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Sigma Power 120

Posted by CliffStamp 
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Sigma Power 120
September 20, 2014 03:06PM
Ad copy from TFJ :

Quote
Tools from Japan
This small ceramic stone looks like a small concrete block, and to touch, feels about the same.

Useful for gross metal removal to correct damage to blade edges or as a stone to restore the clogged surface of finer stones, this stone is unique due to it being so hard and so coarse.

Use with caution...

200x50x25mm.

*Supplied with #36 SiC loose grit for flattening and conditioning.

A very informative description also from Stu : [www.toolsfromjapan.com]

User feedback which replicates Stu's comments : [www.woodworkforums.com]



+



This is a bit smaller than a standard 3x8 stone which is shown here for reference, this one is :

-2.6 x 5.5 x 20.9 mm

It is really coarse, so coarse I can't even get all of the abrasive in focus :



Note how it is such an open stone with large holes between the abrasive grits. It looks in fact near identical to the TASK :



How does it cut? Standard mirror polish Mora (1095/60HRC) and 50 passes with 1/2 lbs load (0.25 psi) :



It barely scratches the surface and feels glassy. Using the Everyday Essentials Chef' knife and apexing with the same load 1/2 lbs produces a higher pressure of 1.5 psi and the stone now cuts aggressively. In contrast to :

  • Naniwa Superstone 400 : 95 (7) pps
  • Suehiro 'Chemical' 320 : 63 (5) pps


The Sigma Power apexes in 25 (1) pps, faster but not nearly as jaw dropping fast as you might expect. The edge is decent :



but shows the obvious signs of the coarse grit as a few large pieces are knocked out.

At this point you might be saying, ok, this all sounds l-a-m-e if you look at the promotion. Well lets take this up a notch and apply a 5 lbs load, pressure ramps up to 15 psi, the performance now is an apex in :

-5 (1) pps

Note as well this is a large blade, 7.5" which means each section of the blade actually apexes in just 1-2 pps, i.e. as soon as it hits the stone. This is how you use this stone with a LOT of force, it produces no swarf, it produces almost no breakdown of the stone and if you wipe the blade you see none of the black "carbon" being lost.

If the stone is cutting so fast how come you don't see the steel being removed as it common on other stones? Because that blackening isn't simply the steel, it is actually iron oxide and it happens because the steel is being removed in such small bits that they instantly oxidize (rust). This stone chews off such large pieces of steel that doesn't happen.

It also leaves the edge pretty chewed up :



In short, this is very similar to the TASK but it does not break down/wear at nearly the same rate, in fact it doesn't seem to do so at all. The big question then is why don't all stones act this way - isn't it just better? Well no because if the abrasive isn't being released it means once it wears the stone will just stop cutting. In order to get it back you have to recut the surface of the stone - that is going to be the interesting part.
Re: Sigma Power 120
September 21, 2014 10:32PM
I did some work with the Yanagiba : [www.cliffstamp.com] . The problem is that in order to generate the kind of pressure where this cuts well (15 psi) you have to apply a load of 50 lbs, not practical. I was able to apply forces of about 5 lbs which meant I would get a contract pressure of 1.5 psi. As noted in the above the stone is still faster than the Suehiro 'Chemical' and others but only about 2:1 and trying to do a lot of grinding at that force requires a lot of effort. For how I sharpen the Shapton Pro 120 is likely a better choice as it can work at much lower pressures. However I am going to do some high force grinding with a different setup just to check.

I did three rounds of 750 passes on the Yanagiba and this did finally cleanly bring the edge to a very rough apex and the chips are now mostly gone. I will put up pictures shortly. However that amount of work also greatly reduced the aggression of the stone. It is completely obvious now that unused side is very different than the used one. I tried using various loose grit abrasives on it (36 grit and 90 grit silicon carbide). However the stone is so porous they just fall inside it almost immediately and thus you get very little passes where they do anything.

However as soon as you ramp up the pressure by doing reduced contact area work like tip shaping the stone will cut again, it is very sensitive to pressure applied and you really can't gouge this stone, and it doesn't produce any kind of slurry. It also doesn't load or glaze, you can just spray it to flush out the particles as it has a very open structure.

