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Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 12:33 pm
by fallguy1000
OneWayTraffic wrote:
Fri Jan 24, 2020 12:22 pm
piperdown wrote:
Fri Jan 24, 2020 10:21 am
Also, to keep them from sliding apart you can use wooden dowels to keep them lined up.
After cutting and shaping, clamp them together and drill some holes for dowels. Precoat the wood ( I also don't think you used enough nor thick enough) let gel, mix up some more epoxy and thicken it appropriately, spread, then insert the dowels in the first piece and then put the second on top lining up the dowels.

I used screws to clamp some items together along with weights spread out.


Have you gone around to any commercial woodshops and requested their sawdust? From there if you have a sieve you can use it to get the fine particles. Can't recall who it was on here but that's what they did. From a 5 gallon bucket of sawdust they got about 2 lbs of woodflour.
WEST recommends ketchup for bonding large flat surfaces and mayo or pb for general bonding or uneven surfaces. I was working within those guidelines, or so I thought.
Ketchup is a little thin. You really want peanut butter enough so a v notch trowel application doesn't collapse into a puddle.

Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 1:12 pm
by OneWayTraffic
I think that that was it. Especially the even pressure.

I have just gone back and reread my Gougeon book and also had another look at Tolman's book.

The Gougeons recommend just enough filler to thicken the epoxy enough to ensure good coverage and that there is complete contact.

Tolman actually writes regarding gluing a transom doubler to 1/2" ply: "When you glue the doublers, unthickened epoxy is probably sufficient. Just give them plenty of open time, and add more epoxy if necessary."
When gluing wood he uses cabosil to thicken the epoxy to a point where he can still roller it out. But he uses plenty of screws to fasten the surfaces.

So if I read that correctly, and the advice here from people on here building/built Mertens designs the only important thing is that the surfaces be in full, even, but not excessive contact for the whole setup time of the epoxy.

I can assure this by:
using more glue (even more than what Gougen bros reckon I'll need for bonding.)
using a thicker mix (more like a fillet thickness)
precoating and then waiting until gel instead of precoating and going straight to the glue. (Gougen say it's not needed, but it couldn't hurt. I can then precoat again if need be.)

I am feeling more optimistic about my transom. The panels were almost completly flat and I put more weight on. I'll still take some plugs out of it and check for peace of mind.

Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 1:13 pm
by OneWayTraffic
And I have a name for my boat:

With a little help from my friends!

Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 7:56 pm
by Dan_Smullen
You got a lot of good advice. Only thing I will add, lay a 2x4 down the length of the stringer, place weights on top of it. It will distribute the weight. This is what I did on my C19 stringers.

Screw method sounds hard to beat though.

Good luck!

Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 8:36 pm
by joe2700
I would really try to bring in someone locally who has some experience working with epoxy at this point to help with your next glue up. There are so many variables when you don't have experience with successful glue-ups(please correct me if I'm wrong about that).

Re: Stringers AARGGHHH!

Posted: Fri Jan 24, 2020 9:12 pm
by OneWayTraffic
joe2700 wrote:
Fri Jan 24, 2020 8:36 pm
I would really try to bring in someone locally who has some experience working with epoxy at this point to help with your next glue up. There are so many variables when you don't have experience with successful glue-ups(please correct me if I'm wrong about that).
I built a D5. That taught me glassing, filleting, marking and cutting panels etc. I made my share of mistakes with that too.

The D5 did not really involve splicing panels or large laminations of plywood. I don't know of anyone nearby who has built a boat sadly.

I spent time today going over my transom lamination with a fine tooth hole drill. I was looking for obvious voids in the panels. The middle of the laminations looked ok actually. So I took a couple of plugs out. One of them was good, the other down by the bottom had the same lack of contact. Moreover the edges of the transom had gaps in a couple of places.

If that was all it was, I'd probably fill with epoxy and put it on the boat. But with the stringers and the promise I made myself at the start of this that I would do the best work that I was capable of I have decided to bite the bullet, buy a sheet or two of ply and start again. It will take me a week or so to get into Christchurch, buy the ply and get things in order, but at the end I will be happier. I will use screws this time and more glue.

Re: Stringers AARGGHHH!

