Sandpaper Shoot Out

 

We have been investigating alternatives to the Wet and Dry paper currently favoured for sharpening the inside of hollow forged curved blades. there was a surprising number of non starters, but eventually two new contenders were delivered to the workshop:

1. Micromesh mx– a slightly cushioned  cloth backed abrasive, it promised a very fine finish and up to 10 times the life of normal abrasive papers. But on the other hand It costs nearly 10 times as much. It was unclear how the cushioned effect would work when applied to sharpening, would bevels be rounded? we have been very careful to use hard backings for polishing and honing when sharpening these blades and the improvement in edge quality has been noticeable.
2. 3M film, we settled on the lapping film for this test, an Aluminium Oxide slurry coated polyester film. Meant to also leave a finer finish compared to the electrostatically oriented finishing film also on offer. Not quite as expensive but still a step up in price.

At this point it is worth pointing you to this video– it explains the process currently used to sharpen these blades.( longer version here)

One thing to remember about using abrasive papers is that they are blunting from the second you start using them, you can use a new spot to regain the cut ( you can often hear a slight hiss) but they are always going down hill. Don’t hang on to paper too long, change it regularly. A phrase often used in knifemaking is ‘treat it like it is free’ – hard to get used to when you are paying for it, and we used to use belts and papers for far too long, but eventually realised it truly was false economy.

There was a fairly large run of spoon blades to sharpen and so we compared the two newcomers against the standard 3,000 grit paper. First up a picture of the edge tramline of the hook that we were going to be sharpening, it has been finished to 600 grit parallel to the edge,  It sounds like a huge jump but we can go straight to 3,000 and get through these marks

 

we should point out that this all looks pretty gruesome at 200X- we could have carried on longer and got better finishes from all the papers shown, but  wanted to show how they looked after a standard number of strokes (20) at high pressure, we wanted to show how well they did ( or didn’t) get through the initial 600 grit scratches.  They all looked polished to the naked eye and not that bad under a x30 loupe. Images are not great either as the blades are curved in both planes and very hard to focus on. Here you can see the scratch pattern from fresh 3,000 grit paper- it pretty much obliterates the 600 grit. 20 strokes, approx 10 seconds. Strangely this edge looks slightly rounded.

We use the fact that this paper breaks down really quickly to our advantage, carrying on sharpening on the same section of paper for a few extra strokes, the 3,000 grit now acts like a finer paper.  You can see a few faint traces of the 600 grit I started with but the overall finish is an improvement. Again the edge looks rounded. This is probably not the case though as you can just see the remains of the 600 grit scratches near the edge, so any rounding, if present was put in at the 600 grit stage.

 

Obviously you can’t keep using this bit of paper now so we tend to reverse the paper ( hold the other end) and use a fresh section to do the initial cut, polish up on the newly worn bit and then bin it, and start on a new piece. Working life of each piece is about 30 seconds, which is why it makes no sense to use adhesives in a production schedule.

 

In these tests we used sections half the size of the standard wet or dry paper strips, ie enough for one blade. This allowed use to directly compare how much longer the paper would last. We used 5 microns 3M film and 600mx (also 5 micron)  Micromesh, depending on whose conversions you are looking at this is a bit finer than 3,000 grit, but then I am aiming for a finer finish then 3,000 grit gives when fresh.

So first up – 5 micron film-  not a bad finish but you can see some much deeper scratches than you would expect from a fresh section of film.

Carrying on to see how long the paper lasted- by the fourth blade is was apparent the film was worn out. A mixture of little cut and deep scratches was not really acceptable. Looks very flat and fabulous burr though.

Next up micromesh 600mx- apart from a huge 600 grit scratch across the middle of the tramline ( which could never reach the edge incidentally) the finish is pretty good.

 

I carried on with the same piece and this was the finish on the fourth go – you can see the cut has been reduced and there are some deeper scratches but this has lasted 4 times as long as the standard wet and dry paper. Strangely these look really flat, despite the paper feeling noticeably spongy.

What is happening and what are our recommendations?

Firstly the film- we will not be using this for sharpening spoon blades, It seems that what is happening is that the narrow tramlines have such a small area of contact that the pressure is too high and thin film breaks down, the broken up sections of abrasive producing larger scratches.  A bit of a shame as the whole idea of the tramlines are that the small surface area should be easier to sharpen but in this case it is not a positive trait. This is perhaps exacerbated by hard polyester backing of the film. It will have its uses but not for spoon blades with tramlines.

