There has been some interest in using carbon fibre lams in traditional bows over the last few weeks.

I suspect that one of the main reasons why more people are not prepared to experiment with carbon is that it is quite expensive compared to glass. I make my own and a pairof carbon lams 72" long, 1.5" wide and .030" thick costs me a few dollars per pair.

In the interests of promoting the use of carbon fibre and reducing the costs of making bows, over the next few weeks I will show how I make my carbon lams.

First the materials. I have used two types of carbon: uni fabric and carbon tow. The uni fabric makes a very attractive laminate, but the tow makes a very stiff laminate.

The first photo is two different types of uni fabric. One has a thread which holds the carbon together which is made of carbon. The other (with gaps) has a cross thread made of polyester.

The second photo is a pic of carbon tow.

I will finish now and see how the photos have loaded and what they look like.

It appears as though I can post only one pic at a time.

Here is the fabric.

Here is apic of a fly reel loaded with carbon tow. I use this to lay the tow in the mould.

A word or two about tow vs fabric. I have just started using tow because I cannot obtain the fabric which worked for me. When I worked out how to make the laminates (and I am still learning) I made a bow which is identical in dimension and materials to my own bow.

My bow was a hybrid 62" long, 48# @ 28" from the back of the stave. The limbs were 7.6mm thick at the mid-point. The first bow made with carbon tow lams is identicla in all respects except: I used the carbon tow lams and the limbs were 7.4mm thick at mid-limb.

The draw weight of the bow made with carbon tow limbs is 63# @ 28".

This is a fair indication of the stiffness of the two lams.

Now for the mould. The mould is made of steel because i learned through bitter experience that a wooden mould shrinks and twists in the hotbox and it sometimes created lams which were not of uniform thickness.

It is in2 parts, the base and the top. Both the base and the top comprise a piece of .25" flat steel to which I glued with epoxy, a piece of 2mm sheet steel from a sheet metal shop. The thickness of the lams is determined by pieces of thin sheet steel glued to the base of the mould to form shallow channels.

In this photo you can gain some idea of the depth of the channel

This pic shows how I make a pair of lams using the thin pieces of sheet steel. The dark sections are the base of the channel and te light sections form the walls of the channel.

This pic shows one end of the mould. The carbon tow is tied of at this end to start the lay-up and it is tied off at this end to finish the lay-up. The "fence" is to keep the pieces of tow parallel to each other.

This pic shows the other end of the mould. Pay particular attention to the hi-tech, sophisticated devise for tensioning the carbon two: some rubber bands.

Oops, please excuse the spelling mistakes in the previous post.

I will not be posting any more pics and comments for a few days. The next set will show the process of laying up the carbon tow, applying the epoxy and working the epoxy into the tow.

I have created a separate thread for comments and questionas. Please use it and leave this thread to the pictures and the text. This should make it easier for people who want to save the finished thread and use it.

I will gladly answer your questions, if I can, in the other thread.

Thanks Norman, that was cool. Look forward to the next installments!

Patiently,

Ernie

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Keep going norman! Have you ever tried using smooth as the epoxy for the lams?

smooth ON... I wonder if you heated it so it was real runny...if it would work?

Ernie

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Where's the Beef? as in information.

What do you use for a releasing agent? Tell us about the process of laying it up. What type etc. is the carbon tow?

BBP

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Hi,

Sorry it has taken so long to post the next instalment in this build along, but I have not been able to get to the workshop for nearly a week.

Next time I do something like this I will wait till I have all the pictures before I start the thread.

I laid up a new pair of lams today. Most of the photos I took are not useable because the lighting in my workshop where I use the mould is not adequate for photography. The first set were taken on a separate bench which is well lit with two fluourescent tubes.

But I will post what i can and try and use text to explain how I build the laminates.

Hopefully this pic will show the scraper in one of the channels. This is the tool I use to press the epoxy into the carbon tow.

