DIY grit file – first blood

[Vidar]

Some time ago another thread here infused me with monkey brains, melons and a DIY grit file compulsive disorder. I won’t mention names, but I totally blame him and not Kirby.

Thus I got hold of some tungsten carbide at 60 grit sized particles. If I can make that stick to steel then custom files and grinding wheels might be within reach – and that could come in handy.

I have a few options that might work in theory, and I figured I just start with the most naïve one: It is unlikely to work, but I should get some answer and indications of issues on the way. Thus it might not work, but unlikely to be a failure. And if it does work then all the better of course.

So first off I took a donor SAK sawblade which I washed, degreased, rinsed, gave a soothing acid bath, and rinsed off yet again. Water spread evenly afterwards so fairly clean I figured.

My most straight forward approach to this is to just put the grit on top of the saw, and then sprinkle some nickel and flux on top of that again. Then basically melt the nickel, with the flux hopefully keeping oxides away. With both the steel and tungsten carbide having far higher melting temperatures there should be a window for just melting the nickel, and hopefully the nickel would stick to both the tungsten and steel afterwards. What can possibly go wrong?   

So, to start off, one piece of clean steel and some tungsten carbide, nickel and borax for flux. (Only thing I had around).

[Vidar]

Sprinkle sprinkle - clean blade, then tungsten carbide grit, then nickel, then borax for flux.

[RF52]

I remember you guys throwing some ideas, monkeys and melons around, will be interesting to see what you come up with

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[Vidar]

I put the blade in a small induction heater. It quickly became clear that the flux wasn't really fluxing, but rather keeping to itself and trying to escape this project.

I continued heating nevertheless, and while it did get to red glowing hot the small induction heater couldn't quite make it to the nickel melting temperature in free air.

[Vidar]

Not looking that great so far - everything is still just dusty grit on top.

Thus, the introduction of a small crucible to bring up the temperature a few notches. Now we're cooking! 

[Vidar]

(Just in the off chance anyone should have the same ideas: Many metals give off dangerous fumes when heated enough, among them some present here, so I wore a powered air purifying respirator at all times).

[Vidar]

I let this thing cool down naturally in air. As it got cold enough to see and feel it was clear that there was indeed some gritty surface. However it was also clear that this gritty surface wasn't flat, but rather lumpy. Now, having tried to file with a lumpy file, I can say with authority that flat surface files work a lot better. So that is an issue - not only does it need to stick it needs to end up fairly flat too.

After filing away at some wood and stainless steel another issue was the grit was removed from the file as fast as stainless steel was removed from the test piece. While the nickel and the tungsten grit seemed to have bonded (and made lumps), the nickel to stainless steel bond was not really there. Thus after a bit I ended up with a saw blade again without any grit on it. That is kind of an issue..  (Picture 2 - brighter areas show were the lumps were somewhat connected I guess).

Heating and cooling and doing weird stuff to a presumably already hardened saw blade can be expected to have some consequenches. So I decided to try what state it was in by bending it. I never got that far. It broke clean off just with me applying pressure with my thumb. Clearly a guarantee issue!  Either way, not good news for this non-working method even if I get the grit to stick.

So I've basically modded a sawblade into two sawblades... Now it might fit a 58mm. 

[Sam Lim]

  Nice read. The process sounds fun enough! I didn't think that u will go ahead to test this. 

[styx]

that could turn out interesting

[lister]

This must be the craziest mod attempt I ever run across on this forum! 

So want to braze the carbide particles to the steel? Maybe if you look up what filler metals work for stainless steel and tungsten carbide and use that? Though as my metal working skills are limited to basically filing, hand cutting, drilling and soldering what I suggested is totally useless.  And any way, the chemicals involved are likely to be of the not good for humans kind. 

I really hope you pull this off. 

[Vidar]

This must be the craziest mod attempt I ever run across on this forum! 

So want to braze the carbide particles to the steel? Maybe if you look up what filler metals work for stainless steel and tungsten carbide and use that?

Yes. I have a suspicion that the normal filler metal for brazing would work just great, but with 56% silver content that isn't too economical. (Of course it would be fine for a single mod). I plan on doing that with oven brazing in a third go just to test though.

Before that though I'll give this melting nickel approach a second go but in a controlled atmosphere to keep the oxides away. And or possibly just melting the tungsten directly into the stainless without the nickel? We'll see. I guess I need to sacrifice a few more donor SAK pieces to the mod God as well.

[Don Pablo]

I have one or two extra saw blades (no springs) that I can donate for the cause if you want them.

[Vidar]

I have one or two extra saw blades (no springs) that I can donate for the cause if you want them.

Thank you for the offer O'Don Pablo - much appreciated. It wont be necessary though. For now I'm just trying methods to stick grit to stainless, not modding an actual part just yet. So for now there is always can opener with file (worst idea ever!), bottle opener with file, knife with file (ok, even worse idea), and of course scissors with file (now that is truly bad), and wine opener with file... 

I have a fair bit of general stainless steel material as such laying around too, so still a lot to go on.

[Don Pablo]

 

[lister]

Silver huh? 

So it's a bit like the new, ROHS compliant, solder. At least the one you have to use if you don't want to melt the parts you were supposed to be soldering. Also expensive as smurf. 

[Don Pablo]

Eh, I think the older lead solder was better. No whiskers leading to electrical shorts in a relatively short amount of time.

[lister]

Eh, I think the older lead solder was better. No whiskers leading to electrical shorts in a relatively short amount of time.

As a semi professional EE I declare the older stile of solder to be superior. 

[Don Pablo]

Eh, I think the older lead solder was better. No whiskers leading to electrical shorts in a relatively short amount of time.

As a semi professional EE I declare the older stile of solder to be superior. 

