Rebooting the 'micarta' production line

@O @oafpatroll 2 years ago

[member=67]Tripodmvr[/member] has been posting pics of Ausie knives with micarta type scales and that inspired me to break my two day streak of Christmas present book reading to make some again. I've been meaning to do so for quite a while as I have two knives that are long overdue some new scales and two handguns that I would like to make grips for. Fabric based micarta is really useful stuff in that it can be made at home and is very durable, inert (depending on the resin you use), flexible, impact resistant and grippy as hell wet or dry. I made a fair bit of the stuff years ago for knife scales and for a friend who used it for building drones when they were still more of a fringe uber geek thing than they are now.

Having not kept record of my resin/fabric mix ratios or work time I decided to do a recalibration run with stuff I had on hand so as to avoid wasting money. Used a really manky pair of khaki cotton canvas work pants and some leftover polyester tooling resin for the material and 16mm clad chipboard offcuts for a press.

I'd forgotten how much resin cotton fabric absorbs even when it's threadbare and paint stained like this stuff was so I had to mix a second batch post haste to finish the layup as the first lot was starting to gel.

Worked lekker though and the first block will be used to re-scale a chopper knife I made out of a roller bearing nearly 20 years ago. It's as ugly as hell and has paint inclusions and oil stains and all sorts but it's rock solid and completely homogeneous. I'll make up some more this weekend using alternating layers of virgin khaki and olive drab cotton canvas for aesthetics and use those on the second knife and the two handguns.

The white colouring in the pics aren't dry spots but paint and bleach stains in the fabric. I thinned the resin a touch with acetone after catalysing and consolidated with a roller so it was completely saturated.

A tip for anyone who may like to try this is that baking paper is the thing to use as a mold release rather than wax paper. It's completely counter intuitive but matte baking paper almost jumps off the mold and the slab while slick slippery wax paper needs to be laboriously peeled off. That's one thing I'm dead glad to have remembered.

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@O @oafpatroll OP

Pic of the slab attach for those who can't see onedrive pictures

@O @oafpatroll OP

Pic of the slab attach for those who can't see onedrive pictures

@O @oafpatroll OP

Something I forgot was that if you want absolutely parallel faces on a slab you need seriously rigid plates to clamp against. I thought that a layer of 16mm chipboard with 20mm of pine on top of that would do but the slab was more than 1mm high in the middle of its 200mm length. The stuff I made for my mate with the drones was made in a press consisting of two 16mm mild steel plates with 8 bolts around 6mm thick steel spacers. With that I just piled in the layers and then cranked down on the bolts and the slab was a perfectly uniform 6mm across its usable area. With this janky chipboard press I will need to add clamps in the middle and measure a bit more carefully but given what I intend using them for that should be fine.

@O @oafpatroll OP

Made a few more slabs with virgin fabric. First one that I got out of the mold and ground an edge on and wet sanded to 320 grit is this black bull denim. I like it a lot and will be using it to make a set of grips for a stainless Ruger revolver. I have fine hessian and a khaki cotton canvas/duck still in the molds. looking forward to how they come out. Will be having a crack at some much finer fabrics in the linen range as well as craft paper next. Paper has the advantage of piling up in thin and perfectly aligned layers that don't deform when clamped.

@T @treeman

Interesting stuff this ! What would happen if you put something like a dagga leaf or feather or R100 note as the top most layer ? Would it be as imagined ?

@D @ds-j

And would you please give us a photo of the polished blue stuff? It looks good.

@O @oafpatroll OP

Interesting stuff this ! What would happen if you put something like a dagga leaf or feather or R100 note as the top most layer ? Would it be as imagined ?

As long as whatever you put in is permeable to or completely encapsulated by resin it should work fine.

@O @oafpatroll OP

And would you please give us a photo of the polished blue stuff? It looks good.

Unless you coat it with clear resin or varnish this stuff doesn't polish to a bright surface as the bulk of the block is fabric. It doesn't really seem to change much after 320 grit. Since I want it for the grippiness it imparts I won't be coating or polishing the grips or scales I make from it.

@O @oafpatroll OP

And would you please give us a photo of the polished blue stuff? It looks good.

Unless you coat it with clear resin or varnish this stuff doesn't polish to a bright surface as the bulk of the block is fabric. It doesn't really seem to change much after 320 grit. Since I want it for the grippinessnit imparts I won't be coating or polishing the grips or scales I make from it.

While what I've made doesn't polish well in it's raw stae it does absorb oil which chnges its appearance a bit. This is the black denim with some thinned boiled linnseed on the 320 grit cut edge.

@O @oafpatroll OP

Pulled the hessian this morning and it looks a lot like . . . . . hessian. Be interesting to see what the cut edge looks like. Expect that this will make for the grippiest of the sample so far so I may use it on the frankenchopper rescale as that wouold benefit most from more grip.

@T @tripodmvr

Patiently waiting to see the final product as fitted. Do you need some medium to contain the resin or can it be used as is and colored with some stain or powder?

@O @oafpatroll OP

Patiently waiting to see the final product as fitted. Do you need some medium to contain the resin or can it be used as is and colored with some stain or powder?

