# Do laminates *really* need pins?



## Byudzai (Aug 31, 2013)

Oldmiser asked me about pinning my G10 slingshots. I certainly see a lot of pinned laminates and the idea of providing support against shear strain or temperature changes to avoid delamination SOUNDS right, but has anyone ever actually seen an epoxied G10 slingshot delaminate?


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## Sanch (Jun 24, 2015)

I have had the small mini hunter I made out of micarta and ABS plastic delam on me I wish I had pinned it. I plan on revisiting it sometime.


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## bigdh2000 (Feb 9, 2015)

This topic is being visited at length on the Slingshot Community Forum. They are going a little overkill over there by sticking them in the freezer and then placing them in the sun to watch the aluminum come loose.

Here is the question I always ask:

Does it really matter if it delaminates? As long as you do not have small scales at the tips of the forks that can delaminate separate from the rest of the frame and hit you in the face, to me, there is really no problem. Take the pieces to your shop and epoxy them back together. A few minutes of sanding touch up and you are good to go again.

Under normal conditions, I have found the following to work very well and have yet to have a delamination.

Roughen and wipe clean (dry rag on wood, rubbing alcohol on other materials) the join surface on both. Use two part clear JB Weld rubbed in with a wire brush to generate better bonds and some "filings" in the epoxy. Clamp with spring loaded $1 clamps with a 1" gap between adjacent clamps. Let dry for 1 hour before removing clamps and overnight before doing much further on the slingshot. The wood burns off before the glue lets loose (in case you drop it in your campfire) and I do not have conditions where I leave my slingshot covered in snow. If it is that cold outside, I find a hotel room. 

As for wood to wood connections, I only use TiteBond 2.

The only time I ever had a delamination was when someone convinced me that the two part epoxy they had was better than JB Weld.


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## bigdh2000 (Feb 9, 2015)

PS: That is one nice looking set of lams you got set to go in that picture.


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## quarterinmynose (Jan 21, 2012)

I'm not going to say that you absolutely do or do not need pins while laminating G10. But, I will give my experiences with it.

I have used g10 in almost every slingshot I have made(not counting nattys) over the last two or more years. Out of all of them (to my knowledge) only one has displayed any delaminating. It was the first one I made, and I blame more my laminating techniques needing adjustment than anything else. I still own this slingshot and it is one of my favorite shooters. Most of these slingshots have no pins at all, occasionally if I speak with someone who has one from me I will ask if their slingshot is doing alright and if there has been any problems with the lamination. I haven't heard of any problems so far.

I'm really diggin' the color combo of your frames in the pic. Those are gonna be tight!


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## quarterinmynose (Jan 21, 2012)

bigdh2000 said:


> This topic is being visited at length on the Slingshot Community Forum. They are going a little overkill over there by sticking them in the freezer and then placing them in the sun to watch the aluminum come loose.
> 
> Here is the question I always ask:
> 
> ...


That topic was about metal laminations, which I would consider a fair bit different considering the effect temperature can have on metals. Not saying you do or do not need pins with those either as my experience with metals is much more limited, but I would not treat the material characteristics of G10 vs. aluminium or steel as one and the same.


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## peppermack (Dec 10, 2013)

I will say that they do need to be pinned if you never want them to come apart. I have had g10 layers delaminate under a number or normal use situations. One, it you drop it on a hard surface it lands whith most of the force pressing on the to layer it can pop it right off. In addition, I have had a frame delaminate at the fork tip because with the holes and other cuts there is a lot more flex possible in that area. Luckily because it is a big solid piece delamination would not be a safety risk, it would just be a situation where the end user may be unhappy and have to send it back to you to be fixed.

I myself like to pin everything, and the pins are peened over. There is no chance that it is ever going to come apart. even if the adhesive completely failed for some reason the peened pins will not. Epoxy and other adhesives do not do well with flex, so if there is a chance any flex will occur it should be pinned. I've made 100s of slingshots, and probably near 1000 knife handles, and never had a pinned and peened handle come off. I have had non-pinned lamination failures though.