[Vidar]

So, when I find the time, I have following ideas lined up: (They might come and go depending on moon cycles and mood swings).

1. TIG weld the tungsten and nickel to the stainless with argon shielding gas. No filler material.
2. TIG weld the tungsten directly to the stainless with argon shielding gas. No filler material.
3. Resistance weld tungsten particles to the stainless.
4. Oven braze the tungsten to the stainless using 56% silver paste.
5. Repeat the first experiment but with a controlled oven temperature to melt the nickel, and with a oxygen depleted atmosphere.

That sounds like an entire evening, but vacation time is coming up..

Then there are all the electroplating options. Somehow I find that less interesting (maybe because it is known to work?), but if all above fails I might go there too in due time.

Any other ideas? Super strong glue? They do make resin bonded grinding wheels - that sounds like fancy for "glue"? Possibly some bronze alloy instead of stainless for base material?

[Vidar]

I did a quick little test with resistance welding and some 316 stainless washer. Different kind of stainless, but resistance welding tend to be forgiving about that so I figured if it works on 316 it will likely work on multi-tool steels too.

The washer was quite tiny (M6 or thereabouts) so to connect it to ground I pushed it down at a larger nut that was connected. That worked but also resulted in those two being welded together - as if a file on a washer wouldn't look silly enough on its own... 

Anyway, I trickled on some tungsten carbide particles and gave them some suitable shocks. The ones to the left got about 400v DC, while the ones at the right got about 180v DC - not sure about the amps as the machine doesn't show that, but likely overall in the very low kVA range. Judging from the looks of those something in the middle might be best.

The particles that I hit with pressure seems to be stuck pretty good. I tried getting them off by filing a black umbrako key, but they stayed stuck. So far so good.

Trying TIG welding next I think.

[Don Pablo]

 

[Gerhard Gerber]

 

 

 

[Poncho65]

Just seeimg this Great first attempt and the second one is even more promising hope you can figure this out and can mod what you wish

[Nix]

This is fascinating. 

[Vidar]

Ok, so I went ahead and tried resistance welding onto the back edge of an actual SAK awl. Likely not a very useful position at all for a file, but I get to try the method with the SAK steel material.

This time I didn't want a nut stuck to the awl afterwards so instead I connected ground to a sheet of copper. Then to keep the awl in the right position I welded it onto a washer, but quite weakly so it should be easy to break off later.

The awl was washed with acetone, the rag disposed of in a firesafe garbage bin, and then the awl was lightly grinded. It should then be pretty clean. Then it was back to sprinkling on some tungsten carbide, and finally going a over it with some shocks. Based on the previous test I tried 300v DC as a middle ground.   

The sparking photo was a hands on challenge - one hand to hold the business end of the welder, one to activate the welder spark, and one to take the photo. Timing was also a bit difficult - I'd love to say I have great timing, but actually it was more about the patience to try 20 times..

[RF52]

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[Vidar]

So the results were a bit mixed.

A fair bit seemed to have stuck at first. Then I broke off the washer, and went ahead and filed on some stainless steel nuts and bolts laying around. Some tungsten bits then fell off, and a fair bit stayed stuck.

I guess this is more a question of finding the right setting for the material - it does get stuck, but it varies with how connected it is and maybe with the geometry of the particle too.

[Vidar]

While I was at I thought I'd give TIG welding a try too. The idea not so much being a weld connection, but making a molten puddle of stainless steel which the heavier and far high melting point tungsten can sink down into and get stuck in when it hardens again.

I had considered trying this with the addition of nickel too, but I only had nickel in fine powder form. The gas cover would likely blow it away, and I'd end up with fine particulate nickel powder around electronics and my lungs ever after. It was windy outside so that wasn't an option for TIG either.

So Victorinox have been nice enough to make a little tool perfect for scooping out powder and dividing into lines. I think they call it a cuticle pusher. Anyway, cleaned the test SAK part and spread some tungsten over it. I wanted some clear lines so I would be able to see the state of the stainless underneath as I was welding.

Then it was onto welding with quite low power. A major problem that showed up was that despite my lines I had no way of seeing what I was doing under the tungsten particles. Moreover the welding helmet was on the dark side for this. I was basically welding half blind, and I never saw any welding puddle at all. Here goes nothing!

[Vidar]

I tried doing two stripes. To my surprise I had made a mountain at the end of one, and that it had some clumpy appearance all around. I also noticed that there was no grit sticking up in the actual paths.

The part was both thicker and heavier after so clearly there was an addition of tungsten. I figured that the tungsten carbide might just have sunk down a bit too far. No problem I thought, I'll just get a little band grinder and grind it flat...

The result after that is picture 2... Ok, I might have a surprise problem here.. Notice the minuscule scratches at the top edges - that was the result of about a minute of band grinding..

Sand papers don't work? Ok, surely the angle grinder will make short work of this less then flat surface. I got out an angle grinder with a grinding disc for steel on. I then went to grind for over a minute, and messed up said grinding disc... The result of that is picture three... Yes, that still looks exactly like number two. This is some hard smurfing stuff!  (Edit: And or something that can withstand the heat the grinder generates).

Finally, a diamond cutting wheel. That did cut. I made a few notches and tried it on the stainless steel washer from earlier. It will cut. It is very smooth though, so it is basically just the cut edges that cut.

I'm not entirely sure what happened here, but I suspect the tungsten carbide disintegrated and I ended up with some stainless steel/ tungsten combination matrix instead. Which evidently is very hard and abrasive resistant. (I tried it mano a mano against a proper file afterwards - the proper file lost).

Hm.. Wonder if this stuff will keep a cutting edge? And can I replicate this and make more of it?

Anyway, very unexpected result, but also quite interesting on its own. And if you make grooves it would certainly file.

[Don Pablo]

It sounds interesting enough to be patented.