Rear stay bonding.

Having spent a while getting the shape of the rear stays how I needed them, and then a delay getting the epoxy, it was great to finally bond a set together.

As I mixed the epoxy up the process came flooding back to me, wetting up, micing the microfibers and then clamping together.

It was quite warm last night so the pot life of the resin was going to be short, so I worked as speedily as I could. It is a fine line between getting it all done before the resin goes off and going so fast that mistakes are made. I think I got it right, just as I finished the mix was setting.
I am using West System Epoxy as shown in the previous post.

I need more clamps really.

Scrap wood to spread the load.



The rear stay blocks will start as five layers of 9mm ply, but i have only laminated four at the moment. This block will be for the bottom rear stay and it needs a grove cut into it to take the bottom bracket reinforcments. Last time I had to retro cut this into the already shaped stay and it wasnt easy, so a lesson learnt, I will cut the grove in this block then laminate the final layer to cover the cut.

Just enough pressure to get good contact with the resin.

 

Once the resin is all set I can start the proper carving and shaping.

Epoxy resin

I splashed out on the West System epoxy resin for the build today. Hopefully this much should be enough.... It was last time.

Making rear stays.

So having done a lot of thinking and working out on paper, I decided to test my ideas. So I set out to prove myself wrong. I made a straight stay, and to be fair it could be forced work, but not very well.

So having proved that I was correct in my assumption about shaped rear stays, I set about making them.

 I cut a test shape, but forgot to allow for the extra clearance for the disc brake, so I started again. Here is the revised shape, with extensions to all the ends to allow for trimming. One thing I learnt from the www.plycycle.co.uk project was best to have too much and cut it back than not have enough and wish you had more. Its like any type of carving, or reductive sculpting, once it's gone it's gone. Having spent ages marking out the straight stays, I dove straight in, marked out the vital measurements and drew the rest free hand. I like the more organic approach.

Final shape with extension for disc brake clearance.



Having got the shape how I think it needs to be, I cut more. Four for the top ( the top stay is slightly longer at the top where the frame connects) and four for the bottom.

 

 

Here they are stacked up ready to be laminated together. I will go for West System epoxy resin again as I got to know its curing behaviour on the last bike. I have found that the local candler has started to sell it, so I won't have to trek across town to get it like last time.

Making the rear stays work...

 

On the first Plycycle the bottom rear stays came together with relative ease, it has become apparent that this was for several reasons. First, I didnt know it could be a problem area, but mostly because I had chosen to build the frame around 700c wheels with racing tyres which are very thin. I was also lucky in that the chain set I chose was a design with a large gap between the crank arms. Both of these factors allowed me to make the bottm rear stays straight and strong with no need for fancy shapes to get clearance.

 

However on the Plycycle Mk2, I have decided to use 26 inch wheels with slick tyres. These are essentially mountain bike wheels which are wider, even with the slicks on they are nearly twice as wide. Added to that the chain set i had planned on using (the Simano Alfine) has a relatively narrow clearance between the crank arms. I think I will have to look into an alternative crankset as I will need all the space I can get.

 

 

 

This drawing shows the problem, in order to make the new rear stays I am going to have to make the bottom rear stay a fairly complex shape. I may even have to set the wheel futhur back to make the space I need. I have already toyed with the idea of moving the botton bracket forward by an inch to help make more space, but this may compromise the cycling position.

 

I started to try and plan it out with some card board, and as things stand I would need a shape similar to the drawing above.

  

This is about as fat as I can get the bottom rear stay,

the fatter the better as it is a point of high stress in the frame.



From the side the geometry looks like it will all work out fine.

I like scribbling notes amd measurements down on bits of wood.





 

 I think the best way forward is to get the chainset, then work to that, otherwise it will all be a guessing game.

 

 

 



Frame shaping continues.

This was a trimming and tweaking session. Earlier in the week I had spent some time looking at the frame, trying to work out what should stay and what should go from the initial (rather generous) frame cut. I marked out my thoughts with pencil and today I started trimming.
In some places I took off about 6mm, and in others it was just enough to get all four layers to match exactly.
There was lots to do with the jig saw, and I used an angle grinder with a car paint stripping disc to do some edge rounding. But both of those tools while quick are a bit heavy handed. They leave little bumps and irregularities that are best fixed with hand tools. I started a bit if hand tool work, but that will mostly start in ernest in the next session. So the power tools are quick but it is vital to remember to leave a little extra to alow for the refining with the hand tools, which does inevitably take more off the frame.

 

It is good to see the shape coming together now. I am always guessing how much to take off, as once gone it can't go back. I want this bike to be lighter, but it also needs to be strong enough. The first plycycle was strong, but a touch on the heavy side, so I am trying to improve on it. Only time will tell.

 

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This clip shows what I have described above in more detail.

Digital design.

I had a go at knocking up the old Plycycle in Google sketch up, with a view to useing it as a tool to push the design of Mk2 in the digital world, but to be honest I was fighting a loosing battle.
I think that the best way forward is as with the first project, just get into the garage and make the thing.
In the past, I have often had the oppotunity to learn computer animation, but it just never sat very well with me and I have always felt more at home working in the physical stop motion world, where things are made and you can touch them. I do like the digital design world, and I do use it alot, but with other people driving the computers. I think I will leave it that way for a bit longer.

Any way here is a little animation of what I did build in Sketchup.

 

So I failed to move the design on digitaly, but I did have more sucsess (as seen in the last post) with a sheet of card board.

Cutting the main frame shapes.

Just getting on with it is often the main problem on a project like this, so I grabbed the opportunity to get started today.

I adapted the frame shape using the original cardboard template from Plycycle, I added extra around the bottom bracket area, and I am going to try a wooden seat post structure this time too. So with those additions I cut out four shapes from the template.

Last time I used dowel to hold the elements together, but this time I have used some bolts, the dowel was tricky to get out of the finished frame without damaging it last time.

That was a solid two hours work, including the thinking, prep and cutting of the main frame elements from the template.

The cardboard template on the fresh sheet of plywood, ready to be cut.

The four frame elements all bolted together.

It feels great to get it started!

A fresh sheet of ply.

I made the first move in building the Plycycle MK2. I bought a fresh sheet of plywood. I made the trip to Avon Plywood, who are the main retailer of ply near Bristol. They store it flat and have a huge choice. This time I went for 9mm long grain birch ply. The first Plycycle was made from 12mm birch, and this worked very well, but having looked it over and ridden it a lot now, I think 9mm birch ply will be strong enough and be lighter into the bargain.

The Avon Ply warehouse, they got alot of ply.

I think it is great that a sheet of wood can become a bike.

The original Plycycle.

The first wooden framed bicycle I made was the Plycycle. There is a website showing the finished bike at www.plycycle.co.uk there you will also find a link to the blog of the build.

The Plycycle Mk2 starts here....

Ok, so this is only the blog, but this is where i will track the build of my second wooden framed bicycle, the plycycle Mk2.