Monday, May 26, 2014

Using a diamond grit lap to repair a cracked Japanese plane blade

There's more to show about working with the loose diamond grit, at least as far as using it in lieu of a coarse sharpening stone. Out of all the combinations that I have tried so far, the maple plywood showed the most promise.

In light of that, I made a full sized lap out of solid maple,

charged the plate with a pinch of #125 diamond grit,

and got to work.

As with the plywood, the solid wood lap bedded nicely. The grit rolls around for a bit, then gradually gets less noisy as the abrasive sinks into the substrate.

The single application of grit didn't spread out very far, so I applied a second pinch and worked that in as well.

You can tell that the abrasive grit is bedding into the substrate, shearing the metal rather than rolling around, by how little definition there is between the soft iron and hard steel laminates.

If you look closely, you can also see why I want a coarse grit for fast stock removal....

Zoom in and take a look at that crack! It's about 3mm long, at least what I can see so far. It might extend further, but I won't know for certain until I do ura-dashi.

Speaking of ura-dashi, that's probably why this blade is cracked in the first place. I suspect that someone was not as careful as they could have been, and used a big hammer on a poorly supported blade. I doubt that I could do a very good job, field sharpening using a regular carpenter's hammer, and I'm glad that I took the time to make a special ura-dashi hammer. Now I enjoy the process!

I have a few hammers that I can use for ura-dashi, but here is a simple one made from an old tack hammer. *NOTE* THIS IS NOT HOW TO SUPPORT A BLADE FOR URA-DASHI! This is just an old photo showing the hammer marks.

The key point (for me) is that the hammer have sharp edges. I want something that will dig into the soft iron, rather than skidding or slipping. The nasty marks get removed during sharpening, it's nothing permanent. 

Another point about ura-dashi: A nice ren-tetsu wrought iron is a LOT (!!) easier to work with, compared to regular soft iron. I think that the main reason that wrought iron is used in better blades is specifically to make ura-dashi easier. My guess....but it can be a huge difference. If you are starting out and have a choice, pick a blade made with wrought iron!

OK, back to the blade repair. 

I grind the edge of the blade until all evidence of the crack is gone.

I square it up on the disk sander.

And back to the grinder to hog off some of the waste on the bevel. 

I try not to hollow grind the bevel, and leave about 0.5mm at the edge......

....and back to the sander again, to even things up.

I am setting the bevel angle at around 28° for starters. The blade was originally around 25° or so, so the bevel face will look a bit uneven for a while.

There is still a lot of hand work ahead, working that bevel down. THAT'S why I want a good coarse grit stone!

The diamond lap works well enough, and it only takes a minute to remove the grind marks left by the sanding wheel.

Still lots of work left, though.

The nice thing about making your own lap, is that you can make it big enough to use with a grinding aid. I made this lap 3" x 10" to work with an eclipse-style guide.

And the punch-line?

Worn out, crap-ass Al-Ox sandpaper glued to a piece of glass is about 10x faster, haha!

Want a great coarse grit sharpening stone that is fast, stays flat, and is cheap? $15 will buy a roll of PSA backed sandpaper that will grind 100 blades, AND be faster than any grindstone. Hell, the 3-pack of 3M 3x 80 grit sandpaper, glued to glass (use a good spray glue), would be sufficient for most anyone, and you don't even need to order anything, just drive to the store.

Sad, I know...... I'll keep looking for the perfect natural stone, though. I REALLY hate sandpaper....

It's definitely time for ura-dashi.

Thursday, May 22, 2014

More home-brew diamond sharpening stone stuff....

Still goin'....

Call me masochistic, a slow learner, what ever.....I have a problem with wanting to reinvent the wheel.

The acrylic showed some promise, but maybe can be improved? This time I used a file to prep the surface, leaving a scratch pattern that was perpendicular to the primary axis. Side-to-side, as it were. I was thinking that maybe the grit would set into the substrate more evenly.

A sprinkle of gems...

Then set, using a hardened steel roller. A large roler bearing, mounted on a handle is what you SHOULD be using, but.....

This time, I just sprinkled the grit loose, no glycerine. I had a chip-breaker/back blade/secondary blade (laminated construction, just like the main blade) that I had shortened, so am setting a whole new bevel here. Well.....I hog out most of the material with a grinder first. This is refinement, I guess. Babbling..... Sorry.

I rinse off the accumulated swarf and any loose grit that still remains, then have at it again. 

Yep, it works. The action is peculiar, like the blade is riding in tracks, on rails, so I try to incorporate a swirling or erratic stroke. This can speed up the sharpening process (think "random-orbit" sander vs the older vibrating palm Sanders), but it is hard to maintain a flat bevel this way. That's why the scratch pattern looks all screwy.

Maybe acrylic isn't the best material, or maybe this stuff was too hard. The material that is commonly used for a lapping plate varies. Balsa wood, copper, brass, even lead, it all depends on what you are lapping and what you are trying to achieve.


I liked this MUCH better. The grit bedded down well, possibly too well? The scratch pattern tamed down quickly, probably because the larger grains bedded more deeply during use. This combination felt more like a sharpening stone, but still not particularly fast or aggressive.

Derek Cohen has a great writeup on his blog, about making lapping plates from old cast iron plane bodies.

A cast iron clutch plate. Cast iron is made in a whole variety of hardnesses and densities. I think that a "soft" iron would be nice to try. This clutch plate is pretty hard.

It works. It feels like the diamond is mostly rolling around, and only a portion of the grit is getting embedded into the cast iron. If you look at the bevel, you can see a division between the soft iron and hard steel laminations, just like you would see if you were using a waterstone. It is the loose grit, tumbling around and putting microscopic dents into the iron, that gives the characteristic "hazy" look that is so pronounced with a laminated blade.

