Sharpening with lapping film

[Glynne]

Before everyone dons their tin hats, this is a specific question about using lapping films rather than a general debate about sharpening.
I've been happily using films (3M etc.) for some time for both plane blades (eclipse jig) and chisels (Richard Kell jig) and manage to get a really good edge. However, once I start to go below 15 micron film, I seem to pick up a lot of debris which results in the film getting torn with crud dragging chunks out of the film.
I'm only really honing existing edges so not taking off a huge amount of material and I'm using proper lapping fluid so am I doing something wrong or just trying to go down to too finer film when using jigs?

 

[Doug B]

Only hone on the pull stroke, I find the tendency for film to tear is when you push the blade as it digs in.

 

[custard]

The wire edge can tear lapping film all by itself. But there are workarounds. Extreme care, a separate bit of lapping film used for the first stroke and viewed as sacrificial, a tiny initial touch on a slightly coarser grit, etc, etc.

 

[matthewwh]

Hi Glynne,

A couple of suggestions spring to mind.

It helps if you always go through the grits, even if you are just touching up. Look for a clean full width track in the honing fluid before moving on from the coarsest grade as this will guarantee any protrusions from micro dings in the edge have all been cleared.

Ideally the pressure used on your pull strokes should reduce with the grades of abrasive, the finer you go, the less pressure you need.

Keeping the films clean is important for both longevity and performance. A honing fluid that dries fully with no greasy residue will help, as will storing your sharpening kit in a big poly bag or at least covered with a cloth.

 

[Mike.S]

I use lapping film down to 3 micron and find I can lap on the push and pull stroke (using Veritas Mk2 jig) as long as I've cleaned the film properly. Generally, I'll either wash the film (adhered to glass plate) under the tap or soak it with a spray bottle and wipe it off. They key thing is keeping any grit/muck afloat on whatever 'honing' compound is being used. I find water with a squirt of washing up liquid works as well as any of the honing liquids I've used in the past.

I also always start with a pull stroke, to dislodge any wire edge and then go back/forth at a steady pace. If I'm just touching up a slightly blunted edge I'll start on the 40 micron and work finer i.e. never just go straight to the finest grit - this ensures that the blade is held in the jig exactly paralell to the film before I get to the finest and most delicate film.

P.S. crossed with Matthew's post which covers similar ground.

 

[Glynne]

Thanks everyone for the replies.
I'm pretty much doing what you recommended in terms of honing on the pull stroke and working down through the grades so it's probably down to the wire edge and keeping the film clean. Coincidentally I did wash under the tap yesterday so it's good to know that works for others. The plastic bag is a good idea as I store my plate in an old drawer with just a piece of hardboard on the top so it's not exactly dust proof.
After honing the edge, I do run the back of the blade flat over the film so if there is a wire edge, I'll be pushing it back over to the edge so perhaps one more stroke on the same grit should sort that out.
Thanks again.