Plywood
  • I realise of course that solid wood clocks do have a long history, and there are examples out there that are still functional even though they are hundreds of years old, but it is the use of plywood that allows us to make filigree skeletal clocks.

    You can of course make your own plywood, but that is a discussion on its own.

    The plywood I use for cogs, pinions etc. is aviation grade birch, it is tego film bonded and generally has 2 plies to 1 mm. It has grade A faces and and is just a superior product. It is not cheap, but if you are going to the trouble of building a clock why not go for the best.

    Another kind of plywood that is often used in clocks is baltic birch, it does not have as many plies as aviation grade, but even so, it is more than stable enough to make cogs from. My problem with it is aesthetics, quite often it is bonded with a dark coloured glue eg. phenolic, which makes it water resistant, but looks awful, also it is often susceptible to checking, these are the small cracks that appear in grain direction. So if you want to use baltic birch I would recommend you only buy ply you have personally inspected, I have mail ordered baltic birch, which was so "ugly" I would not have even used it to back a cabinet.

    The plywood I use for the frames is also birch. Here you can use standard plywood with less layers than aviation grade. Most of the frames on my clocks are in multiples of 4mm, the reason for this is that plywood is seldom plane, and sometimes the warping can be too great to use for a clock. So instead of using a 12mm sheet, I laminate 3 times 4mm sheets (3 ply) which ensures the piece is straight as possible. If you do make your frame from a single 12 mm piece be wary of plywood with very thin facing veneers, as the bonding is often not so good and it can happen that it tears out, especially if you are CNC routing.
  • If you use "interior" grade birch ply or "laser" birch ply it does not use the phenolic glue and you don't get the dark line you mention! The phenolic is not laserable with "hobby" lasers.
    I use this quite successfully on a number of frame and gear parts!

    Chris.
  • That is a good point Chris, it is of course only exterior or marine grade plywoods that need to be water resistant, and therefore mostly use phenolic. But I still stand to my statement, it is always best to buy plywood that you have personally seen, or ask some very specific questions when mail ordering, and as a clock only requires small amounts of plywood do not necessarily be guided by the price eg. you get what you pay for.
  • Hullo, chrisekendal and Dave,

    I would like to use marine ply as I just would suck at sticking 1.5mm aircraft ply together. Do you suggest that the veneer on the sheets be thick? I have a choice of quite a few different types of ply wood sheets - which would you suggest? Unfortunately I have to buy my ply in 8ft by 4ft sheets and cannot get smaller pieces and what I buy has to be good enough.

    a) Marine Plywood BS1088 (Durable hardwood plywood bonded with phenolic glue)
    b) Birch Plywood BB/BB WBP(Excellent strength for cabinet making and exterior use and Low Formaldehyde )
    c) Birch Plywood Moisture Resistant BB/BB(MR) Moisture resistant grade for interior use )
    d) Malaysian WBP Plywood (good durable hardwood plywood for exterior use /interior use )

    Or, would I just be better off getting solid hard wood and bond sections together to get the widths I need and build my clock that way - gears and all?

    Thanks
    Lesueur
  • Lesuer,
    I can only reiterate what Dave has said, if possible look before you buy and check the quality!
    Of the materials you have listed, the only material I have used is c. Interior grade birch ply. I was using this for other things at work so was able to see the quality from the supplier and bought myself 2 sheets of 3mm to play with and laminated as required to get the thicknesses required. This worked for me!
    I laterly started using aircraft ply for cogs only and yes it is very good, but not a must have!
    Seem to remember reading somewhere that the best quality interior grade birch ply comes in 5ft by 5ft sheets! Think this is the size I bought.
    Hope this helps.

    Chris.
  • Lets not forget that a wooden clock is a low speed, low load mechanism, so at the end of the day you could make a functioning clock from cheap plywood, with voids, checks, repaired deck ply and only 3 or 5 plies, it would work, but it would look shit.

    I build wooden clocks because I love their kinetic beauty, which of course also includes using aesthetic materials, so my personal preference (and this is very much my personal preference) is aviation grade plywood.

    I can only agree with Chris, of the listed plywoods I would go for C.

    @Chris
    Could you name a UK supplier please. As all the German suppliers sites are only in German.