--

Before any conclusions are reached, Stu did note that the top mm or so is much harder than the rest of it and once you break through this top load then the stone starts to wear a little and cuts more aggressively. I also have to do much more cutting to round out the experience with the stone. However based on some initial evaluations this really looks like a stone which you need to get a very high pressure for it to work well but if you are a high pressure sharpener I think you would like this because it is very dish/gouge resistant.
Re: Sigma Power 120
September 22, 2014 03:37PM
I was finally able to turn this up again : [www.woodworkforums.com] . It is one of the few complaints about this stone :

Quote

I want to use it to put new bevels on a bunch of chisels and planes.

I ground away at them for a few solid hours, and haven't yet managed to put a bevel on even a single #4 plane iron.

I'm clearly doing something wrong - I read that these things should take off a mm of steel every few minutes.

If you read further on then he consumes most of the bottle of silicon carbide powder, wears away a lot of the stone and doesn't achieve much of anything. The other reports I have read are similar to the above, this stone will cut fast if you put a lot of pressure to it, ideally you need to have this mounted and fixed in place so you can actually lean into it with your body weight and really ramp the pressure up.
Re: Sigma Power 120
September 24, 2014 11:16PM
I went back to the Everyday Essentials Chef and did some grinding on the Suehiro 'Chemical' and again got the same results, it was apexing in 50-60 pps. The Sigma Power would apex readily in 20-25 pps, but as soon as I leaned into it again it would apex instantly, just 1-2 pps per section. The critical difference is the pressure, the thin bevel on the Chef ramps up the pressure more than 10X over using the Yanagiba and trying to use that pressure on the Naniwa and Suehiro waterstones cuts the abrasive right off them unless you run them dry and then they just load.

This stone looks to be a really nice choice to condition old kitchen knives as it will grind out recurves, redo tips and just rip off all those faceted multi-bevels and then you can clean up on the Suehiro and the micro-bevel as desired. I am going to see how it works on grinding some harder-high carbide steels with the same very high pressures and as well lock the stone down and generate some high pressure on wide bevels from just raw force applied.
Re: Sigma Power 120
September 27, 2014 08:55AM
A round of work on some very damaged kitchen knives :

Henckels fine edge Chef : < 0.005" at the edge

-heavy light reflection, minor deformation, one spot of major deformation (bevel turned)
-5 pps and the bevel is fully reset

Wiltshire bread knife :

-very heavy light reflection, continuous flattening in the last 3" of blade
-15 pps and the edge is fully reset

Levco utility knife

-this gets frequent use
-continuous flattening, a lot of isolated dings
-55 pps and the bevel is fully reset

I would buy this stone just for the way it handles these knives. It will rip new bevels on them instantly and generates no swarf.

--

Now to be clear, in these grinding sessions I am using high loads. I am putting 5-10 lbs on the stone so the pressures are extremely high 25-50 psi. Can you do this on stones like the Suehiro or Naniwa Superstone 400? Not really because the knives would cut deeply into the stone at those pressures, remove abrasive at an extreme rate and be very wasteful on the stones and still not achieve those kinds of extreme cutting speeds. The Sigma Power 120 still formed no slurry there and a quick spray cleaned the stone with no glazing left.

--

Ss an extreme check of another sort : [www.cliffstamp.com]

That blade is very soft, I am not even sure it is martensite. The edge was just mangled and I had to recut it completely and take about 1/64" of an inch off as the TiN coating was impacted to that depth. The Sigma Power cut this steel easily, no surprise, but because it was cutting so deep the abrasive would on occasion get ripped out and in a short period of time it did build up a slurry.

Thus a way to keep this stone cutting very aggressively is to instead of using the recommended method of recutting it with the ultra-coarse lapping compound provided is to just use it on some very soft/easy to grind steels, really lean into it to generate high contact pressures and let that rip off the worn grit. This also will tear a new bevel on whatever knife you decide to sacrifice to it.

