Flattening chisel backs with waterstones

[Pat Barry]

Yeah, that is one extremely soft stone, and not worth the hassle IMO.

In other posts I've argued the "layer model of waterstone life", i.e. the stones contain a certain number of usable layers of abrasive, and you can roughly compare them to other media on that basis. 220# is about 60 um, so the 25 mm thick, $30 Norton 220 contains about 400 layers of abrasive (maybe a bit more because of the way the grains pack in, maybe a bit less because of the volume taken up by binder).

You're therefore paying about $0.08 per 3" x 8" layer of abrasive, or $0.30 per 9 x 11 sheet equivalent, which is not all that much cheaper than comparable quality Al-Oxide sandpaper. What this serves to demonstrate is that waterstones cease to have compelling economics at such coarse grits, and are therefore not worth the hassle.

Cost is probably at least double what you have outlined. Two reasons: 1) you need to periodically flatten that stone and that wastes away abrasive; and 2) you can't use the entire thickness - there must be some lower limit, what, maybe 1/3 to 1/4 of the original thickness?

Have you done similar calculations for the finer grit waterstones?

[Brian Holcombe]

Thin stones can be glued to a piece of float glass and continued to be used until they're basically gone.

[Patrick Chase]

Cost is probably at least double what you have outlined. Two reasons: 1) you need to periodically flatten that stone and that wastes away abrasive; and 2) you can't use the entire thickness - there must be some lower limit, what, maybe 1/3 to 1/4 of the original thickness?

w.r.t. flattening waste, that depends entirely on the user. Some people are so good at distributing the work that they barely ever flatten. Others flush basically the entire stone down the drain. Note that sandpaper has exactly the same issue, with uneven use leading to early demise.

w.r.t. lower thickness limits, most people deal with that by either gluing the stone to a holder (in which case you can basically use all of it) or cutting it up to make slips. Either way you do get full use of that remaining abrasive.

Have you done similar calculations for the finer grit waterstones?

Yep, in other threads. The short version is that stones have extremely favorable economics at grits higher than 1000# or so. A 10000# polisher has something like 25000 layers of abrasive. You can almost convince yourself that a Chosera 10K is a bargain if you torture the numbers enough (and don't include a Sigma 13K or any of the Imanishi polishers in your analysis).

[Patrick Chase]

Great analysis Patrick....the premise here is that one flattens often, and just until the pencil marks are gone?

Now we're getting into why I said it's a "rough" comparison.

Abrasives wear out, and need to be replaced when they do. With sandpaper you simply grab a new sheet. With a waterstone you do one of two things:

1. Pick a stone with binder hardness "matched" to the steels you hone, such that the stone releases abrasive grains right about when they're worn out.

2. Periodically reflatten the stone to expose fresh grain.

As an example of where the analysis becomes really rough, consider a very soft stone like a Sigma Select II 1000. That stone is designed to be used with HSS tools, so the binder is very soft and the abrasive (SiC) is itself prone to breaking down. If you use it on, say, HCS then it will shed abrasive long before the abrasive wears out, and you'll basically be flushing money down your sink,

[Pat Barry]

w.r.t. lower thickness limits, most people deal with that by either gluing the stone to a holder (in which case you can basically use all of it) or cutting it up to make slips. Either way you do get full use of that remaining abrasive.

I was thinking that waterstones would be porous and therefore would be susceptible to glue wicking up into the stone and creating other problems.

[David Ragan]

Now we're getting into why I said it's a "rough" comparison.

Abrasives wear out, and need to be replaced when they do. With sandpaper you simply grab a new sheet. With a waterstone you do one of two things:

1. Pick a stone with binder hardness "matched" to the steels you hone, such that the stone releases abrasive grains right about when they're worn out.

2. Periodically reflatten the stone to expose fresh grain.

As an example of where the analysis becomes really rough, consider a very soft stone like a Sigma Select II 1000. That stone is designed to be used with HSS tools, so the binder is very soft and the abrasive is itself (SiC) is prone to breaking down. If you use it on, say, HCS then it will shed abrasive long before the abrasive wears out, and you'll basically be flushing money down your sink,

Who knew?

I didn't.

Is there a central source for this oft-underappreciated information (i.e. discerning hardness/friability of stone w type of steel to be sharpened)?

[Rob Luter]

That looks simple but effective. Nice!

