I welcome any questions or comments about building carbon fibre lams.

Awesome Norman, very glad your doing this. Cant wait to see more.

Very interesting! I admire you guys that 'go public' with your projects and pictures with the desire to help folks.

This will be neat to watch.

I think it's awsome. I guess my question would be....where do you get the materials? Carbon is expensive and I'm cheap.LOL

Thanks Kevin

Hi Cutty Secondly, have you ever experimented with kevlar, or kevlar/carbon fabric for tip overlays?

I have experimented with carbon and timber veneers and they worked well. However there was no real advantage over several layers of timber veneers.

Also, have you ever worked with, or researched, high compression composities for use on the belly of your bow? Specifically, polymer-glass, or ceramics?

No. I am a hobbyist, not an engineer. Carbon fibre is a material which resists compression almost as well as steel, and is a fraction of the weight. Again I am limited in what I do by what I can buy at the local or interstate fibreglass outlets.

I have made some syntactic foam as an experiment using glass microspheres and laminating epoxy. The problem is I would have to make another mould about 2.5mm deep to make it useable thicknesses.

Oh, and before I forget...I was trying to remember the speed you quoted for one of your early "D" longbows...it was rather impressive for the style.

I have since learned that the chrono was wildly inaccurate. They are quick for a longbow but not as quick as one of my hybrids.

Hi Kevin I order my epoxies through a local fibreglass supplier who caters to boat builders. I purchased the carbon tow from a source in Melbourne, Australia.

It is not difficult to obtain epoxies and fibres. I suggest that you try "fibre glass" in the commercial section of your phone book. If you live in a small town, try an on-line phone directory.

Norman: I'd like to show everyone my fixture and methodology but don't want to deter from what your doing here, I'm going to start another thread.

-Mike

Whats the thread Half?

Gil, On laying up the carbon, how do you ensure the cloth/tow doesn't compress so much that it squeezes out all the epoxy?? Just put stops on the press?

CM...there is a picture on BS's site that has carbon in the middle of some action wood.. is that method still in use there or just solid wood cores?

Ernie

Im interested in knowing what resin/epoxy was used, Looking forward to the next instalments :)

See Carbon Lam Fixture. Let's keep comments specific to that fixture on that thread.

-Mike

Whats the thread Half?

There is a separate thread I am putting together which will show anyone who is interested how to make their own lams. I have asked that questions be submitted in this thread so that the other thread will not become too cluttered. Do a search for carbon fibre and when you find it you may want to add it to your favourites. I will do a TTT each day to keep it visible.

Gil, On laying up the carbon, how do you ensure the cloth/tow doesn't compress so much that it squeezes out all the epoxy?? Just put stops on the press?

The mould is rigid and the sides of the channels form the stops. The top is clamped to the sides of the channel, rather than the channel itself. This prevents the fabric from becoming starved of epoxy and it maintains a uniform thickness in the laminates.

Ernie

have you ever made fiberglass laminations using the same process ? It would be nice to get some of the old colors back.

There are aftermarket additives to color the epoxy with some subtle shades.

-Mike

I saw that Norman...thank you. You and Half both have a good looking press/form there..

Ernie

So are your carbon lams 2MM thick? BBP

Gill You mntion puting weight on te other thread to put the fiber under tension during the resin setup.

You said 11# on each was ther a reason for this weight? Would adding more weight put the carbon under more pre-tension so that the finished lam was stuffer?

Also what epoxy/resin are you using? What others have you tried? Do you use any type of release agent?

Cutty I made another post and addressed the Kevlar thing. Kevlar is heavier than carbon and not as strong in the way we are using it. Kevlar is also a very abrasive material and I dont think would work well in a moving limb because it would weaken its hold within the resin

Here is a simple graph I found that shows a quick over view of fibers. Also notice that thereare different types of carbon threads.

Something Ive been wondering about is graphite. Graphite is carbon fiber that has been heated, maybe also under preasure, til its crystalizes. Kind of like the coal and diamonds idea. I wonder what new properties graphite takes on.

http://www.azom.com/details.asp?ArticleID=978

vacuum bag pic.

http://www.acp-composites.com/acp-ucfl.htm

Apex, i could be wrong, but I think IM7 is graphite.

