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Some of my recent slingshots have used home-made laminated boards made of cloth in resin. I thought I'd show you how to do it for yourself. I haven't done one of these laminates in literally years and never did more than a few slabs, so forgive me if I am a bit rusty.

First, assemble everything you'll need.

  • Ventilation. The resin is noxious. Especially if you mix the catalysts.
  • A good table and something to protect your surface.
  • Disposable rubber gloves.
  • Cloth; I'm using a yard of denim here.
  • A pair of scissors.
  • A resealable (or non resealable, but tends to be a bit more messy) plastic bag bigger than your intended slab.
  • A couple of fairly rigid boards bigger than your plastic bag.
  • Clamps.
  • Resin; I'm using clear polyester fibreglass resin here, but epoxy and other strong clear two-part resins are fine too.
  • Disposable or cheap plastic containers to mix resin in. Note the catalyst melts styrene cups like these. Guess how I know.
  • Something to use as a rolling pin.
  • Something to stir the resin with. Ignore the paint brush, I used that as a stirrer.


First cut your fabric into equal and appropriately sized panels. If you keep the corners square and the dimensions the same, you'll not have to trim much off the edges later. The best materials are strong (silk and linen), absorbent (silk, linen, cotton), thin and not too tightly woven. The colour or pattern should not be too dark. The slab will come out roughly the colour that the fabric becomes when wet. For this reason, I'm using pre-washed denim. Denim is a classic material for home-made slabs, but most people choose a denim that is too dark. Regular denim will turn dark-blue and dark denim will go almost black. Sometimes, you may not have enough ofone material. It's possible at a pinch to use another similar material at the bottom or centre of a stack as long as you later remember not to sand down into it, or you'll expose the different material. Some people use layers of contrasting colours to make layers like tree rings in wood.



Measure out the resin. I used 500ml (17 US fluid ounces) for a slab that was only 0.8 sqft by 3/8 thick. I always over estimate the amount of fabric needed and that I can lay-up in the 20 minute pot life and under estimate the amount of resin needed to bind it. I could (should) have used 600ml (20 floz.)



Measure out the catalysts. The resin I'm using needs 100:1 ratios, so I should really have scales that measure in smaller increments than 1 gram. It'd be better if it was a glass top than plastic and I should really have a way to pour liquid with more control. HereI am using film cannisters which seemed to work OK for the catalyst (didn't melt into a puddle like the styrene cups).



You have to add polyester catalysts separately (follow the instructions). My school plastics shop class teacher mixed up the catalysts together without stirring in between .... in 1984 and a cupful created so much smoke that I remember it vividly to this day. If that happens you'll want to get it outside in a hurry. If your cup melts in the vigorous exothermic reaction, that'll be difficult.



The clock is now ticking so the rest happens in a big hurry. Invert your bag and use it as a work surface cover. Pour the mixed resin on the bottom sheet.



I spread it with a squeegee (the edge of my hand in a glove). Get this layer really thick with resin and flip it over so the resin is in contact with the bag. The bag must be flat and not kinked and don't trap an air bubble under the fabric.



Lay up layer on layer, with a puddle of resin in on top of the last layer, then fabric then resin on top. Each layer must be 100% soaked into the fabric from both sides. In the picture below, the fabric has soaked through from the layer below; it's not wet enough yet. As you lay up, this is your best opportunity to make sure there are no dry spots or bubbles. Either will create a dry spot, which will be weaker and will concentrate stresses later too.

If I'm making knife slabs, I lay them all the same way up because the back is glued to the tang, but for slingshots, which are seen from both sides, I lay half the layers one way up and half the other so that the face sides face out.



You know when to stop when you run out of fabric, resin, or time. You'll know when times up, because you'll notice a slight thickening in the resin as you pour it. You should nevver leave it so long that you get gel lumps. I find judging by eye is better than setting a timer (though I do anyway) because a small difference in catalyst can affect the time.

Finally, I flip the bag the right way round, seal it with the slab inside and gently roll it with a rolling pin from the centre to the outside so that any large air pockets are excluded. You don't want to squeeze out every last micro-bubble; pressing too hard will squash out all the resin.



Gently clamp the bagged slab between the boards. You only want to ensure the sides are flat and the thickness is the same. Otherwise, it may be bent, uneven, or big air pockets might get in. Again don't clamp too hard or you'll push out all the resin you spent so much time applying.

 

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By this time, the resin will be starting to gel and this is the last opportunity to clean your work surface.



After a couple of hours (ideally a day), you can examine your slab. I do this after only a couple of hours, because I do a run of slabs since I'll be making a mess anyway and I'll need the boards and clamps for another slab. You can see another set on the floor in the background of this picture.

Don't worry about what looks like streaks of bubbles in this picture below. I think the catalysts are slightly melting the bag and it's creeping a bit. The slab is unaffected.



After 24 hours, it's ready to test. First, it should sound like a board if tapped by something hard. Then i trim it on a bandsaw and inspect the edges for voids. The one below looks OK. I bend the off-cuts to see if the resin is hard. For slingshots, it's worth making a mock fork arm and finding the static load breaking point. You could also overload test the finished frame. Otherwise, just proceed like you would when making any other board-cut. Also, inspect the board regularly, such as before and during a day's use.



The picture below shows that you can even lay-up prints. The key is making sure the topand bottom layers are flat and perfectly parallel, as you won't be able to sand through the layers. The only way to fix that is to apply a layer of surface resin and sand down.



Well, I hope this tutorial was interesting and that someone will be inspired to give it a go. I'm ready to answer questions if you have them. Please also let us know if you have tried this yourself and how you did it and how it came out. Do you have any pictures of completed projects?
 

