bare wood or sealed
  • I have just received my kit (Sextus) and as luck would have it I became very busy with my job (thank God).
    I am thinking a lot about the actual build process so here is a question.
    What finish is usually applied to wooden clocks? I have read a bit about wood clock parts expanding and contracting due to moisture in the atmosphere.
    Should I varnish and seal all parts?
    Has anyone any preferences on product?
    Multiple coats of varnish or lacquer may give a finer finish to gear teeth when sanded, i.e. no "hairy" bits.
  • I used a polyurethane varnish for the base of my septimus, and that was fine - what was less so was the nasty gloss varish I put on the front of it - that seemed to soak into the wood and caused it to swell slightly - if I build another, I'll still with a poly-u based varnish for the base, and will instead stain the other parts. I wouldn't have though varnishing the gears or escapement is a good idea though - you might have to then send down the teeth again to get them to mesh properly.
  • Now that is a good question, and to set the record straight once and for all I am going to give you a more longwinded answer than you maybe wanted.
    Wood, as we know, shrinks and expands with changes in humidity, the higher the humidity the more moisture it can absorb and the more it expands, the lesser the humidity the more moisture the wood will be able to give into the atmosphere and the more it contracts. In grain direction (longitudinal) the movement is generally around 0.2%, which is pretty much negligible, the problem is cross grain (tangential or radial depending on how the board is cut) which can be up to 10%, so if you were to cut a wheel from solid wood Dia. 20cm, then worst case scenario that could be a difference of cross grain direction 2cm, but that really is worst case, normally it would only be a millimeter or 2, but even so, enough to stop your clock.
    Which is why I use plywood for all cogs and pinions, each layer or ply is glued 90 degrees to the preceding one so that the cross grain expansion is held by the relatively stable longitudinal grain, but even plywood is susceptible to humidity, although in a much smaller measure than solid wood.
    As clocks only move in one direction, we can use something called backlash, which is basically the gap between contacting teeth, if there was no backlash and the teeth were to contact on both sides with no gap whatsoever, then the slightest expansion would cause the teeth to bind, move the cogs slightly apart and you create a gap between the non contacting surfaces, backlash. This gap allows expansion.
    So to cut a long story short, if you make your cogs from ply and you have enough backlash, then you do not need to “seal” the cogs. And secondly any kind of finish that develops a surface will eventually wear of the contact surfaces of the teeth and probably would start to literally gum up the works, staining is no problem as the pigment particles are so small as to be absorbed by the wood, but from my own personal experience I can say DO NOT use any kind of wood oil on the cogs/teeth, been there, done that and ruined an otherwise good clock.
    I leave all my cogs in their natural state, the aviation birch ply looks great as is.
    All non moving/contacting parts (frame, hands, dial etc.) you can treat as you wish, on plywood I use an acrylic coloured varnish and on solid wood tung oil.
    This is by no means a definitive answer and I would very much welcome any further comments.
  • I'd like to color cogs with mordant, but I notice the wood become a bit rougher. This could be a problem and vanish the excellent cnc surface on the teeth. Of course, natural state is preferable, but for the style I decided, I first have to try to varnish the surfaces without touching the internal part of the teeth (not on a cog! but on the external scrap) and analyze the outcome of the experiment...
  • Lorenzo, as you are thinking about using mordant on your clock, and if I am correctly informed it is a dye fixative, I would recommend you get in touch with George (use search to find him on the forum). He dyes cloth for a living and knows a whole stack about dyes and how to dye cogs, which he did with his Tertius(see picture).
    600 x 500 - 83K
  • Hi there. I have recently received my Sextus kit, and plan to start building in the New Year. As per Dave's instructions, I have read through the manual, and notice that the first stage is to assemble and apply finish to the frame.

    I am very happy to leave the cogs bare, but would prefer to colour and finish the frame, the pendula, and the dial.