Thx Animal, Ive also seen T700 talked about as being very strong but dont know where it comes in.

Here is a vacum setup ACP offers.

http://www.acp-composites.com/acp-vbs.htm

Isn't the IM6, IM7, IM8 the same carbon that they use in fly rods? I've seen these codes listed in describing the different rod blanks.

Jim

Here's one. I'm interested in trying carbon cloth layed over or under fiberglass (thin) at a diagonal pattern along the limb, not to act in tension or compression, but to help stablize the recurve to prevent side to side movement and decrease oscillation.

Will it work? Who's done it? What do I need to worry about or look out for in my designing process?

What have I started here?

DRT have you ever made fiberglass laminations using the same process ? It would be nice to get some of the old colors back.

I used to make fibreglass lams using uni fabric. When I started making carbon lams I realised that there is no reason why you could not make glass lams using glass tow. But I would not use glass roving which is a different cat altogether.

BBP So are your carbon lams 2MM thick? The mould is 0.7mm thick and the lams are about 0.9mm thick. They are about .035" thick when sanded on one surface.

Apex Archery Gill You mntion puting weight on te other thread to put the fiber under tension during the resin setup. You said 11# on each was ther a reason for this weight?

I believe that within reason, the more weight the better. I only had enough weights for 11# on each half of the strip of fabric. There is also the practical consideration of how to tie the weights to the fabric.

Would adding more weight put the carbon under more pre-tension so that the finished lam was stuffer?

The objective is not to tension the fabric but to straighten it to avoid crimping in the laminate when it is under load. The carbon tow only has a few of of tension to keep it straight. I will illustrate this with some pics later. Too much tension prevents the tow from laying flat and it bunches up into a cord. This means the laminate is not solid.

Also what epoxy/resin are you using? What others have you tried? Do you use any type of release agent?

You need a release agent on anything except plastic when you use epoxy. I use a laminating epoxy which is made here in Australia but you will find many manufacturers in the USA. Perhaps CM Sackett can assist with recommending products.

Cutty I made another post and addressed the Kevlar thing. Kevlar is heavier than carbon and not as strong in the way we are using it. Kevlar is also a very abrasive material and I dont think would work well in a moving limb because it would weaken its hold within the resin.

I have never used Kevlar for several reasons: it is gold in colour, it is difficult to wet out properly and it is apparently weak in compression, altho stronger in tension than carbon. Graphite is carbon fiber that has been heated, maybe also under preasure, til its crystalizes. Kind of like the coal and diamonds idea. I wonder what new properties graphite takes on.

I cannot help you here. It is my understanding that carbon fibre and graphite are essentially the same thing, but in a different form. However I could be wrong.

Springbuck Here's one. I'm interested in trying carbon cloth layed over or under fiberglass (thin) at a diagonal pattern along the limb, not to act in tension or compression, but to help stablize the recurve to prevent side to side movement and decrease oscillation. Will it work? Who's done it? What do I need to worry about or look out for in my designing process?

You can buy carbon and glass fabrics which are woven diagonally. I cannot assist with your design question. But my only response is try it and tell us all how it works.

BBP you must have had your reply window open for a while on this thread.

If anyone gets the vacum thing let us know how it works and what ends up being you final material costs in laying up your own stuff.

Id like to know if its worth the time in doing so.

Apex I did not thank you for the diagram. I apologise for being so negligent.

In the other thread I was asked if heated smooth on would work to make laminates.

I would not use it because it is an epoxy adhesive. This is a different animal from laminating epoxies which are not good adhesives. If you start to play with epoxies there are several different types, and they all have different characteristics: epoxy adhesives, laminating epoxiess, epoxy paints and casting epoxies. There are probably other types that I am not aware of.

CM, can you help out here with some advice on the differences between the various epoxies?

Gil, it is I that should be thanking you. Very good build along, I am really getting alot of info out of it.

All this is new to many of us especially me.

Keep up the good work.

For anyone who wnats to learn about composites, this link takes you to the SP systems technical data.

http://www3.gurit.com/marine/products.php

SP Systems were a British high tech composites company who specialised in epoxies and various composites. I used one of their laminating epoxies and one of their epoxy adhesives for a couple of years until they changed their marketing policies and would not sell it in quantities of less than 20 kilos.

