Thread: Sharpening Rasps. Is it possible?

liquid honing services may be able to more or less blast away a good part of the tooth on those until the contacting surfaces are sharp and have relief.

However, they're not that cheap for rasps and milled tooth files in the US and often cost more than just finding decent used or NOS versions of same.

I'm going to take a wild guess on those teeth that the way the graver went into the steel, instead of having a half a hill with a flat face on the front, you have one that's leaned over and there's a lack of clearance.

and that honing or acid removal isn't going to work much, nor would liquid honing.

I also have some cabinet maker's rasps (even branded) that are really hard to find a use for....to the point I've never found a use for them. they must've been for really heavy handed work in softwoods or something where the clearance wouldn't be as much of a problem.

Hi Paul

I have used citric acid for files and rasps. Mostly it has improved cutting quite significantly. Some of the files were quite worn, and I was genuinely surprised that they could come back from the dead.

I am not sure if the citric acid simply cleans the metal surface from all crud, leaving behind cutting steel. Or whether the acid etches or removes metal to create a fresh cutting surface. It would be interesting to do some before-and-after photos of the teeth ... David?

Regards from Perth

Derek

You confused me Paul; not a difficult task.

You have some crap rasps; they are blunt and you are sharpening them with citrus acid. If it works, then you get some nice smelling temporarily sharp crap rasps. Why bother?

Then I re-read your post until your objective floated through the mist. You will learn a technique for sharpening rasps. And you are not risking buggarring some good rasps.

Thanks.

Originally Posted by derekcohen

Hi Paul

I have used citric acid for files and rasps. Mostly it has improved cutting quite significantly. Some of the files were quite worn, and I was genuinely surprised that they could come back from the dead.

I am not sure if the citric acid simply cleans the metal surface from all crud, leaving behind cutting steel. Or whether the acid etches or removes metal to create a fresh cutting surface. It would be interesting to do some before-and-after photos of the teeth ... David?

Regards from Perth

Derek

Derek

It is fair to say I don't know either, which is pretty much the essence of the test. There are five rasps being treated and I have four untreated. They were all the same type and all were diabolical so we should be able to compare.

Regards
Paul

Originally Posted by GraemeCook

You confused me Paul; not a difficult task.

You have some crap rasps; they are blunt and you are sharpening them with citrus acid. If it works, then you get some nice smelling temporarily sharp crap rasps. Why bother?

Then I re-read your post until your objective floated through the mist. You will learn a technique for sharpening rasps. And you are not risking buggarring some good rasps.

Thanks.

Graeme

You hit the nail on the head, after one miss hit . Really, it is to prove or disprove the technique. It is probably unusual to have such a number of tools all identical, which would otherwise make comparison more difficult and less scientific. We should end up with five test cases and one, actually make that four, controls.

If (the big "if") this works, it means other good or once good rasps may no longer be for the tip. I am particularly thinking about the Liogier and Auriou brands where most of the rasps are at least $100 a pop in today's world. Used on the likes of Radiata Pine they last a long time. Use them on some of our heavier than water hardwoods and they quickly become a consumable.

Regards
Paul

Originally Posted by derekcohen

Hi Paul

I have used citric acid for files and rasps. Mostly it has improved cutting quite significantly. Some of the files were quite worn, and I was genuinely surprised that they could come back from the dead.

I am not sure if the citric acid simply cleans the metal surface from all crud, leaving behind cutting steel. Or whether the acid etches or removes metal to create a fresh cutting surface. It would be interesting to do some before-and-after photos of the teeth ... David?

Regards from Perth

Derek

I could probably phosphoric etch some files and take pictures. Something changes in the top layer of steel with an acid etch - whether some is consumed off and more is worn off until "good steel" is reached, I don't know, but a layer eventually leaves leaving something shorter but pointier.

Paul, we've been down this road a few times already, here & on at least one other forum I used to follow a bit. Years ago, Fence Furniture did a very small scale experiment with acid "sharpening" of a file. He slipped it in the batch of files that were sent to 3 people to test as saw files (I was one). He didn't tell us he'd done it, & the files all had their identifying marks removed & were just numbered, so we had no idea of make or model. Without exception, each of us remarked on that particular file as the crappiest in the bunch (& there were a few crappy ones that were brand-new). It wouldn't cut butter on a warm day in Brisbane!

One swallow doesn't make a Summer, but it made me think about the whole idea. Others have posted elsewhere with similar thoughts, and the gist of it is this: When a cutting edge is dull, it's because the sharp edge has been worn rounded. Etching the metal with acid takes away a small surface layer & theory suggests this layer will be pretty even over the whole surface, so you should end up with a surface that is a micron or two lower than before, but still essentially the same shape i.e., rounded, without a sharp cutting edge. So it's pretty hard for me to see how etching can make dull teeth sharper. Does anyone etch a plane blade to sharpen it?

However, one important reason a file doesn't cut is because of buildup of crud on the surfaces & in the "gullets" of the teeth (I've been confirming this regularly over the last couple of days 'cos I've been doing a lot of filing ). An acid bath removes the crud more thoroughly than any file card & a clean dull file cuts a bit better than a dull file impacted with crud. The claims that etching improves dull file performance are probably due to the cleaning effect more than anything else. If they could be backed up with micrographs of sharper teeth post-etching, I'll happily re-think my theory.

I think Dw's analysis of the tooth form may be the key to why your rasps aren't cutting worth a damn & I strongly suspect there's not a lot you'll be able to do about it save annealing them, grinding off the old teeth & cutting new ones.. But it's a worthwhile experiment, well-conducted within the limitations of sample-size, & should shed some light on the matter. We await results.....

Ian

Just a couple of comments on these rasps particularly following DW's and IanW's posts.