I'm going to do a bit more prototyping and testing with cheap leftover polyester resin I have before making the blocks I'll use for my nice knife and the two handguns with good quality epoxy resin so it will be a little while before I have anything final to show. Given my near non-existent woodworking skills I'm far from confident of the outcome, especially of the revolver grips as working the stuff is a fair bit like working dense hard wood.

I know you get casting resins that are strong on their own but I've never tried anything like that and have no idea if it would be strong enough on its own for use as a scale or pistol grip. My gut feel is that it wouldn't be but I don't know that for sure. I understand that the properties of the micarta (especially the compressive and tensile strength) come from the combination of the material in the composite so leaving out the fabric would probably lose you something. As to the staining I once tried an alcohol based black stain in some polyester resin and it worked well.

@T @tripodmvr

Thanks. Something totally new to me and although the name "micarta" is known to me I have never queried the source of the product. Will do some browsing to catch up.

@O @oafpatroll OP

Thanks. Something totally new to me and although the name "micarta" is known to me I have never queried the source of the product. Will do some browsing to catch up.

Pleasure. 'Micarta' is actually the trade name of a phenolic resin based composite that was developed pre-ww1 by Westinghouse. It was a thermoset composite of phenolic and paper or fabric and was cured in serious presses. It was originally used in industrial electrical applications and apparently also for some decorative stuff.

The term now is used in much the same was as 'damascus' is as a generic term for pattern welded steels. The few bits of the real vintage stuff I've seen is very smooth and has barely a hint of the fabric patterning.

@D @daavg

Thanks Oafpatroll, very interesting! Where do you source your raw material from as a matter of interest? I assume offcuts?

@O @oafpatroll OP

Thanks Oafpatroll, very interesting! Where do you source your raw material from as a matter of interest? I assume offcuts?

My pleasure, hope it's useful to someone. Apart from the black denim sample which was made from virgin fabric bought for the purpose from Chamdor in North Riding the rest were from stuff I had at home. The cotton canvas one was from a criminally manky pair of work pants. I have new khaki and OD-ish canvas/duck, also from Chamdor, for this weekends production.

@O @oafpatroll OP

A cross post of random tips that I put on GS for anyone who may like to try it.

* If you want perfectly parallel sides faces you need a seriously rigid form with hard stop spacers or the ability to accurately measure the thickness of the clamped layup all round. When I did this before to make plates for a friend who built drones way back when I used two 16mm mild steel plates with 6mm spacers and through bolts. The press in the pic was a quick lashup of 16mm formica chickboard with 20mm of pine on top and it flexed enough to make the first 200mm long block >1mm high in the middle.

* Baking paper (not wax paper) is excellent as a mold release. A few sharp taps with a mallet and it jumps apart clean enough that you can reuse it. Wax paper has to be laboriously peeled off.

* You need more resin than you probably think. Depending on the thickness and weave density of the fabric you use that amount will vary. You need enough to thoroughly saturate every layer of fabric but if you're using polyester resin and you catalyse it enough it may go off before you're done layering so it's best to mix smaller batches as you go. This obviously doesn't apply if you're using a slow cure epoxy.

* A credit card works great for squegeeing the resin through and then out of the fabric. It doesn't need to be dripping but it must be saturated and anything beyond that is just squeezed out when you clamp.

* A small painters tray is ideal for applying the resin. You dip the fabric in the reservoir and then pull it through under the credit card on the slope. Makes it really quick and you get good saturation and minimum waste. When the resin has completely cured it comes off the tray in one or two big pieces.

* Disposable nitrile gloves are a win.

* The more accurately you can cut your fabric to match the dimensions of the mold (if you are using one) the more of the block will be uniform and usable

* Loose threads must be cleared from the faces as you layup as they show through really badly when you expose them when shaping.

@J @jamesnotbond

Interesting post this is. 40 years ago we made handles by wrapping thin rope, cord around a knife or tool that had been wetted with surfboard resin. We would wrap one layer wet it with resin and wrap again and again. The last wrap had a brick tied to loose end and left hanging in the vice overnight.
We would then shape and polish the end product as a school holiday achievement, no cell phones, TV to brain dead us back then.

@O @oafpatroll OP

Haven't come across that technique before. Sounds like it could look really lekker and I'm sure it was very functional. I have an ancient integral hatchet with a rotted away stacked leather handle that would be nice to try that out on.

@T @treeman

Interesting post this is. 40 years ago we made handles by wrapping thin rope, cord around a knife or tool that had been wetted with surfboard resin. We would wrap one layer wet it with resin and wrap again and again. The last wrap had a brick tied to loose end and left hanging in the vice overnight.
We would then shape and polish the end product as a school holiday achievement, no cell phones, TV to brain dead us back then.

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We did exactly that as well, my father would join us and add copper wire and other things like coins to the back of handle. Greenshields Park kids, we grew up proper me thinks. I recall using super glue on wood then polishing it, and burning wood for natural patterns, sanding it to various degrees and dipping in resin. We would then polish the resin BY HAND, till it was like glass.
I wonder where all the stuff we made ended up, some of it was pretty enough to be someone's treasure.
Oh yea ! One more thing was copper earth strapping, the flat braided type. We cleaned it super shiny and the did the resin thing. Was super pretty, but never lasted long because we did not know how to deactivate the pool acid - neutralize it.
Ya we played with pool acid as kids.