--

There is a downside to this stone though, or at least a complication. The stone is so aggressive on those steels it is not trivial to tell if you are on the bevel exactly. On the Wiltshire paring knife I accidently reground the beveland took 5 degrees off the back side because when you apply really high force on this stone on small contact areas it grinds very aggressively.



Edited 1 time(s). Last edit at 09/27/2014 08:58AM by CliffStamp.
Re: Sigma Power 120 - Mine is a little different
October 11, 2014 11:53PM
First up if Cliff wants to move this to a separate thread that's fine by me.

I already had one of these on order when Cliff started this review. I was concerned reading this that the stone would not be suitable for what I wanted which was thinning/flattening blades and setting up new scandi grinds ( I have a cheap, Swedish steel fetish). Cliff's results suggested the stone would be an awful lot of work to do this and would probably glaze/clog before I got anything done. The stone arrived on Monday and I am happy to say, this is not the case.

I suspect mine must be from a different batch to this one. Stu has commented on differences in hardness before.

On arrival the stone looked just like Cliff's right down to the same scuffs on the box. One side seemed fairly flat but the other had a kind of raised rim around the edge, possibly squeeze out from being compressed. I also received two little bottles of loose Sic 34 and 120 grit I assume, there were no labels.

I had a quick and inconclusive play with it that afternoon then left it soaking over night. Next morning I lapped the stone in the approved manner - using loose grit on a piece of glass (I protect the glass with a sheet of lapping film) this took a while and I discovered that the you can't rely on a pencil grid to see when it is flat as the pencil marks just won't stay put until ground off. Eventually the stone was flat, edges chamfered and generally looking ready to go.


This is actually after I had used it a couple of times I forgot to take a photo right away.

500 passes on a wide beveled Bahco later


We have a little mud. Using plenty of pressure the stone cut fairly quick but Stu's blog described it as 'blood spittingly angry and aggressive' which so far, it was not. Hmm, Stu said you could speed it up by adding a little loose grit, Cliff says you can get it cutting by using a soft steel blade to pull some grit free. Let's try both at once!



Ooh mud. Cutting far faster now. She's ready for her close up.



The grit (I have tried 50,90 and 120 Sic) stayed on the surface until it broke down and began to form mud. It makes the stone feel pleasingly crispy and cuts very fast. Combining that with a Santoku that has wrought iron as the outer layers really got the slurry flowing and the stone cutting well.

After a little while though I discovered some new issues. The stone is very porous and the mud gets very thick very fast. I found, when I went back to another Scandi grind, that I had to wipe the blade on the stone when I switched sides or the build up would prevent the bevel sitting flat. No photo of this I had too much slurry on my hands to touch my phone! Also, when the stone really starts to generate mud it gets out of flat fairly quick. Even when there is a lot of slurry a good amount of pressure is required or you just grind with the broken down abrasive floating on top which gradually gets pushed off the stone and stops revealing fresh grit. Pressure seems to be essential for this stone to cut well but eventually equals dishing. Typically I am getting 500+ high pressure passes, after the mud forms, before this becomes an issue but it is still an issue. As a comparison the pressure I am using on this stone would visibly dish a 240grit King in 20-30 passes.

So I had to lap it again. I don't like lapping stones with loose grit. It is slow, messy and the loose grit wanders off to make friends with my polishing stones. I looked for an alternative. There in the corner was an old and virtually worn out DMT XXC. I wonder. I tried to lap a 400grit Sigma with the DMT once and the Sigma just laughed and called it names. But I also tried it on a coarse Crystolon in a desperate (and failed) attempt to make the Crystolon cut better and it lapped that very hard Sic stone pretty well. Nothing ventured and all that. Turns out that while I thought the Sigma 120 would finally finish the DMT off for good, the diamond stone cut it like it had been designed for the job. Takes less than a minute to get the Sigma back to flat and there is a side benefit.



MEGA MUD! Spitting blood and everything now.

When the stone gets like this it can be difficult to push a blade across it. I did an experiment with a no name stainless blade and working on the edge the Sigma is so aggressive that sometimes the grit bites deep enough to stop the pass altogether.