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## sharp eye (Jun 3, 2014)

I had a a wooden laminated pickle frame delam when it dropped and hit the foor tiles.


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## bigdh2000 (Feb 9, 2015)

quarterinmynose said:


> bigdh2000 said:
> 
> 
> > This topic is being visited at length on the Slingshot Community Forum. They are going a little overkill over there by sticking them in the freezer and then placing them in the sun to watch the aluminum come loose.
> ...


I have never had a metal core delaminate with clear JB Weld. My comments above were general to all laminations, including G10, aluminum, plexiglass, corian, etc. I have never laminated HDPE or nylon sheets.


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## bigdh2000 (Feb 9, 2015)

Would everyone be kind enough to list the epoxy/glue they use? I only ask because there are several out there that are truly useless for what we do.

I always use clear JB Weld.

I did try Loctite once - never again! It delaminated while just sitting in my shop which only fluctuates 20 degrees F.


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## Can-Opener (May 11, 2013)

If it is all G-10 and properly prepared and glued I know it is very strong. I put the off cuts from these slings in a vise and I had a hard time destroying them with a sledge hammer. If you add dissimilar materials it changes everything 

So this discussion you need to pay attention to what materials people are referring to using the pins with  I am addressing G-10 with G-10 and I used G-flex epoxy to laminated it with


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## bigdh2000 (Feb 9, 2015)

Can-Opener said:


> If it is all G-10 and properly prepared and glued I know it is very strong. I put the off cuts from these slings in a vise and I had a hard time destroying them with a sledge hammer. If you add dissimilar materials it changes everything
> 
> So this discussion you need to pay attention to what materials people are referring to using the pins with  I am addressing G-10 with G-10 and I used G-flex epoxy to laminated it with
> 
> ...


Do you ever insert epoxy "pins" or leave holes in the inner material to fill with epoxy? I did once as an experiment but never witnessed any benefit yet. At the time I was trying to prevent those sharp ridges you get between the wood and aluminum when the wood shrinks/expands due to moisture in the air.

BTW, those are two beautiful shooters. I sure wish G-10 was cheaper as I would use it far more often.

PS: Please tell me you took a video of the destruction of the cut-offs. That would be fun to see.


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## Can-Opener (May 11, 2013)

bigdh2000 said:


> Can-Opener said:
> 
> 
> > If it is all G-10 and properly prepared and glued I know it is very strong. I put the off cuts from these slings in a vise and I had a hard time destroying them with a sledge hammer. If you add dissimilar materials it changes everything
> ...


I have used a dremel to cut grooves in the center of a lamination like these. Just to create a deeper tooth for the epoxy. Drilling shallow holes same effect.

One of the most common mistakes with an epoxy lamination is to much clamp pressure. Clamping the materials to tightly forces all of the glue out of the joint creating a dry joint 

The reason to use a epoxy like G-flex is that it is flexible and can move with material when it changes size due to temperature and humidity.

Sorry no video on the destruction


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## Lacumo (Aug 18, 2013)

With regard to metal core/wood scale frames... I remember seeing a post or two about how a Performance Catapults SPS with wood scales had delaminated. In the end, the owner returned it to PC and was completely satisfied with whatever repair/replacement work was done. This tells me that even well-made, costly, high end metal core/wood scale laminated frames can delaminate---without being subjected to freezer tests or any other such extreme tests. That in turn tells me that pins are probably a good idea and peened pins are probably a better idea---at least for metal core/wood scale laminated frames.


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## Byudzai (Aug 31, 2013)

I used 40 grit sandpaper to create a pretty healthy cross-hatch on the surfaces, made sure not to get any hand oil on them, washed with dish soap and air-dried, wore rubber gloves while handling, then used that west G-Flex epoxy and just the spring clamps to avoid over-clamping.

maybe i'll put this one through a torture test and see if I can get it to delaminate.


