Titanium dive knife sharpening

[7carson7]

Hey, So a buddy of mine came to me the other day and asked me to sharpen his titanium diving knife. So of course, I jump on the opportunity Due the the fact that I've never seen titanium anything before. The knife its self was recently bought and it was apparent, It was alright sharpness, but there was no wear or tear, But of course the was a secondary bevel. So today I took my 1000 grit stone to turn it into a convex edge, Then I went on to refine that on the 6000 grit, Then stropped with compound, as per the usual with any other knife I sharpen. But I noticed it was having trouble with cutting paper, So I did some more work with the 6000 going slowly with medium to light pressure to get a clean edge, Then went to strop it, But to no avail. I have sharpened tons of knives and all to pristine edges, From chefs knives to Bush craft and all sorts of types of grinds, bevels and edges. But this knife won't get sharp no matter what I do, Can anyone give me some pointers on this? 

[ThomasPowers]

What alloy?  In general Ti does not make a good blade; especially in the straight CP grades and won't hold a great edge.  That is secondary to it's being tolerant of salt water immersion and having a zero magnetic signature.

[7carson7]

ThomasPowers I have no idea what kind of alloy it is, I just texted him and he says he has no idea either, He does a little scooba diving here and there but usually has a steel knife that I've sharpened a few times. 

[Anachronist58]

In Aerospace, for titanium in general, conventional abrasives are not permitted, as they smear the metal, rather than cut.

Very sharp, friable, self-dressing Silicone Carbide is used, to counter titanium's toughness against abrasives.

Perhaps a high end wet/dry SiC paper on a plate will be helpful. Always drawing the edge across unused, sharp paper.

My question is: did this blade pass the paper test when new?

Robert Taylor

[Kozzy]

Wow.  The subject got me diving into a web search and this subject is definitely one where 5 different people will give you 10 different answers, claiming the other 9 (including their own) is completely wrong.

I did found a few commonalities:

If it's actually TI and not some fancy military grade version, it's going to tend to be soft and the edge will always be pretty mediocre.  

The most common method mentioned is the silicone carbide wet and dry paper on plate glass...grits to about 1200.

Part if the trick is a very light hand when you are sharpening.  Higher pressures tend to smear the edge and sort of "un-do" some of the work.

But I've never done it...so I suggest you do that web  search yourself also and see if you can spot any other "trends" in methodology.  On items that are highly opinion oriented like sharpening methods, I find that rather than specific advice it's the informational trends that are usually more useful to follow.

[7carson7]

Anachronist58 to answer your question. It sorta did sorta didn't, It would have a rough semi passable cut only at certain angles. For me I like an edge that I can go 90° to the paper and slice curves without pulling or pushing the blade very much, and same goes for my friend. 

[Anachronist58]

Would that necessitate pulling your finish hone perpendicular to the body of the blade, or more, rather, the ultimate keen smoothness of the cutting edge?

I have read that case carbiding is the best solution for Ti.

Robert Taylor

[Frosty]

Why didn't you call a dive shop and ask for the proper sharpener? You could've asked about the wisdom of altering the bevel while they sold you the right tools. 

I don't get Ti dive knives, what makes them better?

I have an old, plastic handled 440C dive knife I wore for a couple decades when we did barge jobs. Our drill rigs had a lot of line and by time we got 4 or more anchors set, suction hoses, buoys, skiffs ,etc. rigged there were lines every darned where and I kept my knife taped to the outside of my rain gear in case I got tangled and taken over the side. 

I brought that knife with  me when I moved here in 1972. never a spec of corrosion, holds a decent edge and I can sharpen it like any other steel knife. A couple strokes on a strop is all the convex the bevel ever needed.  It has to be 50+ years old and still perfectly serviceable. 

I'm not taking issue, I'm more curious than anything. 

Frosty The Lucky.

[BIGGUNDOCTOR]

As stated Ti does not make a knife like high carbon steel does. Good enough to cut some kelp if you get hung up, or possibly sticking a toothy fish that wants to taste you. Knives are also made from beryllium copper alloys for similar reasons, but the most important one for BeCu is non sparking when used in explosive atmospheres and explosives. They will cut many items, but do not take an edge like steels do.   If it was pretty dull, I would draw file it with a single cut smooth, and then sand as above. I would never expect a razor edge. Ti is used for its corrosion resistance, light weight, super toughness, and cool factors.

[ThomasPowers]

"Cool Factors"   when you can get a Titanium credit card you know that the hype is strong out there! I had a boss that fell for the Ti hype---he was bragging about the Ti laptop shell he had.  He was not happy when I pointed out that since Ti does not transmit heat as well as Al and that heat was the killer of laptops; a nice stressed Al shell would be much better for a laptop than a Ti one.   As I'm back in town with him and his wife goes to my church; I must make good on my threat to forge him a Ti door stop from some of the scrap Ti I have around...

Ti does make light tongs that don't heat the handle up as fast when used in a gasser.   I forged a set and picked up a commercial set years later, (cheap at Quad-State).

[jlpservicesinc]

Any titanium dive knife will not carry the cutting edge most are used to.. the alloys are not great and for the money are an ok knife. 

I used to make and sell a special designed knife for scuba for cutting lines but not cutting your own suit.. Most line entanglements happen in spots you can not see and usually are right against you so using a knife can cut both the suit (not much of a problem in a wet suit but disaster in a dry suit). 

I used to make the knives out of 300 or 406 series stainless and they cut well in use but the edge would not hold an edge like 440C..  but a knive will rust and have had many 440c knives break at the tange/handle because that area never dries and stays with salt water on them. 

The 308 and 406 knives never rusted and were designed to come apart for cleaning.  They were forged, then were cold forged, then filed, polished and handled with Delrin. 

Anyhow, I was a dive instructor, worked with GUE and the titanium knifes were not very good at holding an edge.. the metal is not hard per say. NOt like carbon steels but its far more important to have a tool that will last and is the reason the TI knives came on scene and stayed.