Is a Single Pulley a Bad Idea?
  • I'm just about to commence building a Sextus. Ultimately this clock will find it's home on my office wall. Is there any reason that I couldn't double the weight and add a single pulley to the design to decrease the frequency at which it needs to be wound? It would be nice if I could get it to run over the few 3-day weekends that occur every now and again and a single pulley should provide about 4 days.
  • Basically you can double the run time of any clock by adding a pulley, the only thing to watch out for is the double increase in weight which can put a big strain on the frame, but will in any case increase the frame sag, which if not allowed for can cause arbor "clamping". But the Sextus frame is pretty sturdy and you could attach the one end of the winding string to the lower wood spacer, just keep it as close to the wall as possible to reduce leverage.

    Dave
  • You might also want to see what a minimum amount of weight is needed to drive your clock when you've finished building and trimming it. They'll all be different, but mine (a Septimus) is nearly (but not quite) capable of running with almost half the specified weight. Obviously - for me- this is slightly annoying, as it means I cannot simply add a pulley to my existing weight. But it's something to think about and would help the pressure on the frame as Dave suggests.
  • Oh, and less weight should make a quieter tick.
  • In case you add a pulley, I suggest to glue the spacers of the frame in order to reduce the frame sag. I had some problem with it, with no pulley: I screwed the three frame screws but after some weeks they become loose again, screwed again with risk of arbor clamping, the tick was getting slower, moved the weight of pendulum. Not very good solution but it works.
    I suppose that the head of the countersunk nuts is too tiny and, slowly, squeezes the wood. Glueing is the final solution.
  • I found fitting the brass spacers one of the hardest things with the septimus - after varnishing the frame components, I had to spend a considerably amount of time filling and sanding down the holes on both the back and the frame to get the spacers to sit deeply enough to allow me to properly do the bolts up - much more time than I would have expected. (mostly my fault for using some really rubbish varnish on the frame, I think)
  • @wembley
    You are right, fitting the brass spacers can be a bit on the fiddly side. The problem is getting the fit tight enough to prevent frame sag, but loose enough to allow insertion, and it really is a fine line between the two. As opposed to using wooden spacers the brass spacers have absolutely no give, which is why it will become harder if any varnish/finishing should "contaminate" the hole.

    I checked this fitting several times, and I realise it is a bit of a careful joint, but also, hopefully, tolerable.

    Dave

  • An easy way to determine the least amount of weight for your clock is to let the weight drop onto a scale. When the clock stops look at the scale and add perhaps a quarter pond and that should be the correct weight for that particular clock.

    DaveMc
  • I am not sure BUT if the line from the weight was run through a pulley mounted ABOVE the winding drum and not attached to the frame, would that reduce the force on the frame but not the weight? My Sextus is still on route so not sure but equal forces in opposite directions cancel out one another (I think I got that from a Physics class a very long time ago)
    Andy
  • @DaveMc
    In principle what you say about determining the weight is a good idea, but should it not be the case that the weight displayed by the scales should be subtracted from the total weight plus a bit extra, and not as you suggest using the weight measured by the scales with a bit extra ?

    @AndrewN

    The Sextus needs approx 2.5 Kg of drive weight, and this must at some stage pull or push the winding barrel for it to tick, so even running the string over a pulley changes nothing on the fact that the force still has to be applied, frame sag can be an issue but it is fairly easy to detect and compensate for.
  • How can frame sag be detected and more importantly resolved? I ask as due to hammer drilling in an adjacent room close to and at a similar level to my Primus it stopped a few hours later. I noticed a little binding on escapement cog 14 as if the distance between had grown very slightly, also the post mortem found a scratchy bearing on the escapement arm. Bearing replaced and a little dentistry it runs fine again. Could the vibrations caused either of these problems?
  • Ideally, when looked from the side the frame should form a rectangle which angles are 90 Degrees, but gravity being the superior force it will start to sag and the rectangle will become a rhombus, eg. the angles are no longer 90 Degrees.

    You can measure this by holding a carpenter´s square or similar under the frame and measuring the distance to the square back and front, so if the bottom of the frame is originally on the same level as with the Sextus, then the gap at frame rear will represent the frame sag at front.

