Design

Geometry
My current bike is a Condor Pista single speed. I use it for everything from my daily commute into London to the 110 mile King of the Downs ride every year. To be honest I don’t know why i’m building a new one, because I love my Pista, but it’s always fun to have a project. Conveniently Condor have a full frame spec for all their frames on their website so it was just a case of finding my frame size and reading off the dimensions.

Style
I drew a whole series of curvy frames where the top tube blended into the seat stays. However, once i started to work through the actual construction I realised that the curved tubes would be much harder to form as you obviously want the wood grain to run along the length of the tube. Renovo achieve this by laminating the frames in 2 directions around curved templates to get vertical stripes but curved tubes. Sounds tricky, so straight tubes it is then. It also turned out that using straight tubes minimised material wastage and hence the cost of the wood (the cost of the wood was looking like it could jeopardise the project at the point i made this decision).

I work in an engineering office, so I have access to CAD software that I use regularly. I put the basic frame geometry in and started fleshing it out with the shape of frame that I had in mind. I knew that the frame was going to be around 50mm wide with a 60mm deep down tube, 40mm top and seat tube, 20mm round stays and i’d aim to get the whole lot formed to a 5mm thick tube. These numbers weren’t entirely plucked out of thin air and i’ve written a bit more about it in Why Wood. I also spent some time looking at the various high end carbon fibre frames that all have the same style of oversized, thin walled tubes to maximise stiffness but minimise weight.

The frame was going to be built up from vertical layers in 2 halves and then bonded together like the Renovo frames. I found some really useful photos of Renovo frames during construction that helped focus my design.

You can see in my CAD drawing, i’ve left in some solid bands inside the tubes where my bottle cage mounts are going to go and to provide some internal stiffeners like the Renovo frame above. The one part of the design that I was struggling with was how to join the different straight sections of wood together. Renovo use a very neat finger joint at each of the joints that you can see here

I don’t have a finger joint cutting tool for my router and they tend to be quite expensive, so I came up with an alternative (in retrospect this decision added a lot of time to building up the frame but i feel quite happy with the strength of the joints). At each of the main joints you can see i’ve left it solid in the CAD drawing. The idea was that each layer would be fully lapped onto the next over the full length ot this solid region with each layer running in the opposite direction to give the joint strength. It is probably easier to see this in the construction pics .

Materials
Wood – I’ve never worked with exotic hardwoods before so there was quite a bit of homework to be done here. My goal was something like this frame which uses wenge, maple and padauk hardwoods.

Rather than copy it verbatum, I wanted to understand why they had used the different woods that they had chosen. I’ve written about some of what i’ve learnt about the different woods that are suitable for bikes in Why Wood? but the short version is that the woods chosen for the bike above are all both dense and stiff. That means that you can build a fairly thin walled frame that will be light, stiff and still dent resistant.

I contacted a whole range of UK hardwood suppliers for quotes and ended up placing my order with Timberline hardwood specialist. They were very helpful and helped me get the wood I wanted for a lower price than many of the other suppliers.

I ended up running with 2 x 10mm thick maple central layers, 6mm wenge and 10mm bubinga outer layers. The bubinga is very similar to padauk in material properties but is slightly browner and seemed to be more readily available from the suppliers I spoke to.

Aluminium Donor Frame - Bottom bracket, head tube and seat tube

Other parts – The bottom bracket, head tube and top section of seat tube are all formed from aluminium inserts glued into the frame. I scoured the streets for a discarded aluminium frame that could be used as a donor bike. After a couple of weeks of keeping my eyes open for suitable candidates, I noticed a Kona racing bike frame locked to the bike racks next to my house. The bike had been stripped of EVERYTHING and the rear stays had been bent till they were touching each other. There’s no way anyone was coming back for it. 10 minutes later with a hacksaw I was the happy new owner of 2 halves of frame (well it was easier cutting through the frame than the lock!)

I used West System epoxy to glue all parts together which i got from The Fibreglass Shop in Brentford. I also picked up some 25mm wide 175gsm fibreglass tape to use for reinforcing the frame at the aluminium to wood joints.