You appear to be using 1 um (green) and 0.3 um (white) 3M 261X film. Are you using an extra-extra-fine DMT plate (3 um abrasive) or something like that before the films? How long do the films last for you?

I use that stuff stuck to sticks a fair amount for tools with curved edges.

I just use a Smiths coarse and a DMT fine diamond stone to start. That will usually take care of any heavy lifting. I switch to the film after the backs are flat, rotating through all the grits in order to get a mirror polish. On plane irons I use the "ruler trick" with the two finest films. I use a Veritas guide to keep all the angles consistent when sharpening the bevel side. I wind up having to change the film a couple times a year, but I'm a hobbyist as opposed to a production woodworker.

[Patrick Chase]

I was thinking that waterstones would be porous and therefore would be susceptible to glue wicking up into the stone and creating other problems.

We use glues with high enough viscosity that they can't be pushed (much less wick) through the waterstone's pores. Also, you would want to make sure that the stone is very thoroughly dried before using anything that can be thinned by water, because the last thing you want to do is lower the glue's viscosity. Epoxy seems to be the most popular choice.

Without going into the fluid mechanics, an opening that just barely passes liquid water would be an effectively impermeable barrier (very high threshold pressure differential for migration) to any sort of gel-like glue.

[Rob Luter]

We use glues with high enough viscosity that they can't be pushed (much less wick) through the waterstone's pores. Also, you would want to make sure that the stone is very thoroughly dried before using anything that can be thinned by water, because the last thing you want to do is lower the glue's viscosity. Epoxy seems to be the most popular choice.

Without going into the fluid mechanics, an opening that just barely passes liquid water would be an effectively impermeable barrier (very high threshold pressure differential for migration) to any sort of gel-like glue.

I'm guessing that molten wax would work well too. Plenty of resistance to shear to keep the stone anchored. Easy to get it to release if you want as well. Just warm it up.

[Dan McGonigle]

Wow! A lot of useful info here, some of which went way over my head. So thanks everyone. Took me a few days to get out into the shop but I finished a chisel tonight and I'm satisfied with the results. May not be up to the standards of some of you guys but a marked improvement for myself. I flattened the back with sandpaper on granite, 220 - 320 - 400 - 800 - 1000 - 1500 (these are the grits I already had on hand), then onto 6000 and 8000 king waterstones. Still some very light, almost unnoticeable scratch marks, but I have a "mirror" finish in which I can see my reflection quite clearly with no distortion. I then used my honing guide (cheap one, forget where I even got it) to bevel at 25 degrees on my 1000 king waterstones, then honed at 30 degrees on 6000 and 8000. I then stropped the bevel and back. The chisel looks great with no visible imperfections in the edge or back and I'm paring white pine end grain with no effort at all. One thing I'm a little confused about...originally I worked the back with sandpaper, 220 - 320 - 400 - 800, which gave me a nice glimmery almost mirror sheen. I then moved to my 1000 king waterstone and that sheen was gone, turned very hazy with no "mirror" or reflectiveness (is that a word?). That's why I skipped the 1000 stone and kept with the sandpaper. Is this due to the abrasive grading difference between sandpaper (using p scale) and waterstones? Ultimately I don't care, I've found what works for me (for now).

[Patrick Chase]

Who knew?

I didn't.

Is there a central source for this oft-underappreciated information (i.e. discerning hardness/friability of stone w type of steel to be sharpened)?

You can get a lot of it from old SMC postings from when the "waterstone gang" were active (David Weaver, Chris Griggs, Stu from TfJ, etc). Stu also covered it a bit in his blog and various informational articles on TfJ. The Lee Valley waterstone information page (click "Guide to Full Size Waterstones) is pretty decent for a "quick start".

One thing that a lot of people miss is that the friability/speed tradeoffs are fundamentally very similar between grinding wheels and waterstones. The main difference is that the penalties for overly hard binder (and therefore worn-out abrasives) are worse when grinding. A waterstone with dulled abrasives at the cutting surface will just slow down, whereas a similarly degraded grinding wheel will dump heat into your tool and burn it.