I really like this stone. Assuming it actually was 25mm thick when it arrived, then after roughly 20 hours use and give or take 9 flattenings I have used 2-3mm of abrasive. Currently I have left it on my work bench to dry out with the slurry left on so I can see what happens. I have done some half arsed playing about using low pressure and just the mud to grind. I think there will be some merit to this but I can't say anything conclusive yet.

Cliff, it might be worth lapping one surface of your stone fairly aggressively to see if that alters it's performance.

Did I mention I like the stone?
Re: Sigma Power 120 - Mine is a little different
October 12, 2014 10:12AM
Quote
HedgeChopper


Cliff, it might be worth lapping one surface of your stone fairly aggressively to see if that alters it's performance.

Stu mentioned that and that the stone would perform as you describe after it has been lapped as the surface is harder. However I actually like the very hard surface for kitchen knives. Locally kitchen knives get used very hard and when I go to sharpen them they have visible damage, recurves, broken tips and faceted bevels. This stone chews through all of that with no wear/slurry and often in as little as 25-50 pps will have the bevel restored. This allows me to sharpen even those damaged knives in under two minutes. I would not want significant mud formation on those steels as it would just be a waste of the stone. The TASK stone will act like that already as it has a very loose abrasive bond.

It is curious though as to the nature of the change seen and just think about how much this will make people see a different stone. A lot of people will lap a stone immediately, some will not. On this stone, that plus the variability in pressure and steel will make tremendous differences in how the stone acts.

Approximately how much force were you using, just roughly, when you were doing the Bacho primary grind?
Re: Sigma Power 120 - Mine is a little different
October 12, 2014 12:17PM
Quote
CliffStamp

However I actually like the very hard surface for kitchen knives.

I thought you might. I suggested lapping one side so you would essentially have a dual density stone. Hard side for kitchen knives and muddy side for more abrasion resistant steels and blood spitting anger. Actually I wish I had thought of that earlier as I have lapped both sides of mine.

Quote

It is curious though as to the nature of the change seen and just think about how much this will make people see a different stone. A lot of people will lap a stone immediately, some will not. On this stone, that plus the variability in pressure and steel will make tremendous differences in how the stone acts.

Absolutely. I said at the start of my post that the description of your stone made me wonder whether it would work for what I wanted to achieve at all. I hadn't considered the possible effects of lapping the surface or how the stone could be manipulated to make it perform the way that I wanted.

I generally lap stones soon after I get them as they often have surface issues. In this case it was a raised rim around the edge that was a good 1-2mm in height and would have cut into the blades. I bought an india stone recently and the fine side arrived much rougher than the coarse.

Playing about with the pressure on this stone is interesting. Light pressure on a clean stone just scratches up the blade a little. With some mud in play you can get it to start cutting finer.

Steel hardness makes a big difference. The Bahco and the Hultafors in the pictures are both SK5 steel and listed as 57-59HRC and 58-60HRC respectively(though I can cut them with a file, the Hultafors especially). I did some work with an O1 blade that is harder, I would guess low 60s, and, without the mud in play, it would just glide over the surface and pick up a few scratches.

The biggest revelation was using the DMT to lap it. The stone is 8 years old and has done an awful lot of work it can barely cut steel anymore. But it is very quick to cut this stone (even though it will barely touch my 400grit) and leaves an instant slurry. That means I can choose how the Sigma cuts. It can be very fast and muddy, for wide bevels and hard to grind steels or wear resistant and low mess for edges and easy to grind blades. Because the stone needs mud to make mud, this all just depends on whether I rinse off the lapping slurry or not.

Quote

Approximately how much force were you using, just roughly, when you were doing the Bacho primary grind?

I can't give you any kind of number in terms of pounds force as I have nothing to compare to. Subjectively though I would have visibly and obviously dished a king 240 in 20-30 passes at most. After 100 passes on the Sigma I feel the need to stretch my hands and shake them out and I wouldn't expect to have much of a diamond stone left doing alot of work at that pressure.