    In the past, I have had very poor success with staining plywood, with blotchy results. I have heard about pre-stain treatments, but have never used them. I have spoken to a few suppliers, and have come to the conclusion that the difference between stains and dyes is not well understood, even by experts.

    I would like some advice please on how to get a nice even deep colour (maybe dark walnut, but I'm not yet sure about this) on the frame and the pendula without the end grain layers being too obvious, and what finish coat to apply.
  • Hi all, hope i can help with staining ?s
    I decided to use dyes from work as an experiment as never had success with traditional of the shelf wood stains. The ones i used are bi-functional in that with different conditions and chemicals they can dye both protein (wool) or cellulose (cotton, viscose - which is made from wood pulp ) By mixing a red/blue/yellow combination i finally got the right shade by simply adding to water in a weak concentration. The only chemical added was a wetting agent which lowers the surface tension for better absorption, if added to a pond for instance it will sink a duck never mind a pond skater.
    All stains i know of are made with pigments which have very large molecules as opposed to dyes which are very very small and will penetrate and migrate evenly.
    Pigments are more like a filler and will fill in scratches or softer more porous grains darker giving a bad finish. Hope i put this across in laymans terms and happy to answer any questions.
    Must admit its nice to add a comment on something i know for a change.
    See link below for a much better answer.

  • Hi George. Thanks for that. It makes a lot of sense.

    I recently went to a woodworking trade show and asked 3 wood finishing suppliers about this, and I was appalled that they didn't know whether their own products were dyes or stains. What is even worse is that if you go into Wickes or B&Q, there are products labelled as woodstains which are actually coloured varnishes.

    I have time, so I will experiment. Can you give me a lead on dyes to try which are commercially available in small quantities?
  • Hi Paul

    Drop me an email -
  • Hi, this is just a note to thank George for his help with dyes. By coincidence, George lives only about 10 miles from me, and I went round to his place and he kindly supplied me with 3 water soluble dyes in primary colours. Using a recipe suggested by him as a starting point, I was quickly able to come up with a formula for a nice even walnut colour on a baltic birch sample, far better than proprietary pigment stains.

    I can now press on and assemble and finish my Sextus frame.

    Thanks again, George.
  • That is great, just living around the corner from each other.

    Now having read your exchange it has really whetted my curiosity, dies, stains and the like are very much a closed book to me, and it would be great if you two could come up with a kind of step by step guide to dying/staining, I often get asked about clock treating and your method would be a great addition to this forum.

    I have started a new category "Finishing" and it would be great if we could kick it off with your expertise.

  • Dave, can you please move this to the FINISHING discussion, as I can't see how to add a comment to a discussion with no entries.

    As a cabinet maker, I have always found finishing difficult. It has been said that if cabinet makers were any good at finishing, the trade of French polisher would not exist.

    Over the years, I have stumbled across a handful of simple methods which work for me, and I stick to them. Up until now, I have only been concerned with tinting and polishing hardwoods, such as oak, walnut and mahogany.

    The Sextus kit which I have just acquired is the first time I have been faced with the challenge of transforming the appearance of the plywood frame and pendula into what is conventionally accepted as “show” wood. There are good technical reasons for the interacting parts being made of plywood, so leaving these unfinished does not worry me.

    Plywood is notoriously difficult to colour well, because the density of the grain varies enormously over its surface. And then there are the end grain “stripes” to contend with. Most of the proprietary wood colours are “stains”, which are just ground up pigments suspended in a liquid. The grain characteristics of plywood mean that the particles of pigment lodge in the rough grain and give a blotchy appearance.

    Unlike stains, dyes are “liquid colour”, and tend to colour the wood fibres more evenly.
    George is an expert in the dyeing of textiles, and, from the help he has given me, I am confident that he has the knowledge to overcome this problem of uneven staining of plywood.

    I am still on a steep learning curve, and maybe the final solution will involve combinations of dyes and stains. I will be very interested to see how this discussion develops.