Bo Tuff - How Its Made

[Elison]

Hy guys!


So, I was searching something about "how it's made" a Bo Tuff, but I can't find the exactly way to do it.

In some places I saw tips to use fiberglas clothes, in other to use Rooving...  :|

The properly resin to use also confuses, because some places people say: " - Use flexibe resin epoxy."
Others: " - Use rigid resin epoxy."
In the worst case, I was saw too: " Mix the flexible and rigid epoxy... "  :?

Has anyone tryed to make his own Bo tuff and know what is all the correct way to do it?

Thanks very much!

Cheers!

[Pago]

Me to, inquiring minds want to know.

[JamesV]

What would be the purpose to building your own glass even if you could get it done???? I remember when I was building black powder rifles that I would buy a 3/16 bolt and turn it down in a lathe to make a specialty bolt I could buy from the supply house for $1.00. Have fun with your project and let us know how it works out. Also maybe you could make some clear glass so we won't have to buy the second (or third) rate glass that Gordon's is producing.

[Elison]

JamesV, the main motive is because here in Brazil we don't have Gordon's glass...
We can import, sure, but this process is very expansive. For example, for each strip imported we paid almost the double of the original price because of the government tax and shipping.  =(
( actually 60% of tax and plus shipping for Brazil)
If would be some way to make our own bo-tuff, even a little worst than Gordon's, will be can progress in archery in our country, because importing is almost inviable.

thanks guys.

[Nezwin]

Gentlemen,

I registered just to share this knowledge - so you're in luck!

Gordon's Bo-Tuff is a prestressed, unidirectional weave, fibreglass lam - similar in concept to a prestressed, steel-reinforced concrete beam, only with fibreglass acting as the steel & resin acting as the concrete. My background is largely in composites, so when I started in bowmaking I was naturally inclined toward making my own fibreglass lams and, after a few years of research & experimentation, I've got to a point where I'm producing workable specimens, albeit not quite up to Gordon's standard (yet).

To make your own fibreglass lams you need,

- Unidirectional fibreglass
- Epoxy Resin (an aradur derivative is what I use, but in a pinch any epoxy can be used. Don't use polyester resin as it doesn't have the bonding or bulk strength). This resin, when mixed with a thickening agent, like colloidal silica, also make for excellent glue. Better, or at least as good as, Smooth On.
- A curing procedure. In Brazil, assuming you're in one of the sunnier, hotter parts, this might just be a black cloth wrapped around the item & left in the sun. Basically, you need to get the item as much over 30 deg. C (but no higher than 80 deg. C) to cure the epoxy properly. Many people use hotboxes to cure their glues, which work really well. I've built a digitally controlled hotbox, which is not as good as you might think.
- A fibreglass form. I used a length of C-Section steel, 2m (7', almost) long x 50mm (2") wide with 25mm (1") walls. At either end I have removable plugs with foam rubber feet to grip the fibreglass as it is tensioned & stop the resin from flowing away.

I'm not sure on the policy regarding posting from other archery forums, so this link may need to be removed, but here's some pictures of some of the products I'm using & the finished results -  http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=14869

The process for making this is,

1. Cut 2 to 4 layers of fibreglass to length & width (for a thin 1/16" lam, 2 layers will do, for a 1/8" lam I use 4 layers). I make 6' lengths, so I cut to 6.5' to 7' lengths, to give some purchase for the plugs at either end & the bit to hold onto when you tension it.

2. Clamp one end of the fibreglass in the form with the plug. The rubber foot on the plug really helps here to make sure all the fibres are gripped.

3. Making sure there are no twists in the fibres, remove the thin crossweaves. This makes little structural difference (so if you want, you can skip this step) but it does improve the finished look.

4. Pull the fibres tight along the length of the form and, without removing the tension, clamp the second plug down. It's easier to do this with two people - one holding the tension in the glass, the other operating the clamp. This is the really important part as it allows the glass to really work as the limbs are bent.

5. Mix up your resin. I use 120grams of resin (inc. hardener) for 2 layers of glass, 160grams of resin (inc. hardener) for 4 layers of glass.

6. Pour the resin into the form, or apply with a brush, then roll with a fibreglass/carbon/kevlar steel roller for 10-15 minutes. This is very important! It means that the resin works all the way through the lam and there won't be any dry spots. You may even want to put a layer of resin down between steps 3 & 4, to ensure the resin is all the way through. As the resin works it's way through, you'll see the glass change from white in appearance to clearish.

