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Re-bushing a clock barrel

clockboy

By clockboy
in All Things Clocks

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clockboy Distinguished Member

clockboy

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Hi Guys,

I have a clock barrel that needs re-bushing as I cannot find a suitable replacement barrel. The issue is the existing bushing has worn and is out of centre. I have measured and the existing hole which is approx. 7.5mm the new bushing will be 9mm. I have purchased a replacement bushing that has the required inside lip and when fitted will just need broaching out. However my question is how do I make the new hole exactly in centre. I have a watchmakers lathe (Star) and I can fit a three jaw chuck and it does hold the barrel. However my end stock will only take a 7mm bit. I am presuming I will have to broach the new hole but the issue will be broaching and still keeping dead centre. I have a pillar drill so was wondering if there is a centering bit I could purchase and then drill and smooth out for the final friction fit.
Any ideas much appreciated.

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Tmuir Distinguished Member

Tmuir

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You really need to be able to drill the hole out on your lathe, or set up a boring bar as a second option to bore the hole to size, its the only way you can be sure to keep it central.

The way I did this a few months back was to set up the barrel in my 3 jaw chuck and use a dial test indicator on the machined part of the barrel and rotate the barrel checking the runout and adjusting until I had it down to a couple of hundreds of a mm.

I then  drill it out to 10mm and carefully measured the hole to check it didn't drill oversize.

I machined my own bush from brass tube stock I had previous purchased for making large clock bushes making it 0.05mm larger diameter than the hole I drilled and 0.2mm ticker than the barrel, with a small chamfer on the leading edge to make it easier to start.

I then friction fitted it using my arbor press to push it in, but I could of just as easy put a block of wood ontop of it and gently tapped it in.

I then reamed out the hole in the bush to fit.

I did not do any broaching to fit the bush.

As I had lots of space between the barrel and the plate I put a lip on the bush that sat on the outside of the barrel for extra strength.

 

 

centering.jpg

drilling.jpg

bush1.jpg

press1.jpg

press2.jpg

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clockboy Distinguished Member

clockboy

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2 hours ago, Tmuir said:

You really need to be able to drill the hole out on your lathe, or set up a boring bar as a second option to bore the hole to size, its the only way you can be sure to keep it central.

The way I did this a few months back was to set up the barrel in my 3 jaw chuck and use a dial test indicator on the machined part of the barrel and rotate the barrel checking the runout and adjusting until I had it down to a couple of hundreds of a mm.

I then  drill it out to 10mm and carefully measured the hole to check it didn't drill oversize.

I machined my own bush from brass tube stock I had previous purchased for making large clock bushes making it 0.05mm larger diameter than the hole I drilled and 0.2mm ticker than the barrel, with a small chamfer on the leading edge to make it easier to start.

I then friction fitted it using my arbor press to push it in, but I could of just as easy put a block of wood ontop of it and gently tapped it in.

I then reamed out the hole in the bush to fit.

I did not do any broaching to fit the bush.

As I had lots of space between the barrel and the plate I put a lip on the bush that sat on the outside of the barrel for extra strength.

 

 

centering.jpg

drilling.jpg

bush1.jpg

press1.jpg

press2.jpg

 

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clockboy Distinguished Member

clockboy

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Thanks Tmuir,  Unfortunately I do not own a large enough lathe. If I had then this job would be a relatively simple job to achieve. I have a pillar drill and a watchmakers lathe. The watchmakers lathe does have a three jaw chuck and I have tested and the barrel fits. However the tailstock will only take a 7mm drill. I have measured with callipers and using the teeth to centre the existing hole is worn to one side. I might have to broach out to get the existing hole into centre then drill with a 8mm and broach out the rest for nice friction fit. Thats my thoughts for now anyway.I have purchased some pre-made barrel bushes that have a rim for the inside of the barrel that stops the arbour binding. It's the hole thats the issue. What fun !!!!

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