If I can work out a way to do this over a set of scales, without harming them, (that would result in harm to me!) then I will take some measurements. Any suggestions for methods?
Re: Sigma Power 120 - Mine is a little different
October 12, 2014 12:42PM
Quote
HedgeChopper

...
The biggest revelation was using the DMT to lap it. The stone is 8 years old and has done an awful lot of work it can barely cut steel anymore. But it is very quick to cut this stone ...

That is interesting, I wonder if it isn't the DMT cutting the Sigma but the Sigma digging into the nickle plating and being torn out.


Quote

Any suggestions for methods?

I am just interested in a rough measurement, press down on a set of scale until you have the same force/effort. The force you apply will vary significantly anyway, I just want to know if you are close to 10 lbs, 50 lbs or closer to 100 lbs. I want to see if the pressure range you are working in is similar to mine in terms of how the stone responds.
Re: Sigma Power 120 - Mine is a little different
October 12, 2014 03:09PM
Quote

I am just interested in a rough measurement, press down on a set of scale until you have the same force/effort. The force you apply will vary significantly anyway, I just want to know if you are close to 10 lbs, 50 lbs or closer to 100 lbs. I want to see if the pressure range you are working in is similar to mine in terms of how the stone responds.

Right had a play about with this. I think I am applying 10-15lbs force when working on the Bahco. The bevel width on this is around 14mm. You can probably calculate the pressure from that. I make it roughly 900g per cm2 but it must spike as I reach the curve and tip of the blade because the surface area is so reduced. Apologies for mixing metric with imperial. I had to use a set of bathroom scales and they read from just under to just over a stone at the peak of the force used. I checked multiple times because I know those scale aren't the most accurate. One stone is 14lbs or roughly 6.36kg.

Was interesting to see how the force I am applying varies over the course of a single pass. Could go part way to explaining why different parts of a blade sharpen at different rates even though each pass shows them roughly the same amount of abrasive.
Re: Sigma Power 120 - Mine is a little different
October 13, 2014 11:17AM
Thanks, that is cutting with significantly less pressure than the one I have requires, but again Stu did mention that it does change after flattening/wear. I am curious how long this will happen with natural wear as it would seem to me that the same thing should happen.

--

I contacted the guy who had the problems I noted in the above, the reason was he was using the stone in a severely clogged state. When he was lapping he was doing too much grinding. He noted that he found minimal lapping was necessary to get ideal results and prevent clogging. The one I have is very porous you can just blast water at it to unclog it with a normal spray bottle, but if you don't it will get pretty slick or at least not nearly as aggressive if you are cutting on a heavily loaded surface and it isn't generating fresh slurry.
Re: Sigma Power 120 - Mine is a little different
October 14, 2014 07:46PM
Quote
HedgeChopper
Currently I have left it on my work bench to dry out with the slurry left on so I can see what happens.

Nothing good!

This is the first time I have been able to thoroughly glaze and clog the stone. Normally just needs a good rinse to clean or a squirt from a spray bottle to keep it cutting. The mud had not dried out but had gone rusty over night. I had to clean it and lap it again to make it cut. Untill I did that the only thing cutting was the mud which broke down but did not release fresh grit from the glazed surface.

Quote
CliffStamp
that is cutting with significantly less pressure than the one I have requires, but again Stu did mention that it does change after flattening/wear.

I have been playing around using more and less pressure on different bevel widths. Whilst everything gets cut it does seem that the more pressure you can apply the better this stone works. If you put a few passes on the edge of a fairly soft blade while there is some mud on the stone it gets 'super charged' for a while. Even making an immediate switch to zero grinding a full flat blade you can feel the extra aggression.

Quote

I am curious how long this will happen with natural wear as it would seem to me that the same thing should happen.

If at least some grit is being pulled free by the knives you work on then eventually you must get through the hard layer. I suspect it will happen all of a sudden, like with the Suehiro.
Re: Sigma Power 120 - Mine is a little different
October 15, 2014 01:26PM
Quote
HedgeChopper

[...]

I had to clean it and lap it again to make it cut. Untill I did that the only thing cutting was the mud which broke down but did not release fresh grit from the glazed surface.