It works dry (see above)...

.... And wet. The viscosity of the fluid used to lubricate and flush away the swarf can have an effect on the "feel" of the lap, and the appearance of the blade itself. This is using a (relatively) thick oil, 10w40 synthetic motor oil.

I liked this combo for the "push". It felt like the high viscosity slowed down the rolling action of the grit. It left a more even haze to the iron. Compare the even, gray look of the soft iron to one of the pictures of embedded grit/acrylic substrate. The embedded grit leaves a very shiny/scratchy finish. I think that it's soooo cool that the same material (#120 diamond grit) applied differently, can give such different results.

This is using a thin oil, mineral oil cut 50% with mineral spirits. Is about the consistency of WD40. 

It feels different, looser, light, and very rumbly/roly/crunchy. And VERY messy. The appearance of the iron is more scratchy and not as fine as when used with the thicker oil. It still feels like only a small proportion of the grit is getting embedded into the cast iron substrate. This is a great combo (a cast iron lap w/diamond grit) for finer grit, something like a #400 and up. This coarse...... Not so much.

And a piece of maple plywood. 

The diamond grit embedded well into this material, as is evidenced by the uniformity of the bevel face. There is almost no visible line between the soft and hard metal. That means that the grit stayed anchored and actually sheared the metal, as opposed to rolling. This combination felt the most similar to an actual diamond sharpening stone. That said, the aggressiveness still quickly diminished as the diamond grains got pushed further into the substrate. 

My ideal would be this stone.....

... just a bit harder. Super fast, sharp grit, and fun to use (and it looks like a rock! I love that!), but too soft. It dishes quickly and gives up too much slurry, which gets in the way. I need to get back out to the beach, and find some new "real" stones. Like this one, but harder.

Tuesday, May 20, 2014

Experimenting with diamond grit

I am still in search of my Holy Grail, an effective coarse grit sharpening stone. Preferably one that stays flat, works well with multiple metal types, and eats steel faster than the kid I used to sit next to at lunchtime. Oh yeah, cheap too. My personal Holy Grail would be a natural stone as well...... We can hope, right?

I have used valve grinding compound (silicon carbide in a grease carrier). It's cheap, available at any auto parts store, and it works tolerably well.

You need to find a good substrate, though. This pink granite tile shows significant wear after lapping the backs of 4-5 chisels and a couple of really hard kanna blades.

Don't do this with your nice granite surface plate, OK?

I have a real love/hate relationship with diamond bench stones. Of the two DMT Duosharp stones that I have had, neither was particularly flat (one was seriously NOT flat), both very quickly lost their initial aggressiveness (minutes) which was replaced with a very lackluster bland feeling (forever), both left random large scratches (forever), and both quickly lost their nickel coating at the edges and corners (months). Both were expensive, too.

 The two Eze-lap stones that I have are not flat, but aside from that, still work well after years of use. All diamond stones lose some aggressiveness/harshness as they get broken in, but at least the ezelaps feel like they are still working.

 The cheap Chinese stones that I have wear similar to the ezelaps and are sooooo inexpensive, they would be perfect, if only they were flat.

 I want a diamond stone that has that firm "bite" of a good, coarse sandpaper, and if it could be recharged as it's performance began to fall, more the better. To that end, I have been experimenting with the use of loose diamond grit. The question is what type of substrate will work best. One other wrinkle..... I want to be able to use this for sharpening the bevel side. Others have said that loose diamond works poorly for doing bevels. Why?

I have some thick pieces of acrylic, the remnants of a bunch of old boat hatches that I didn't have time to use. You want to use a substrate that will allow the diamond grit to sink into, to grab onto, rather than just rolling around on the surface, and acrylic seems like it would work well.

I am using a 125-106 micron size, pretty coarse, about a #125 grit.

I put a small pinch into a syringe with a bit of glycerine as a carrier.

I sanded the acrylic to give it a bit of "tooth", then applied a little of the diamond compound. This is just the smallest fraction of what's in the syringe.

I used a piece of hard D2 steel to rub the stuff around, trying to distribute the diamond grit somewhat evenly. The black stick is a piece of oak that helps me bear down on the steel, really grinding the diamond into the substrate.

It works!

It feels funny, though, like the diamonds are mostly rolling around on the surface, instead of bedding in properly.

As the glycerine dries out, it needs to be scraped off of the blade. It is black from all of the iron and steel swarf, and I can't help but wonder how much of this is diamond that didn't embed. Rather than discard this stuff, I wet it slightly, then spread it around as though it was a typical waterstone slurry. You can feel the abrasive diamond rolling around still, and the feedback is pretty poor.

You can see the sparkles of diamond that DID get embedded into the substrate.

The glycerine rehydrates using just a spritz of water. Can't decide whether it is working better wet or dry.

The swarf and grunge rinses off very easily, using just a spray bottle. When I wipe off the nastiness, you can see that the diamond has been well distributed, but the concentration is thin. 

I add more diamond compound to the plate, but it feels like it has reached a short of maximum capacity. This might be a misperception, but secondary (and third) applications don't dramatically improve the "feel" of the lapping plate. 

The feel is hard to describe. There is a very distinct "grab" as though some of the diamonds are much larger than the others and cut deep grooves in the metal. The combination of coarse grit and deep grooves makes the plane iron steer funny. The blade gets pulled around rather than floating, and you get the sense that moving the iron back and forth is just riding in the same grooves rather than removing new metal.

It would be nice to get this figured out, as I have more window sills to plane. The Port Orford Cedar requires a very sharp edge for a nice finish.