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  1. #16

    Default Re: Movement design wheel placement (RE: Dave B)

    I think Scottie's example is a time only. Much easier

  2. #17

    Default Re: Movement design wheel placement (RE: shutterbug)

    11/10/09

    Several years ago I was teaching a clockmaking course, and I wrote a detailed instruction for depthing the train of a banjo clock. I have copied it below because I think it answers several of Scotty’s questions. The instructions require careful reading to make sense.
    In addition, I think most clock movements were designed with the intention of making compact plates so that there would be ample room to fit the movement in a case without the need for awkward case proportions. Further, when brass was at a premium, smaller plates were desirable for economic reasons. Jcl

    How to lay out the train on a banjo clock


    There is an order to planting the train of a banjo movement that simplifies locating wheels so that there are either no depthing problems, or depthing corrections will be easier. Initially the plates were pinned together so that they could be filed, drilled and laid out simultaneously. While they are pinned together, take a file and mark a “V” on the bottom edge, overlapping both plates. This becomes a reference to the order the plates were pinned, in case it is necessary to pin them again someday.

    Strange as it may seem, the top plate of this pair is to become the rear plate. When the pillars are riveted to the pillar plate, after the train is laid out, it will then still be possible to re-pin the plates if necessary. This is also why the minute wheel post should be easily removable. Train layout is often done before final polish of the plates so that any scribing lines can be removed. Not all clockmakers remove their lines, and this leaves a reference mark for convenience of future repairers.

    Locate the vertical center of the clock plates and scribe a light line from top to bottom of the top plate of the stack. (This is the surface that will be the inside of the rear plate later.) Measure the diameter of the center wheel. Determine the radius of that wheel, and add about fifty thousandths to that figure. Using that value, measure from the bottom edge of the plate and make a reference mark intersecting the centerline. This is the location where the center wheel pivot holes will be drilled. The added fifty thousandths is an arbitrary quantity to assure that the wheel will not project beyond the bottom of the movement. Now, or later, make a center punch mark at the intersection of the two lines.

    With a protractor or drafting square, measure an included angle of 60 degrees from the centerline reaching to the upper edge of the right hand half of the plate, and starting at the center wheel pivot mark. The right angle leg of the triangle is kept parallel to the top edge of the clock plate; perpendicular to the centerline. If the dial were on the clock, this line would run to the chapter mark for the numeral two. Lightly scribe a line, which does not have to run all the width of the plate. The mainwheel and winding arbor pivots will be located on this line.

    You can now put the center pinion and mainwheel in the depthing tool, find their proper center distance, and scribe a discreet arc intersecting the sixty-degree line. This will be the location of the winding arbor assembly, and you can make a center punch mark at that location.

    Now you will have to determine the pitch diameters of the center wheel, the third wheel pinion, the third wheel, and the escape wheel pinion. Using that information, you need to find the pitch radii of all those wheels and pinions. Multiply the module by the number of teeth on the wheel or pinion to get the pitch diameter. (The module for this particular clock is .065 and you will have to divide the number from multiplication by 2.54 to convert the diameter of the pitch circle from mm to inches.)

    Add together the pitch circle radii of the escape pinion, the third wheel, the third wheel pinion, and the center wheel. Make note of that value and adjust your sliding caliper to the sum of those figures. Set the caliper aside. The same setting can be made, of course, using a pair of adjusted dividers.

    Next, install the pallets and the escape wheel in the depthing tool; adjust them to the best action you can get. Measure and note the depth of the pivot hole you drilled in the pallet bridge from the top edge of the bridge. (That hole should have been drilled exactly at the bottom of the suspension spring mount, which is a part of the bridge, so that the pendulum and the pallet fork will swing at the same radius.) Mark that distance on the centerline from the top edge of the movement, but do not center punch it. This assures that the pallet bridge will not be located above the top edge of the clock plate. It can, in fact, be located a little below the top edge of the plate. This will allow for movement of the pallet bridge at some future time, when a repairer re-depths the pallets after repairs. (We all know that doing this is not desirable, but I assure you many bridges have been bumped up or down to get the escapement to work optimally. The fault of this is that the pallet arbor may be left in an out-of-upright position.)

    Place one center point of the depthing tool on the mark related to the pallet bridge pivot hole, and use the other center point of the tool to make a small mark on the center line to represent the escape wheel pivot. With the previously adjusted calipers, place one point on the center wheel mark, and notice where the other point is in relation to the potential location of the escape wheel pivot. Ideally, the caliper points will span a much larger distance than that between the center pivot location, and the escapewheel mark. If that is not true, and all the measurements are accurate, it becomes necessary to lower the escapewheel pivot location, and the corresponding pallet pivot location, until there is an overlap of .130” to .180” between the setting of the caliper and the escapewheel pivot. If the overlap is much greater, it is necessary to check to be sure that the third wheel will not be in line with the winding cable which is attached to the upper left pillar when the clock is complete, or that it projects beyond the left edge of the clock plates, although this is not an important matter. This point will become clearer ahead.

