J Wilding scroll frame clock - fusee arbor pivot sizes?

Hi Folks, I'm new to clocks, have recently started the John Wilding scroll frame clock and already need help. In my book (2002) the drawing of the fusee arbor shows the rear pivot as .225" dia while the front is .265" dia. I was expecting these to be both the same size to enable reaming both plates at once, and also to use a common size of reamer. Am i missing something? Can I make these .25"dia and wiz thru both plates with a reamer once I have depthed the great wheel with the centre pinion? Or, why are they marked as different sizes?

And I haven't yet got to the old chestnuts of DP vs modulus cutters and wheel sizes (errors or not)! Scary stuff.....

Hi Mike, the front pivot of the fusee arbour carries the grunt of the mainspring power during all operations, winding / running etc and bears the full load of mainspring power when fully wound and the chain against the fusee stop, it needs to be fairly beefy to carry the load otherwise it would chew the front plate hole oval very quickly,

The rear pivot by contrast bears an indirect torque reaction to the load bearing on the front pivot, and being at the other end of the cone it's a much reduced load, which as the spring unwinds will reduce further to the value of the pre-load of the spring as the fusee chain reaches that end of the cone, so that pivot doesn't need to be as big, it also doesn't suffer someone heaving on the winding key,

The main factor against making the rear pivot hole as large as the front, is that you will increase drag unnecessarily on the rear pivot and gear train, a larger hole means a larger bearing surface creating more friction, my advice would be 'don't do it', and go with the original plan.

There's nothing stopping you making both pivots the same size and drilling through both plates "As an initial machining process" and cutting both holes the same size to suit, but you will still need to broach both holes to suit each associated pivot individually, the holes should be finished to size with tapered broaches from both sides of the plates, the holes are not parallel walls, they should taper inwards equally from both sides towards the centre of the plate for every pivot, the taper is also very slight and invisible to the naked eye, even under a loupe, (100:1 ish)

Please forget about precision engineering fits and thinking you'll get away with doing both holes at once with a straight reamer and hoping it will do, if you go down that road it will end in tears because the wheel train will bind up as soon as you pin the plates together, the tapered pivot holes compensate for a degree of miss-alignment of the plate pillars and pivot holes which Will invariably happen,

Hope this makes sense.

John.

Edit footnote: I don't have the plans for this clock to hand anymore, so my comments are just based upon experience of restoring antique fusee movements in general,

Edited By RJW on 05/01/2018 19:35:40

Thanks John,

Yes that does make very good sense.

My father made a couple of clocks and I remember him saying that he thought they worked because he wasn't very good at making good fits (I still think he was doing himself down). Unfortunately he is no longer around to ask and now I realise I should have paid attention when I had the chance.

I feel happier about progressing the build again, so thanks for taking the trouble to reply,

Mike

I agree with all that John says. These are running shafts, under a bit of load, so the holes should be tapered and burnished, and the shafts polished and burnished. A traditional method of lubrication would be to add a small oil sink on one side of each of the frames (the outside, usually). Adding an oil sink at the front would mean it was quite visible, and, on this kind of clock, you may not wish to do that. The BHI Journal recently had an interesting article and discussion about oil sinks on the inside of the frames, a method which has been found on some existing clocks, and prompted some debate. I'm not so sure they would be sufficiently accessible there, or that the oil would not be smeared out of the sink by end movement of the fusee shaft, in this clock.

There has been some discussion, on this forum, about the shape of the back cock; and a discussion, too, about the gearing (DP or module sizes). My book is a 1998 edition, so you probably have a more up to date version.

Lovely clock, and a nice project.