These rasps are machine made rather than hand stitched. Generally, hand stitched rasps are regarded as vastly superior and of course a lot more expensive. While I have a good idea of how hand stitched tools are made, I don't know the commercial production technique. Obviously it was not good with my rasps. Either the steel is poor (it may be, but not the reason for this problem) or the cutting tools were inferior. There is clear evidence of rounded and blunt tips.

Secondly, these files are new so there is no buildup of crud in the tooth depressions. The video I particularly watched made actually emphasised de-clogging the teeth with wire brushing first. What it lacked after the rasps were treated was any testing.

Thirdly (my couple is always a minimum of three) I can quite see that on small tooth files there is nothing to work with. If, (the ubiquitous "big if") there is indeed a removal of metal from acidic action on, say, a 4" DEST saw file I can imagine you are left with nothing. I can't really see that this test could work on anything less than a rasp. Having said that, even with coarse toothed rasps (8 grain in this instance), I am highly skeptical that it will work at all. As I mentioned before, it is likely unusual to have a number of similar blunt files on which to conduct a test. Having just this scenario and because they are useless as they are, it seemed a golden (maybe a poor choice: maybe just gilt) opportunity to give it a go and prove or debunk once and for all. A modest attempt at "Mythbusters."



Regards
Paul

I'm into seeing what you get here. I think I typed some long response before the last couple of posts and then decided not to post it. to the extent i repeat something I already posted, my apologies.

I put mostly dead files into phosphoric acid and I think the whole deal of etching files with a mild acid is a matter of keeping up a file that's relatively slowly worn, but was of a good design. Boggs tool here (liquid hone) seems to get great accolades for doing files that are clapped out - they blast the files with a liquid and abrasive, apparently - how the tooth wears away is curious - does the liquid hone do something different than acid such that it's biased toward leaving a crisp edge? Most accounts I've gotten of boggs' services suggest that the liquid hone process leaves a better initial tooth than the factory finish (sharper). this is pretty easy to figure out - if a file with any tooth size slices skin off of your fingers like a new vixen does (the bigger ones - the mid sized ones have forever been less sharp new).

My fault in this process is that I am hard on files because I usually use them for toolmaking and not for surface clean up. A file could live for months if it gets light duty, or it could be spent in a day (even a large mill file) if I am making several of something hard on them. And I don't think the etching can help there, so I've given up.

But I'd be struck by lightning if I ever said any experiment wasn't worth doing - I'll be curious to see, even if it doesn't help with tooth geometry, what you find that it does to the metal on the surface. Phosphoric leaves a fairly deep gray etch and the metal surface is brittle and changed. On a flat surface, it can be abraded off relatively easy, but it's deep and noticeable.

There may be some disparity by trade here - like a jeweler with fine files - there's certainly some value to leaving files in lant to prevent rust if they are very fine high quality files. Especially in the context of shops without climate control. I've found more files than I'd like to admit that have come up with rust on them before I ever got a chance to wear them out. Sometimes, it's also superficial and you can just use the files and what's under the rust is usable (if life shortened).

However, if it doesn't work out saving the teeth on these because they are punched in at an angle and laying forward, let's compare notes - you and me - we'll make some! it's a lot easier to get a straight up tooth with a rounded top and a flat face by hand than it is to get teeth like the machines make (tall and skinny or long).

I can visualise how blasting the backs of teeth with an abrasive/etching mixture could sharrpen them. You are only removing metal (or mainly) from the "bevel", not the "face", and done carefully & controllably, it could result in a 'restored' cutting edge. That seems far more intuitive to me than dipping the whole thing in an etching fluid which is going to remove an even amount of metal from every surface.

File makers have definitely lost the art, I reckon. I broke out a brand-new file to level the pins after peening that SS mitre plane I showed a couple of weeks back. The plane is only a bit over 175mm (~7 inches) long and by the time I'd roughed down both sides, the file was well past its prime! I had to remove ~1.5mm of excess metal from each side, excluding the gaps for the side tails, so not a huge task for a 10 inch 2nd-cut file, I would have thought. And even more annoying, the darned thing did not cut the way I expect a new file to cut. I was prepared to put that down to the SS, which is well-known to be hard on cutting edges, but I was struggling with a similar file yesterday on plain old mild steel!

I have an old Wiltshire made in Aust. sometime in the late 60s/early 70s. It was from a stash of NOS a friend of mine scored. It lasted & lasted like no file made this century. I keep discarding it, then digging it out again because even worn as it is, it still cuts better than any of my equivalent newer files that have been used a few times!

Cheers,

Originally Posted by IanW

I have an old Wiltshire made in Aust. sometime in the late 60s/early 70s. It was from a stash of NOS a friend of mine scored. It lasted & lasted like no file made this century. I keep discarding it, then digging it out again because even worn as it is, it still cuts better than any of my equivalent newer files that have been used a few times!

Cheers,

Ian

The Wiltshire brand is the best file I have encountered.

Regards
Paul

Originally Posted by IanW

I can visualise how blasting the backs of teeth with an abrasive/etching mixture could sharrpen them. You are only removing metal (or mainly) from the "bevel", not the "face", and done carefully & controllably, it could result in a 'restored' cutting edge. That seems far more intuitive to me ....

Sorry, but I cannot visualise this at all Ian. [NB: I have zero metal working expertise.]

It seems to me that the level of precision required for that abrasive blasting process would be extraordinarily high. Realistically, would you not blast away any part of the teeth within range and not just the bits you wanted to remove?

Originally Posted by Bushmiller

The Wiltshire brand is the best file I have encountered....

Was....

There are still a few new ones available on ebay & "used" (a bit dodgy!), but they'll be a footnote of history soon...