    To plant the third wheel and its pinion, it becomes necessary to “bend” the straight line that was the total of all the wheel and pinion pitch circle radii. The mainwheel occupies most of the available space to the right of what will be the locations of the escape wheel, center wheel, and the mainwheel assembly. The third wheel will have to go to the left of the centerline. If all of the measurements and manipulations described above are correct, it is time to mark the escapewheel pivot location with a center punch.

    Adjust the third wheel pinion and the center wheel in the depthing tool. With one leg of the depthing tool in the center wheel punch mark, sweep a small arc to the left of the centerline. Do the same thing with the escape pinion and the third wheel. Sweep an arc, which should intersect the first arc. Obviously that intersection is the location of the third wheel pivots. This completes finding the locations of train and escapement pivots for both plates.

    Now for some practical matters: in order to avoid unnecessary scribing marks on the actual clock plates, some of this layout can be done on paper first. The information derived from making a paper plan will enable the clockmaker to make very discreet marks on the plate itself. As I noted earlier, some clockmakers deliberately leave a lot of marks on the clock plates for future reference. I have mixed feelings about it. I want my clocks to look sufficiently planned that their birth throes are not turned into birthmarks. On the other hand, I have taken advantage of layout marks when I needed to do so in repair situations; your call.

    In this text we are considering reproduction of a traditional clock movement. If this were to be a clock designed for a special application, wheel ratios, diameters and thus pitch and module would all have to be planned in advance, and the train laid out on paper before any metal were cut. Any other approach would lead to some disappointing surprises when the parts were being laid out on the clock plates.

    It must be too obvious to dwell on the point that if the plates ever have to be pinned together again, the front plate, when the plates are pinned together, should become the rear or pillar plate when the clock is completed. This means that after layout, small pilot holes are drilled in both plates while they are still pinned together. Afterwards plates are separated, and the various holes are drilled and finish-reamed to correspond to their specific pivots. Remember that the actual front plate has to be cut out and drilled to accept the pallet arbor and bridge on a banjo movement.

    I prefer to do most of the drilling on each plate before the pillars are installed and riveted. This means that every hole I drill should be slightly undersized, and I ream or bore the holes to fit after I have the pillars in place, and I am testing the freedom of the train.

    The minute wheel on a banjo clock can be located almost anywhere on a circle drawn from the center wheel hole, the radius of which is actually the pitch diameter of either the minute or cannon wheel, since both wheels are identical. As a practical matter it should be located at a point where there is no danger of it encountering the pendulum yoke which is a part of a banjo pendulum assembly. Most of them are located at about 90 degrees perpendicular and to the right of the centerline. Unless the pendulum has an abnormally wide swing this usually assures that the yoke will not reach the pinion or its post.

    All of the above procedure is directed towards eliminating the need to disturb pre-determined measurements while still leaving flexibility in most of the depthing. The same rules apply to almost all clocks. At the time American and English clockmakers had to make grandfather movements that would fit pre-drilled manufactured dials, there was only one dimension that was outside the control of the clockmaker. It was the distance between the center pinion and the mainwheel. Provided he made or bought those two parts precisely enough produced so that the pitch circle radius of the center pinion, and the pitch circle radius of the mainwheel added up to the center distance of the center wheel hole and the winding arbor hole, the clockmaker could do just about anything he wanted to do. Neither the pre-determined location of the seconds hand (escape wheel pivot) nor the winding hole for the strike were a problem. Think about it.


    John C. Losch
    September 23, 1999

  3. #18
    Registered User Jim DuBois's Avatar
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    Default Re: Movement design wheel placement (RE: John C. Losch)

    John and Mike have it pretty well "nailed" and so does Harold. the 3rd wheel can be planted anyplace it fits, and John also points out why it is often planted to the left. Harold's example is what is found (time side only) in thousands of jewelers regulators (obviously weight driven, but laid out in a straight line) just like the time and strike Morbier. There is no mechanical advantage, or disadvantage. to one position over another. Clearance to other parts is needed....and that is pretty much it....I have converted several old fusee movements into skeleton clocks with the train going in a straight line....a few tower clocks have their trains in a straight line horizontally....and some very early ones in a straight line vertically.....

    Of course your seconds bit will be off in the chapter ring, but they don't usually beat seconds anyhow in a Vienna regulator.....

    really a nice write up John! Thanks, it is more than useful!