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## Rayshot (Feb 1, 2010)

I feel you don't need to torture test a finished product. If you did the prep right you should be fine.

If it makes you feel better I will buy the one you didn't torture test so you can test something that doesn't have but the labor invested in it, to glue it and let it cure, .


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## Chuck Daehler (Mar 17, 2015)

Darn this is a great thread!

I've used epoxy since it was invented when I was a kid. I found that surfaces must be absolutely clean and roughed up to ensure a good bond JUST AS YOU DID. Not all materials bond to epoxy well. Some not at all such as polyethylene and polypropylene. It may seem at first they do but in time they unbond. Al and G10 ought to bond fine but I'd bet the Al bond is weaker than the G10 bond. Al has a perpetual and instant coating of aluminum oxide the millisecond you sand it. It looks like bare Al but there is a 1 molecule or more skiff of AlO2 on the surface. AlO2 doesn't like adhesives as much as G10 for it is neutral, less electronic + or - attractions for an adhesive to link to. More on this at the bottom of this gibberish.

Pinning is in your case, Alex, more for looks and sex appeal than strength. It could improve sales but of course cost a bit more... due to appearance and those who do think pinning is better. The buyer is the king here and overkill the salesman. You might offer two options, pinning costing perhaps a bit more.

Delamination is encouraged by flexing and heat/cold expansion/contraction differences (coefficient of expansion in engineering speak). The freezer/hot sun analogy is such an example but extreme for a slingshot. I saw a wood/fiberglass recurve bow blow up in the sun when I was a kid at an archery tournament, sure glad no one was hurt, I mean, geez, it exploded and fragments/string etc. were flying around like a lawn mower blade. But there were lots of bows in the sun right beside it and nothing happened to them (although we all put our bows in the shade quckly!).

Since your aluminum core construction eliminates flexing altogether and no delaminations would result, possibly hot/cold would do it but likely not. If you rough sand the Al cores to produce surface irregularities and rough sand the composite, that would help greatly. Rough sanding with say 90 grit or so AFTER a thorough cleaning with solvent de jour, is the best you can do. Rough sanding increases the surface area for the stickum to stick.

Also you can take advantage of "mechanical fastening" without pinning by drilling small partial holes in both the composite and aluminum core so as to create internal rivets so to speak by filling the holes with epoxy when you spatula on the epoxy, then slap the two together. Inside the holes are epoxy "pins" but internal so you can't see them but they mechanically bond both sides. That would be an alternative to rivets/pins and do the same thing...without showing and without the painstaking task of perfectly aligning pin holes...and expense thereof. Consider this as a real alternative to pinning where pins show. I did this many times using epoxy on many projects over the years to much success. If you would drill a few holes all the way through the Al core so epoxy traverses from one side to the other, that would also add to the mechanical fastening advantage. Just a few holes lest the core weaken and flex upon stress due to elastic pull. Your cores are thick so no flexing will result if not too many holes are drilled all the way through. I'd bet if you did this you would be unique in the market for fastening laminates. I've done this, essentially making internal epoxy rivets.

I haven't used JB weld, we can't get it here in bananaland for me to try, but from what I read it's one heck of a good adhesive. You could do tests with scraps of materials and different adhesives to see just what it takes to unbond pieces after glueing...and publish the results...justifying your choice of adhesives for X composites and cores.

I found also that using a solvent that partially dissolves at least one of the sides, then using epoxy, things sort of meld together better. Slow curing epoxy is a better bonder than fast curing...it seems to "get into things" better and have more time to do it's bonding thing. The study of adhesives and the various ways they bond stuff to gether is interesting. On a molecular level different bonding agents do different things to "stick". Finding an agent that sticks WELL to both types of materials obviously is the ticket. "Adhesion" is accomplished by certain sites on a bonder molecule having an electronic attraction to certain sites on molecules of the stuff to be bonded. It's not a chemical bond but sort of in that a sharing of electrons or shall I say a sharing of local charges bonds stuff together.