On to Construction

18 thoughts on “Design

  1. Hi, Loving the information thus far. I too went down the route of “exotic hardwoods” after looking at a couple of youtube video’s from Craftsman Chen.


    the first employs using planed wood, after much searching for a company that would plane the wood, the cost of the “rework” of the planing scuppered that route although i like the mahogany, beech combinations. I ended up looking at the marine ply options as a cheaper option to keep the “stripes”, although of recent days I’ve been pondering over the solid beam options instead of laminate and carving the shape out of the beams by milling

    • Hi Peter,
      Thanks for the comment and thanks to the link to Craftsman Chin, I’ve never heard of him before but his frames look nice. To answer some of your queries about wood selection.

      Firstly, I do not consider marine ply to be a good subtitute for a dense hardwood. The material properties of typical marine plywood are nowhere near as good as a solid hardwood as half the wood grain is facing the wrong direction. Using a high quality marine ply made from dense hardwoods would help but it will also be more expensive.

      Solid wood, rather than laminating up several layers comes with other issues as the wood will have a much higher tendency to warp if carved from a single piece. This will mean that there is no guarantee that your frame will stay straight.

      I notice that the Chin frames are solid rather than hollow. They will be seriously heavy as a result.

      As a cheap option i’ve recently looked at sourcing used maple floor boards that I could clean up, plane to thickness and use for frames. Haven’t tried this approach yet though.

      Talk to the wood supplier and find out what thicknesses they can easily produce then design your build around that. 10-15mm should be easily achievable without much additional cost. Thinner sheets are harder depending on the machinery they have to hand.

      Hope that helps
      Nick

      • hello Nick,

        the only reason i looked at marine ply was due to price, in hindsight it would not be the best route to take so that one has been discounted out of the runnings as not only would it make a heavy bike it would lack the integral stiffness im after.

        Looking at your designs they make much more sense in grain orientation.

        I will give timberline a shout for a price, do you have an invoice number to hand that i can get them to search for your orignal shopping-list of wood for the build?

      • I don’t have an invoice number I’m afraid. It came to around £200 for the wood. If you’re worried about cost then it will be cheaper using european or mass produced hardwoods from a non specialist timber merchant. Try Ash, Walnut, Sapele, Merbau, Oak….. There are also some very sustainable reconstituted wood products with good material properties that I’ve always thought it would be interesting to use or even bamboo boards (lamboo). So many choices!

  2. Hi Nick,
    Thats much more reasonable cost wise than the wood i was looking for the craftsman chin frames, they were the interesting end of £700 after all the rework required. Im happy with that price. What sort of board widths did you have to get in as i noticed you eluded to the lengths of the board being 2m.
    I’d be happy to try other woods as long as they dont detract from strength and ridgidity.
    in respect to gearing i’m happy going with a 9-10spd on the back and not having the hassle of the front mech.

    • if you do have any further information on sizes of wood you obtained from the stockist mentioned above that would be very useful as they are currently looking into this for me, although i beleive they are running low on maple and are substituting for sycamore, would that greatly afect the frame integrity?
      If you have any further information please give me a shout on petebarchetta at yahoo dot co dot uk
      thanks for your help so far

      • Sycamore Maple is different to the Sycamore plane tree and is part of the maple family. If they have suggested it as an alternative then it should be fine. Worth double checking though.

        I can’t remember the order so you’ll have to add it up yourself. At a guess, the boards were about 130mm wide and needed about 5m in maple and bubinga and about 6m in wenge.

  3. thanks i will ask about the Sycamore maple and sycamore plane tree and see if there is a discernable difference.
    I’ve contacted the exotic woods and he has priced up a set going by the information you had given me. Do you have a set of CAD drawings i could look to print templates out of?

  4. I am too considering buidling a wooden bike… an Ash/Sapele Mountainbike……if anybody needs CAD drawings I found rattleCAD, http://www.rattlecad.sourceforge.net which is a FREE bike frame design software has both road & mountainbike drawings… can change all parameters, ie: tube dimensions, angles etc…

    • Hi Thijs. You want the wood to be as stable as possible (i.e no warping and minimal tendency to crack). To achieve this i would use planks that are cut with as straight grain as possible. The best way to stabilise the overall frame is to use multiple laminations and if you are cutting several layers from the same plank then flip the direction of the plank for each layer. This means that any tendency for one layer to warp will be resisted by the adjacent layer.

      For example pic1 will tend to curve upwards, pic2 will probably twist and pic3 may end up splitting along the grain

      Its worth noting that even though pic1 looks like it doesnt have straight grain on the surface it would probably perform fine when laminated in multiple layers.

  5. Thanks ! I will buy some nice wood this month. When my build is finished, i send some photo’s ! Hopefully the bike is ready at the end of the year haha

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s