Does it make sense to sharpen rasps?

[Steve knight]

Boggs does a great job they come back sharper then new. it's been a long time but cost was around 5.00 last time. I would buy my files from them and have them sharpened before I got them it made that much of a difference.

[Chuck Nickerson]

Since Boggs is close to me (Los Angeles basin), I use him all the time. He has sharpened my Auriou rasps. Cost (as of early 2008), not including shipping, runs about $.25 an inch. If the rasp is too far gone to be sharpened, he charges $.25 period and gives it back to you. His service is so reasonable, I buy boxes of files and rasps at auction. Between auction cost, Boggs' sharpening, and rehandling, I can get better than new files and rasps for $4 per.

[Doug Shepard]

Wow. I had no idea how much that might cost, but it's too cheap NOT to do it. Thanks guys.

[David Keller NC]

"Strikes me that Schwarz has had some Nicholsons sharpened by Boggs, not Aurious."

You're right - I just looked up the blog entry and reviewed it. Can't see why it wouldn't work, though, unless the case hardening is very, very shallow.

Might be interesting to call them (Boggs) to see if they've ever had any experience with the Aurious.

[Bill White]

Strikes me that Schwarz has had some Nicholsons sharpened by Boggs, not Aurious.

Cliff,

My little tub I soak the rasps and files in is room temperature water. Well, a couple hours after coming from the tap it is. I suppose the plastic tub holds a couple gallons if it were filled to the rim. It was just a tub bought from a second-hand store. Nothing special, just with deep sides and about 18" or so in length.

I really do not know how much citric we use because we add to it over time. It does become ineffective after a while without adding to it.

The biggest give a heck is a really thorough cleaning before plopping files/rasps in the mix and cleaning off the gunk that builds up periodically. The gunk is a black slime that prevents the acid from acting on the body of the rasp (where it tends to collect most). Your hands will get blackened a little from handling them.

Time? Good question. Generally I leave them in over night, putting them in before I knock off for the day. Sometime the next day they are usually pretty sharp. I clean them first thing upon arriving the next morning and usually again during the day. I suspect they are in the acid for a full 24 hour period.

I have mixed up a fresh batch and had files done in a work day. That was probably too strong a mix. I literally just dump in a bunch out of the 1 pound bag I buy it in. Warm water does help it dissolve better, but isn't necessary.

If you Google it, I suspect you'll find discussion on it. It's not a new thing. I tried it because of the old shop practice of using a bucket of urine to renew files and rasps. Sorry for the picture that may invoke.

Take care, Mike
back to writing...

and is there a specific brand? I am hearing that it is a dry (powder) product. Correct?
Bill

[Tony Zaffuto]

Before sharpening, be it with citric acid, cat urine or by Boggs, you should check to make sure the rasp teeth are clean. Auriou suggested a (IIRC) fiber type of brush and not a wire brush of any sort. I have a very stiff bristle brush that works very well. I have also used a Bic lighter flame (very carefully) to char badly stuck debris, and once charred it readily comes out. I have had rasps and files sharpened by Boggs and they come back better than new. But more than anything, when using a rasp or file, remember to not drag the rasp or file back across the piece being worked. And don't store them so that the teeth come in contact with anything else made of metal.

T.Z.

[David Keller NC]

Bill - Citric acid is a commodity product (in other words, the brand doesn't matter). There are different grades for different purposes; ironically enough, "food grade" is considerably less pure than the analytical grade intended for laboratory use. However, any grade will be close to 99% pure and will work. Sometimes pharmacies stock it, but as mentioned before, home brew stores is an easy place to get it.

[David Keller NC]

Tony - a slight modification on the bic lighter trick you mentioned that I've tried (and it works well) - dip the rasp in dentaured alcohol, then set it on fire. It's quick and relatively safe if done outdoors, if a bit spectacular. The nice part is that since the alcohol burns at a very low temperature, there's not much danger of damaging the tempering of the teeth.

[Tony Zaffuto]

Good trick to dip in denatured alcohol Dave! For file users, it helps to run the tool over a piece of white chalk to keep debris from remaining in the teeth. I've also done this on my rasps and it seems to help a bit, though not nearly as much as on a file. Make shure that white chalk is used as it is non-staining (as an aside, for those of you who use chalk boxes, it helps to use white chalk in those boxes for the same reason. Blue chalk is bad, but red is horrible! White does not stain!).

T.Z.

[Cliff Rohrabacher]

room temperature water [...] plastic tub holds a couple gallons [..]
I really do not know how much citric we use because we add to it over time. It does become ineffective after a while without adding to it.

Hmm OK would it be about the same concentration you use to de-rust?

I have learned that a 50 - 50 ratio of Citric will de-rust and is good for Stainless cause it doesn't strip away the Chromic-oxide passive layer.

Time? over night, putting them in before I knock off for the day. Sometime the next day they are usually pretty sharp. I clean them first thing upon arriving the next morning and usually again during the day. I suspect they are in the acid for a full 24 hour period.

Interesting.

Thanks.

[Dave Cav]

Some years ago I bought a bottle of "Chemsharp" for sharpening files and rasps. It works fine and is obviously some sort of acid. I notice that it is no longer available, but I still have some left.

A few months ago I bought a quart of battery acid from a local battery dealer. I soaked a few files and rasps in it and it sharpened them just fine, just like the Chemsharp stuff. I think I left them in for an hour or two. I have never used citric acid for sharpening, but have used it a number of times for rust removal; it works great for that.

The key to using acid for sharpening is to get the files or rasps as clean as possible. I use a wire brush or file card first, then spray them with oven cleaner (which is mostly lye) to get the rest of the crud and any oil or grease off of them. The wash well in water to remove the oven cleaner/crud, and soak in acid. If you use battery acid, all the usual precautions apply; it's nasty stuff.

Dave C

[David Keller NC]

All - Just a note that any acid, whether strong (battery acid = sulfuric acid, will burn your skin very quickly) or weak (citric - will not burn your skin unless left in contact for hours) will generate hydrogen gas when metal is placed in it. In small quantities, this is no big deal as the hydrogen gas will rapidly mix with the air and its concentration will go below the lower explosion limit (i.e., it won't combust, even in the presence of a spark).

However, putting a large quantity of iron parts into an acid solution (either for cleaning or sharpening) and in a small shop with few air exchanges can potentially lead to an explosion, and perhaps even a big explosion. Better to do this sort of thing outside if possible.

[Bill White]

Where does one buy citric or phosphoric acid?
Bill

[David Keller NC]

Bill - As noted above, you can get citric acid from a home brewery supply store, and from some drugstores. Also, if you have a scientific supply store near you, they will sell certain items to the public, no account required. That would be one source for Phosphoric acid, though there are others.