    The remedy for frame sag is to get the frame as stiff as possible, but also make sure that there is enough play in the arbors to allow for movement.
  • This is how I got rid my frame sag. I made the frame 4" longer and put the support on and it works great.
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  • That is a good solution, and by the way do I detect some solid wood cogs there ?

    It is the same approach I used on the Secundus and will pretty much reduce your sag to zero, however, and this is purely my subjective opinion, I would rather compensate for some sag than have the frame dominate the works of a clock.

    I am working on the Duodecimus at the moment and although it has cogs of 270 mm Dia. the frame is as good as non existent, although it is my biggest clock to date.

    Increasingly my designs have been about transparency, making the moving parts of a clock the main feature.

    As I said that is my opinion and I am always happy to see someone else´s solution.

    How about a complete picture of your Sextus so we can see how your modification fits in with the rest, which might just prevent me from obsessing :-)
  • I'm sorry I don't know why the pictures are coming out side ways.There not like this in my files.Could someone turn these on your end. from the front you can't hardly see the extension .I'll try to post a front view also.I had read a lot of people were having problems with sag so when I was making this one I added this to help eliminate it.One less problem to deal with. Mine is running and keeping good time. It is made out of Quarter Sawn Cheery, Yellow heart. and the verges are made from Lignum Vitae.
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  • I see now if you click on them they are the right way. Here is a front view. Thank you for a great clock.
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  • I've been ticking for the last 48hrs. I am also looking to add a few pulleys. But I'm going to come at it from a different angle, literally. I'm thinking of setting up pulleys so that drive string leaves the drive arbor to the right an left. One off the top and one off the bottom keeping the frame in equilibrium in theory. Has anyone attempted this? The diagram show 3 masses I may just make one mass dovetail box that connects all 3 lower pulleys. I was also toying with going out and up to two brass weights on a single pulley one on each side of the clock for symmetry
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  • My Sextus is just ordered but I have been mentally designing my compound weight system. My idea is to mount one of those little wooden curtain rod holders to the wall just below the clock and terminate there.. The frame will see one half the force and the wall the other half. This is all a dream right now but may have some merit... Walt
  • Precision, so how is your pulley concept coming along? Your goal is not to have to wind every week or are you targeting even more? Got to post us a picture if you have set up your idea.
  • I know it has been a while. I've been slow to pull the trigger on my final weights. I have the symmetrical double weight system working. Each side has one pulley. One picture is how it is now, while I try to make the time accurate. The other is the layout of where I am headed. I am placing the whole assembly on MDF skinned with copper sheeting. Any thoughts or ideas. Thanksimageimage
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  • Not to be a stickler, but would you mind adding the phito? I am interested in seeing it.
  • I attached 2 pictures to the first post I can see them. I have to jump through hoops just to post. I have to disable my IPv6 and use IPv4 only i tried to attach the picture to this post let me know if it works. otherwise here are links


    NOTE FROM WOODENTIMES
    The pictures used in the original post where way too big, over 4000 pixels in height and above 2MB, the forum limits big pictures as they just fill server space, I have reduced the size to 1000 pixels height, which is pretty much what most monitors can show.
    Dave
  • Precision that is quite an awesome set up! The mounting plate looks cool and simply the best way to keep the whole assembly / clock as a single wall hanging.
    My two cents in spite of a really first class example of Dave's clock, would be to make the clock face and hand components copper colored? This tweak would facilitate (for me ) reading the time.
    (Great to see you still monitoring this board Chirs! I need to post an update)


  • Thank You great suggestion. A copper face would tie it together



  • Model railroad has some pretty good paint colors.
    Cheers!.
  • Beautiful mechanism at work there precision. Really like the idea of a double pulley setup and the execution is spot on. Was wondering if you might consider placing the static mount of the weight cords on a separate arbor to make the pulleys face directly front? And potentially adding a small pulley just above the rewind side of the weight cord so that from the front both cords are parallel? It is a beautiful piece :)
  • Thanks, adding the static side location is a great idea to keep the pulleys facing front.
    I was trying to keep the frame in equilibrium that's why I went 180° out on the drive arbor. I don't see how I could add the other pulley to make them colinear. let me know how you see this being done.
    I just uploaded a video of it running to Youtube https://youtu.be/z7E8-IYNDog
    Thanks again