I wet out the tow thoroughly with laminating epoxy using a brush. Then I clamp the tow in place with a piece of flat steel at each end of the mould. This fixes the tension of the tow and prevents movement lengthwise as I work the epoxy into the tow.

This worked out better than I hoped.

Here is another pic. If it works it shows the wetted fabric clamped in place using the flat steel.

First things first: when I finish making a pair of laminates I remove all dried epoxy from the mould and apply a coat of wax to both parts of the mould. All surfaces which MAY come into contact with epoxy MUST be covered in wax. I then put the mould aside until I use it again.

So the first step is to buff the wax to a sheen using a cloth, any type will do.

The next step is to wind the tow onto the fishing reel. I find that one reel full is required for one lam. I use four lengths, two deep, making a total of eight lengths. Each is about 84 inches long. So each lam uses abut 56 feet of 50K tow. This means that in a single laminate ther is approximately 400,000 individual fibres (8 X 50,000).

I set the mould up by clamping the wooden block with the rubber bands to the mould. Then I clamp the mould to the bench.

Starting at the end which does NOT have rubber bands, I tie off the tow to the outside hook. I then pass the tow through the first gap in the fence, along the channel and through the corresponging gap in the fence at the other end of the mould.

I then pass the reel through a rubber band and stretch the rubber to a point where the carbon is straight, but NOT tight. If it is stretched too much, the tow will not lie flat and it bunches up into a cylindrical shape. This will leave gaps in the laminate where ther is no carbon. If there are any, I do not use the laminate.

I then pass the tow through the adjacent (the second) gap in the fence and down through the corresponding gap in the fence. The tow is wrapped around a hook several times and I then pass the tow through the next gap in the fence (the third).

The tow is taken through the third gap in the fence, through a rubber band and through the fourth gap in the fence. I then pass it through the fourth gap in the fence where it was first tied off and it is wrapped around a hook. and I tie it off.

This is the first layer. I then repeat the process to produce the second layer.

I then follow the same process with the second channel.

When the lengths of carbon in both channels tow are tied off I slamp them in position using the two pieces of steel.

In the last sentence above, it should read: "... I clamp them in position..."

I then mix the epoxy. You will have to determine the quantity you require, if you make your own lams. But here are some pointers which should help you arrive at the right quantities. If you make two lams 72" long, 1.5" wide and about .030" thick, use about four ounces of laminating epoxy. This should be too much, but you need too much rather than too little.

You will then wet out the tow with epoxy. I use a brush to apply the epoxy and a scraper to press the epoxy into the tow. Be generous. If you try to use just enough, you will probably find the lams will have shallow depressions in the top surface. The mould is unuseable if this happens.

I work the wetted tow for 15 to 20 minutes with the scraper. I drag the scraper along the tow with the edge trailing. I apply enough pressure to bend the scraper so that about an inch of the blade is flat and parallel with the bottom of the mould.

When the tow is dry it sits about .050" above the mould. When it is wetted out thoroughly it sits about .020" above the mould. Further pressing of the epoxy into the tow is not required. The tow is fairly bulky even when wet and it will continue to be proud of the mould. This is normal. The important point is to make sure that the tow is thoroughly wetted. When the tow will not compress any more, you can stop working it.

I find that the tow will tend to overflow the channels. When it is wetted out I then move it back into the channel with the scraper.

When this is done I put the lid on the mould.

When I had my mould weld up I had two pieces of steel welded to each side. Thes ensure that the lid fits snugly onto the mould without the possibility of side ways movement. I line one end up with the end of the channel and lower the lid. I also had steel handles welded to the lid so I could control it easily. When the lid is i place, I do not move it. The wet epoxy acts as alubricant and moving the lid will cause the tow to be displaced from the channels.

Here is a picture of the epoxy. I will deal with clamping the lid to the base of the mould in the next post.

The following sentence

"The mould is unuseable if this happens"

should read

The laminate is unuseable if this happens.

I start to clamp the lid to the base at the centre and I work outwards from the middle to both ends. This tends to force the wet epoxy along the mould and it completes the job of saturating the carbon tow.

