Thread: Sharpening hardened tooth bandsaw blades

Forgot the photos..
Jim

Sounds brilliant. But I wasn't aware that soaking a blunt bandsaw blade in vinegar would sharpen it.Can you tell me more I am very interested just having disposed of a couple of used blades that maybe coul have resurrected.

I have sharpened them on a bench grinder fitted with a cutoff disc.

Setting them is the tedious bit.

Hi Powderpost,

That's interesting. I was speaking to Richard Vaughan the other day about file and rasp sharpening using citric acid or rust sharpening them and using electrolysis, following another thread on WWF. When he wrote a story on rasps for AWR, he looked into this fairly well and I was surprised that he couldn't find any evidence that it really did work. HUH? . He said certainly the cleaning effect of these methods would reinvigorate blades/files that appear dull due to clogging with resins, gunk etc, but could see no way it would resharpen a work-bluntened tool. HUH?
He drew a highly magnified tooth of a file on the whiteboard, then rounded the end over and simply asked me to explain how the methods that remove a layer of steel could resharpen the tooth. Hmmpph! I don't know, you present a very good argument, I said...
I've attached an image of a work bluntened tooth, and would like to open this up to anyone who can explain how that rounded edge can be made sharp again by any means other than selective removal of material. You dissolve a layer of steel off it and you've still got a rounded edge. Interesting no?

Cheers
Michael

I like a few other members on the board have "sharpened" files etc., in a variety of acids. This information can be found with a search. Like many others, I was sceptical, but it does work. I guess if you approach any idea with a closed mind, and not prepared to try the idea, then it won't work. I chose vinegar because it is relatively harmless and easily obtained. If a blade has been blunted by hitting a nail or something similar, presumably in Vaughns' sketch, this idea probably won't work I think there are limitations. The blades I used had been blunted to the point they burnt a track instead of cutting cleanly.
The experiences I had with file is that the "gunk" etc. has to be wire brushed away to let the vinegar (a mild acid) work on the steel.
What ever the reason, I now have a that I know works well where it previously was blunt. I just wish I had woken up to this 40 years ago.
I also have a non-ferrous blade and will give it a working over to see what happens.
Jim

Originally Posted by powderpost

I like a few other members on the board have "sharpened" files etc., in a variety of acids. This information can be found with a search. Like many others, I was sceptical, but it does work. I guess if you approach any idea with a closed mind, and not prepared to try the idea, then it won't work. I chose vinegar because it is relatively harmless and easily obtained. If a blade has been blunted by hitting a nail or something similar, presumably in Vaughns' sketch, this idea probably won't work I think there are limitations. The blades I used had been blunted to the point they burnt a track instead of cutting cleanly.
The experiences I had with file is that the "gunk" etc. has to be wire brushed away to let the vinegar (a mild acid) work on the steel.
What ever the reason, I now have a that I know works well where it previously was blunt. I just wish I had woken up to this 40 years ago.
I also have a non-ferrous blade and will give it a working over to see what happens.
Jim

I don't have a closed mind on it at all. I would love to be able to tell Richard why it does work and prove him wrong just once! I'm just playing devil's advocate now. How can you be sure that your blade wasn't just dirty? If a blade or file work-bluntens to a round shape (no not only because it may have hit a nail) through ablation of the steel, then how can the round shape be brought back to a sharp shape without selective removal (by filing for example) of metal. Please don't infer that I'm suggesting I don't believe it works, I'm not, I realise there is anecdotal evidence it works, I just need a more rigourous explanation than I know it works...


Cheers
Michael

Michael,
I most certainly did not intend to suggest you had a closed mind, rather it would appear Richard Vaughn does. His comment would suggest that he had not even tried the idea. My comments were not directed at you. I understood from your post that you suspected the process did work but were looking for supportive evidence that it did work.
I have been in the woodworking game, professionally, for about 50 years, and am quite capable of recognising a "blunt" or gummed up blade as opposed to a damaged blade. I did mention that the process would not remove "gunk etc." and would not restore every blade.
All I ask is that anyone interested try it out. The post was not intended to boost my ego, only to tell people what I have been up to, practically, not theoretically. I would like to hear from others that have actually done a restore job on files etc..
Cheers
Jim

Jim I use the above process to clean my table saw blades as they blunten with resin from the timber. after a good clean they are as good as new.
Regards Michael

Just guessing Mike, but if a file were to have the "grains" of iron lying along the surface of the file, and then the surface was cut and lifted to form the tooth, the grain would still be parallel to the surface of the tooth. Once the end of the tooth becomes rounded over it is deemed blunt. If a mild acid is applied then perhaps it removes some of the surface metal - which is a larger surface area than the rounded point - of the still elongated grain. The end of the grain is the pointy bit and because it has little discernible surface area it looses little of its outer layer relative to the flat surfaces. Hence the point becomes more pointy again.

I did not believe this before, but I think I have just talked myself into it.

Maybe the weak acid is etching the surface, to create sharp surface imperfections... like a steeled knife edge?

Originally Posted by prozac

Just guessing Mike, but if a file were to have the "grains" of iron lying along the surface of the file, and then the surface was cut and lifted to form the tooth, the grain would still be parallel to the surface of the tooth. Once the end of the tooth becomes rounded over it is deemed blunt. If a mild acid is applied then perhaps it removes some of the surface metal - which is a larger surface area than the rounded point - of the still elongated grain. The end of the grain is the pointy bit and because it has little discernible surface area it looses little of its outer layer relative to the flat surfaces. Hence the point becomes more pointy again.

I did not believe this before, but I think I have just talked myself into it.

You lost me after "just" I suspect there is a story to it at the microscopic level as you suggest, perhaps a metallurgist could explain. I also expect that thinking of that rounded tooth as some kind of homogenous material that dissolves uniformly is probably very simplistic.

Also Jim, I'm sorry to have hijacked the thread Would you like me to start a new one?

Cheers
Michael

pity we can't sharpen tungsten tipped blades with vinegar

Keep it going Mike, some interesting stuff is coming to the surface. I am watching with acute interest.
Jim

I have sharpened dozens of old files and rasps with Citric Acid. There is no doubt that it works, blacksmiths were reputed to use the urine bucket - I have not tried this, my SWMBO is only so tolerant.

Now why does it work? Firstly in the illustration above of a very blunt file, of course you will not get much joy - but the file will cut again but for only a short time because there is only a fragile edge created by the acid. I am no metallurgist, and I have not heard an explanation I understand. Apparently the acid etches the steel at different rates, depending on the surface area, and this leads to the sharpening. A uniform coating of light rust may speed the process.

My experience is that a very blunt rasp cuts like a finer rasp after acid dipping.

Cheers
Peter