I have sharpened them but it isn’t exactly an easy thing to do.
It’s simpler to take them in to a sharpening service as they have the specialist jigs.
For a “bush” fix you will need a straight and flat bar to fit the cutter halves to. I used an aluminium extrusion from the scrap merchant. It was part of a door frame off a commercial building. I was actually looking for a piece of steel but this was flat in both length and width and provided support across the full width of the cutter. When I say flat, I mean properly flat not flattish, if it’s bowed in any direction you’ll make your cutters worse not better.
I had a piece of plate glass about a metre long which I used for sharpening big planer cutters. It needs to be thick and truely flat glass, not house glass as house glass has ripples in it. I got my bit from the glass bloke down the road, when he replaced a shop window he cut me a bit off. This piece of glass needs to be about 200mm wide. To the glass you glue a long strip of 800 grit wet and dry sandpaper off the roll using contact adhesive. My bit of glass sits on a thick chunk of mdf.
I separated the two cutter sections from the machine and thoroughly degreased them and superglued a cutter to the aluminium extrusion with the non-contact face of the cutter stuck to the extrusion. After applying a spray of water to the wet and dry paper I used the extrusion as a handle to evenly apply force to the cutter and move it back and forth across the wet and dry glued to the glass. I found that the edges were more worn than the centre so the aim was to get the whole cutter uniformly flat. I kept applying water to the wet and dry to keep the metal particles floating and not gum up the paper. You make a mess but I just mopped it up with old rags so it didn’t ever get past the edge of the glass.
Once one cutter assembly was uniformly abraded around the edge of allthe “teeth” I swapped to the other and repeated. Don’t worry if the centre section of the cutter is slightly concave, this is by design as it allows the outer sections to remain in contact under pressure..I went up the grits to 1200 and 1500, stripping off the old wet and dry paper each time. Once you’re done superglue releases using heat so I just used an electric heat gun and wiped the residue off the cutters with acetone. It’s then important to oil the cutters using a light oil before reassembly or they can rust.
It’s a bit fiddly but it does a decent job in a situation where you may not have easy access to a sharpening service.