Marcus

My pleasure Mike, I've learned a ton of stuff on here over the years, so it was nice to be able to help with something I actually know about,

I'd suggest not getting too hung up over the pivot sizes, if you cut them a bit small or even slightly over size if you're afraid of overcooking things it isn't a big deal, it's always a moveable feast on clocks because whatever pivot sizes you end up with you will always cut the holes to suit each individually, you'll be drilling the initial holes under size anyway in order to broach them to suit the pivots, so personally I'd make all the arbours and pivots first then drill the plates

Another tip I would give, is to avoid cutting a sharp root where the pivot blends into the arbour, if it's cut sharp it'll create a stress raiser, and can guarantee if the clock ever suffers a mainspring or line break, that's where something is likely to break, best to cut the fillet with a small radius for the strength, which brings me to a point Marcus made,

Totally agree with what Marcus wrote, but where oil sinks are concerned I personally would add them front and back (outside only) because they do tidy the job up no end, that's just my preference though but there are other reasons for my thoughts on this,
In every case on antique longcase clocks where the winding barrel arbours invariably run in plain holes, the oil has stained the plates where it's run off the holes and they're always very badly worn, but on the clocks where I've added an oil sink no appreciable wear has been apparent on subsequent servicing or repairs years later, 'But', the oil sink on large holes are best cut Very Shallow, because on those anything removed from the front of the hole will reduce the bearing surface in a greater proportion to the smaller train holes, in my experience though, a very shallow sink works wonders with the oil less likely to run off!

Regarding oil sinks on the inside of the plates, some may advocate it but I don't, they further reduce the depth of the pivot hole and the pivots suffer less support = wear, they will also cause an excess of end shake on associated arbours,
However, this brings me back to my comment about forming a small radius on the root of the pivots,
I Always run the oil sink cutters over every pivot hole 'Inside' the plates, not an oil sink, but just enough to crack the sharp edge away because, if you have a radius on the pivot root and a sharp edge on the pivot holes, I can guarantee this will cause the wheel train to bind and stop the clock or cause poor performance at some point,

The arbours may feel free when you spin them by hand, but when any wheel train is working under spring or weight pressure, the arbours will always migrate to either the front or the back plate depending upon any gradient formed when cutting the gears, arbours and pivot holes, it's unavoidable, the best way to get you head around this, is think of what happens on a belt sander or flat belt drive if you tilt a roller, the belt will move across as the roller tilts, and exactly the same thing happens in a clock wheel train, so if a pivot root radius runs against a sharp edge on a hole, it'll cause friction which will have a greater impact the closer it gets to the escape wheel where the power available to the wheel train is lower,
If you look at any clock movement that's done a fair amount of running, you'll always find on every arbour that one end has left witness marks on a plate around a hole where it's rubbed, but the other end will just have a mucky ring of dried oil around it.

Most of all though, don't rush it and enjoy making that clock.

John

Hi John,

Thank you for the above very helpful posts and detail. One of the most interesting and informative series of posts I have read on this forum.

Mike, good luck with the clock!

Cheers,

Julian

Thanks to all for the replies. When I decided to make a clock I thought I was going to be dealing with more model engineering - now I begin to think I am delving into black magic. Its certainly different to things I have tackled before. But, the comments I see help to back up other information and I think I am getting more of a feel for the job now.

As for not rushing it John, there is not much chance. I read the book, go to the lathe, return to re-read the book - and so it goes on. But I'm still enjoying it - I smile at something minor I have made, and then tremble at the thought of the complexities to come. Hopefully I'll get there.

Mike

Hi Julian, Many thanks for your kind comments, they were very much appreciated,

Mike, I felt very much the same as you when way back in the 90's I first delved into repairing clocks and watches, but to be truthful, when you dig into them there's no real mystery or black magic at all, they're actually quite crude as mechanical devices,
In many ways I find clocks far easier to deal with and more forgiving of ham fisted activity than 'model engineering' projects if comparing to making live steam or I.C. engines.

Just keep asking questions when you get stuck, it gives our grey cells a bit of exercise, Lol.

John.

Mike if I can add my tuppence worth. Don't make anything too tight, I was taught that if it dosen't rattle it won't work

Good luck

Roy

Feel free to use small roller bearings on the bottom end of clocks if you prefer.

regards Martin