Aghhhh - bamboo backed ipe keeps lifting at the fades... Help!

[willie]

in the second pic down at the top of the page, it looks like the handle you have doesn't extend out to the widest part of the limb. maybe stops short by 1/4"? or so?

If so, I would cut/sand off the handle and remake longer in addition to feathering in more

[Tommy D]

Ok ... so here we go. I’ve made two thin tapered lams. A shorter one and a longer one. I am planning to glue these up today ... then fit the handle.

Any thoughts before I go ahead.

Am in two minds about this G-Flex epoxy. Does anyone use it? Has anyone added a thickener - microfibres to it?

Otherwise I might use the West 105/205. It’s a “stronger” epoxy. Just not as flexible. There seem to be two conflicting schools of thought as to whether flex is good here or not...

I have a hot box.

Here are some pics...

[willie]

I thought the gflex already had some thickener? Is the gflex you removed brittle hard or slightly rubbery?

[Tommy D]

It’s hard - but not brittle - a little rubbery. I have used Ampreg epoxy in the past on boats - so when I called the Gurit technician to ask if they sold something like EA-45 for bows - a little rubbery - he laughed and told me “just don’t mix your epoxy right!” But in serious, Gurit’s attitude as a company to these “flexible epoxies” is that they are basically taking a premium glue (epoxy) and making it weaker. So they don’t have an equivalent to the West G-Flex system is what they said!!

So I am in two minds - I know Urac or Cascamite is meant to dry hard hard - but needs a really good glue surface - which I am reluctant to work on too much cos it will mean thinning the parts I don’t want any thinner on the bow limbs

[willie]

I use system 3 so I can't speak directly to the use of gflex, but I agree that the products with additives are usually weaker. I have had problems when mixing in small quantities. and mix by weight now. I do use a thinner product mostly. I believe with the new handle and doing the job over, you will most likely get the glueing right as I think your previous handle design was the primary cause of problems. I dont think you can have a "too hard" glue in the handle area of the bow

[Tommy D]

What do you reckon? Two of these “skinny lams” and a handle over the top should achieve the “Eric Krewson” method?!

[Tommy D]

Side view... the shorter one will be under the longer one I think!

[PatM]

I use G- flex all the time.  It's not "rubbery" at all. 

   You can also use  105 mixture  and add a small amount of pre-mixed G flex to it to add toughness and thicken the mix a bit.

[Hamish]

You don't want the glue line to flex at all, that's how you get a lift. Glass hard is the glue line you need. Worth the trouble to get the cascamite. Scuff sand the surfaces with 40 grit.

[PatM]

He DOES want this glueline to flex.    The added on bits have to be helping the working limb.

[Hamish]

The wood is going to flex, and needs glue line needs to be rigid, rather than flex. The glue line has been failing, due to it being rubbery and peeling away from the wood.
 Its a bit counterintuitive so I can see how it might be hard to accept. I've had this same argument with die hard lovers of TB3(which is an excellent glue by the way, it just won't hold up to this kind of joint on such a shallow belly lam) . Admittedly I've never used G-Flex(so I'm happy to be proved wrong), but I have had total success with bowmakers epoxy, urac/cascamite, and resorcinol. These glues give an absolutely rigid glue line. Every other glue I tried with a shallow belly lam has lifted at the riser. I have had some success with non rigid glue lines, when the belly lam was substantially thick and the join was higher up the dip/ fade area. I also had failures sometimes despite having a thicker belly, so that's why I now always glue up the riser with a rigid glue, even if the lams have been glued up with TB3.

The only way I've seen for this type of joint to work(without a power lam) is with a really hard glue line. Most glues just aren't up to it. It doesn't even work all the time with the best bowmakers glue.

I hope the G Flex will work, it just might. The addition of a  power lam is definitely stacking it for success,. If it is successful it could be due to the power lam, not the integrity of the glue.

I'd personally go with something that has had 70 years of proven success on tricky joins, like cascamite, rather than risk it, and have to take it apart again and try again.

[PatM]

"Bowmakers" Epoxy/glue doesn't actually exist.  It's just re-purposed epoxy or glue.

 His handle is failing because of its construction and execution, not the glue choice.    The longer lams need to bend and carry some load.

 If his epoxy is rubbery the mix ratio might be off.

 

[Hamish]

Bowmakers epoxy, is just a term for an epoxy that has been proven to work in all aspects of bowmaking, eg Smooth On, or Techni Glue(industrial formulated recipe for strength). They were used by early fibreglass bowyers, because epoxy has a better bonding ability than Urea based glues in the wood/glass bond.
Not all epoxies are equal, regardless of mix ratios of resin to hardener, some wont dry rock hard.  5min or even 24hr hardware store epoxy falls into this category. Even quality boatbuilders epoxy don't usually meet the requirements.

Urac and resorcinol are stronger than most epoxies in a wood to wood bond, water and boilproof/heat proof more than any other glue. You can't say that about epoxies when it comes to heat resistance. Epoxies are popular in this day and age because they are a little easier to use, have a longer pot time, and a much, much longer shelf life. Urea based glues are not as popular these days due to their reputation as being carcinogenic( I bet epoxies are no less toxic though). 

His handle is definitely failing due to construction and execution, but not all glues have equal strength regardless of their type whether PVA, epoxy or animal based. So choice of glue can play a big role in the success or failure of a joint.

My friend is primarily a glass bowyer.  His first foray into board bows was a success, no lifting at the riser whatsoever.
I kept getting frustrated with some of my risers lifting at the fades, with TB3. Hell I was more experienced than my friend with all wood bows. I had thicker belly slats but was still getting problems. I then used 24hr epoxy, then West Systems and still getting issues. I asked him what his secret was. He said he didn't do any thing special he just used techni glue. I bought some, gave it a try on the same bows that had lifted at the fades, and hey presto no lifts. That was enough to prove to me all epoxies weren't equal.

[Tommy D]

Pat - when I said rubbery I would say to me it definitely felt a little softer than the West 105 ... which it is if you look at the Technical Data Sheet. When I get a chance I will have a look at the specs for Hamish’s techiglue. I find this all very interesting. As I said I’ve built quite a few epoxy/ wood boats over the years. I know that temp and post curing make a big difference. As does mixing enough and perfectly. I use a grain scale to mix these small batches.

One thing with Ipe I am curious is how much pre-glue wiping with acetone go
to do. I try and keep going till I get paper towels with till that yellowish look all gone. But I’ve noticed the glue itself takes on a reddish tinge from being in contact with the Ipe.

Anyways .... here is how it looks with the inner table off. Gonna fit the handle to this and see how she holds up.

Went with the 105 for the glue up - so I have something to blame if she comes apart again!!

[Tommy D]

Ok well I debated adding another thin taper - between the handle but I have two now already - one is quite long - you can see in the picture how far it extends and the other is under it - like a power lam. Went for this way round because it filled the handle section better which had developed a sort of hollow from cleaning up the several handles that had not worked!! Anyways when I floor tiller it you can definitely see that I have moved all the bend away from the handle - so fingers crossed we can get this to work. It’s been interesting - gonna make one of those Eric Krewson tillering gizmos which has been a pleasant side discovery from figuring out what to do with this handle ...