Sharpening Obsession - Grit Confusion?

[Steve Mathews]

I've been working on preparing a bench chisel for the first time by first flattening the back and then establishing a primary bevel of 25 degrees. It's been a long and tedious process but it looks like I'm close to finishing it. Something interesting and confusing came out of the effort though. I used DMTs Extra Course (220 grit), Fine (600 grit) and Extra Fine (1200 grit) 8" x 3" diamond stones for the most part but found that I couldn't remove all of the scratches created by the DMTs unless I used wet/dry sandpaper. I found 400 grit sandpaper removed most of the scratches but then followed up with 800 and 1200 grits for what I considered to be a nice finish. The sandpaper was used on a 1" thick steel plate that was Blanchard ground. It seems that sandpaper grits do not correspond to grits identified with the DMTs. Am I missing anything with my understanding?

Also, I'd like to kick my sharpening obsession up a notch. Are ceramic stones recommended for this?

I forgot to mention that I'm using HoneRite Gold mixed with water regardless of abrasives.

[Jim Koepke]

Last question first, the type of stones should be suited to the type of steel you are sharpening.

Grit comparison can be confusing. Even more confusing is the comparison charts seem to change over time.

Here is my most recent if I can attach a pdf:

Stone, Belt, Paper Grit Comparison 2013.pdf

Not sure if this will help or be more confusing. Some diamond stones can have a rouge piece or more of diamond that leave deeper scratches.

jtk

[Malcolm Schweizer]

Because diamond stones have diamonds embedded in a fixed substrate, the diamonds leave a very defined scratch pattern. The diamonds don't abrade away like other abrasives such as those found on sandpaper. The abrasive on sandpaper breaks down and those particles move freely and cause a more random scratch pattern. Also as the abrasive breaks down it becomes a finer grit. This is why you get a smoother looking finish with equal grits of sandpaper versus diamond stones.

A 220 diamond stone is very coarse and will leave deep scratches that are hard to remove with subsequent grits. The above-mentioned scenario is more obvious in coarser grits. Remember also that diamonds are harder and so they cut deeper on each pass than grits made of stone or other substances.

Imagine you took a bunch of ball point pens and glued them together to make a block and you did the same with a bunch of pencils. The ball point pens are going to always leave a fine line. The pencils will break down and leave a progressively wider line. The ball point pens represent diamond stones and the pencils represent sandpaper. A block made of crayons would best represent water stones.

[Steve Mathews]

Jim - Thanks for the comparison chart. It was very helpful. I made a hard copy for future reference.

Malcolm - Also, thanks for the info. I really like your analogy using the pens, pencils and crayons. It was a good way to drive home the point.

Having now a better understanding of what happened with my first efforts at preparing and sharpening a bench chisel I'm still a little uncertain what might have been a better approach. On one hand the diamond stones did relatively quick work at removing unwanted material but they obviously left deep scratches that required at lot of time using other abrasives to remove. Would it have been better to use the less aggressive sandpaper from the start? I suppose that could be easily answered knowing if the deep scratches caused by the diamond stones were as deep as the initial amount of material needed to be removed, if that makes sense. Onward with my new found obsession.

[David Eisenhauer]

Many folks use 80 grit sandpaper mounted on a piece of glass or a flat tile of some sort to do their initial rough flattening or shaping. Typically, that is a one-time operation that does not need repeating unless some type of serious chipping occurs. I don't believe that I (my shop, my tools , my method) would get my moneys worth out of a very, very coarse diamond for initial flattening.

[Stewie Simpson]

Many folks use 80 grit sandpaper mounted on a piece of glass or a flat tile of some sort to do their initial rough flattening or shaping. Typically, that is a one-time operation that does not need repeating unless some type of serious chipping occurs.

Some rather interesting advise to be handing out.

[David Eisenhauer]

In my experience, after an initial back flattening or main bevel creation of a chisel or plane iron, I do not have to go coarser than 1,000 grit to maintain the edges. Unless an edge becomes severely damaged to the extent that a complete re do is required, I do not see any need to go back to the very coarsest grit used to initially flatten or shape the blade. Perhaps your sharpening method may have different requirements.

[Steve Mathews]

Some rather interesting advise to be handing out.