[Brian Holcombe]

Wow! A lot of useful info here, some of which went way over my head. So thanks everyone. Took me a few days to get out into the shop but I finished a chisel tonight and I'm satisfied with the results. May not be up to the standards of some of you guys but a marked improvement for myself. I flattened the back with sandpaper on granite, 220 - 320 - 400 - 800 - 1000 - 1500 (these are the grits I already had on hand), then onto 6000 and 8000 king waterstones. Still some very light, almost unnoticeable scratch marks, but I have a "mirror" finish in which I can see my reflection quite clearly with no distortion. I then used my honing guide (cheap one, forget where I even got it) to bevel at 25 degrees on my 1000 king waterstones, then honed at 30 degrees on 6000 and 8000. I then stropped the bevel and back. The chisel looks great with no visible imperfections in the edge or back and I'm paring white pine end grain with no effort at all. One thing I'm a little confused about...originally I worked the back with sandpaper, 220 - 320 - 400 - 800, which gave me a nice glimmery almost mirror sheen. I then moved to my 1000 king waterstone and that sheen was gone, turned very hazy with no "mirror" or reflectiveness (is that a word?). That's why I skipped the 1000 stone and kept with the sandpaper. Is this due to the abrasive grading difference between sandpaper (using p scale) and waterstones? Ultimately I don't care, I've found what works for me (for now).

There is a trick to maintenance that is not immediately apparent that will make life easier moving forward now that the back is flat. When use the chisel it will be considered dull when there is a visible "wear bevel", accompanied by a difficulty in starting a cut. This wear presents as a bright line along the back at the edge. When you next work the bevel you must remove this wear bevel completely. Most often when someone wants to cheat the back (lift while sharpening the back) it is because the wear was not completely removed and so the burr is unable to be removed entirely and the chisel's edge will perform like a dull blade.

If you strop the back with compound you will find it difficult to maintain your blade, my suggestion is for you strop the back with a clean strop only.

[Robert Hazelwood]

I then moved to my 1000 king waterstone and that sheen was gone, turned very hazy with no "mirror" or reflectiveness (is that a word?). That's why I skipped the 1000 stone and kept with the sandpaper. Is this due to the abrasive grading difference between sandpaper (using p scale) and waterstones?

Partly. On the JIS scale that waterstones use, 1000 grit is indeed coarser than 1000 grit on the P scale. It is maybe in the 400-600 range, but it varies from stone to stone. But I think the haziness from the King is due to the scratch direction being more randomized than you get with sandpaper- this is due to the mud coming off the stone and creating loose abrasive slurry. On sandpaper the scratches are aligned, which seems to gives a more reflective surface for a given grit- even fairly coarse grits can give a reflection amidst the scratches.

Also, sandpaper particles, especially if Silicon Carbide, break down in use and become smaller and/or duller, which makes the paper effectively finer. Waterstones constantly release new grit so they cut at a more consistent rate.

But importantly, a mirror reflection is not an indication of sharpness. Most natural stones leave a hazy finish compared to a fine synthetic, but can produce extremely good edges.

[Jim Koepke]

Hi Dan, Robert explains this better than me. If you look at the back of a new Veritas blade it will look cloudy due to the randomness of the scratches. The scratches are at the micron level and the back is as perfectly flat as it can be, yet no mirror finish.

The large particles of coarse abrasives will burnish the edges of the scratch and look like a mirror even though there is quite a bit of roughness on the surface.

Scratches in coherent alignment may look mirror like. Incoherent out of alighment scratches on a sub micron level will have a cloudy look.

jtk

[David Ragan]

There is a trick to maintenance that is not immediately apparent that will make life easier moving forward now that the back is flat. When use the chisel it will be considered dull when there is a visible "wear bevel", accompanied by a difficulty in starting a cut. This wear presents as a bright line along the back at the edge. When you next work the bevel you must remove this wear bevel completely. Most often when someone wants to cheat the back (lift while sharpening the back) it is because the wear was not completely removed and so the burr is unable to be removed entirely and the chisel's edge will perform like a dull blade.

If you strop the back with compound you will find it difficult to maintain your blade, my suggestion is for you strop the back with a clean strop only.

Hi Brian,

I understand what you are saying-sort of.

Am familiar w wear bevel. It does seem like a lot of work to have to re-flatten the back of a chisel periodically. This is where the David Charlesworth ruler trick comes in?

Then, you say to strop the back w clean material (cloth/leather/wood,etc) only. I'm not getting the connection of why stropping w compound would make for more trouble.

Thanks, David