while sharpening my hand files,I thought it would be of interest to some of the builders, what method I use. If you look at a new file, under light, you will notice that the cutting surface appears matte. If you look at a dull file, you will see an irregular shiny surface.If you examine the cutting areas of the file with a x10 loupe you will see the worn cutting edges. Note that a good pattern makers hand cut file will cost in excess of CDN100..so..
To sharpen the file it must be absolutely clean of all oil and ANY imbedded cuttings both metal as well as wood. This is the only hard part of the process. I use a very hard needle pointed scribe..sharp..and with the file held under good light and using a x5 or x10 loupe, remove any and all debree.
Once you are certain all has been removed, scrub the file using detergent and a stiff brass wire brush.Rinse well with hot water a couple of times and allow to dry. Re examine for debree especially metal particles.
The actual sherpening medium is phosphoric acid. This can be acquired in some of the grocery stores in the form of rust removers..check the label for contents.You can also go to a body shop supply house and purchase their equivilent called metal prep. You don't need a strong solution, 20% is adequate.
To sharpen, select a plastic zip lock bag of a size that will accomidate the file. Place the file in the bag and add sufficient solution to completly cover the file. Seal the bag and allow the file to remain immersed for approx. 1.5 hrs. Remove and wash in hot water and scrub the file with the stiff brass brush. Examine the cutting surfaces with the x10 loupe. if there are no shiny edges it's done, if they still are visable give it another go, say 1/2 hr. oruntill you are satisfied.
Once satisfied, wash well with hot water and scrub well to remove the oxide...That's it.I have found that this process leaves me with a file that is sharp or sharper than a new file..attached are three files I did this PM...Give it a shot...Gavin