If you have used too much epoxy, it will flow out the sides as well as out of the ends. If you use enough, it will flow out of the ends of the mould and you may get a few drops appearing on the sides of the mould.

This photo illustrates the clamping process.

When the laminates are fully cured I will take some photos of them as they come out of the mould. This will illustrate the surplus epoxy which has flowed out of the mould at each end. It will also illustrate that some wastage of tow is inevitable. It will take several days before I can post those photos.

When the clamps are in place, I leave the epoxy to attain its initial cure.

The manufacturer stipulates 24 hours at 21 deg celcius or 70 deg Farehheit. It seldom reaches 21 deg C in my workshop so I leave it for 2 to 3 days. Then I place the mould in my hotbox at 50 deg C (122 deg F) for 24 hours. I then turn off the power and I leave the mould for another 24 hours to cool down before I remove the lams.

So the next few posts should be in 2 to 3 days.

This photo shows the carbon tow tied off and wrapped arround the hooks at the end where it is not tensioned.

Here is the photo.

The next step in the process of making the carbon laminates is the the elevated temperature cure.

The steel mould when it is clamped together is too heavy for one person to lift and two people can manage it, with difficulty. So in order to place it in the hot box I remove all clamps except the clamps holding the flat steel in place on the carbon tow, the pair of clamps at each end of the lid ofthe mould and a pair of clamps in the middle.

Here is a photo.

Interesting

How difficult would it be to put some reflex into your mold??

I can lift this much weight, although it is awkward to manoeuvre in the confined space of my workshop.

I place it in the hot box and replace the clamps. Here is a photo.

This photo shows the thermostat control on the front of the box and an electronic thermometer which I use to monitor the temperature inside the hot box.

The laminates will cure at 50 deg Centigrade for 24 hours and I allow them to cool fully in the mould, in the ho box for 24 hours to eliminate any possibilty of the laminates twisting or distorting.

The pieces of steel which clamp the tow into place are important in this stage of the cure. The epoxy softens slightly when it is heated to 50 deg C and if the pieces of tow were not held in position they may move slightly and produce an inferior laminate.

Clamping the tow in place reduces the likelihood of movement while the epoxy is soft. With continued exposure to the heat the epoxy cutres completely and is hard at 50 deg C.

At this point the heat distortion temperature of the epoxy in the lam is 65 deg C or 150 deg F.

The mould is in the hot box as I type this, and the power will be switched off in about six hours. The mould will come out of the hot box in about 24 hours after that.

At that time I will take some pics showing the rough lams in the mould and how I turn them into lams which I will use on my next bow.

The next set of photos shows the laminates in the mould, how I remove the waste epoxy and carbon tow and how I make the lams safe to handle.

A word of warning here: the qualities which make carbon fibre and epoxy such a great laminate also make great carbon splinters. They are long, fine and sharper than most needles. They can also break under the skin.

At this stage I always wear safety goggles to protect my eyes and leather gloves to protect my hands. I do not handle the laminates until the edges have been sanded round and smooth.

This photo is one of several which will sshow the laminates in the mould before they are removed.

It is important to note in this and the next few photos, the waste epoxy at the end of the channels and the waste epoxy and carbon tow which has flowed out of the channels.

This is normal (for me anyway).

The next photo shows more of the same.

This photo shows how the tow will overflow the channel.

More of the same.

When the lams have been removed, I clean up the mould and put it aside until I need it again.

The first step is to remove waste epoxy from the base and the lid of the mould.

This is a photo of a patch of dried epoxy on the lid.

I then clean the mould with a piece of very coarse steel wool. Finally I apply a thin coat of wax and put the mould aside.

This photo shows the laminates separated from each other.

To separate the lams I simly snap the thick waste at each end and then carefully tear the remaining waste down the middle.

To remove the waste and prevent the lam from being shredded in the process, I clamp the waste between two pieces of timber and clamp the lot to the bench to prevent it from moving.

I leave about 0.25" of laminate protruding.

