smooth broach. This technique is also seen on cheap old clocks where in former times a bush would not be worth the bother. Nowadays mending a clock is an expensive job so the French technique it is.

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Thank you for that, Alan ... very civil.

I would, however, prefer to be 'respected' for my knowledge, and my ability to pursue a reasoned investigation.

... Anyone who uses this forum should be capable of searching the web.

MichaelG.

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P.S. ... I do often provide web links to support my own postings, but that is generally as a courtesy to the reader.

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Just returning to this, Roy

Bergeon previously offered [at an eye-watering price] a selection of small round files, but I cannot find them in recent catalogues.

My cheapskate alternative was to scrounge some root-canal files from my Dentist ... this [emotionally] helped me offset the cost of my treatment !!

MichaelG.

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Root-canal : https://m.youtube.com/watch?v=G7IOrLoHKo4

Edited By Michael Gilligan on 30/08/2019 09:42:18

Michael The smallest files I can find are listed as being for opening out watch hands. And I can only find round and square. The smallest I have is 0.95mm and is round, the smallest square is 1.0mm

As you say the price is eye watering, they are in Meadows & Passmore on line catalogue

Roy

The smallest round files I have is Vallorbe LP1680 nr.2, diameter starts at 0.60 mm. Niko.

This may, or may not be the set that I was thinking of: **LINK**

http://www.julesborel.com/products/tools-files-file-sets/bergeon-1031-r-assortment-of-12-round-files#jbpid-prod-details-link

Surprisingly little information offered by Jules Borel

MichaelG.