7. Once adequately rolled, cure for the appropriate period.

8. Remove the plugs at either end & gently pull the lam out from the form. Trim the ends (and if necessary, the edges) then grind with a thickness sander (or similar, but not a thickness planer, that just won't work) to desired thickness.

9. Congratulations, you have a pre-stressed, fibreglass lam!

I would advise that you source your materials from a dedicated composites supplier, which you may find working in boat building services. The resins/glues/fibreglass are commonly used in that sector, so you shouldn't have too much difficulty sourcing it. From a price perspective, it's actually pretty much the same as buying Bo-Tuff, but if you want the flexibility & satisfaction of doing it yourself, this is the way to go.

Hope you have some luck with that! It's taken me a year or so to work this procedure out, I'd love to see how you do with it.

P.S. A big shout out to Sam Harper who inspired me to give this a shot. Cheers, Sam!

[KellyG]

Nezwin,

That is awesome instruction. You should do a build along on here with pics. There was a post of a kid making glass limbs in south or central America on here. He cut out the cloth put it on a form and brushed on the resin, and be damned made a bow. It might have been a youtube video.

[Elison]

Hy guys!

Nezwin, First I'd like to thank you so much for the amazing response!  You really show me the light path.  

Second, I'd like to sorry for late response, I taked some time to read  and read again until understand all the process. English is not my native language, so it's a little dificult to me translate, reply, etc...

If you can, the idea of KellyG is a good deal, it will be marvelous a build along with pictures.

I can admit that the process is a little simple than I thought! hehehe...

I've saw some videos when It used a process called pultrusion, where they use expensive industrial machines to make laminates apparently equals than Gordon's...  but I just never see any of this pultruded laminates in my hand to confirm it.

An example of this kind of process:

 

But looking in the link that you shared, I saw the specs in a Gordon's pdf and they don't tell nothing about pultrusion.

About the materials, I have some of they.  
My resin epoxy just arrived today ( bought in the internet).  Have parts of fiberglass cloth, but it's BD...   :(

I will buy a UD and start to make experiences. For sure will share all here with you.  

One question: Following the idea of pultrusion, it wouldn't be better use rooving in the place of cloth UD?


Thanks again Nezwin!
And thank you guys!


P.S.:  A big shout out to Sam Harper too...   hehehehe...  he always inspire me with the tutorials and videos.  

Cheers!

[KenH]

I believe tha pultrusion is a completely different process than the process of making fiberglass laminations.

[Nezwin]

Ola Elison,

I'm afraid I don't speak Portuguese, but my Italian wife speaks Spanish if that's any help?

I would imagine that Gordon's probably use a process similar(ish) to pultrusion, maybe, but for the small scale guys like us, it's not an option. I did speak with a technical representative from Gordon's about a year ago and he was very co-operative in explaining the properties of the Bo-Tuff product. It was through speaking to him that I was able to work out it was pretensioned.

I've used bidirectional cloth to back bows before and it works by stopping splinters lifting. However, it is a completely different way of working than a pre-tensioned lam - indeed, a cloth backing applied directly to a limb won't actually do any "structural work", it only stops splinters lifting. To get a fibreglass lam performing "structural work" you need depth (which is achieved by using the form, which stops the resin flowing away) and appropriate tensioning (achieved by pre-tensioning).

I'll do a build along over the weekend and try to work out how to upload pictures, etc. Is there a thread explaining how to post pictures and things like that?

[Elison]

Hi Nezwin!

Don't worry about language, english for me is ok. Spanish sounds a bit more similar to portuguese, but I believe I can understand english much more.  

I didn't saw any post explaining how to post photos here, but I've been using the photobucket as well to post my photos here...

You will need an account there to upload the photos ( or just sign in with facebook). After you upload the photos, you need to select the photo who you will share and click in the field "IMG" inside the area "shared Links". This will copy the entire url to photo inside the tag used by the forum. Then it's just paste here and post... It's quite easy, but if you have some difficult, you can send the photos to me and I'll be glad to share for you.

Nice tip about the bidirectional cloth...  I tried use it before, but I didn't had much success...  especially in belly, where the fibers broken with the compression.

Are you already tried with rooving?
 http://www.fiberglass.name/UploadFiles/200751622220683.jpg


Is there any differences to work between it and uniderectional cloth?

I ask it because I tried to find unidirectional cloth here, but found nothing for now. (Even in internet)

Thank you again!

Cheers

[Pago]

I think you will have better luck if you search for a unidirectional E-Glass tape if comes in many different widths.