They were subsequently taken over by a German composites firm. Luckily their archive is still available on line. I found it to be easy to read even though I am not an engineer. Where the chemistry or the physics was beyond me I simply bypassed those sections.

The documents were all PDFs and it is worth downloading the lot and storing it in a folder so you can use it as a resource if you ever want to find out more about composites.

thank you Gilnockie. I have a few more questions but I will wait until after you finish your demo .

The SP systems technical people have been great to talk with and very knowledgeable. I suggest anyone wishing a deeper understanding of this should call them, phone numbers are on their website http://www.guritcompositetechnologies.com/html/spcontact.html and go to the contacts, SP Systems. It is a tall order to find their products in the US, but that's part of the game, none of this is easy and it can be frustrating at times. I'd email [email protected] and call their United Kingdom office, Mr Armstrong there has been very helpful. The composites folks I've contacted in the US have generally been less knowledgeable.

-Mike

Gil did you really think their adhesive epoxy wsa better than Smooth On?

20kilo is what 44lbs? I just bought Smooth On in the gallon buckets and the total weight we 16lbs (2-8lb buckets) that would be like 3 orders if it was really better you could probably find a couple people to split an order up with. I wonder what size containers that is broken up into or if its just 2 containers? I want be needing any for a while :(

As for the lam epoxy what are some factors one should look into or consider for lam epoxies compared to adhesive epoxy (smooth on)?

Apex Archery

Gil did you really think their adhesive epoxy wsa better than Smooth On?

No it was not better, but it was more than adequate. I do not use Smooth On as it is very expensive in Australia when you take into consideration exchange rates and freight.

I believe that the epoxy I do use to glue up my bows is at least as good as Smooth On. It is formulated to resist peeling, ie de-lamination. It is made in Australia and it is relatively cheap. It is Techniglue HPR5.

Here is a link to the page where you can find the data sheet:

http://www.atlcomposites.com/products/epoxy-resins/adhesives/index.htm#

When I compared the data sheets, the local product is at least as good as Smooth On. I am not being critical of Smooth On, I am simply saying that considering cost, technical specs and availability, the local product is the logical choice.

As for the lam epoxy what are some factors one should look into or consider for lam epoxies compared to adhesive epoxy (smooth on)?

CM Sackett may be able to answer this question better than me, but the variable I believe is critical is the Tg (glass transition temperature) or the HDT (the heat distortion temperature). This is the temperature at which the epoxy softens. It should be as high as possible.

Here is a link to the page which contains the laminating epoxy I use:

http://www.atlcomposites.com/pdf/KINETIX_R240_high_perf.pdf

if needed i can post a how-to on vaccum bagging. since im a boat builder (vaccum bagging is very common there)and a boywer who has made his own lams i can share my knowledge. just let me know. shantam

Thx Gil, I didnt think you were knocking Smooth ON was just asking. ANd thx for the link.

Shantam, that would be great!

ttt

Shantam, please do!

-Mike

i will no problem,butgibeme some slack please. ihave to finish 3 bows this week. shantam

i will no problem,butgibeme some slack please. i have to finish 3 bows this week. shantam

Hi BBP

In answer to your questions:

Where's the Beef? as in information.

I will start to lay up a new pair of lams in the next few days. I only lay them up when I am about to start to buid a new bow. I have been gluing up and shaping a bow and that has taken all my time.

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

Please be patient. I was going to deal with these topics as I laid up the lams.

You can use a commercial release agent or a wax furniture polish. I used Johnson's paste floor wax until it was no longer available through the supermarket. The wax must be a soft paste. I have used two types: beeswax and carnaubra. The beeswax is easy to apply and buff to a sheen. As it comes from the tin the carnaubra I use is very hard to polish to a smooth surface.

I warm it in my hotbox until it becomes a liquid and then I dilute it with vegetable based turpentine while it is liquid. This is not the mineral turpentine you use to clean up oil based paint. The wax is then very soft and it enables me to apply a thin coat. It also polishes to a smooth finish.