There is something going on here I don't fully understand. I first saw it heavily on the Suehiro, but I have seen it several times after that. It is possible to form a mud which when it dries is actually similar to the stone in hardness/strength.



This is the Suehiro if you let it build up a mud which takes :

-high pressure
-easy to cut steel
-very wet stone

It is a combination of all of these and they can compensate for each other (a really easy to cut steel doesn't require as high a pressure). Now when this happens if you let that mud dry then those tracks can't be scraped off, even if you soak the stone they basically have set and you have to wear them off just like they are a stone itself. It makes the stone insanely aggressive initially as they form very high pressure points.

Why is this happening, I believe it is a cementious reaction. In traditional cement used to make concrete there is a mixture of oxides which when exposed to water form hydrated compounds which is what bonds everything together. What are the oxides, typically calcium, silica and aluminum oxide .One of these things should jump out at you immediately (though slica is also used in abrasives).

I have been poking around in concrete chemistry a little and the cementious additives do have to be of certain sizes to work well which may be why I have seen this happen so strongly in the Suehiro and not at all in the Naniwa. The larger the abrasive size then the larger the pieces it will tear out as well from the knife so the aggregate size is strongly correlated.

This isn't overly practically useful, but I did find it curious and the only thing it really means is that you may (or may not) want to be careful in rinsing heavy slurry from stones before putting them away because if you don't them may actually cement together.

(plus as noted yeah they can rust heavily)
Re: Sigma Power 120
October 26, 2014 04:01PM
Initial sharpness, speed of grinding/ease of forming an apex, edge retention in slicing 1/2" hemp : [www.cliffstamp.com] .
Re: Sigma Power 120
October 26, 2014 11:30PM
Bevel resetting on 63 HRC/M4 : [www.cliffstamp.com]

-300 pps to recut a bevel from 15 to 25 dps to 11.5
Re: Sigma Power 120
January 14, 2015 02:36PM
Just got mine in the other day! A few quick notes...

1. There was some raised, very coarse, bumps on the surface of both sides which required lapping to get it smooth like the rest of the stone
2. I just tried one knife on it quickly w/ little to no mud, and no soaking. It does definitely seem to require both soaking and mud to work efficiently, although I was able to apex the edge after about 10 minutes. I can see how it requires high pressure as well.

Is this stone designed for soaking? Curious as to thoughts of taking some SiC grit, putting it on the stone, and rubbing two stones like this together to start the mud?
Re: Sigma Power 120
January 14, 2015 08:57PM
If the stone needs soaking then it isn't the same as the one I have which is so porous it gets saturated as soon as you put it in water. If you need mud for it to cut well then the grit on yours is very dull/worn which likely was caused by the lapping.



Edited 1 time(s). Last edit at 01/14/2015 08:58PM by CliffStamp.
Re: Sigma Power 120
January 15, 2015 03:58PM
Quote
CliffStamp
If the stone needs soaking then it isn't the same as the one I have which is so porous it gets saturated as soon as you put it in water. If you need mud for it to cut well then the grit on yours is very dull/worn which likely was caused by the lapping.

Reason why I am asking is because on pg. 1 of this thread HedgeChopper makes remarks that:

1. he let it soak over night
2. he had to generate a bunch of mud to get it cutting really well

Mine also appears porous so much that there is no water left on the surface after you put it under running water for 15-20 seconds... it all just absorbs into the stone. that's why I was wondering if I should soak it at all. HedgeChopper loaded his with the SiC powder to get it to generate more mud and start cutting more effectively so I may be exploring this as well.
Re: Sigma Power 120
January 15, 2015 04:23PM
The initial surface of mine was very hard, it will not release grit, if you lap it then you just generate a surface which is rounded/worn and won't cut well. A lot of people do this automatically, especially with things like India and Norton's silicon carbide stones, but what this does, unless you use a grit which is more coarse than the stone is polish the surface and reduce the cutting ability. If the stone doesn't release grit then the stone is rendered at this point very ineffective - unless for some reason you have a coarse India stone (or whatever) and you have to use that for a polishing stone.