Do you concur or is there another approach that you advise?

[Rob Luter]

Many folks use 80 grit sandpaper mounted on a piece of glass or a flat tile of some sort to do their initial rough flattening or shaping. Typically, that is a one-time operation that does not need repeating unless some type of serious chipping occurs. I don't believe that I (my shop, my tools , my method) would get my moneys worth out of a very, very coarse diamond for initial flattening.

That seems a bit coarse to me.

[Jim Koepke]

I agree, 80 grit is a bit coarse for most situations.

One caveat, my Veritas Mk.ll Power Sharpening System uses 80 grit for the first platter. It tends to wear down quite a bit and doesn't leave deep scratches one might have from fresh 80 grit paper.

jtk

[Andrew Pitonyak]

For extreme changes, I will go to 80 grit, but, it leaves pretty deep scratches that take a long time to get rid of. I am more inclined to start with 120. Then again, for extreme shaping I use a grinder and my sandpaper use is usually flattening.

The jump from 80 to 120 does not seem that great, but it seems to make a big difference in scratch patterns. It is probably related to the way that standards define your "grit size".

Disclaimer: I am not an expert in this field, but..... If I say that sandpaper is 120 grit, what does that mean? I usually thing something like "hey, this sandpaper has particles of average size of 125 microns". In other words, some are smaller and some are larger. How much smaller and how much larger, and the actual distribution of these sizes is dependent on standard used by the manufacturer.

Understanding that I do not know the real answer to this, but, I expect the range to be wider for larger particles than smaller particles.

I found one chart for sand blasting medium that listed some ranges as follows (in inches):


Max Average Min Spread
0.0095 0.0057 0.0035 0.0060
0.0080 0.0048 0.0025 0.0055
0.0065 0.0040 0.0020 0.0035

There is overlap from the size below and the size above. The question is how uniform are the particles in the sandpaper that you use. I will readily admit that I do NOT know the answer to that question for the sandpaper that I own and use.

[Steve Mathews]

I stopped using the Extra Course diamond stone for flattening the back of chisels because of the deep scratches it produced. The scratches took too long to remove. The 600 grit stone worked well for getting most of the work done but found the 400 grit sandpaper worked the best in finishing the rough cut. It even removed the scratches left by the 600 grit and 1200 grit stones and left a smoother finish. I then followed up with 800, 1500 and 2000 grit sandpaper. I worked the stones in a 45 degree pattern on both sides and ran the chisels across the sandpaper 45 degrees to that to keep track of the fine scratches produced by the stones. I don't have anything with finer grits but plan to look into some ceramic stones. Overall I'm pleased with my progress so far.

[Jim Koepke]

If I say that sandpaper is 120 grit, what does that mean? I usually thing something like "hey, this sandpaper has particles of average size of 125 microns". In other words, some are smaller and some are larger. How much smaller and how much larger, and the actual distribution of these sizes is dependent on standard used by the manufacturer.

Andrew,

The chart (as .pdf) in my first post in this thread has the information to answer your question above.

As an example, P120 grit European paper has a particle size of 127µ. However the variance chart start with coated P240 with a particle size of 58.5µ and a variance of +/-2µ if my reading of the chart is correct. F240 paper is bonded abrasive size of 47.5µ with a variance of +/-2µ with the same caveat.

It doesn't have a variance chart for US (ANSI) abrasive papers.

It also looks like there may be an error in the chart. It lists some F/P grits in the 2xx range, then the 3xx range and jumps back to an F240. It may be my misunderstanding of the variance.

It does show that not all grits are equal even if they have the similar numerical designations. It can be confusing.
jtk

[Todd Stock]

I'll use P80 if there is a big hump or hollow to remove, and that was the case on nearly every blade in a large set of 1970's vintage Ulmia Two Cherries chisels added to the shop stash a few months ago. Not the place to start with a new Blue Spruce, LN, LV, etc., but tool maintenance is a task that accumulates against overhead, so I buy my way out of what I can and minimize the time spent on what I cannot avoid doing.

[Todd Stock]

On diamond stones - better for quick removal of a worn edge than mass removal of tool steel...as mentioned, abrasives on flat substates do it for me.