I do not know the brand of carbon tow. It is 50K tow and I bought it because it was available. This tow comprises 50,000 individual fibres, or so I am told. I carried out my tests with 12K tow which is a better tow for my purposes. When I do the next lay up I will take more pics and post them to the other thread. I will try to explain in more detail how I make the lams.

Keep it coming Gil :)

For me it boils down to can we create a better material than what is commercially available and still be cost effective.

The next instalment in the buildalong thread has been completed.

7 Lakes asked a question on the buildalong thread: how difficult would it be to put some reflex in the mould?

The answer is it would be possible if you had access to an engineering shop which could shape flat steel which is .25" thick, 6" wide and 84" long.

The next question is why would you want to?

As far as I am aware all lams used by bowyers are flat and straight. I can twist mine into a circle less than 12" in diameter without any indications of stress. Given that the curve of a bow limb is comparitively gentle compared to a curve with a radius of 6", the benefits of moulding a curved laminate would far outweigh the cost.

The next batch of postings has been made to the thread.

They show the laminates in the mould and how the waste material is removed and how the splinters are removed to make the laminates safe to handle.

I've given some thought about putting reflex in the mould, we machine big rings and you could cut a channel into a section of one of the rings and lay up the carbon there, it would only be useful on the tension side of the limb and might be something to consider.

-Mike

ttt

The next batch of postings has been added to the buildalong.

They show how to sand the lams so that they can be used to build a bow.

ttt

Norman:

You had emailed me that you had put epoxy into the mould and let it gel prior to laying in the carbon to minimize bubbles, do you still do that?

Have you noticed any improvement in the performance of your bows since going to the tow from the uni fabric with crossthread? It would seem the more dense laminate made with the tow might improve performance.

-Mike

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I have two of the ACP auto vac systems and can reliably pull 20" Hg with them for vacuum bag forming large R/C sailplane wings using carbon, kevlar, and glass cloth over foam cores. The smaller "fish tank" type are unsuitable for pulling & holding higher vacuums on a larger area. I use carbon (tow, cloth, laminate) & kevlar (cloth & tow) when molding fiberglass fuselages also. Carbon provides stiffness, and resistance to bending, and kevlar provides toughness and is used to toughen up molded parts to resist denting and breakage in crashes/midairs, etc. I deal with ACP also, and also http://www.cstsales.com/ & http://www.fibreglast.com/ for supplies. I am also interested in bow limb construction, and am enjoying this thread. Bill G.

You had emailed me that you had put epoxy into the mould and let it gel prior to laying in the carbon to minimize bubbles, do you still do that? Hi Mike This is an issue I will raise in the thread when I add some posts about using fabric. But to answer your question: it seems to be essential with uni fabric. The epoxy, while it wets out the fabric adequately, does not wet it out as well as it wets out the tow. This means that there is a greater likelihood that there will be shallow voids in the bottom of the mould. I applied a layer of epoxy to the mould and allowed it to gel ( about two hours, depending on the ambient air temperature) before laying up the fabric. This layer of epoxy then acts as a gel coat and produces a smooth, flat surface on that side of the lam. On the upper surface, the pressure of clamping the over full mould produces a flat surface. I will be experimenting with a layer of epoxy in the mould over the next few weeks. Have you noticed any improvement in the performance of your bows since going to the tow from the uni fabric with crossthread? It would seem the more dense laminate made with the tow might improve performance. Most definitely; the first bow I built using the lams made from tow duplicated the bow I was using. The original bow, made with uni fabric lams, drew 48# @ 28”. The first bow made with carbon tow lams drew 63# @ 28”. It was very, very fast. The interesting feature is that I would not normally be able to shoot a bow of that draw weight. Shooting it with a square, unshaped riser, it felt like I was drawing a bow of about 55#. I have just completed building a new bow for myself using carbon tow lams. It is 50# @28” and it is noticeably quicker than my other bow. A friend who has a bow I built with uni lams which is the same length (62”) and which draws 50# tried my new bow a bout three weeks ago and commented that mine was quicker than his and that it shot flatter.

You had emailed me that you had put epoxy into the mould and let it gel prior to laying in the carbon to minimize bubbles, do you still do that?

Hi Mike

This is an issue I will raise in the thread when I add some posts about using fabric.