Posted: Sat Jan 25, 2020 12:29 am
by Evan_Gatehouse
Again, glue squeeze must be minimal when done right.
That's exactly right. No need for massive pressure. Just enough glue and even pressure to make sure the two pieces are stuck together.

Nothing at all like woodworking with tight glue joints.

Totally agree with notched trowels to make sure you have enough. Don't obsess about the flavour of the glue (PB/mayo/ketchup). All will work pretty good but I would lean toward thicker than runny.

Re: Stringers AARGGHHH!

Posted: Sat Jan 25, 2020 2:21 am
by OneWayTraffic
Cheers. From a designers point of view, what could happen if I simply filled all the holes I drilled in my stringers and now my transom with goop, glassed over it a few times with some of that 100 metres of biaxial cloth I have sitting in my garage, did the same to the transom, put a five year warranty on it and sold it to some unsuspecting sod in a boat yard?

I know that it's anyones guess but I'm thinking that it would hold together, until water gets in somewhere, and then would spread throughout the transom/stringers in those little voids.

I've made the decision to have another go at it, using the screw technique as it seems most likely to be foolproof. I've also ordered WEST microfibres for the thickening agent. It seems to me that it should work better for large glueups.

Re: Stringers AARGGHHH!

Posted: Sat Jan 25, 2020 5:49 am
by fallguy1000
Most of the studies and reading I have done suggest 40 mil to be the perfect glue joint thickness. (1 millimeter) You cannot achieve the ideal thickness on epoxy alone. And most designers that recommend mechanical fastenings or require them, say like in a bolt on appendage, require glass to avoid squeezeout. 1708 wetted, for example is about 0.040" or pretty close to 1 millimeter. Your approach on the prior stringer to just butter the thixo is a big part of the issue, the glue joint thickness varied too much. It was thick in some places to the point of lifting the parts away from each other where thin...

You need to use a v or u trowel 1/8" for a one side, or 1/16th for both sides, or the joint will be uneven. It does take some time to trowel both sides, so if you try to do the work with fast epoxies, it is pretty hard to do..

I have never used screws for any lamination work. I have always laminated by being careful with even application of thixo and by making sure the weight applied or force applied (vaccum) is even. I realize screws are important for some laminating, but you need to avoid squeezing out the glues.

If you only use a trowel and thicken the epoxy to peanut butter and position the boards so they don't slide, your results will be much better. In the past, I used stainless brads to keep the laminate panels from sliding off each other. I simply predrilled with the nails and then dropped them in. I spotted like 4 nails in each board. They actually stayed in the part.

My panel weight was 10" of mercury under vac, but you can get that at 5 psi, so for a 60"x6" board, you'd need 1800 pounds. Of course, that is crazy too much, so I would try more for 1 psi or say 2-300 pounds or so..balanced on some 2x4s that run the length of the part...or screws.

The caution with screws is oversqueezing things, but they can get you closer to 2-5 psi than just weight. Just remember when you screw to avoid forcing the glues out much. And you don't need a ton of screws...maybe like 8 or 10 or so.

I also won't use anything but a 1/16th u or v trowel and I always do both sides. The 1/8" or 3mm can work in a pinch, but you end up a bit thicker than 1mm when done.

A boatyard would know to use a trowel. Do you know how when you put water between two shiny surface flat objects they tend to stick together? That is what will happen if you trowel out the mix. Only a force of a twist or a non-flat board will overcome that force; so it is also wise to keep boards to be laminated flat on a table vs leaning on a wall and bending out of flat...

Re: Stringers AARGGHHH!

Posted: Sat Jan 25, 2020 5:59 am
by fallguy1000
Your volumetric needs will be about 2 parts cabosil for one part epoxy.

A liquid measure of say 12 oz epoxy and a volume of about...25 oz of packed lightly fumed silica is about right. (Not weights! You might wish to start a bit lower at say 9 oz epoxy and 18-19 oz silica and see if you have enough. You can stretch it a wee bit by angling the trowel at the end over the entire part bs making more if you are short.

It is really hard for me to estimate it perfectly. But I can tell you I am always a little surprised at how much is needed...always seems a little epoxy thirsty.

You can calculate the neat coat needs at 2 oz per sq yard.