I can see the need to tension the material for lamination it makes sense.  I think this can be done in a way that might produce a superior product by using vacuum bagging to form the strips which should eliminate all the tiny air bubbles and reduce streaking/improve clarity.  I don't have the solution yet but I'm working on it.  Need to work out a form that can hold the strips under tension that will go in a vacuum bag and into the hot box. That should do it.

[Pago]

Forget the previous, after reading the following I think I'll stick to trying to learn to make bows.

   Gordon Glass Profile

[Nezwin]

Thanks for the information on Photobucket, I'll see if I can get it working when I do the buildalong over the weekend.

Bidirectional cloth will eventually breakdown due to internal stresses - basically, the threads rub against one another & the friction breaks them. Using it on the belly would do almost nothing. In fact, using any fibreglass on the belly of a bow will no almost nothing, only the resin will actually perform any work in this instance. Take a length of fibreglass cloth & compress it longitudinally - it will just go limp, like string! The resin though, as a strong plastic, will take the compressive force very well. My advice is that when making belly lams, only use resin. Any fibreglass used will be wasted. Or you can just use a decent timber - something like Ipe or Osage should be able to handle the compression stress from a thin fibreglass backing lam at lower poundages.

The only difference between roving & unidirectional cloth is that the cloth is easier to use. With the roving you'd be required to cut each thread to length before placing it in the form, which would be annoying. Alternatively, you could create a jig to thread the roving through the form which, if done correctly, would work well, although then applying tension would be a further challenge. At a later date I'll lay out some ideas on how that might be done.

As Pago pointed out, unidirectional tape would be good, if you can source it. It makes it easier for cutting to size to fit into the form. Pago is also right about the vacuum bagging, but it would make it very difficult to cure in a hotbox while applying a vacuum... If ambient temperature was high enough (ie, you live in a desert..) that would be fairly achievable.

I didn't read the entirety of the article Pago posted, but looking through it there were some interesting insights - for instance, Gordon's use roving, and they produce their lams 1/3 resin, 2/3 glass. It's given me ideas for an improvement on my current process, but I'll have to test it to see.

I think it's important to stress that what I'm producing, and what I've explained in the process above, is not the same as Gordon's Bo Tuff. It's a pre-stressed fibreglass lam, which had very similar properties to Bo-Tuff, but it is the responsibility of the individual making it to ensure the final result. Ultimately, it would be exceptionally difficult to reproduce the Bo-Tuff product at home (Gordon's have a HUGE amount of dedicated equipment & years of experience) but what I've described would produced a good product that would perform in a similar function.

[Pago]

Dont get me wrong this is a fun problem to think about.  I actually think a person could make a far superior lam at home, but at the cost of time, money, space, energy and lost opportunity to do other things, at least for me.

However if you build a form that can pre tension the material and use lots a wax+release agent pre-lay up (something like milled aluminum), its just a matter of throwing in a heat resistant vacuum bag (already available) and baking in a hot box like we already use for bow lay ups with the vacuum tube hanging out of the box.  But then you need a regulated vacuum pump, bags, mylars and all the trimmings. BUT, the lams should come out crystal clear.

I have done similar lay ups before building aiplanes, the vacuum pulls all the air out and leaves a beautiful streak free layup.

My problem is I don't have time to work on bows as is and I would be wondering off in another direction to make a product that is already available and spending a great deal more in resources and money to make it.  Doesn't add up for me, but its still fun to think about.

[Pago]

If you read the linked article above many have tried to do their own and in the end most buy from gordons because of the economy and quality.

[Nezwin]

Agreed, Pago - in the end, it's cheaper, quicker & easier to buy the Gordon's product, but, you know, it's fun to make the lam too... I'm pretty short on time, in general, but sourcing Bo-Tuff in the Australia is difficult (there's one guy) and I don't like the idea of not being able to do it myself.

For a form using roving, I was thinking of mounting a series of pins to each end and wrapping the roving around them, end to end, not dissimilar in manner to how a flemish twist jig is used (kinda). With that, you can either tension them yourself as you thread them or, if you want to get technical, you could have a screw mechanism which when turned increases the distance between the pins. A sketch would relay the idea better, but what do you think?

Re: release agent, I've moved away from using wax and had no problem so far. I line my form with sticky tape, which provides a very low friction surface and the lam never sticks.

Re: vacuuming, it's a good idea but a hell of a lot more work & materials! As it is, I'm already at the point where I'm looking at bamboo and thinking "that looks waaaaaay easier"! You're right though, vacuuming would give a great result.