I am sure you know most of what I just wrote but I'm doing it for those who don't. Eager to see your posts in the future of SSs you've produced.

Speaking of attractions, I invented an antigravity device. Since a piece of toast always falls on the floor jelly side down and a cat always falls to the floor with its feet pointed down, if you tie a piece of toast with jelly onto a cat's back, jelly pointed up, both the toast and cat want to land on their sides but can't due to conflict in forces, producing a floating assembly of toast and cat. Right? If you place 1000 cats with toast on a structure it will therefore float. Um... From the laboratories of Chuck of course, (gafaww)


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## bigdh2000 (Feb 9, 2015)

Thanks for starting this topic Byudzai. These are the types of topics where we all learn a little something.

If you do choose to ruin one of those beauties, we want video from all angles!


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## Resigned User (Jul 4, 2015)

Only one question... 
Why not?!
What's the matter in putting another "plus" that can make this catty safetier as before!?


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## Chuck Daehler (Mar 17, 2015)

the post with the idea of drilling holes in the middle laminate to produce epoxy internal rivets is a good suggestion, it's actually the best way to bond using epoxy if the laminates are thick enough...the middle one especially.

the post where dissimilar materials were brought up is likewise good advice

This is an excellent thread, Fred.

The post saying G10 is expensive...I made micarta from blue jean squares and polyester resin, it's a cheap poor man's G10. You can use linen as General Electric did for circuit boards, they invented it. G10 is micarta. General Electric's nomenclature is micarta. If you can get un-perforated circuit board, that's G10 or micarta as well...say from a dollar store that doesn't know what they have...or from whatever source that buys stuff from big mfg's. So if you want micarta, just make it. Here's a good vid on that:





 I used this method, works well. Using old raggey bluejean denim and $26/gallon polyester resin with hardener, I made a huge billet over an inch and a half thick and about 11inches square. You could make, say, 12 billets 11 inches square, 1/4 inch thick, for that. Cheap and trade your micarta here for other stuff. Paper micarta is very strong and using different colors of paper and clearish resin, the world is your apple.

Instead of non stick baker's paper which I can't get here in bananaland, I used plastic wrap since the surface would be ground off anyway in making ergo slingshots. You can use a thickness planer to flatten micarta sheets afterwards or go to a cabinet shop to use theirs and bring a sixpack of flothingslosh. ;^?

Here's another vid but there are a number of micarta vids on youtube.






A paracord micarta with the inside fibers removed:






This needs no "lay up"..just wind it around a handle and smear on a resin...epoxy etc.

Fabric scraps micarta: camo






My micarta projects:
http://slingshotforum.com/gallery/image/22024-micartamagnum1ergo1a/

have at it!!


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## JonM (Aug 17, 2013)

In my use of the various BSI 2 part epoxies, I've never had a delamination on a pinned or unpinned slingshot. Tempurature variables haven't been an issue for me.


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## Chuck Daehler (Mar 17, 2015)

http://slingshotforum.com/gallery/image/22024-micartamagnum1ergo1a/ my blue jean micarta..an example of what one can do with cast off rags. Try it! Hey, if I can do it first time, anyone can.


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## peppermack (Dec 10, 2013)

As far as surface prep here is a pic of the two surfaces before I laminate. 60 grit and then heavily scored.









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## JonM (Aug 17, 2013)

propper prep prevents problems :rofl:


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## bigdh2000 (Feb 9, 2015)

Chuck - I have made a round or two of felt micarta with fiberglass resin. Great stuff but still need to perfect my technique. Thanks for the info on G-10.

The biggest problem with micarta is that you need to make sure whatever resin used hardens like glass. Some do not.


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## filipino_saltik (Oct 7, 2011)

pvc and wood 2part epoxy never had any delamination yes
















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