The Micromesh performs much better, it seems to last 3-4 times longer than the wet or dry. A 6″ section on dowel should last for 10 or so blades. As this will last most people a good while it is worth attaching it so we are offering this in a self adhesive version. Although it does wear down it doesn’t break up to the extent that the 3M film or Wet and Dry does, maybe partly because of the slightly cushioned action mentioned earlier. We could see no rounding under the microscope, but it is noticeably softer so were surprised, expecting some to be present.

Encouraged by this we had some 3,000 grit paper with adhesive backing made up. The slightly softer backing seems to increase the life slightly, 25-50% and it is less likely to break down and cause scratching.  On the other hand the time it takes to remove the paper means you are more likely to use it longer that you should.

Our preferred option for production is still 3,000grit paper hand held, used for sharpening two blades then discarded. This does take more skill as holding the paper in place is not that easy ( something we weren’t really aware of until we tried the backed versions then went back to standard- it was noticeably more difficult)

Also the technique of using a fresh section of paper to cut and then carrying on using it to polish, but not so much that the paper breaks down and scratches the paper is tricky. This is a technique that has been settled into largely by trial and error but is not an easy option for a beginner. You could use a fresh piece of 3,000 grit paper to cut, then rather than use a worn section to polish switch to a finer grit such as 7,000 for the polish. This is also true for the Micromesh, we are offering a finer 1200 ( 3micron) that can be used as a final stage before or instead of stropping.

The Wet or Dry paper actually softens when used wet so it really has to be used quickly( hence the working life of 30 seconds when using it this way)  or it will tend to break up.

 

– you can see here how the abrasive layer has broken down completely and flaked away from the paper backing, it is these flakes that cause the scratches that you really want to avoid. In light of this we no longer recommend or use the wet or dry paper wet when sharpening the tramlines of spoon blades, the potential to scratch the tool is too high.

An option that works well with the backed wet or dry is to wash it after use, the softening issue is then avoided as it will dry before the next time you sharpen and you can prolong the life of the abrasive avoiding it loading ( clogging ) . Micromesh doesn’t soften and break down in this way and can be used wet, or at least should be washed out between sharpenings for the same reasons. I have found a drop of detergent in the water helps with cleaning. The adhesive backing is not obviously affected by the water, but I wouldn’t leave a dowel submerged.

One point to note about these adhesive backed paper is that they stick really well, you can wrap it round a dowel and the edges will not peel back at all, this is really useful, but it is not simple to remove especially on clean wood. The paper peels off easily enough but leaves a gummy layer, it scrapes off readily with a blunt knife but the remments will often re-adhere to the dowel in another place, scraping under a running tap stops this, but it does mean you need to let the dowel dry before sticking on a new layer. Solvent such as Cellulose thinners or nail polish remover is excellent for removing any last traces, but it is not the prefered method due to the solvent fumes. We tried a light coating of boiled linseed oil on a dowel to see if this would help with release, for the first few days the paper wouldn’t stick but after a week it was fine, it stuck well but released completely cleanly.

**  We now have a new self adhesive paper- this has a much thinner backing and acts like plain sandpaper, there is no perceptible give, it also releases cleanly from a variety of surfaces, including wooden dowels and our honing blocks. This paper can be found here.

Our recommendations 

1. Plain Wet or Dry paper: The most difficult to use well, but ultimately giving the best finish, also the least expensive.
2. Adhesive backed Wet or Dry: A mid price point, and more forgiving and easier to use, finish is indistinguishable to plain paper- just don’t be tempted to use it for too long.
3. Micromesh adhesive backed: If you want to make up a dowel that will sharpen a decent number of blades, with little risk of it breaking up if over used this is the one to go for. It is more expensive but not excessively considering its increased life. The easiest to use, little to go wrong with this paper.

All these abrasives can be found HERE

 

After these stages all the edges were then given a final polish with our white compound applied directly on to a clean hardwood dowel to further refine the scratch pattern.

This is what the final inside edge looks like, We have purposely made sure that there is a coloured object reflected in the tramlines, positioned the same distance from the blade as the camera as this is much less forgiving than reflecting off the sky.

 

We will be testing various sharpening products and will write up the results posting images, warts and all, If we find a product that is significantly different or better we will offer it for sale on this site. We have many contacts in trade and industry and it would be very easy to just pick up the phone and populate this site quickly with exotic sharpening supplies but that is not what we are trying to achieve.