[Pago]

I feel for you Aussies when it comes to sourcing materials.  I wish you all the success in the world.  I get your pin idea and think its a good one.  The question is how many strands you need in width and how tightly distributed they need to be.  You might need two rows of pins on each end slightly offset and experiment to get the right thickness somewhere in the 0.040-0.050 range.

[aus-archer]

The expense and scarcity of supplies for bow making is exactly why I mainly make bbb longbows and recurves.

I'll have to try woven fiberglass this summer those results look good

[Nezwin]

Never done a buildalong before but here goes...

I'm pretty lazy, so I'm going to copy my original post & add pictures & notes.

To make your own fibreglass lams you need,

- Unidirectional fibreglass

   

   

- Epoxy Resin (an aradur derivative is what I use, but in a pinch any epoxy can be used. Don't use polyester resin as it doesn't have the bonding or bulk strength). This resin, when mixed with a thickening agent, like colloidal silica, also make for excellent glue. Better, or at least as good as, Smooth On.

- A curing procedure. In Brazil, assuming you're in one of the sunnier, hotter parts, this might just be a black cloth wrapped around the item & left in the sun. Basically, you need to get the item as much over 30 deg. C (but no higher than 80 deg. C) to cure the epoxy properly. Many people use hotboxes to cure their glues, which work really well. I've built a digitally controlled hotbox, which is not as good as you might think. Edit: It's working great!

- A fibreglass form. I used a length of C-Section steel, 2m (7', almost) long x 50mm (2") wide with 25mm (1") walls. At either end I have removable plugs with foam rubber feet to grip the fibreglass as it is tensioned & stop the resin from flowing away.

The process for making this is,

1. Cut 2 to 4 layers of fibreglass to length & width (for a thin 1/16" lam, 2 layers will do, for a 1/8" lam I use 4 layers). I make 6' lengths, so I cut to 6.5' to 7' lengths, to give some purchase for the plugs at either end & the bit to hold onto when you tension it.

   

2. Clamp one end of the fibreglass in the form with the plug. The rubber foot on the plug really helps here to make sure all the fibres are gripped.

   

   

Rubber foot at the top, steel plug at the bottom.

   

The lateral weaves have been removed in this picture but no tension has been applied.

3. Making sure there are no twists in the fibres, remove the thin crossweaves. This makes little structural difference (so if you want, you can skip this step) but it does improve the finished look.

   

4. Pull the fibres tight along the length of the form and, without removing the tension, clamp the second plug down. It's easier to do this with two people - one holding the tension in the glass, the other operating the clamp. This is the really important part as it allows the glass to really work as the limbs are bent.

   

You can see in this picture that the glass is very much centered - I didn't have anyone to help with the tensioning! After applying some resin & having a think, I loosened the tensioning clamp & spread the fibres evenly over the 2" base of the form, then reapplied the tension.

[Nezwin]

5. Mix up your resin. I use 120grams of resin (inc. hardener) for 2 layers of glass, 160grams of resin (inc. hardener) for 4 layers of glass.

   

6. Pour the resin into the form, or apply with a brush, then roll with a fibreglass/carbon/kevlar steel roller for 10-15 minutes. This is very important! It means that the resin works all the way through the lam and there won't be any dry spots. You may even want to put a layer of resin down between steps 3 & 4, to ensure the resin is all the way through. As the resin works it's way through, you'll see the glass change from white in appearance to clearish.

   

This roller is cut down from a larger one & I made my own wire frame from an old coat hanger.

   

Note the uniform colour with no white streaks. This means the resin has penetrated the whole way through for the entire length.

7. Once adequately rolled, cure for the appropriate period.

   

Few other bits & pieces in there, but the fibreglass form is on the left.

8. Remove the plugs at either end & gently pull the lam out from the form. Trim the ends (and if necessary, the edges) then grind with a thickness sander (or similar, but not a thickness planer, that just won't work) to desired thickness. Only grind the 'rough' side of the lam - the smooth side, the side that was in contact with the form, shouldn't be touched from now on. I will cover it in 2" masking tape prior to using it in a bow layup and leave the tape on as the bow is built.

Very important! When grinding the fibreglass WEAR A RESPIRATOR. The dust is exceptionally fine and very, very nasty if inhaled. You'll also want to be wearing throwaway gloves (like the latex ones doctors use) when handling the resin, and make sure you have plenty of acetone around for cleaning brushes, rollers, etc.

   

Fresh out of the form.

   

Improvised thickness sander.

   

Beautiful!

   

This might look rough & white now, but as soon as more glue or resin is applied, it turns transparent and will show any grain beneath.

9. Congratulations, you have a pre-stressed, fibreglass lam!