    Once Nonus is up and running I will be looking into offering plywood packs for each of my clocks, including a service with the cogs pre-drawn on the sheets for hand cutting, but it will be a few weeks in the future.

    Making cogs from solid wood can be a very frustrating experience, so if I was you I would stick with ply.

    Yours Dave
  • Dave,
    I get interior grade birch ply from Illingworth Ingham, they have a branch round the corner from work and I pick up as required!
    My aircraft ply come from Swindon Aircraft Timber Company.

    Chris.
  • chriskendal & Dave,

    Thanks a lot guys you have set my mind at ease. This is my first clock ever and I am hell bent on succeeding. I bought what I though was good plywood - 6mm and started with the escapement wheel and the tips, because they are so sharp, looked terrible as at the ends on some of the teeth the "filling" did not extend all the way. Side on it looked perfect. At least I got some practise in :-). In spite of all this I have not lost my will to live - yet - and will keep on trying until it is spot on. Thank heavens I did not make the escapement wheel last to only then find out that my choice of plywood sucked. I will get the proper 3mm ply tomorrow, glue them together, (it is clear now why thick ply does not give a good finish when doing fine work - live and learn) and hit the tools again this weekend - no shortcuts this time.

    I will let you guys know how I got on.

    thanks a stack
    Lesueur
  • Hi David,
    I have just received some aircraft plywood 5mm thick with 10 layers and as I unpacked everything I realized my plywood is warp. I do not realize how this will impact on my wheels since the sheet is big (600mmx1200mm) but I have cut some other bent plywood before and on big wheels this looks bad. In order to correct the movement I have to cut two pinions for one wheel and glue them together because my bended wheel movement was exciding the thickness of one pinion.
    Now I have made some research if there is any method to flatten the plywood before cutting the wheel and I found the following article:

    “Even new plywood can warp if not stored properly or if left in the sun. Before you give up in frustration, though, try a little moisture therapy.
    Like the underside of a shriveling leaf, the plywood’s concave side has lost moisture and shrunk. Reversing the warp can be accomplished by adding moisture to this concave side and drying the convex humped side. I use a sponge or sprayer to wet the concave side of the plywood (hot water works best). Then I lay the sheet, moist side down, on a shop floor or a driveway. Now the sun, or the warm interior air, helps to dry out the convex, humped side of the plywood. At the same time, moisture is being absorbed into the concave side. This process works faster than you can imagine, so keep an eye on the material. If it warps the other way, just reverse the process.”

    I want to ask your opinion before I will proceed to apply this method on my plywood. Did you encounter such a problem?
    Thank you for your advices
    Mihai
  • @Mihai

    One thing that should be remembered when designing a wooden clock is, thin cogs and fat pinions. There will always be some wobble on a cog, and the bigger the cog the greater the potential wobble.

    It is a common misconception that plywood is absolutely stable, but as with all materials that depend largely upon a natural component, it is affected by moisture, albeit to a vastly lesser degree than solid wood.

    So your plywood will warp when one surface has a greater moisture content than the other. I would be cautious of wetting or drying a surface in order to remove warp.

    What can be an eye jarring warp on a 60 cm sheet, will probably end up being hardly noticeable on a 20 cm cog.

    Once a cog is cut from a warped sheet, and built into the clock then the moisture content back to front will stabilize anyway, so drying or wetting becomes unnecessary.

    However warping is not always a case of moisture difference but can also come from the manufacturing process. I have had sheets with such an internal tension that by applying pressure I could cause them to warp in the other direction with a snap.

    I personally have very low tolerances as far as warp is concerned, a fact that my supplier knows and accepts, I use 25cm/100cm sheets and if the bow is greater than 2 mm in the 25 cm direction then my supplier will not send it.

    So as far as your case is concerned, it would surprise me if your aviation grade was so badly warped as to be useless, try cutting some cogs and I think you will find that they will end up pretty warp free, remember a 100% percent warp free plywood cog is as achievable as a tasty alcohol free beer :-)

    Dave





  • Thank you very much Dave,
    When I will order plywood next time I will make sure I will put some conditions about warp tolerance like you did.
    Mihai
  • Has anyone found a source in North America for plywood like Dave sources (A/A faces, 2 layers/mm, tego film bonded)?

    I've been unable to source anything close, despite several hours with google (some close in description, but not in quality).

    russg / US
  • Thank you Chris!