But to answer your question: it seems to be essential with uni fabric. The epoxy, while it wets out the fabric adequately, does not wet it out as well as it wets out the tow. This means that there is a greater likelihood that there will be shallow voids in the bottom of the mould.

I applied a layer of epoxy to the mould and allowed it to gel ( about two hours, depending on the ambient air temperature) before laying up the fabric.

This layer of epoxy then acts as a gel coat and produces a smooth, flat surface on that side of the lam. On the upper surface, the pressure of clamping the over full mould produces a flat surface.

I will be experimenting with a layer of epoxy in the mould over the next few weeks.

Have you noticed any improvement in the performance of your bows since going to the tow from the uni fabric with crossthread? It would seem the more dense laminate made with the tow might improve performance.

Most definitely; the first bow I built using the lams made from tow duplicated the bow I was using. The original bow, made with uni fabric lams, drew 48# @ 28”. The first bow made with carbon tow lams drew 63# @ 28”. It was very, very fast. The interesting feature is that I would not normally be able to comfortably shoot a bow of that draw weight. Shooting it with a square, unshaped riser, it felt like I was drawing a bow of about 55#. I have just completed building a new bow for myself using carbon tow lams. It is 50# @28” and it is noticeably quicker than my other bow. A friend who has a bow I built with uni lams which is the same length (62”) and which draws 50# tried my new bow about three weeks ago and commented that mine was quicker than his and that it shot flatter.

I have two of the ACP auto vac systems and can reliably pull 20" Hg with them for vacuum bag forming large R/C sailplane wings using carbon, kevlar, and glass cloth over foam cores. The smaller "fish tank" type are unsuitable for pulling & holding higher vacuums on a larger area. I use carbon (tow, cloth, laminate) & kevlar (cloth & tow) when molding fiberglass fuselages also. Carbon provides stiffness, and resistance to bending, and kevlar provides toughness and is used to toughen up molded parts to resist denting and breakage in crashes/midairs, etc. I deal with ACP also, and also http://www.cstsales.com/ & http://www.fibreglast.com/ for supplies. I am also interested in bow limb construction, and am enjoying this thread. Bill G.

Hi Bill I do not use vacuum bagging because I have a small workshop, but if you use VB to make some lams, I would be interested to learn of your results. Perhaps you could post them to this thread?

Well Gil, I'm going to dig up this old thread and ask a quick question.

In your build-a-long you mention 2mm (.079") thick sheet metal for the mold, but then you get .035" lams from it. In this thread you say you use .7mm (.027") sheet metal and get .9mm (.035") from them. I assume the 2mm is a typo in the build-a- long???

And by the way, let me also say thankyou for giving away your trade secrets for our benefit :) You've been informative and thorough.

I ask because I am assembling parts for a shameless copy of your project, and just wanted to be sure of the thicknesses.

The channel is overfilled with carbon and epoxy to place the contents under pressure. Unfortunately there is some wastage of both. The carbon lams come out of the mould between 0.9 and 1.1mm thick. I then sand them down to about 0.9mm or .035"

The 2mm sheet steel forms the bottom of the channel. The 0.25" steel provides stiffness but it was slightly curved. So I glued 2mm steel to both the top and the bottom and, with a sheet of plastic between them, I clamped them together. The result was two flat surfaces.

Then I glued the three pieces to that piece of steel to form the channels.

So the top has two layers of steel: 0.25" and 2mm sheet steel. The bottom has three layers of steel: 0.25", 2mm sheet steel and 0.79mm sheet steel to form the channels.

The biggest problem you will have is minimising the bubbles in the top surface. I am going to re-make my channels do that they are 1.0mm deep so that I have less over flow of fabric out of the channels but I will grind the waste off the top surface which is the gluing surface.

The following text:

"Then I glued the three pieces to that piece of steel to form the channels."

should have read:

"Then I glued the three pieces to the bottom to form the channels."

Don't be concerned about copying my mould. If you have any questions, please email me and I will provide you with as much help as I can.

If you have the time to build your mould you will be pleasantly surprised at the monetary cost of a pair of carbon lams which you make yourself. Then there is the satisfaction of seeing other people shooting bpows with carbon lams which YOU made.

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