Pivot hole bushing

[PlasmaParticipant @plasma]

Hello all.

I’m no clock repairer but was asked to cast an eye over a pretty standard mantel clock by a friend.

Its a Bentima or Perivale movement with Westminster chimes.

One of the pinion holes in the chiming train is badly worn and needs bushing.

Can anyone tell me the best type of drill to use for boring the oversize pivot hole for a bushing?

I’ve seen images of something that looks like a D bit but tapered. I am guessing so that it gently opens up the hole in the backplate.

I’m pretty sure that it’s a repair I can carry out, with the right tools and knowledge.

May just keep this old bird ticking for a while longer.

Mick

[Michael GilliganParticipant @michaelgilligan61133]

First thing … unless you have a dedicated bushing tool … is to ‘draw’ the egg-shaped  hole using a round needle-file, so that it is a symmetrical ellipse.

It can then be much more easily opened-up with a drill or a five-sided broach.

MichaelG.

.

Ref. https://www.cousinsuk.com/sku/details/bushing-tools/b0290

[Paul LousickParticipant @paullousick59116]

The bushing tool in the link would be good but £1,295.00 purchase price is a bit too expensive for a one off repair.

You may be able to just ream the existing hole to suit the bush (or drill undersize and ream). Either for a press fit or sliding fit and fix in place with Loctite.

 

[Paul Lousick]

On Paul Lousick Said:
The bushing tool in the link would be good but £1,295.00 purchase price is a bit too expensive for a one off repair.

[…]

But I showed it to illustrate the design-concept … easily adapted if you wanted to make one.

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

On Paul Lousick Said:
The bushing tool in the link would be good but £1,295.00 purchase price is a bit too expensive for a one off repair.

[…]

But I showed it to illustrate the design-concept … easily adapted if you wanted to make one.

MichaelG.

Also have a look at the attachment for the GHT pillar tool in the Workshop Techniques book.

Andy

[DellParticipant @dell]

I am a clockmaker and It’s easy enough to bush by hand but I do it on my mill , I use a tool to align the hole with a tapered tool then clamp it down then I use tapered reamer to open hole , if you don’t want to get the tapered reamer then as Michael said file the hole on the opposite side of the wear and drill hole with a short spot drill first so hole is central then with size drill you need , the bush needs to be a press fit into plate and if you are making bush drill hole smaller than pivot in bush and broach out after fitting .

if you need any more help PM me

Dell

[Peter Cook 6Participant @petercook6]

I’m with Dell. If you have a mill then the easiest way is to use a small end mill to recut the hole. Clamp the plate. Use a suitable sized pin guage (or the shank of a drill) in the mill to find the centre of the original hole. Replace the drill with a small mill and cut the hole.

Make a bush with the correct OD  and a slightly undersized ID and press it in, then ream the hole to suit the pivot.

[PlasmaParticipant @plasma]

Hi all.

Many thanks for all the advice, it’s very much appreciated.

I looked at the problem of opening up an ovalised hole from a purely engineering perspective and came up with much the same ideas as were provided by much more experienced hands than myself.

Most clock repair sites advocate no power tool use at all. I guess clocks were invented before electrickery so tradition is important,  plus it gives more feel and control to do things by hand.

I have a very small rack and pinion press that will be perfect for pressing in a new bush, a good enough substitution for the bushing tool Michael G mentioned to illustrate the methods employed.

I set the backplate up in my jig borer trying several methods to line up on the damaged pivot hole. The basic way of using a suitable sized tool to locate the hole was very straight forward. And using a centering microscope to check on the alignment confirmed I was on the right track.

Cousins provided me with a selection of bushings and a set of reamers that should get me where I need to be with a nice new bushing hole.

If the first one succeeds I will do all the primary holes which wear because they bear the most pressure from the spring barrels.

I won’t work on the actual clock plates until I’ve done a couple of trial runs on some scrap brass to make sure I’m doing things right.

I’ll report back later on my progress.

Thanks especially for the tip on opening out the ovalised hole with a needle file to avoid off centre drilling, that was one of my big concerns for this job.

Best regards Mick.

[PlasmaParticipant @plasma]

So,

I made a tapered 4mm drill from silver steel, simple point with a flat on the tapered section to make a fancy D bit.

I tried the tool out on some brass the same thickness as the clock plate.

I used the centre scope in my jig borer to line up on a 2mm hole in the brass and bored the 4mm tapered hole.

Swapping the drill bit for a 5mm silver steel rod I pressed an English bush into the newly bored hole.

I tried again with a badly ovalised hole as instructed and again got a perfectly centred hole.

The two are shown below, the one with a witness rich around it I countersunk before pressing in the bush. May work as an oil reservoir?

I will move on to the actual backplate and see if I can replicate my method with that.

1. 

[PlasmaParticipant @plasma]

The bushings are done, pretty successfully i think.

I am rebuilding the movement now and looking at how the chime and strike mechanisms are timed to get things working properly.  The actual running of the clock is fine, it’s the trigger of the hour and quarter strikes that are fun and games.

I’m sure I will work it out, but any tips on setting the striking cam that lifts the geared quadrant to vount the number of strikes would be a start.

Mick

[DellParticipant @dell]

Have a look at this

https://mb.nawcc.org/wiki/Encyclopedia-Subjects/Clock-Repair/Chime-Clock-Basics

[CirclipParticipant @circlip]

But there is a £64.75 saving on the Bergeon tool if you buy two, be quick though, only 21 left.

Regards  Ian

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