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SM 100 for the Knife Maker and Hands On Fabricator
It is very easy to read about the end use properties of SM 100 and think it is somehow unworkable without waterjet cutting capabilities and diamond grinding machines, but it is. You might even be surprised how many of the properties that make SM 100 such an indestructible material actually contributes to making it easier to work with in in-hand operations common in the custom knife making field. Let’s start with the basics:
Out of the box SM 100 has a matte gray surface finish that facilitates layout without the use of layout dyes. Scribe lines are clear and sharp in this surface finish and it scribes easily with carbide scribes, hardened steel calipers, and most other metal marking tools. It is literally as easy to draw on as paper.
This is a high wear resistance material once it is hardened, but in its annealed state it readily workable with all the standard tooling you would use to work with many of the common blades steels on the market today. The one area where this material does require a specific change in tooling from those which are viable in annealed steel use is drilling and milling.
Drilling and milling SM 100 does require the use of Carbide bits. If the bit is designated for use in hardened alloy steels then it will work for SM 100. Strait fluted carbide drill bits yield the best results turned as slow as your machinery can go and using proper drilling technique. Hand milling work should be done with 4 or more fluted carbide milling bits with as slow a feed rate as possible and at as slow a spindle speed as possible. Here in machining you may find one of SM 100 unique quirks; you can dry machine it and it will remain within touchable temperatures.
Cutting SM 100 is similar to cutting hardened steel. Abrasive water jet seems to have the best results, but even a seemingly crude cutting method like cutoff wheels on an angle grinder are effective. If you have a band saw that will cut hardened steel that should work as well. Cutting SM 100 will take more time than cutting steel or titanium.
Grinding SM 100 should be difficult right? Not really, the lower coefficient of friction and its ability to dissipate heat makes it less complicated to grind than steel. However it will take longer to grind than steel. Don’t be afraid to use very coarse grits for the major stock removal, SM 100 does not gouge like steel will at coarser grit and heavy grind marks can be removed quickly with higher grit belts and hand finishing.
Hand finishing is surprisingly easy with this metal. It will take satin finishes at 320 grit and will start showing mirror finishes at 600 grit with any standard buffing wheel and white buffing compound. It can be polished to a full bright mirror finish with all the buffing wheels and compounds that you might use for steel.
Now we can move on to more complicated operations like tapping and anodizing.
SM 100 can be tapped, I was the first to do and I did some of the standard tap size I commonly
use which are 2-56, 4-40, and 6-32. The key to tapping SM 100 is using a 50% tread tap hole, or maybe
even wire size larger than the recommended 50% tread tape hole if you are having trouble. Standard
HHS taps work up to 6-32, which you might need to go with something a little harder like M42 or even
carbide. Tapping fluid is not necessary but if you’re used to using it then it won’t hurt either.
I generally hand tap tough materials like thick titanium so I didn’t even attempt to mechanically tap SM 100, you
can and I’m sure the knife making community would like to hear about your results. I would
recommend using new, sharp taps and don’t plan on get too much life out of HHS tap after you’ve
tapped a few holes in SM 100.
Now the real fun part; Anodizing SM 100. Let’s be very clear SM 100, while made of titanium is
not titanium and thus does not anodize as quick and easy as titanium. I have literally spent months
playing with electrolytes and voltages to no avail. Then I did some more research into other types of
anodic coloring and found that the nickel content was playing a larger role than we had previously
thought. I have by no means perfected any anodizing formula, but it seems that TSP and Borax solutions
yield color, but at very high voltages. I have a 500V, .4Amp DC power supply that anodizes titanium with
no problem what so ever, but SM 100 has been very challenging.
It appears at this point that, unlike titanium or niobium, the amperage is a major factor along
with the size of the work piece. I can consistently get a light gold color by letting a blade sit in a 10:1 TSP
solution for about 30 minutes at 500V and .4 Amps, so a full 200 Watts. In smaller pieces I have been
able to get light blues and purples with deep bronze colors by preforming the same formula.
The surface area of the cathode is there for important without the ability to increase the
amperage. It seems that double or triple the work piece surface area is needed to produce any color
and the better the ratio of cathode to work piece surface area the better the colors that can be
achieved. But remember this is all taking place at 300-500V. I have been using titanium as my cathode,
but tungsten or niobium might work better.
Because no other industry is interested in anodizing nitinols for color, we knife makers are sort
of on our own on this one, but with more people playing with it and the wide variety of anodization set
up we have we should be able to find some concrete methods for doing everything we can do in
titanium in SM 100. I am strongly considering building an anodization unit just for SM 100 with high
degree of variability in amperage as well as voltage so I can keep attacking this interesting aspect of SM
100. You and I know the market likes color, especially on blades, so it is worth my time to keep
exploring anodic coloring, I hope others do as well.
The Warning Section:
SM 100 can and does work harden, especially when drilling larger than .125in holes at higher
than recommended speed (as slow as you can go). Sharp bits reduce this, but it something you should
be aware of. I have found it very difficult to overheat SM 100 during belt grinding, but if you use a
bench grinder for any sort of profile work you can get little hot spots that will harden. If you’re used to
working with air hardening steels and practice good cooling procedures then it shouldn’t be an issue, I actually had to deliberately try to get SM 100 to work harden on a bench grinder.
In its annealed state SM 100 is very flexible, but it can be bent permanently like a steel and will need to be straitened as you would steel. It can be done by hand in the annealed state, once hardened it will have shape memory unlike anything steel does so make sure it’s strait before you heat treat.
It is possible to heat treat SM 100 yourself, but I would recommend sending to Summit for heat treatment. I’ve been working with Fred Yolton to perfect his methods and he has heat treated more SM 100 than anyone on the planet. One of the things he and I have worked on are the particular oxides formed on SM 100 during heat treatment. It forms a “black oxide” which is very hard, NASA tests it at 72 Rc and I can tell you from experience it is hard. We were also able to get an olive drab colored oxide that is equally as hard. Fred will also test the hardness for you so you can be sure it is as hard as you wanted it. Having been working with Fred I could heat treat SM 100 myself, but I still prefer to send it to him, he’s worth extra money.
The last thing about SM 100 regards sharpening. You will get lots of question about it, as I do, and it is no more difficult to sharpen than M390, S90V, S110V, S125V, Cowry X and Y, and M4 at high hardness. It does take time, but something as simple as wet/dry sand paper on a hard surface will sharpen SM 100. Ceramics, diamond and more exotic sharpeners will work just fine, but are not necessary. I might dissuade customers from using course grit wet stone, but I do that with any knife I make since most people tend to remove too much metal on those.
I am always willing to answer any question I can and can be reached via email at firstname.lastname@example.org
I am by no means an absolute authority on SM 100, but between the good people at Summit and I, we can usually come up with an answer. I have been willing to take risks with some of the material Summit was gracious enough let me play with so I have done some things that others have not or will not do in the name of science and my own curiosity.
I hope you too will come to appreciate the modern marvel that is SM 100.