Then I use a hacksaw to cut the waste off eac end.

Here is a piece of waste.

The tools I use to trim the waste are cutting board, a pair of leather gloves and a Stanley knife, and of course, safety glasses.

I used to clamp a batten onto the carbon to keep it in position, but now I cut off the waste free hand.

The blade will tend to follow the fibres and all I do is separate them. Most of this process therefore is simply allowing the blade to do what it wants.

The tricky part comes when the fibres in the waste want to rejoin the main part of the laminate. At that point you have to cut through them and cut parallel to the sides of the lam. It is very easy to allow the knife to open up some fibres on the side of the laminate. If this happens, I simply cut straight through to the outside edge. Later, as you will see below, I then remove any serious dips with abrasive paper.

The reason for this is simple: I will remove a good part of the laminate when I release the bow from the stave. Provided the laminate will cover the bow, it does not matter if the sides of the lam are not dead straight.

This photo shows how easily the fibres will split. Keep in mind that the waste is thinner than a sheet of paper.

The laminate will split, but not as easily, and it will never split when it is glued to the core as long as the core remains intact.

I then stand the laminate on its edge and remove the remaining waste.

This photo shows a jig I made to enable me to work with timber veneers about .020" thick.

It works even better with carbon fibre about .035" thick.

I clean up the edges in three stages.

In the first stage I use a 10" bastard file. This cuts the waste down to the edge of the laminate. It can leave loose fibres however and these are dangerous.

In the second stage I use a sanding block and some 60 grit abrasive paper. This removes all but the finest splinters.

In the third stage I use 120 grip abrasive paper to remove the remaining splinters and I remove the square corners from the laminate. During this process I lightly rub a piece of cloth along the edge to pick up remaining fibres. I then remove them with the 120 grit paper.

The final stage is to inspect both surfaces to determine which has the most shallow voids. This pair were quite good. This laminate has a few on one side and none on the other. I sand the worst side and use the epoxy adhesive to fill the holes.

This is not a problem and does not affect the bow. When the carbon on the back is put into tension it is stretched across the core. When the laminate on the belly is put into compression, it is pushed into the core.

I do not use a laminate which is severely pitted with voids.

This photo shows one of the voids on this lam.

Here is another.

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The next few photos show one of the laminates beside a piece of flat aluminium bar I use as a straight edge.

Here is the next pic.

Here is the final pic. It purposely shows the gap between the lam and the straight edge.

This photo and the next shows a flaw in one of the laminates. The tow has separated in the mould and the light streak is all epoxy.

Above I noted that such lams are unuseable. What I should have said was that the WHOLE lam is unuseable. I will easily cut a sound section out of this lam and with another section from another faulty lam (of which I have several) I will obtain a pair for my next bow.

Oops! I did not realise the photo was that bad.

This photo shows the lam ready for sanding. Note that it is about 1.75" off the bench so as to give me plenty of clearnce for my knuckles.

The flat aluminium bar is to smooth out any minor irregularities in the surface of the wood.

Finally, note how the laminate tapers toward the end. This is caused by the gaps in the fence being inside the channel. I must have one picket against each edge of the channel so as to maintain the straightness of the ribbons of tow. The curve of the laminate also illustrates how the ribbons of tow will flatten and overlap in the channel.

I have to exercise care when I sand the laminates. They are very flexible but they are not indestructible.

To sand them so that there are no low spots or high spots I clamp them to the alunium bar and the long piece of timber.

I first clamp one end to the supporting bar and timber, so that about six to eight inches can be sanded. This length is stiff enough to be sanded without buckling. This exposed end is then sanded. I use a cork sanding block and 60 grit abrasive paper.

I then sand the opposite end of the lam using the same technique.

I then clamp both end which have been sanded to the support and sand the remainder of the laminate.

This photo shows the lam, part way through the sanding process.

Finally, the end result: a laminate about 1.4" wide,72" long and .035" to .040" thick.

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Wow...thanks Norman...very thorough!

Ernie

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