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Great post ZDP and you won't find me doing any resin work any time soon! Too messy!!! Flatband
 

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Discussion Starter · #9 ·
Thanks for the encouragement everyone.
I promised to do some realtree for someone anyway and it was no great effort to photograph and describe the process. I will do more tutorials if I decide what's doable in the home workshop and applicable to slingshots.

It is a little messy, but with the gloves, bag and a bit of newspaper, it's no problem. Actually, this process is slightly modified from normal. When I do print laminates, I use a smooth greased film on the boards no bag and precise spacers to limit clamp pressure and make the thickness even. However, that is altogether messier and you might not want to do it on the dining table. The bag works well and limits the mess.

keeco, the cost was about US$6.50 for the resin, a yard of denim was $3.30 and the other consumables took it up to about $10 in total. There's about an hour of labour in making a slab and you'd get maybe 2-4 frames out of the denim depending on whether you doubled the stack for additional thickness. A small bit of G-10 of carbon fibre big enough for a slingshot is more, but not so much more that they cost more than hardwood; at least for me here in Hong Kong. A nice bit of wood would cost me much more when factoring in shipping. I used to regularly pay more than $50 before for a couple of stabilised knife slabs. No, the big advantage is the ability to make exactly the style of board that you want.

It's important to say that this is not as strong and rigid as G-10 or even micarta. The layers are too thick, the material not as strong as glass fibre sheet and polyester is not as strong as high-tensile epoxy. Whereas I might have gotten away with just a tiny thickness of carbon fibre, you really need 3/8" plus for this to work on a slingshot. To do that, you have to either double up layers by gluing them together (with or without a steel core), or use stronger ingredients. The silk (in 2-ton epoxy if I remember right) that I used for the One Night in Bangkok slingshot allowed me to make forks that are strong but relatively thin; thinner than you'd dare use for wood, anyway.

Dayhiker, when laying up, I work as fast as possible to get as many layers down as I can during the pot life of the resin. There's no time for beer till after.
 

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MY VOTE FOR ZDP FOR PRESIDENT!!... OF THE WORLD!

this is the coolest post i´ve ever seen, this micarta deal is just way too fun to do!!

a "MUST DO"!

tanxs for the info Mr. ZDP
 

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The Realtree slab was made at the request of forum member Scott (Fork Hunter) for a slingshot in my T1 template. I profiled this board-cut with a bandsaw and a scroll saw, then radiused the edge with a coarse file. This is the result.



Notice that I was careful not to round the edges too much or file too much into the board. That would end up looking like a contour map and I kept it as flat as possible to preserve the print.



As an 'experimental' laminate, I stress-tested the frame. I did this in more-or-less the same way that I would test a heat-treated steel blade. I clamped the fork in a vice mid way down the handle and applied a gradually increasing load on each fork in turn, rising to the limit of my postal scale of 70lbs. It bent but did not delaminate or snap and returned to That suggests it could support almost a person's weight (a Chinese person) without breaking and certainly more than a person would pull on a fork. Obviously I would not recommend such heavy bands; considering that there are sharply applied forces, vibration and fatigue effects to contend with, I suggest this particular laminate be subjected to no more than 22 lbs to 25 lbs of draw force.

If a stronger material and resin were used and if the resin had penetrated more deeply, I would probably assign a higher duty load, but it pays to add a generous safety factor.



It is not good enough to know that a material can take 70 lbs per fork. I want to know how it fails. Some materials fail in a catastrophic way - some glasses or ceramics could shatter flinging heavy and sharp lumps at one's face. The same goes for many woods. Steel may bend, but again a weld may fail. These materials' saving grace is a very large safety margin.

In this case, I took a 1"x4" off-cut and tested it clamped in the vice and in a cheater bar so that the forces were applied over 2" length of laminate. I applied a fairly large force - less than would be required for a steel blade, but of comparable magnitude. The laminate bent gradually and eventually failed when bent over about 30 degrees from the vertical. At this degree of bending, it should be very obvious to the shooter that he was pushing the slingshot far past its design limits. When it did fail, it delaminated as shown above due to compressive forces on the inside of the curve shearing against tensile forces on the outside. The delamination only reached half way to the vice. The laminate did not snap, shatter or splinter and I think the bands may have even stayed on of there was a proper groove/slot for the tie bands. It was a good result and I am happy to pass the slab and the frame.
 

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Discussion Starter · #16 ·
Following up on the first slab I made in this thread, the denim turned out to be very similar to the heavy canvas print. However, to demonstrate, I made something to show some things that can be done to make these laminates stronger.

First, the denim slab was a bit thin. I increased the thickness by stacking two slabs which were rough cut then adhered with epoxy. The thicker the slab, the more the outside is in tension and the inside is in compression, potentially leading to the kind of shear slippage delamination shown in the test above. The way I made sure that couldn't happen this time was to inset some brass rivets, making them look even more like blue jeans. The rivets aren't so much to resist opening up as to resist shear.

The look was completed by distressing the denim, rather than varnishing it for a deeper colour. I'll call this the "Cowboy Catty". The pattern is a slightly modified T1 template.





 

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Great work ZDP! I first became aware of the bauty of resin (micarta) style frames from Knifemakers. They use a lot of this stuff,denim,lexan,nylon, silk etc. for the scales on their blades. Very strong stuff and when done right (like yours) nice looking and very functional. Cool!- and I still love your shop and want to live in there!!!!!!! Flatband
 

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wow that was amazing!
im on this site just a few days and im in love with it.

how do i know when i should retire the frame and stop using it?
and how long do these creations last?
 

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Discussion Starter · #20 ·
I haven't had a proper failure. You should retire any frame, of wood, metal, plastic or whatever as soon as you see any cracking, unnatural bending or anything that would indicate structural weakness.
 
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