  4. #19
    Registered User Scottie-TX's Avatar
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    Default Re: Movement design wheel placement (RE: Jim DuBois)

    A special thanks to JOHN for the reprint on his excellent article and counsel.
    Still I ask, JOHN;
    To plant the third wheel and its pinion, it becomes necessary to “bend” the straight line that was the total of all the wheel and pinion pitch circle radii. The mainwheel occupies most of the available space to the right of what will be the locations of the escape wheel, center wheel, and the mainwheel assembly. The third wheel will have to go to the left of the centerline.
    I think the answer to "why the third wheel must be moved" is space - space available in plate dimensions. Did I read that correctly?
    DAVE, thanks for the slap to wake me up - uh - "WOOD?" uh "Duh?"
    Thanks as well to all others, I think we conclude and agree:
    1. It will work. It can be done. It has been done. It does work.
    Onliest difference I can see in wheel placement is direction bushing will wear.
    Remaining only then (in my mind) is the aspect of efficiency.

  5. #20
    Registered User Scottie-TX's Avatar
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    Default Re: Movement design wheel placement (RE: Scottie-TX)

    So, "efficiency".
    Whaddya tink?
    I've had straightline pinwheels here. Most efficient was reliable on eight pounds. To compare a pinwheel to a wiener would be unfair - unproductive.
    The pinwheel is vastly different with it's massive wheels, heavy pendulum, etc. A Comtoise with a recoil movement is no comparison.
    But now, comparing apples to apples - a typical one weight wiener with third wheel shifted off center - comparing that to another with third wheel on a vertical center - could one be more efficient than the other?
    What about a wiener with the third wheel placed opposite of typical? Why did they ALL choose to shift it to that SAME side?
    Last edited by Scottie-TX; 11-11-2009 at 01:03 AM.

  6. #21
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    Default Re: Movement design wheel placement (RE: Dave B)

    Quote Originally Posted by Dave B View Post
    Seems to me the minimum width of a straight line movement would be dictated by the diameter of the largest wheel. That sucker 'uld sure be a long one, if time and strike were all in one line, though.

    Actually, I spose it could be reasonably done, if the time train were mounted above, and you used a one-second pendulum.
    Most lantern clocks and posted frame longcase clocks are like that.
    Mike - banned member of the throwaway society.

  7. #22

    Default Re: Movement design wheel placement (RE: Scottie-TX)

    11/11/09

    Scotty, and others,

    You wrote: 1. It will work. It can be done. It has been done. It does work.
    Onliest difference I can see in wheel placement is direction bushing will wear.
    Remaining only then (in my mind) is the aspect of efficiency.


    The wheels can be planted in a straight line, in a circle, or randomly but in sequence. Where they are located will have no measurable effect on power delivery in such a slow moving train. Since all wheels rotate 360 degrees, even imbalance of the wheels is insignificant unless it is great enough to stop the clock. As to wear in the bearings, that is a function of vector forces. Wheels always want to travel in a straight line, but their bearings force them to travel in a circle. The direction of wear in a bearing is the point where the force of a wheel wants to spread away from the wheel it is driving. That is a calculable direction --- but not by me. Ask your neighborhood physicist how to calculate where wear will occur.

    The straight line is a theoretical but practical measurement. Were you to plant a scape wheel, then the center wheel, and the straight line was less than the distance between the two designated pivot points, you would be unable to engage the third wheel with both the center and scape wheel. Aside from the already stated reason for having the third wheel out of line with the 2nd and 4th wheel --- to shorten the clock frames or plates --- correction of bad depths from error or wear is easier when re-planting one wheel can correct two faults at the same time.

    Incidentally, with a depthing tool, there is a very easy way to get the pitch circle measurements between wheels and pinions. Adjust any given pair of wheels in the depthing tool for the best action. Measure straight across the runners of the depthing tool as near to the wheel and pinion as is possible. Assuming that all the runners in your depthing tool are the same diameter, and points and female centers are concentric with their runners, you can subtract the diameter of one runner from the measurement, and you have the center distance between wheel and pinion added together at the pitch circle. Not surprisingly, that measurement my vary noticeably from one derived by theoretical calculation, particularly in hand-made clocks.

    In summary, whether the wheels are planted in a compact configuration, or in a straight line, has no effect on the efficiency of the wheels being considered. Jcl

  8. #23
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    Default Re: Movement design wheel placement (RE: John C. Losch)

    Here is a banjo movement with the gears in a vertical line.
    Larry
    Attached Thumbnails Attached Thumbnails Attachment0.jpg  

  9. #24
    Registered User Scottie-TX's Avatar
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    Default Re: Movement design wheel placement (RE: Larry)

    Okey dokey. General consensus seems to be that efficiency is not a function of or affected by wheel placement. No dissenting opinions.
    So again; THANK YOU all very much and now I'll move this over to "Skeleton" forum where it will have more relevance.

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