Laminating the frame: the real stuff

All preparations are ready now, and it is time to apply epoxy and carbon.

The epoxy I use is multipoxy, bought from Polyservice in Nieuwekerk a.d. IJsel. It is well priced, has a nice viscosity and usually enough pot life. For the uninitiated: pot life is the time that you can work with the mixed epoxy before the fluid starts to get thick and to sticky to handle.

When laminating the front beam one of my batches epoxy cured far to quickly, probably because of the rather high temperatures in the attic that is my workspace. To prevent this I now use the biggest paint holders that I can find, mix a maximum of 300 grams epoxy, and I use a second paint holder for cooling. The second paint holder is filled with an icepack and some water, and the paint holder with epoxy is placed on top of this. It keeps the temperature low and slows the curing of the epoxy. Here the paint holder with icepack:

The plug is placed on the table with the right hand side up. Some foam blocks are used to support the frame.

First step after mixing the resin is covering the plug with a layer of epoxy. This makes is easier to fixate the first ply of carbon on the plug. After this the first ply is placed carefully upon the plug.

The large side surface is impregnated with epoxy, and afterwards the material is word around the upper and lower edges of the frame. When the plies are slightly to large the material is cut using normal scissors. Difficult areas may require small cuts into the ply to conform it around bends.

Nitril glooves are used to prevent skin contact with the epoxy. I take several new ones during one session as they tend to get sticky on the outside, this makes the work more difficult.

All epoxy work is done using cheap disposable brushes. large brushes work well for the larger areas, and the 30 mm size is ideal for working the details around the edges.
Andries is working on the head tube area:

Carefully ply after ply is added to the plug. Between the first and second ply we add a number of local plies in the high stress areas around the bottom bracket and the forward head tube.
A nice view of the frame with me and my lathe on the background:

Before the last ply the area around the bottom bracket is strengthened using carbon fibre roving wrapped around the bottom bracket tube.

The last ply is a diagonally oriented one. The advantage is that this ply does not fray at the long edges. This makes it easier to achieve a nice edge. I intend to leave the carbon visible, so a beautiful laminate is important. In ths laminating session we use about 500 grams of epoxy. Not all will be in the bike, as the bruckes do take quiet some epoxy, and excess epoxy will get into the peelply and breather material.
After the last ply we cover the frame with a piece of peelply. The peelply is larger than the pieces of laminate. The peelply is cut at the edges to make in form around the edges of the frame as is is much less deformable than the carbon. After this two layers of breather material are added. The breather is smaller to ensure that is only does touch peelply, and never bare epoxy as it is very diffucult to remove breather that is bonded to the cured surface . Any sharp points on the rearframe get a layer of breather as well to prevent a puncture of the vacuum bag.

Making the vacuum bag is a difficult and hasty job, so we have few photographs. We use foil that normaly is used for covering the floor when you paint the house. We start with a piece of foil with a width of 1 m and a length of 5 m. The foil is placed on the floor, and the laminated frame is placed on top of it. With a silicone gun we go along the edges of the foil, making sure we leave no gaps. The uncured silicone will seal the vacuum bag. Then the foil is folded over the frame, and in the rear triangle the foil is tucked in between the frame stays.

Vacuum connections are worked into the silicone between the upper and lower foil, or on the flat foil using a suction cup. Regretfully we put the vacuum hoses into the lower seam. This is not a good idea when you intend to place the frame on a table as we discovered to late.

We put on the vacuum and carefully work around the edges of the foil to check for leakages. We work the silicone into any creases in the foil. Slowly the vacuum builds up and we align the frame on the table.
It is a lot of work to find the last leaks, and as I had to pick up the kids Andries did most of this alone. We end up with a fairly good vacuum bag. A pressure of 0.8 bar below atmospheric, and a pump that runs for about 5 seconds out of every 13. Not perfect, but good enough.

And now the long wait for the frame to cure........

laminating the frame: preparing the carbon

Today is the day to make or break the project. The plug will be covered with carbon, or the be more precise: half of the plug. If anything goes really wrong is this stage it will completely mess up the plug, requiring a lot of extra work (like making a new plug).

This is the black gold (at 35 euro ex. VAT per sqm) that will cover the frame:


Laminating a frame like this is not something you can easily do alone (I know, I did it with my first tandem), so today my good friend Andries is comming to help (if he wakes up).

You have to laminate in two stages, because I use a positive plug. If you would laminate it all around in one go, it is impossible got get the material really tight around the plug. When you would put on the vacuum the carbon will start to wrinkle as it has nowhere else to go. Laminating half of the frame prevents this.

My first idea was to cover first the bottom half of the frame and in a later stage the top half. Some discussion with Andries lead to a better solution. We laminate first the right hand side, and later the left hand side. This make the laminating much easier to do.

We start with preparing a cardboard template to cut the carbon.


The templates are used to cut the carbon. We use electric scissors. They are much reasier to use than normal scissors because the cloth can stay still and almost on the table. The cloth is easily damaged as the fibres are quite loose.



The first ply looks like this:

The laminate consists of carbon with a weight of 200 gr/sqm in a keeper weave. we use 6 layers of this. 4 layers have a normal fibre orientation (horizontal and vertical on the frame), the tird and last layer have the fibres oriented under 45 degrees. This greatly increases torsional stiffness.
The result of the work is this:


And of course these expensive leftovers:
The last preparation is cutting the peelply and breather material to shape:

Finishing the plug

Today the first part of the frame has been laminated. But as I am a little bit behind with the blog I will start out with some previous work.

The plug now consists of all the major components. To finish the plug first I have to add a metal plate that will function as a connection plate for the chain tensioner. The chain tensioner will keep the forward chain tensioned and will allow the front cranks to be moved forward or backward without changing the length of the chain.
The picture below shows the recess for this plate. On the right you also can see the place where the foam meets the intermediate tube, this gap will get a fillet.

At the positions where the front seat will be mounted a fillet of thickened epoxy is applied into a recess. To mount the seat I will drill a hole in the finished frame.


All epoxy is mixed with cotton and glass spheres. The cotton gives strength, and the glass spheres make the mixture thixotropic and easy to handle.
as already mentioned, the gap at the connection between all metal parts and the foam is filled with the mixture to make a nice and even plug.
The area around the bottom bracket gets extra attention to achieve nice fluent lines in the plug.
After application of the mixture the surface still looks rough and uneven.

The surface of all fillets is covered with the magnificent peelply. After curing the peelply is pulled from the frame, leaving a smooth and lightly textured surface with no sanding required.
The frame with the uncured fillets is mounted onto a table and fixated with heavy objects. In this stage it is still easy to bend the frame and I want to have it as straight as possible.
When you remove the peelply you have to apply a lot of force. The reward is a really cool display of physics: at the point where you pull the peelply from the epoxy a deep purple light is showing, a bit like the black light effect on white clothing.

After some final sanding and shaping the finished plug looks like this:

The plug is now ready to be laminated. All tubes are stuffed with foam or empty filmcans (these fit niceley into bottom brackets) to prevent the vacuum bag from beiing sucked into these tubes. Without this the bag would rupture at the tubes, not a very good thing for a vacuum bag to do.


And now up to next stage: laminating the frame.