As with all comments on stones, they are very sensitive to pressure. This stone also seems to have a top coat (I have not gone through it with mine) that has a much stronger bond than the bottom coat. I would not advise just grinding through it as it would be a waste of stone, but if you like working with mud then ok. Note that in general mud actually slows grinding tremendously. A stone with sharp abrasive which doesn't release mud cuts far faster than one which releases abrasive. The reason why muddy stones in general are noted to cut fast is because stones which don't release abrasive are not used properly.

If a stone doesn't release abrasive then you absolutely have to :

-use a lubricant which reduces friction and prevents wear/rounding of the abrasive by friction
-periodically recut the surface using a very coarse abrasive (~36 grit silicon carbide for example)
-do not let the surface get contaminated with grit or steel

If you do these things then those stones cut very fast and clean, far more than muddy stones.
Re: Sigma Power 120
January 15, 2015 05:21PM
ok thanks. would lapping it w/ the TASK hone be coarse enough? I also have a few pieces of extra chunks of stones you sent me... one of which is very coarse.
Re: Sigma Power 120
January 15, 2015 05:40PM
The TASK and it are very similar, it will work, but not as well as a more coarse abrasive. What you want to do is rub them together just long enough to break up the grit but not polish/wear it down. This depends on the force used so I can't give a time frame but basically the mud/grit/slurry produced should not be very fine, it should be very coarse.
Re: Sigma Power 120
January 24, 2015 04:28AM
Forgot about that! Lol ok thanks man I will keep you posted
Re: Sigma Power 120
February 02, 2015 11:13PM
So I got the stone cut up and mounted on the WE paddles... reprofiled the secondary grind on a folder (not sure of the steel, it was cheap). before doing so I lapped the SP120 with 120 grit SiC. When I went to reprofile the edge it went FAST and removed steel very quickly... however, the SP120 dished very badly. I was using a lot of pressure, maybe up to 10 lbs. And to be clear, this was probably using the center of the larger stone since I cut it up into smaller stones, so I didn't have the 1-2 mm of harder stuff to go through.
Re: Sigma Power 120
February 02, 2015 11:36PM
That is really interesting. Is there any way you could video a little use, even low res, nothing fancy.
Re: Sigma Power 120
February 02, 2015 11:56PM
Absolutely... I will try to get one up and post here within the week. I will lap them flat again first so you can see how much they dish.
Re: Sigma Power 120
February 03, 2015 02:07AM
Could you lap the Sigma 120 with a Nubatama 24 grit stone?
Re: Sigma Power 120
February 11, 2015 05:37PM
Here's the video I just did this morning:



Re: Sigma Power 120
April 15, 2015 01:32AM
On chisels, with high pressure :



In short it can be done, it cuts aggressively, but the bond is too weak.

I was using 20-30 lbs, contact pressure is high : 150 to 300 psi and it was well past the UCP on the Sigma Power 120. The stone was shedding grit rapidly. I only did enough work to take out the damage and then flattened the chisel and repaired another one on the Norton India Coarse which cuts slightly slower, but won't dish excessively even at those pressures.

However if you grind much softer the Sigma Power 120 is better. I had to repair two chisels in an emergency this evening so I didn't have time to play around. The next time I will look at the load and see if I can't find the sweet spot for the Sigma Power, just above the LCP.



Edited 1 time(s). Last edit at 09/08/2015 03:19AM by CliffStamp.
Re: Sigma Power 120
April 15, 2015 07:40AM
question - what stones will use japanese carpenter for repairing damaged chisel edges - is there low grit /100-200 range/ very hard stone which can deal with high pressures

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Re: Sigma Power 120
April 15, 2015 04:11PM
Stefan,

That is an interesting question. I would wonder though if they get that kind of extreme damage I seen on western chisels so often? If I had to sharpen Mark's chisels (as I robbed them all and maybe let them rust) I don't imagine I would need a Norton Coarse. However at some point they may get damaged rarely and I wonder if they do just do that kind of slow and soft grinding that Carter does? Take a look at for example how he grinds out chips on a very soft King stone. He just does a massive volume of very fast passes.